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Accepted papers to appear in an upcoming issue

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Optical Tweezing by Photomigration

Zouheir Sekkat

Doc ID: 245337 Received 08 Jul 2015; Accepted 25 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: Photomigration in azo polymers is an area of research that witnessed intensive studies owing to its potential in optical manipulation; e.g. optical tweezing; the physical mechanism of which remains unsolved since its discovery about two decades ago. In this paper, a detailed theoretical study that reproduces the phenomena associated with photomigration is presented, including the physical models and the associated master equations. Polarization effects are discussed and analytical solutions are given to describe the steady-state and the dynamics of photomigration. Such a theory leads to new theoretical experiments relating materials properties to light action. A photoisomerization force which is described by a spring type model is introduced. This force is derived from a harmonic light potential that moves the azo-polymer. This force is parenting to optical tweezers, but it is quite different in the sense that it requires photoisomerization to occur. The azo-polymer’s motion is governed by four competing forces: the photoisomerization force, and the restoring optical gradient and elastic forces, as well as the random forces due to spontaneous diffusion.

Polarizing grating color filters with large acceptance angle and high transmittance

Shin-Tson Wu, Zhenyue Luo, Guiju Zhang, Ruidong Zhu, and Yating Gao

Doc ID: 250437 Received 21 Sep 2015; Accepted 25 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: We design and simulate a polarizing color filter with sub-wavelength metal-dielectric grating. It manifests several advantages: large acceptance angle (up to ±50°), high transmittance (74.3%-92.7%), low absorption loss (~3.3%), and high extinction ratio. This polarizing color filter can be integrated in liquid crystal display (LCD) backlight system to simultaneously recycle the light according to its color and polarization. In combination with a specially designed directional backlight, this newly proposed LCD system can theoretically improve optical efficiency up to ~2.5X, and also provide large ambient contrast ratio and wide view. Our approach enables an ultra-low power LCD without using sophisticated field-sequential-color technique.

Study and generation of more than 40 W of average output power from passively Q-switched Yb-doped fiber laser

Usha Chakravarty, Antony Kuruvilla, Ravindra Singh, B. N. Upadhyaya, kushvinder Bindra, and S.M. Oak

Doc ID: 250636 Received 22 Sep 2015; Accepted 25 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: We report on the generation of 41.6 W of average output power from passively Q-switched ytterbium-doped fiber laser using Cr4+: YAG crystal as a saturable absorber. This is the highest average power from passively Q-switched fiber lasers reported so far in literature and it has been achieved by using specially designed T-type double-end pumping configuration. Variation in average output power, pulse energy, pulse duration, pulse frequency, and pulse-to-pulse stability has also been studied using saturable absorbers of different linear transmission. The effect of intra-cavity saturable absorber on self-pulsing dynamics was also investigated and it was observed that at lower input pump power near threshold, presence of saturable absorber enhances the peak power of relaxation oscillations to trigger the generation of stimulated Raman scattering in the gain fiber. With an increase in pump power, when the passive Q-switching threshold is reached, high peak power random self-pulses regenerate into low amplitude regular Q-switched pulses. Effect of length of the gain medium on dual-wavelength generation at very low input pump power and broadband generation at sufficiently higher pump power has also been explored.

Performance of the Gemini Planet Imager's adaptive optics system

Lisa Poyneer, David Palmer, Bruce Macaintosh, Dmitry Savransky, Naru Sadakuni, Sandrine Thomas, Jean-Pierre Veran, Katherine Follette, Alexandra Greenbaum, Mark Ammons, Vanessa Bailey, Brian Bauman, Andrew Cardwell, Daren Dillon, Donald Gavel, Markus Hartung, Pascale Hibon, Marshall Perrin, Fredrik Rantakyro, Anand Sivaramakrishnan, and Jason Wang

Doc ID: 250766 Received 24 Sep 2015; Accepted 25 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: The Gemini Planet Imager’s adaptive optics (AO) subsystem was designed specifically to facilitate high- contrast imaging. A definitive description of the system’s algorithms and technologies as-built is given. 564 AO measurements from the Gemini Planet Imager Exoplanet Survey campaign are analyzed. The modal gain optimizer tracks changes in atmospheric conditions. Science observations show that image quality can be improved with use of both the spatially-filtered wavefront sensor and Linear-Quadratic-Gaussian control of vibration. The error budget indicates that for all targets and atmospheric conditions AO bandwidth error is the largest term.

Efficient and compact orthogonally polarized dual-wavelength Nd:YVO4 laser at 1342 and 1345 nm

Zhiping Cai, Bin Xu, Yi Wang, Zhi Lin, Shengwei Cui, Yongjie Cheng, and Huiying XU

Doc ID: 251412 Received 05 Oct 2015; Accepted 25 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: Based on a free-running diode-end-pumped a-cut Nd:YVO4 laser with output power of 3.61 W at single wavelength of π-polarized 1342 nm, we further obtain a 1.82 W σ-polarized 1345 nm laser with slope efficiency of about 22.3% by introducing an intracavity etalon, for the first time to our knowledge. In addition, simultaneous dual-wavelength orthogonally polarized laser at the π-polarized 1342 nm and the σ-polarized 1345 nm can also be achieved with maximum output power of 1.35 W. The dual-wavelength laser provides a potential laser source for THz wave generation.

Correction of illumination fluctuations in phase-shifting technique by use of fringe histograms

Hongwei Guo, Yinyin Lu, and ruihua zhang

Doc ID: 251814 Received 12 Oct 2015; Accepted 25 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: With phase-shifting technique, the illumination fluctuations may decrease measurement accuracy. This paper presents a simple method for solving this problem by use of fringe histograms. A fringe pattern containing bright and dark fringes is recognized as an image having two classes of pixels following a bi-modal histogram, and the optimal threshold for segmenting this pattern enables maximizing its inter-variance between the two classes. Using this optimal threshold, some statistics of the segmented classes, e.g. their means, keep stable during phase-shifting. Using these means of classes as nodes allows us determining a linear transformation function, by which the fluctuations of the fringe patterns in background intensities and modulations are corrected. Numerical simulation and experimental results demonstrate this method to be efficient and effective in improving the phase measuring accuracies with phase-shifting technique.

Optical gain characterization of Perylene Red-doped PMMA for different pump configurations

Md Rejvi Kaysir, Simon Fleming, Rowan MacQueen, Tim Schmidt, and Alexander Argyros

Doc ID: 252108 Received 16 Oct 2015; Accepted 24 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: The optical gain is measured in Perylene Red (PR)-doped PMMA slabs for co-propagating and transverse pumping configurations based on a single pass pump-probe method where a small signal is used as a probe beam. The gain is characterized in terms of the stimulated gain coefficient (gS) for both pump configurations. This material property determines the strength of pump absorption and coupling to the probe signal beam through stimulated emission. For co-propagating pumping, gS was found to be (3.05±0.17) × 10-3 m/W for ~0.05 mM PR-doped PMMA using a 633 nm probe laser, pumping with a 532 nm continuous wave (CW) laser. For transverse pumping, gS was found to be (3.28±0.09) ×10-3 m/W for a ~0.15 mM sample. The small difference in gain coefficient is attributed to the difference in concentration. The stimulated gain coefficient, a material property of the gain medium and independent of the pump configuration and experimental setup, offers a useful and convenient way to characterize the optical gain for solid state lasers or amplifiers.


Igor Panko, Roman Vengrenovich, Bohdan Ivanskii, and Kryvetskyi Vasyl

Doc ID: 252549 Received 23 Oct 2015; Accepted 24 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: Analysis of experimentally obtained size distribution functions in the form of percentage of carbon nanotubes vs diameters of them shows increasing intermediate tube diameters with increasing concentration of the source of carbon atoms. In this paper, the mechanism of growth is associated with the Ostwald’s ripening carbon nanotubes considered as a massive of cylindrical nanoclusters of various diameters and heights, embedded in solution (volume or surface) of carbon atoms. Interaction of nanoclusters is realized through the Gibbs-Thomson effect resulting in increasing their average diameters. Validity of the proposed mechanism of increasing average diameters of nanotubes is proved by comparison of the experimentally obtained histograms with theoretically computed dependences. We use the generalized Lifshitz-Slyozow-Wagner and the Chakraverty-Wagner distributions, both computed in assumption that growth of nanoclusters (nanotubes) is controlled simultaneously both by (volume or surface) diffusion and by speed of chemical connections’ formation, or by chemical reaction (the Wagner’s mechanism of growth). Under specified technological parameters and conditions of synthesis, the obtained theoretically distributions well fit the experimental histograms for single-layer carbon nanotubes.

Beam shaping with same diffraction pattern for multi-color light-emitting diodes

Mengzhu Chen, Wang Qixia, Huarong Gu, and Qiaofeng Tan

Doc ID: 248979 Received 31 Aug 2015; Accepted 24 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: Visible light communication (VLC), equipped with light-emitting diodes (LEDs) as its light source, is raised to meet the increasing demand for high channel capacity. Wavelength-division multiplexing technique can be used in VLC with multi-color mixed white LED to further increase the channel capacity. The area illuminated by each white LED should be transformed into polygonal region to realize cellular network and decrease crosstalk in VLC. Diffractive optical elements (DOEs) can be employed in the optical transmitter system to shape the incident beams into polygons. Same diffraction pattern should be guaranteed for multiple colors, otherwise different sizes will introduce interference within the adjacent areas in VLC with multi-colored white LEDs. In this paper, a hybrid algorithm merging particle swarm optimization and genetic algorithm is introduced to optimize the DOE to obtain multi-color diffraction beams with the same diffraction pattern. A DOE that can realize the same diffraction pattern incident by red and blue LEDs is fabricated, and experimental results show that rather good uniformity and almost same size of diffraction pattern for red and blue LEDs are obtained.

Polarization independent plasmonic subtractive color filtering in ultrathin Ag nanodisks with high transmission

Dongxian Zhang, Xiaolin Hu, Linbin Sun, Beibei Zeng, Liansheng Wang, Zhi-Guo Yu, songang bai, Shumin Yang, lixia zhao, Qiang Li, Min Qiu, Renzhong Tai, HANS-JORG FECHT, and Jianzhong Jiang

Doc ID: 249926 Received 11 Sep 2015; Accepted 24 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: We demonstrate a TE/TM polarization-independent plasmonic subtractive color filtering scheme employing ultrathin two-dimensional Ag nanodisks. These TE/TM polarization-independent subtractive color filters exhibit small feature sizes (below 200 nm) and high transmission up to 70%in the visible spectral region, superior to previously reported plasmonic color filters. Simulated optical transmission spectra and colors are in good agreement with experimental results. The color filtering behaviors strongly depend on thickness and period of nanodisks. Underlying mechanisms are also discussed in details.

Carrier squeezing interferometry with π/4 phase shift: Phase extraction in the presence of multi-beam interference

Qun Yuan, Jinlong Cheng, Zhishan Gao, Kailiang Wang, and Liping Xu

Doc ID: 250875 Received 25 Sep 2015; Accepted 24 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: Multi-beam interference exists when test the surfaces with high reflectivity using Fizeau interferometer. In this paper, multi-beam interference intensity was estimated as the sum of first six order harmonics using the Fourier series expansion. And then an algorithm adopting carrier squeezing interferometry with π/4 phase shift was proposed to extract the phase from multi-beam interferograms. Conditions of the necessary linear carrier in the proposed algorithm were derived to ensure the separation of the lobes of phase shift errors and the phase lobe in the frequency domain. Simulation results indicated that the phase retrieving precision is better than PV 0.008λ and RMS 0.001λ even when the reflection coefficient of the test surface is as high as 0.9 and the phase shift varies within π/4±π/20. The proposed algorithm for multi-beam interference was validated by its good performance in the experiments compared with the other algorithms, especially when the phase-shift error exists.

Quantitative two-dimensional measurement of oil film thickness by laser-induced fluorescence in a piston-ring model experiment

Sebastian Kaiser, Stefan Wigger, Hans-Jürgen Füsser, Daniel Fuhrmann, and Christof Schulz

Doc ID: 247473 Received 07 Aug 2015; Accepted 24 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: This paper describes advances in using laser-induced fluorescence (LIF) of dyes for imaging the thickness of oil films in a rotating-ring tribometer with optical access, an experiment representing a sliding piston ring in an internal combustion engine. A method for quantitative imaging of the oil film thickness is developed that overcomes the main challenge, the accurate calibration of the detected fluorescence signal for film thicknesses in the micrometer range. The influence of the background material and its surface roughness is examined, and a method for flat field correction is introduced. Experiments in the tribometer show that the method yields quantitative, physically plausible results, visualizing features with sub-micrometer thickness.

Large elliptical nanostructured gradient index microlens

Bernard Piechal, Ryszard Buczynski, Adam Filipkowski, Andrew Waddie, Jedrzej Nowosielski, Dariusz Pysz, Ryszard Stepien, and Mohammad Taghizadeh

Doc ID: 247878 Received 22 Aug 2015; Accepted 24 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: We demonstrate the feasibility of the development of a gradient index elliptical microlens with a size of 75 × 125 μm using the nanostructured glass technology. The gradient index is obtained by means of a discrete internal structure composed of two glasses with feature sizes much smaller than the wavelength of the incident light. A modified photonic crystal fiber drawing technique is used for lens fabrication. The elliptical shape of the lens is obtained by a novel final drawing stage where the spherically symmetric lens preform is drawn into an elliptical form by collapsing two large air holes placed in the preform during assembly. The effective focal lengths of 160 and 260 μm for orthogonal axes are obtained experimentally for the fabricated lens and show good agreement with those predicted by effective medium theory and full-wave beam propagation simulations.

Dual wavelength LIDT measurements of UV antireflective coatings

Lars Jensen, Marius Mrohs, Stefan Guenster, Thimotheus Alig, and Detlev Ristau

Doc ID: 249148 Received 01 Sep 2015; Accepted 24 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: An approach for the measurement of the laser induced damage threshold (LIDT) with two wavelengths combined was made while testing antireflective coatings for the wavelengths 266nm and 532nm. The results show that adding radiation of a second wavelength might lead to a significant reduction of the threshold. The damage morphology of single and dual wavelength tests is very similar and does not suggest an altered damage mechanism. Further investigations indicated that the dual wavelength threshold is a function of the temporal delay of the two pulses.

Goniospectrometric space curve for coatings with special effect pigments

Nina Rogelj and Marta Gunde

Doc ID: 249455 Received 03 Sep 2015; Accepted 24 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: Advanced application of eye-catching effects occurring in coatings with special effect pigments requires to control the appearance. For this purpose, angular dependent reflectance must be analyzed in terms of the used flakes and of their distribution inside coating; it is important how large surface area they cover, how they are oriented and how precise is this orientation. These properties were varied using our numerical model which gave angular dependent reflectance factor for each set of coating parameters. The method was applied to analyze how well the calculated goniometric reflectance factor could characterize the appearance of effect coatings. For this purpose, the spectra were transformed in the goniospectrometric space and the obtained curve was analyzed. While its shape, position and orientation in the space reveal the optical makeup of the coating, the goniospectrometric space curve could serve as an appearance fingerprint of the corresponding sample. The applicability of the theoretical predictions was confirmed using a coating with metallic flakes and a coating with mica-based Fe2O3 coated flakes.

Fabrication of plasmonic Au/TiO2 nano-fiber films with enhanced photocatalytic activities

Hua Li, Enzhou Liu, Jun Fan, Hu Xiaoyun, Lin Sun, Jun Wan, and Yang Hu

Doc ID: 249591 Received 08 Sep 2015; Accepted 24 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: TiO2 nano-fiber films (TiO2 NFF) with visible light scattering ability were prepared using a hydrothermal method, Au nanoparticels (Au NPs) were then deposited on the surface of TiO2 film using microwave-assisted chemical reduction process. An overlapped light trapping phenomenon was observed in Au/TiO2 NFF due to the light scattering nanostructures of TiO2 film and the localized surface plasmon resonance (LSPR) of Au NPs. The MB degradation over the composite films is much faster than that of pure TiO2 film. The enhanced photocatalytic activity is primarily attributed to the charge transfer property and the overlapped light trapping nanostructures of Au/TiO2.

Realization of real time interactive 3D image holographic display

Daping Chu and Jhen-Si Chen

Doc ID: 249929 Received 11 Sep 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: Realization of a 3D image holographic display supporting real time interaction requires fast actions in data uploading, hologram calculation and image projection. These three key elements will be reviewed and discussed while algorithms of rapid hologram calculation will be presented with the corresponding results. Our vision on interactive holographic 3D displays will be discussed.

Weak two photon absorption applied to the rapid prototyping of cell scaffolds

Bibi Safia Haq, Hidayat Ullah Khan, Khan Alam, Shahnaz Attaullah Attaullah, and Mamoona Sultan

Doc ID: 250069 Received 14 Sep 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: Abstract. Two-photon polymerization has been employed to generate deep structures using the biocompatible and optically transparent monomer Ethoxylated Bisphenol A Dimethacrylate (EO=6) (EBPADMA) and 4,4’-Bis (diethylamino) benzophenon as the photoinitiator. The two-photon absorption cross section of the initiator was measured to be 1GM (1GM=1×10-50cm4 s photon-1) in EBPADMA. Here we have explored a weak absorption regime whereby deep structures (~300µm) can be generated in a single pass. This allows rapid fabrication of structures suitable for cell scaffolds where the length scales are small, ~10µm, but are required over long ranges, ~ cm. The dependence of the TPP properties on the writing power, speed, exposure time and NA, of the focusing lens were studied in detail. Diffraction calculations for the focussing optics employed, show that spherical aberration plays a significant role in determining the feature sizes achieved.

Analysis of dead zone sources in Closed-Loop Fiber Optic Gyroscope

Kyoung Ho Chong, Kil-To Chong, and Woo-suk Choi

Doc ID: 250263 Received 16 Sep 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: One of intensive studies in closed-loop fiber optic gyroscope is the analysis of the dead zone. In dead zone, the gyroscope cannot detect any rotation and produces zero bias. In this study, the analysis of the dead zone sources was performed by simulation and experiments. In general, the problem is mainly due to the electrical crosscoupling and the phase modulation drift. The electrical cross-coupling is caused by the interference between the modulation voltage and the photodetector. The cross-coupled signal produces spurious gyro bias and leads to the dead zone if it is larger than the input rate. The phase modulation drift as another source of dead zone is due to the electrode contamination, the piezoelectric effect of LiNbO3 substrate, or other organic fouling. This modulation drift has a short or long period of time like a lead-lag filter response and produces the gyro bias error, noise spikes, or dead zone. For more detailed analysis, the cross-coupling effect and modulation phase drift are modeled as a filter and simulated in both open and closed-loop mode. The sources of dead zone are more clearly analyzed by simulation and experimental results.

Finite element modeling of light propagation in turbid media under illumination of continuous-wave beam

Aichen Wang, Renfu Lu, and Lijuan Xie

Doc ID: 250835 Received 25 Sep 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: Spatially-resolved spectroscopy provides a means for measuring the optical properties of biological tissues, based on analytical solutions to diffusion approximation for semi-infinite media under the normal illumination of infinitely small size light beam. The method is, however, prone to error in measurement because the actual boundary condition and light beam often deviates from that used in deriving the analytical solutions. It is therefore important to quantify the effect of different boundary conditions and light beams on spatially-resolved diffuse reflectance in order to improve measurement accuracy by the technique. This research was aimed at using finite element method (FEM) to model light propagation in turbid media, subjected to the normal illumination by a continuous-wave beam of infinitely small or finite size. Three types of boundary conditions [i.e., partial current (PCBC), extrapolated (EBC) and zero (ZBC)] were evaluated and compared against Monte Carlo simulations, which provided accurate results in fluence rate and diffuse reflectance. The effect of beam size was also investigated. Overall results showed that FEM provided as accurate results as analytical method when an appropriate boundary condition was applied. ZBC did not give satisfactory results in most cases. FEM-PCBC yielded better fluence rate at the boundary than did FEM-EBC, while they were almost identical in predicting diffuse reflectance. Results further showed that FEM coupled with EBC simulated spatially-resolved diffuse reflectance under the illumination of finite size beam effectively. Large size beam introduced more error, especially within the region of illumination. Research also confirmed an earlier finding that a light beam of less than 1 mm diameter should be used for estimation of optical parameters. FEM is effective for modeling light propagation in biological tissues and can be used for improving the optical property measurement by spatially-resolved technique.

Fiber refractive index sensor based on dual polarized Mach-Zehnder interference caused by a single mode fiber loop

LEI CHEN, Weigang Zhang, Li Wang, Quan Zhou, Jonathan Sieg, De-Long Zhao, Song Wang, Biao Wang, and Tieyi Yan

Doc ID: 250906 Received 29 Sep 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: A novel refractive index sensor head is proposed and experimentally demonstrated in this paper. The proposed sensor head is composed of a segment of bared single mode fiber and a fiber holder that is fabricated by a 3D printer. The mechanism of the sensor head is based on dual polarized Mach-Zehnder interference. According to the aforementioned mechanism, we derived that the refractive index response of the resonance dips possess an exponential functional manner when the E-field is along the fast or slow axes. In addition, based on the finite element method, we find that the resonance dips wavelength response are more sensitive when the input E-field is along the fast axis. A confirmation experiment was performed, and the results confirmed our hypothesis. The maximum arithmetic mean value of RI response is about 657.895 nm/RIU for the proposed sensor head when the ambient refractive index changes from 1.3350 to 1.4110. Moreover, in the case of the proposed liquid RI sensor head, aligning the E-field along the fast axis is the potentially needed condition for polarization.

Accuracy of image-plane holographic tomography with filtered back projection: random and systematic errors

Nikolay Petrov, Andrei Belashov, and Irina Semenova

Doc ID: 251045 Received 02 Oct 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: The concept of image-plane holographic tomography being applied to measurements laser-induced thermal gradients in an aqueous solution of a photosensitizer is considered with respect to issues of reconstruction accuracy of three-dimensional variations of refractive index. The least-squares estimation algorithm is used for the reconstruction of refractive index variations in each holographic projection. Along with the bitelecentric optical system, transferring focused projection to the sensor plane, it facilitates elimination of diffraction artifacts and noise suppression. The influence of typical random and systematic errors occurring in experiments is estimated. It is shown that random errors such as accidental measurement errors or noise presence can be significantly suppressed by increasing the number of recorded digital holograms. On the contrary even comparatively small systematic errors such as a displacement of the rotation axis projection in the course of reconstruction procedure can lead to significant distortions of the results obtained.

Range Compensation for Accurate 3D Imaging System

Xin Wang, Sing Yee Chua, Ningqun Guuo, and Ching Seong Tan

Doc ID: 251507 Received 14 Oct 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: Range determination has crucial dependency of intensity over distance due to the fact that output of a range gated system is the reflectivity and range information expressed in term of intensity. From our experimental study, the analysed trend-line of reflected intensity versus range agrees with the theoretical model where it underlies an inverse range-squared dependency. Considering the energy attenuation factor for better three-dimensional (3D) solution, a range compensation model is derived based on time slicing technique to compensate the effect imposed by distance beyond an optimum range. A range gated imaging system with pulse profile feedback is proposed in order to apply the range compensation model. Experimental results show noticeable improvement as compared to conventional weighted average method for reflected laser pulse data across different ranges and 3D surface reconstruction using the proposed range compensation model.

Graphite saturable absorber based on pencil-sketching method for Q-switching of an erbium fiber laser

Ju Han Lee, Jin Ho Lee, Junsu Lee, and Joonhoi Koo

Doc ID: 251614 Received 08 Oct 2015; Accepted 23 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: We experimentally demonstrate a practical and simple method for the preparation of a graphite-based, fiberized saturable absorber (SA). Our SA is prepared by using a low-cost graphite-core pencil that is commercially available from stationary stores to uniformly shade the flat end of a fiber ferrule. The saturable-absorption performance of the prepared SA was experimentally tested, and the feasibility of using the SA as a passive Q-switch was investigated through its incorporation into an erbium-doped-fiber ring cavity. The modulation depth of the SA is ~1%, and the Q-switched pulses of a 1.98 μs temporal width were readily obtained at a repetition rate of 46.08 kHz.

Effect of surface cleaning on spectral response for InGaAs photocathodes

Muchun Jin, Yijun Zhang, Xinlong Chen, Guanghui Hao, Benkang Chang, and Feng Shi

Doc ID: 249880 Received 11 Sep 2015; Accepted 23 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: Photocathode surface treatment aims to obtain high sensitivity, of which the key point is to acquire an atomically clean surface. Various surface cleaning methods for removal of the contamination from InGaAs photocathode surface were investigated. The atomic compositions of InGaAs photocathode structure and surface were measured by the X-ray photoelectron spectroscopy and Ar ion sputtering. After surface cleaning, it is found that a cleaned InGaAs surface is arsenoxide-free but small amount of Ga2O3 and In2O3 still remain. The 1: 1 mixed solution of hydrochloric acid to deionized water followed by thermal annealing at 525°C has been proved to be the best choice in dealing with the surface oxides. After the Cs/O activation, a considered surface model was proposed that the oxides on the surface will lead to a positive electron affinity, adversely affecting low-energy electrons escaping to the vacuum, which is reflected by the photocurrent curves and the spectral response curves.

Effects of aperture averaging and beam width on a partially coherent Gaussian beam over free-space optical links with turbulence and pointing errors

It Ee Lee, Zabih Ghassemlooy, Wai Pang Ng, Mohammad Khalighi, and Shien-Kuei Liaw

Doc ID: 241490 Received 04 Jun 2015; Accepted 22 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: Joint effects of aperture averaging and beam width on the performance of free-space optical communication links, under the impairments of atmospheric loss, turbulence, and pointing errors (PEs) are investigated from an information theory perspective. The propagation of a spatially partially coherent Gaussian-beam wave through a random turbulent medium is characterized, taking into account the diverging and focusing properties of the optical beam, as well as the scintillation and beam wander effects. Results show that a noticeable improvement in the average channel capacity can be achieved with an enlarged receiver aperture in the moderate-to-strong turbulence regime, even without knowledge of the channel state information. In particular, it is observed that the optimum beam width can be reduced to improve the channel capacity, albeit the presence of scintillation and PEs, given that either one or both of these adverse effects are least dominant. We show that under strong turbulence conditions, the beam width increases linearly with the Rytov variance for a relatively smaller PE loss, but changes exponentially with steeper increments for higher PE losses. Our findings conclude that the optimal beam width is dependent on the combined effects of turbulence and PEs, and this parameter should be adjusted according to the varying atmospheric channel conditions. Therefore, we demonstrate that the maximum channel capacity is best achieved through the introduction of a larger receiver aperture and a beam width optimization technique.

Steel Surface Defect Detection Using a Switching Lighting Scheme

Sang Woo Kim, Yong-Ju Jeon, Doo-chul Choi, Sang Jun Lee, and Jong Pil Yun

Doc ID: 246849 Received 27 Jul 2015; Accepted 22 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: In this paper, a new lighting scheme and a novel filtering scheme were proposed for defect detection in steel surfaces. A steel surface has non-uniform surface properties and defects of various shapes, which makes it difficult to detect defects. To solve these problems, we propose a switching lighting method with sub-optimal filtering. First, to minimize the influence of the non-uniform surface and improve the accuracy of the detection rate, a detection method based on dual-light switching lighting (DLSL) is proposed. In the DLSL method, defective regions are represented by black and white patterns, regardless of shape, a size, or orientation. Therefore, defects can be found by the black and white patterns in the corresponding images. Second, we propose a scheme for detecting defects in steel surface images acquired using the DLSL method. The presence of scales strongly affects the optical properties of the surface. Moreover, the textures of steel plate images vary greatly because of the temperature and grade of the steel. Therefore, conventional filter design methods are not effective for different image textures. A sub-optimal scheme based on an optimized FIR filter is proposed in this paper. Finally, experimental results conducted on steel surface images from an actual steel production line show the effectiveness of the proposed algorithm.

Analysis on image expressible region of integral floating

Sung-Wook Min, Young Min Kim, and Junkyu Yim

Doc ID: 249091 Received 01 Sep 2015; Accepted 22 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: We newly define the region where 3D images can be reconstructed, named image expressible region, in the integral floating display using the ray-distribution information. In this paper, the image expressible region and the viewing region of the integral floating system are analyzed to resolve the image cropping which is one of the problems of the integral floating system due to the virtual aperture which is called the viewing window. The ray distribution based on ray optics helps us to define the both regions accurately. The image cropping can be removed by floating the 3D image in the newly defined image expressible region. Two experiments for verifying the image expressible region and the viewing region are performed and the results are presented. The analysis of this paper can be useful to maximize the viewing properties of integral floating.

Carrier-envelope phase changes in the focal region: propagation effects measured by spectral interferometry

Balazs Major, Dániel Nemes, Miguel Porras, Zoltan Horvath, and Attila Kovacs

Doc ID: 250801 Received 24 Sep 2015; Accepted 22 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: Spectral interferometric measurements are presented which show how wave propagation affects the carrier-envelope phase (CEP) of an ultrashort pulse in the focal region, and results in variations that are different from the Gouy phase shift. Wavelength-dependent properties of the input beam are investigated and are seen to influence how the CEP is altered. The measured CEP changes show characteristics similar to the variations predicted by theory.

Electrically actuated phase-change pixels for transmissive and reflective spatial light modulators in the near and mid infrared

Joshua Hendrickson, Richard Soref, Haibo Liang, and Jianwei Mu

Doc ID: 251566 Received 07 Oct 2015; Accepted 21 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: Transmissive and reflective spatial light modulators have been designed and simulated for the 1.55 to 2.10 μm spectral region. An electrically actuated layer of phase-change material (PCM) was employed as the electro-optical medium for 2-state self-holding “light-to-dark” intensity modulation of free-space light beams. The PCM was sandwiched between transparent conductive N-doped Si or indium tin oxide (ITO) contact layers in a simple planar structure. A 100 to 500 nm PCM layer of Ge2Sb2Te5 (GST) was employed for optimum performance at 1.55 μm where the transmissive-modulator insertion loss was around 4.5 dB. The GST light-dark contrast was found to be 32 dB. For the GST reflection-device, an included metal film (Ag) improved the 1.55 μm performance metrics to 0.7 dB of insertion loss with a contrast around 26 dB. The calculated performance for both types of spatial light modulators (SLMs) was robust to changes in the input incidence angle near normal incidence. Applications include infrared scene generation and signal processing.

Spectral supralinearity prediction of silicon photodiodes in the near-infrared range

Minoru Tanabe, Kuniaki Amemiya, Numata Takayuki, and Daiji Fukuda

Doc ID: 252491 Received 02 Nov 2015; Accepted 21 Nov 2015; Posted 24 Nov 2015  View: PDF

Abstract: A model describing spectral supralinearity for a silicon photodiode in the near-infrared region is presented. This theoretical model is based on the internal quantum efficiency model of the photodiode using Shockley-Read-Hall recombination, which depends on the inner structure parameters of the photodiodes. Comparing the experimental results with the theoretical calculation results, the model enables us to quantitatively predict the starting power level, shape, and wavelength dependence of the supralinearity for a silicon photodiode. This model contributes to high-accuracy measurements over wide optical power ranges and various incident wavelengths.

Fabrication and application of heterogeneous printed mouse phantoms for whole animal optical imaging

Kevin Webb, Brian Bentz, Anmol Chavan, Dergan Lin, and Esther Tsai

Doc ID: 249996 Received 14 Sep 2015; Accepted 21 Nov 2015; Posted 23 Nov 2015  View: PDF

Abstract: This work demonstrates the usefulness of 3D printing for optical imaging applications. Progress in developing optical imaging for biomedical applications requires customizable and often complex objects for testing and evaluation. There is therefore high demand for what have become known as tissue-simulating ``phantoms'. We present a new optical phantom fabricated using inexpensive 3D printing methods with multiple materials, allowing for the placement of complex inhomogeneities in complex or anatomically realistic geometries, as opposed to previous phantoms which were limited to simple shapes formed by molds or machining. We use diffuse optical imaging to reconstruct optical parameters in 3D space within a printed mouse to show the applicability of the phantoms for developing whole animal optical imaging methods. This phantom fabrication approach is versatile, can be applied to optical imaging methods besides diffusive imaging, and can be used in the calibration of live animal imaging data.

Confidence intervals for the encircled energy fraction and the half energy width

Giuseppe Vacanti

Doc ID: 241574 Received 28 May 2015; Accepted 20 Nov 2015; Posted 20 Nov 2015  View: PDF

Abstract: The Encircled Energy Fraction and its quantiles, notably the Half Energy Width, are routinely used to characterize the quality of X-ray optical systems. They are however always quoted without a statistical error. We show how non-parametric statistical methods can be used to redress this situation, and we discuss how the knowledge of the statistical error can be used to speed up the characterization efforts for future X-ray observatories.

Unified Real-Time Direct and Coherent OFDM Optical Transmission Scheme

Stanley Johnson and Milorad Cvijetic

Doc ID: 249008 Received 31 Aug 2015; Accepted 18 Nov 2015; Posted 20 Nov 2015  View: PDF

Abstract: We experimentally demonstrate a novel unified real-time direct and coherent orthogonal frequency division multiplexing (OFDM) scheme. This self-coherent OFDM scheme simplifies receiver architecture and provides interchangeability between direct and coherent receivers using the same unified transmitter. We have experimentally verified the resilience of the direct detection mode to fiber nonlinearities and achieved receiver sensitivity improvement of up to 1.8 dB as compared to the conventional IMDD-OFDM scheme. We have also verified the effectiveness of a dual analyzer based balanced detection scheme.

Multiple-wavelength double random phase encoding with CCD-plane sparse-phase multiplexing for optical information verification

Wen Chen

Doc ID: 250041 Received 14 Sep 2015; Accepted 18 Nov 2015; Posted 19 Nov 2015  View: PDF

Abstract: A novel method is proposed by using multiple-wavelength double random phase encoding (MW-DRPE) with CCD-plane sparse-phase multiplexing for optical information verification. Two different strategies are applied to conduct sparse-phase multiplexing in the CCD plane, and significant advantages of the proposed optical system are illustrated. The results demonstrate that it is possible to achieve infinite capacity for optical multiple-image verification. The proposed optical verification strategy is implemented based on optical encoding, and the keys generated by optical encryption can further guarantee the safety of the designed optical multiple-image verification system. The proposed method provides a new alternative for DRPE-based optical information verification.

Fast phase-added stereogram algorithm for generation of photorealistic 3D content

Hoonjong Kang, Elena Stoykova, and Hiroshi Yoshikawa

Doc ID: 249896 Received 10 Sep 2015; Accepted 18 Nov 2015; Posted 18 Nov 2015  View: PDF

Abstract: A new phase-added stereogram algorithm for accelerated computation of holograms from a point cloud model is proposed. The algorithm relies on the hologram segmentation, sampling of directional information, and usage of the fast Fourier transform with a finer grid in the spatial frequency domain than is provided by the segment size. The algorithm gives improved quality of reconstruction due to new phase compensation introduced in the segment fringe patterns. The result is finer beam steering leading to high peak intensity and large peak signal-to-noise ratio in reconstruction. The feasibility of the algorithm is checked by generation of 3D contents for a color wavefront printer.

Spectral broadening in high power Yb-doped fiber lasers employing narrowlinewidth multi-longitudinal-mode oscillators

ZHihua Huang, Xiaobao Liang, Chengyu Li, Honghuan Lin, Qi Li, wang jianjun, and feng jing

Doc ID: 252195 Received 21 Oct 2015; Accepted 18 Nov 2015; Posted 18 Nov 2015  View: PDF

Abstract: High power continuous wave fiber lasers with narrowlinewidth is required for spectral beam combining system. A $2.9~\rm{kW}$ Yb-doped fiber laser with output linewidth as narrow as $0.31~\rm{nm}$ employing a narrowlinewidth multi-longitudinal-mode oscillator is experimentally demonstrated. The numerical simulations reveal that the spectral broadening factor of the bandwidth grows almost linearly with injected mode number which provides a potential way to further suppress the nonlinear spectral broadening in high power fiber lasers.

Generation of arbitrary order Bessel beams via 3D printed axicons at THz frequency range

Jinsong Liu, Xuli Wei, Changming Liu, Kejia Wang, Zhenggang Yang, Zhongqi Zhang, and Niu ting

Doc ID: 251407 Received 05 Oct 2015; Accepted 17 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: We present the generation of arbitrary order Bessel beams at 0.3 THz through the implementation of suitably designed axicons based on 3D printing technology. The helical axicons which possess thickness gradient in both radial and azimuthal direction, can convert the incident Gaussian beam into the high-order Bessel beam with spiral phase structure. The evolution of the generated Bessel beams are characterized experimentally with three-dimensional field scanner. Moreover, the topological charges carried by the high-order Bessel beams are determined by the fork-like interferograms. This 3D printing based Bessel beam generation technique is useful not only for THz imaging systems with zero-order Bessel beams, but also for future orbital angular momentum based THz free space communication with higher-order Bessel beams.

Formation of holographic polymer-dispersed liquid crystal memory by angle-multiplexing recording for optically reconfigurable gate arrays

Akifumi Ogiwara and Minoru Watanabe

Doc ID: 251413 Received 05 Oct 2015; Accepted 17 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: Formation of holographic polymer-dispersed liquid crystal (HPDLC) memory for an optically reconfigurable gate array is discussed for the angle-multiplexing recording by controlling the laser interference exposure in liquid crystal (LC) composites. The successive laser illumination system to record the various configuration contexts at the specified region and angle in HPDLC memory is constructed by using the combination of a half mirror and a photomask placed on the motorized stages under the control of a personal computer (PC). The effect of laser exposure energy on the formation of holographic memory is investigated by the measurement of diffraction intensity as a function of exposure energy during the grating formation process and the observation of internal grating structure by SEM. The optical reconfiguration in the gate-array VLSI is executed for configuration contexts shown as OR and NOR circuits reconstructed by the laser irradiation at different incident angle for a specified region in the HPDLC memory.

Spectral Characterization of Nano-Structured Birefringent Porous Silicon

Shlomo Ruschin, Keren Hakshur, Yuval Yifat, and Amit Levin

Doc ID: 246024 Received 20 Jul 2015; Accepted 16 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: We present measurements and analysis of the reflection spectrum of white light from a highly birefringent porous silicon layer at different polarization states. We report an anomalous pattern in the spectrum of linearly polarized light at 450 with respect to the principal axes of the layer. This spectrum comprises a combination of two interference effects, namely the Fabry-Perot type multiple-beam interference present in a simple thin film, and a two-wave interference caused by the beat of two combined orthogonally polarized waves propagating in the birefringent medium. We perform a Fourier analysis of the measured reflected spectra. This analysis furnishes a powerful tool in order to separate the two interference mechanisms and determine the degree of coherence of their superposition.

A neural network method to correct bidirectional effects in water-leaving radiance

Yongzhen Fan, Wei Li, Kenneth Voss, and Knut Stamnes

Doc ID: 246332 Received 20 Jul 2015; Accepted 16 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: Ocean color algorithms that rely on "atmospherically corrected" nadir water-leaving radiances to infer information about marine constituents such as the chlorophyll concentration, depend on a reliable method to convert the angle-dependent measured radiances from the observation direction to the nadir direction. It is also important to convert the measured radiances to the nadir direction when comparing and merging products from different satellite missions. The standard correction method developed by Morel and coworkers requires knowledge of the chlorophyll concentration (CHL). Also, the standard method was developed based on the Case 1 (open ocean) assumption, which makes it unsuitable for Case 2 situations such as turbid coastal waters. We introduce a neural network method to convert the angle-dependent water-leaving radiance (or the corresponding remote sensing reflectance) from the observation direction to the nadir direction.This method relies neither on an "atmospheric correction" nor on prior knowledge of the water constituents or the inherent optical properties. It directly converts the remote sensing reflectance from an arbitrary slant viewing direction to the nadir direction by using a trained neural network. This method is fast and accurate, and it can be easily adapted to different remote sensing instruments. Validation using NuRADS measurements in different types of water shows that this method is suitable for both Case 1 and Case 2 waters. In Case 1 or chlorophyll-dominated waters, our neural network method produces corrections similar to those of the standard method. In Case 2 waters, especially sediment-dominated waters, a significant improvement was obtained compared to the standard method.

Sub-500 nm hard x-ray focusing by compound long kinoform lenses

Weifan Sheng, Keliang Liao, Jing Liu, Hao Liang, Xuehui Wu, Kai Zhang, Qingxi Yuan, and Futing Yi

Doc ID: 247942 Received 13 Aug 2015; Accepted 16 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: The focusing performance of PMMA compound long kinoform lenses (CLKLs) with 70 μm aperture, 19.5 mm focal length was characterized with 8 keV x-rays using knife-edge scan method at 4W1A transmission x-ray microscope (TXM) beamline of Beijing Synchrotron Radiation Facility (BSRF). The experiment result shows a best full-width-at-half-maximum (FWHM) peak size of 440 nm with 31% diffraction efficiency.

Switching from electromagnetically induced absorption grating to electromagnetically induced phase grating in a closed-loop atomic system

Mohammad Mahmoudi and Azar vafarard

Doc ID: 245417 Received 06 Jul 2015; Accepted 16 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: The electromagnetically induced grating is investigated in a four level double V-type quantum system. It is shown that the electromagnetically induced transparency establishes because the cross-Kerr nonlinear effect can be cancelled by the four-wave mixing in a closed -loop atomic system. It is demonstrate that the diffraction of the probe beam depends on the relative phase of applied fields and can be controlled by this parameter. We find that an additional nonlinear contribution is established in the medium response by applying a microwave field to the system and the electromagnetically induced absorption grating turns to the electromagnetically induced phase grating. This contribution leads to 100% diffraction efficiency in the first-order direction, so we can say that the proposed grating could be considered as a special candidate for the optical networking and communication.

Intra-film separation of sol-gel film under nanosecond irradiation

Hu Wang, Hongji Qi, Jiaoling Zhao, Bin Wang, Yingjie Chai, and Jianda Shao

Doc ID: 248880 Received 28 Aug 2015; Accepted 16 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: We have observed large scale intra-film separation after the irradiation of sol-gel film with single Nd:YAG pulse (1064nm, 12ns) in air. The irradiated but undamaged surface or the surface after intra-film separation is densified. These damage features are distinctly different from the scalding surface on physical vapour deposited film or the ripple structures on bulk material, which indicates the extreme pressure gradients at the free surface-film interface. The sub-micron size melted cavity in the center of damage pit is related with the nanoscale absorber. A model combining defect-induced underground explosion and laser-supported surface breakdown wave is used to explain the phenomenon of intra-film separation.

Improved Synthetic-Heterodyne Michelson Interferometer Vibrometer using Phase and Gain Control Feedback

Michael Connelly, José Henrique Galeti, and Cláudio Kitano

Doc ID: 250740 Received 24 Sep 2015; Accepted 16 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: Synthetic-heterodyne demodulation is a useful technique for dynamic displacement and velocity detection in interferometric sensors as it can provide an output signal which is immune to interferometric drift. With the advent of cost effective, high-speed real-time signal processing systems and software, processing of the complex signals encountered in interferometry has become more feasible. In synthetic-heterodyne, to obtain the actual dynamic displacement or vibration of the object under test requires knowledge of the interferometer visibility and also the argument of two Bessel functions. In this paper a new synthetic-heterodyne demodulation method is described leading to an expression for the dynamic displacement and velocity of the object under test that is significantly less sensitive to the received optical power. In addition the application of two independent phase and gain feedback loops is used to compensate for the non-ideal gain and phase response of the anti-aliasing filter required for the signal acquisition of the received wideband interferometer signal. The efficacy of the improved system is demonstrated by measuring the displacement sensitivity frequency response and linearity of a piezoelectric mirror-shifter (PMS) over a range of 200 Hz to 9 kHz. In addition the system is used to measure the response of the PMS to triangular and impulse type stimuli. The experimental results show excellent agreement with measurements taken using two independent industry standard calibration methods.

Real-time measurement of temperature variation during nanosecond pulsed laser induced contamination deposition

Dimitrios Kokkinos, Patrick Gailly, Marc Georges, Georgios Tzeremes, Pierre Rochus, and Karl Fleury-Frenette

Doc ID: 249016 Received 01 Sep 2015; Accepted 15 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: In this paper a study of the heat generation during UV Laser Induced Contamination (LIC) and potentially resulting subsequent thermal damage is presented. This becomes increasingly interesting when optics with delicate coatings are involved. During LIC radiation can interact with out-gassing molecules both in the gas phase and at the surface, triggering chemical and photo-fixation reactions. This is a major hazard, in particular for laser units operating under vacuum conditions such as for space applications. The intense photon flux not only affects the contaminant deposition rate but also alters their chemical structure that can increase their absorption coefficient. Over cumulative irradiation shots these molecules formed deposits that increasingly absorb photons and produce heat as a by-product of de-excitation eventually leading to thermal damage. One could better asses the risk of the latter with the knowledge of temperature during the contamination process. For this purpose thermoreflectance technique is used here to estimate the temperature variation from pulse to pulse during contamination deposition through the analysis of a temperature-dependent surface reflectance signal.

Viewing angle enhancement of integral imaging display using Bragg mismatched reconstruction of holographic optical elements

Byoungho Lee, Seungjae Lee, Changwon Jang, Jaebum Cho, Jiwoon Yeom, and Jinsoo Jeong

Doc ID: 249967 Received 11 Sep 2015; Accepted 15 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: Holographic optical element (HOE) based integral imaging display can be applied to augmented reality. However, narrow viewing angle is a bottleneck for commercialization. Here, we propose a method to enhance viewing angle of integral imaging display using Bragg mismatched reconstruction of HOEs. Viewing angle of integral imaging display can be enlarged with two probe waves, which form two different viewing zones. The effect of Bragg mismatched reconstruction is analyzed with simulation and experiment. In order to show feasibility of the proposed method, displaying experiment is demonstrated.

Microtomography imaging of an isolated plant fiber: a digital holographic approach

Christophe Poilane, Mokrane Malek, haithem khelfa, Pascal Picart, and Denis MOUNIER

Doc ID: 250047 Received 17 Sep 2015; Accepted 15 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: This paper describes a method for optical projection tomography, for the 3D in-situ characterization of micrometric plant fibers. The proposed approach is based on digital holographic microscopy, the holographic capability being convenient to compensate for the runout of the fiber during rotations. The setup requires a telecentric alignment to prevent from the changes in the optical magnification, and calibration results show the very good experimental adjustment. Amplitude images are obtained from the set of recorded and digitally processed holograms. Refocusing of blurred images and correction of both runout and jitter are carried out to get appropriate amplitude images. The 3D data related to the plant fiber are computed from the set of images using a dedicated numerical processing. Experimental results exhibit the internal and external shapes of the plant fiber. These experimental results constitute the first attempt to obtain 3D data of flax fibers, about 10 µm in diameter, with a full-field optical tomography approach using light in the visible range.

Optical compression and encryption system combining multiple measurement matrices with fractional Fourier transform

Guanzheng Tan and Jiawang Yi

Doc ID: 251598 Received 08 Oct 2015; Accepted 15 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: Optical cryptosystems combined with compressed sensing can achieve compression and encryption simultaneously. But they usually use the same measurement matrix to sample all blocks of an image, which make it easy to estimate the measurement matrix in the chosen-plaintext attack. In this paper, we propose a robust scheme adopting multiple measurement matrices to overcome this shortcoming. The matrices can be efficiently derived by applying random row exchanging to a basic one, which is also encoded into the fractional Fourier transform (FrFT) domain to improve visual effect of wrongly decrypted images. Chaos-based pixel scrambling is added into our double FrFT cryptosystem to guarantee its nonlinearity. Simulation results have shown the security and effectiveness of our scheme.

Simultaneous measurement of strain and temperature by two peanut tapers with embedded FBG

Sumei Wang, Lingya Lv, Lan Jiang, Fei Zhang, Zhitao Cao, Peng Wang, Yi Jiang, and Yongfeng Lu

Doc ID: 249369 Received 02 Sep 2015; Accepted 15 Nov 2015; Posted 17 Nov 2015  View: PDF

Abstract: A compact optical fiber sensor for simultaneous measurement of strain and temperature is designed and experimentally investigated. The proposed sensor consists of a two-peanut-taper Mach–Zehnder interferometer (MZI) and in-line embedded fiber Bragg grating (FBG). The sensor at length of 35mm presents strain sensitivities 1.07pm/µε and 0.891pm/µε, the temperature sensitivities are 55.35pm/℃ and 10.85pm/℃, for MZI and FBG, respectively. Through tapering the center of the sensor by a fusion splicer, the strain sensitivity of the MZI is improved to 1.93pm/µε. The resolutions for strain and temperature measurement are ±3.104µε and ±0.194℃with the wavelength resolution of 5pm. The experimental results show that the sensor is able to simultaneously measure strain and temperature by sensitivity matrix with advantages such as simple structure, compact size, ease of fabrication, low cost, etc.

Ratiometric optical fiber sensor for dual sensing copper ion and dissolved oxygen

cheng-shane chu and Chih-Yung Chuang

Doc ID: 252258 Received 20 Oct 2015; Accepted 14 Nov 2015; Posted 18 Nov 2015  View: PDF

Abstract: This paper develops a new ratiometric optical dual sensor for Cu2+ ions and dissolved oxygen (DO) incorporating a sol-gel matrix doped with palladium tetrakis pentafluorophenyl porphine (PdTFPP) as the oxygen-sensitive material, CdSe quantum dots (QDs) as the Cu2+ ion-sensing material and 7-amino-4-trifluoromethyl coumarin (AFC) as the Cu2+/DO practically independent fluorescent dye. The feasibility of coating an optical fiber with the sensing film to fabricate a ratiometric optical fiber dual sensor is investigated. Using an LED with a central wavelength of 405 nm as an excitation source, it is shown that the emission wavelengths of the Cu2+ ion-sensitive, DO-sensitive dye and the reference dye have no spectral overlap and therefore permit Cu2+ ion and DO concentration to be measured using a ratiometric-based method. The ratiometric optical fiber dual sensor has been tested with regard to monitoring different Cu2+ ion (0-10 μM) and DO concentrations (0-38 mg/L). The results show that the luminescence properties of the Cu2+ ion sensor are independent of the presence of the oxygen sensor, and have a uniquely good linear response in the 0-10 μM range. The proposed ratiometric sensing approach presented in this study has the advantage of suppressing spurious fluctuations in the intensity of the excitation source.

Evolution properties of partially coherent flat-topped vortex hollow beam in oceanic turbulence

Dajun Liu, Yaochuan Wang, and Hongming Yin

Doc ID: 249243 Received 01 Sep 2015; Accepted 14 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: Based on the theory of coherence, the partially coherent flat-topped vortex hollow beam is firstly introduced. The analytical propagation equation for partially coherent flat-topped vortex hollow beam in oceanic turbulence is derived by using the extended Huygens-Fresnel diffraction integral formula and the spectrum of oceanic turbulence. The influence of coherence length, beam order N, the topological charge M and the parameters of oceanic turbulence on the evolution properties of partially coherent flat-topped vortex hollow beam propagating in oceanic turbulence are obtained by using the numerical examples.

Real-time pattern recognition using an optical generalized Hough transform

Ariel Fernández, Jorge Flores, Julia Alonso, and Jose Ferrari

Doc ID: 248965 Received 31 Aug 2015; Accepted 14 Nov 2015; Posted 16 Nov 2015  View: PDF

Abstract: We present some pattern recognition applications of a generalized optical Hough transform and the temporal multiplexing strategies for dynamic scale and orientation-variant detection. Unlike computer-based implementations of the Hough transform, in principle its optical implementation does not impose restriction neither in execution time, nor over the resolution of the images or frame rate of the videos to be processed, which is potentially useful for real-time applications. Validation experiments are presented.

Transient gain analysis of gain-switched semiconductor lasers during pulse lasing

Shaoqiang Chen, Takashi Ito, Akifumi Asahara, HIDEKAZU NAKAMAE, TAKAHIRO NAKAMURA, Masahiro Yoshita, CHANGSU KIM, Baoping Zhang, Hiroyuki Yokoyama, Tohru Suemoto, and Hidefumi Akiyama

Doc ID: 249724 Received 08 Sep 2015; Accepted 13 Nov 2015; Posted 13 Nov 2015  View: PDF

Abstract: We analyzed the transient-gain properties of three gain-switched semiconductor lasers with different materials and cavity structures during pulse lasing. All the semiconductor lasers were pumped with impulse optical pumping, and all the generated gain-switched output pulses were well described by exponential functions in their rise parts, wherein the transient gains were derived according to the rate-equation theoretical model. In spite of the different laser structures and materials, the results consistently demonstrated that a higher transient gain produces shorter output pulses, indicating the dominant role of higher transient gain in the generation of even shorter gain-switched pulses with semiconductor lasers.

Multilayer four-flux matrix model accounting for directional-diffuse light transfers

Lionel Simonot, Roger Hersch, Mathieu Hébert, and Serge Mazauric

Doc ID: 249973 Received 11 Sep 2015; Accepted 12 Nov 2015; Posted 13 Nov 2015  View: PDF

Abstract: The four-flux model is a method to solve light radiative transfer problems in planar, possibly multilayer structures. The light fluxes are modeled as two collimated and two diffuse beams propagating forwards and backwards perpendicularly to the layer stack. In the present contribution, we develop a four-flux model relying on a matrix formalism to determine the reflectance and transmittance factors of stacks of components by knowing those of each individual component. This model is also extended to generate the bidirectional scattering distribution function (BSDF) of the stack by considering an incoming collimated flux in any direction, and by taking into account the directionality of the diffuse fluxes exiting from the material at the border components of the stack. The model is applied to opaque Lambertian backgrounds with flat or rough interface, for which analytical expressions of the BSDF are obtained.

Experimental investigation on the infrared refraction and extinction properties of rock dust in tunneling face of coal mine

Yanming Wang, wenzheng Wang, and Guoqing Shi

Doc ID: 250776 Received 24 Sep 2015; Accepted 12 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: A comprehensively experimental research on fundamental optical properties of dust pollution in coal mine was presented. Rock dust generated in tunneling roadway was sampled and the spectral refractive index within infrared range of 2.5-25μm was obtained by FT-IR measurement and Kramers-Kronig model. The experimental results were validated to be consistent with equivalent optical constants simulated by effective medium theory based on the component analysis of X Ray Fluorescence which illustrates the most three mineral components are SiO2 (62.06%), Al2O3 (21.26%), Fe2O3 (4.27%). The refractive index and the spatial distribution tested by Filter dust and Particle Size Analyzer were involved in the simulation of extinction properties of rock dust along tunneling roadway solved by discrete ordinates method and Mie scattering model. The compared results illustrate that transmission are obviously enhanced with the increase of height from floor but weakened with increasing horizontal distance from air duct.

Reconstruction of laser-induced cavitation bubble dynamics based on a Fresnel propagation approach.

Luis Devia-Cruz, Santiago Camacho-Lopez, Victor Ruiz-Cortes, Francisco Pérez-Gutiérrez, Victoria Muñiz, and Guillermo Aguilar

Doc ID: 247589 Received 10 Aug 2015; Accepted 12 Nov 2015; Posted 13 Nov 2015  View: PDF

Abstract: A single laser-induced cavitation bubble in transparent liquids has been studied through a variety of experimental techniques. High-speed video with varying frame rate up to 20×107 fps is the most suitable to study non-symmetric bubbles. However, it is still expensive for most researchers and more affordable (lower) frame rates are not enough to completely reproduce bubble dynamics. This paper focuses on combining the spatial transmittance modulation (STM) technique, a single shot cavitation bubble and a very simple and inexpensive experimental technique, based on Fresnel approximation propagation theory, to reproduce a laser-induced cavitation spatial dynamics. Our results show that the proposed methodology reproduces a laser-induced cavitation event much more accurately than 75,000 fps video recording. In conclusion, we propose a novel methodology to reproduce laser-induced cavitation events that combines the STM technique with Fresnel propagation approximation theory that properly reproduces a laser-induced cavitation event including a very precise identification of the first, second and third collapses of the cavitation bubble.

Optical detection of glucose concentration in samples with scattering particles

Yu-Lung Lo, Li-Han Lin, Chia-Chi Liao, and Jian-Xiang Lin

Doc ID: 248228 Received 19 Aug 2015; Accepted 12 Nov 2015; Posted 13 Nov 2015  View: PDF

Abstract: An optical-based method is proposed for measuring the glucose concentration of samples containing scattering particles. In the proposed approach, a Stokes-Mueller reflection-based polarimetry technique is used to solve the Mueller matrices of a turbid glucose sample with circular birefringence (CB) and depolarization properties given six incident lights with different polarization states. Using an error function defined as the difference between the simulated output Stokes vectors and the experimental ones, a genetic algorithm (GA) is used to inversely derive the optical rotation and depolarization parameters of the experimental sample corresponding to the glucose concentration and scattering depolarization effect, respectively. The validity of the proposed method is demonstrated using glucose samples containing 0.02 ml and 0.04 ml lipofundin, respectively.

Spectral narrowing and stabilization of interband cascade laser by volume Bragg grating

Leonid Glebov, George Venus, Vadim Smirnov, Olexiy Mokhun, William Bewley, Charles Merritt, Chadwick Canedy, Chul Soo Kim, Mijin Kim, Igor Vurgaftman, Jerry Meyer, and Konstantin Vodopyanov

Doc ID: 248709 Received 06 Oct 2015; Accepted 12 Nov 2015; Posted 25 Nov 2015  View: PDF

Abstract: A VBG recorded in PTR glass was used to spectrally lock the emission from an 18-µm-wide ICL ridge to a wavelength of 3.12 µm. The spectral width of emission into the resonant mode is narrowed by more than 300 times, and the thermal wavelength shift is reduced by 60 times. While the power loss penalty is about 30%, the spectral brightness increases by 200 times.

Propagation characteristics of continuously tuning distorted Airy-like beams

Yixian Qian and liangwei dong

Doc ID: 245661 Received 09 Jul 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: We investigate theoretically and observe experimentally a continuously tuning distorted Airy-like beam, which are generated by introducing a controllable rotation angle factor into phase pattern. We can not only tune flexibly beam wavefront by using the introduced angle factor, meanwhile we also can control readily the main lobes of these beams to propagate along specified parabolic trajectories. Their optical behaviors are discussed and demonstrated. The experiments are performed and the results are consistent with the theoretical results. The intriguing characteristic of our proposed continuously tuning Airy-like beams could provide more degrees of freedom, and is likely to give rise to new potential applications.

Fluoride coatings for vacuum ultraviolet reflection filters

Bincheng Li, Guo Chun, Kong Mingdong, and lin DaVie

Doc ID: 247863 Received 12 Aug 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: LaF3/MgF2 reflection filters with a high spectral discrimination capacity of the atomic oxygen lines at 130.4nm and 135.6nm, which were employed in vacuum ultraviolet imagers, were prepared by molybdenum boat thermal evaporation. The optical properties of reflection filters were characterized by a high-precision vacuum ultraviolet spectrophotometer. The vulnerability of the filter’s microstructures to environmental contamination and the recovery of the optical properties of the stored filter samples with ultraviolet ozone (UVO) cleaning were experimentally demonstrated. For reflection filters with the optimized non-quarter-wave multilayer structures, the reflectance ratios R135.6nm/R130.4nm of 92.7 and 20.6 were achieved for 7°and 45°angles of incidence (AOI), respectively. On the contrary, R135.6nm/R130.4nm ratio of 12.4 was obtained for a reflection filter with a standard  stack multilayer structure with H/L=1/4 at 7°AOI.

Numerical analysis of lasing characteristics in highly bend-compensated large mode-area ytterbium-doped double-clad leakage-channel fibers

G Thavasi Raja, Raktim Haldar, and S Varshney

Doc ID: 249553 Received 07 Sep 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: The bend-induced mode-area reduction and thermal effects are vital factors that affect the power scaling of fiber lasers. Recently, bend-compensated large-mode-area double-clad modified hybrid leakage channel fiber (M-HLCF) has been reported with mode-area greater than 1000 μm2, while sustaining the single-mode behavior at 1064 nm for high-temperature environments. In this work, the lasing characteristics of a newly designed ytterbium-doped double-clad M-HLCF (YDMHLCF) have been numerically investigated for strongly pumped conditions. The doped-region size is optimally found through simulations, equivalent to the size of core diameter ~38 μm in order to achieve maximum conversion efficiency for the bend and straight cases. Numerical simulations further confirm that a 2 m long YDMHLCF exhibits slope efficiency of 78 %, and conversion efficiency of 79 % for the straight case and also almost same for the practical bending radius of 7.5 cm when pumped with a 975 nm laser source.

Modeling the whispering gallery microresonator based optical modulator

Nikolay Pavlov, Nikita Kondratyev, and Michael Gorodetsky

Doc ID: 250294 Received 18 Sep 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: We present a theoretical analysis and numerical simulations of electro-optic double resonant modulator based on interaction of fundamental whispering gallery modes with a radio frequency field in a dielectric microdisc made from electro-optical material. Models of the modulator in 2D and 3D are developed and compared. Both optical and RF fields are simulated using finite element method. The magnitude of the effect in such system may be maximized with optimum configuration of a microstrip resonator used for RF coupling.

Beam splitters for p-polarized light using a high-index quarter-wave layer embedded in a low-index cube prism

Rasheed Azzam

Doc ID: 247429 Received 06 Aug 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: A high-index quarter-wave layer (QWL) embedded in a low-index cube prism is designed to achieve 50%-50% beam splitting for incident p-polarized light at 45-deg angle of incidence. This is accomplished when the ratio of refractive index of the QWL to that of the prism is n = 3.336666. Such refractive index ratio is realized, e. g., with a Ge QWL embedded in a LiF cube at 8.357 μm wavelength. Spectral, angular, and film-thickness sensitivities of this mid-IR BS are presented. Free-standing QWL pellicles of GaP and GaAs can also function as 50%-50% beam splitters for incident p-polarized light at 45-deg at visible and IR wavelengths of 0.610 μm and 2.929 μm, respectively. An application in interferometry is briefly discussed.

Source Spectrum Shaping Method for Low-Coherence Interferometry

Anna Pakula, Leszek Salbut, and Slawomir Tomczewski

Doc ID: 247529 Received 06 Aug 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: Low coherence interferometry suffers mainly from low S/N ratio. By using Source Spectrum Shaping Method (SSSM), authors enhance the visibility of the zero-order fringe (V) and S/N ratio in LCI. Presented approach was analysed numerically for a set o theoretical Gaussian light sources, with different central wavelengths and different spectrum widths. The results have shown the significant improvement of the visibility V. Additionally a set of commercially available LEDs was analysed to find best possible setup. Results of numerical calculations were verified experimentally in SSSM n Low-coherence Twyman-Green interferometric setup equipped with three light sources.

Frequency Stabilization of Optically Pumped Far Infrared Laser to the Harmonic of a Microwave Synthesizer

Andriy Danylov, Alexander Light, Jerry Waldman, and Neal Erickson

Doc ID: 248071 Received 17 Aug 2015; Accepted 11 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: Measurements of the frequency stability of a far-infrared molecular laser have been made by mixing the harmonic of an ultra-stable microwave source with a portion of the laser output signal in a THz Schottky diode balanced mixer. The 3 GHz difference-frequency signal was used in a frequency discriminator circuit to lock the laser to the microwave source. Comparisons of the short and long term laser frequency stability under free-running and locked conditions show a significant improvement with locking. Short-term frequency jitter was reduced by an order of magnitude, from approximately 40 kHz to 4 kHz and long-term drift was reduced by more than three orders of magnitude, from approximately 250 kHz to 80 Hz. The results, enabled by the efficient Schottky-diode balanced mixer downconverter, demonstrate that ultrastable microwave-based frequency stabilization of THz OPLs will now be possible at frequencies extending well above 4.0 THz.

Performance characteristics of dual pumped hybrid EDFA/Raman optical amplifier

Mostafa Hussein Aly and osama mahran

Doc ID: 252323 Received 22 Oct 2015; Accepted 11 Nov 2015; Posted 19 Nov 2015  View: PDF

Abstract: This paper suggests a hybrid amplifier using erbium doped fiber amplifier (EDFA) and Raman amplifier (RA) with dual pump configuration. This hybrid EDFA/RA optical amplifier (HOA) is dual pumped. EDFA is forward biased with 980 nm while RA is reverse biased with 1450 nm in the dual pump configuration. Both gain and noise figure are experimentally studied and compared with experimental values of EDFA/Raman HOA with different pump configurations. The optimum values of the affecting parameters are investigated to get the best characteristics of the HOA including high gain and low noise figure. A high gain of 31 dB and low noise of 3.8 dB are achieved. In addition, the flat gain in the wavelength range 1545-1565 nm and the optical signal to noise ratio is reduced to 24 dB.

A precision enhancement method for multiplexing image detector based sun sensor with varying and coded apertures

Geng Wang, Fei Xing, Minsong Wei, and Zheng You

Doc ID: 250295 Received 22 Sep 2015; Accepted 10 Nov 2015; Posted 11 Nov 2015  View: PDF

Abstract: The multiplexing image detector based sun sensor has an extremely high accuracy and a large Field of View (FOV) due to its large focal length, hundreds of apertures and decades of sub-FOVs. Because of the optical interference effect, the diffraction spots of the sun on the image detector will be greatly influenced by the incident sun angles and the sizes of apertures, which affect the extraction precision of sun spot centroid to great extent. In this work, according to “Huygens-Fresnel” diffraction integral formula and the aperture numerical simulations at different incident sun angles, we presented a novel proposal for the mask with varying aperture sizes in different sub-FOVs and encoded the aperture arrays with distance information for sub-FOV distinction. The laboratory test results indicated that, compared with the same aperture pattern design, the extraction precision of the sun spots with the varying apertures pattern design was better in large-angle and more stable in the whole FOV, and the sun sensor could reach precision of 1.32"(1σ) at 50° incident sun angle.

Dual-loss-modulated QML laser intracavity pumped, temperature-tuned subnanosecond KTP OPO

Hongwei Chu, Jia Zhao, Kejian Yang, Shengzhi Zhao, Dechun Li, Tao Li, Guiqiu Li, and qiaowen chao

Doc ID: 249416 Received 10 Sep 2015; Accepted 10 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: Using an acousto-optic modulator (AOM) and Cr4+:YAG as the dual-loss modulation, an intracavity KTiOPO4 (KTP) optical parametric oscillator (OPO) pumped by a simultaneously Q-switched and mode-locked (QML) YVO4/Nd:YVO4 laser was realized. The shortest mode-locking pulse duration of the signal wave at 1573 nm was directly measured as 450 ps at an AOM frequency of 2 kHz and a diode pump power of 10.5 W, corresponding to a peak power of 35.5 kW. The temperature tuning of the output signal wavelength was realized in the range from 1571.99 to 1572.61 nm with a blueshit ratio of 0.027 nm/℃. A set of coupled rate equations for the dual-lossmodulated QML laser pumping intracavity OPO was built up for the first time. The numerical solutions were fitted with the experimental results.

Automated tracking of temporal displacements of red blood cell obtained by time-lapse digital holographic microscopy

Inkyu Moon, Faliu Yi, and Benjamin Rappaz

Doc ID: 249998 Received 14 Sep 2015; Accepted 10 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: Red blood cell (RBC) phase images that are numerically reconstructed by digital holographic microscopy (DHM) can describe the cell structure and dynamics information beneficial for a quantitative analysis of RBCs. However, RBCs investigated with time-lapse DHM undergo temporal displacements when their membranes are loosely attached to the substrate during sedimentation on a glass surface or due to the microscope drift. Therefore, we need to develop a tracking algorithm to localize the same RBC among RBC image sequences and dynamically monitor its biophysical cell parameters; this information is helpful for studies on RBC-related diseases and drug tests. Here, we propose a method, which is a combination of the mean-shift algorithm and Kalman filter, to track a single RBC and demonstrate that the optical path length of the single RBC can be continually extracted from the tracked RBC. The Kalman filter is utilized to predict the target RBC position in the next frame. Then, the mean-shift algorithm starts execution from the predicted location, and a robust kernel, which is adaptive to changes in RBC scale, shape, and direction, is designed to improve the accuracy of the tracking. Finally, the tracked RBC is segmented and parameters such as the RBC location are extracted to update the Kalman filter and the kernel function for mean-shift tracking; the characteristics of the target RBC are dynamically observed. Experimental results show the feasibility of the proposed algorithm.

Calibration of windowless photodiode for XUV pulse energy measurement

Karel Kolacek, Jiri Schmidt, Jaroslav Straus, and Oleksandr Frolov

Doc ID: 250145 Received 16 Sep 2015; Accepted 10 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: For energy measurement of XUV pulses no universal commercially available device is available. Therefore, a coaxial setup of vacuum photodiode was developed and tested. First its unsuccessful calibration at National Institute of Standards and Technology (USA) is mentioned. Then our own single-wavelength (46.9 nm) calibration procedure is in detail described. It is based on tabulated photoemission efficiency and on measured (1) anode collection efficiency, (2) attenuation of Al filters, and (3) attenuation of measuring cables. Some other relevant attenuating factors are also taken into account.

Diffractively Corrected Counter-rotating Rsiely Prisms

Xin Nie, Changxi Xue, and yang hongfang

Doc ID: 250203 Received 15 Sep 2015; Accepted 09 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: Using the vector refraction equation and the vector diffraction equation, we obtain the expressions of the direction cosines of the refractive ray of the two wedge prisms, and the diffractive ray of the two wedge grism, in which diffractive gratings were etched into the prism faces, to correct for chromatic aberrations. A mathematical model between the two vector equations is proposed to compare the difference angle chromatic aberrations when the Risley Prisms/Grisms rotating different angle. We conclude that the use of diffractively corrected prisms offer a new method to correct chromatic aberration in Risley Prisms.

A Multi-Wavelength Interferometry System for the Orion Laser Facility

Siddharth Patankar, Edward Gumbrell, Timothy Robinson, Hazel Lowe, Samuel Giltrap, Christopher Price, Nicholas Stuart, Paul Kemshall, Jim Fyrth, James Luis, Jonathan Skidmore, and Roland Smith

Doc ID: 250369 Received 17 Sep 2015; Accepted 09 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: We report on the design and testing of a multi-wavelength interferometry system for the Orion laser facility based upon the use of self-path matching Wollaston prisms. The use of UV corrected achromatic optics allows for both easy alignment with an eye safe light source and small (~ mm) offsets to the focal lengths between different operational wavelengths. Inteferograms are demonstrated at wavelengths corresponding to first, second and fourth harmonics of a 1054nm Nd:glass probe beam. Example data confirms the broadband achromatic capability of the imaging system with operation from the UV (263nm) to visible (527nm) and demonstrates that features as small as 5µm can be resolved for object sizes of 15mm by 10mm. Results are also shown for an off harmonic wavelength that will underpin a future capability. The primary optics package is accommodated inside the footprint of a Ten Inch Manipulator (TIM) to allow the system to be deployed from a multitude of viewing angles inside the 4m diameter Orion target chamber.

Fully Automated, High Speed, Tomographic Phase Object Reconstruction Using the Transport of Intensity Equation In Transmission and Reflection Configurations

Georges Nehmetallah, thanh nguyen, Dat Tran, Ahmad Darudi, and Peyman Soltani

Doc ID: 250378 Received 18 Sep 2015; Accepted 09 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: While traditional transport of intensity equation (TIE) based phase retrieval of a phase object is performed through axial translation of the CCD, in this work a tunable lens (TL-TIE) is employed in both transmission and reflection configurations. These configurations are extended to a 360o tomographic 3D reconstruction through multiple illuminations from different angles by a custom fabricated rotating assembly of the phase object. Synchronization circuitry is developed to control the CCD camera, and the Arduino board which in its turn controls the tunable lens and the stepper motor to automate the tomographic reconstruction process. Finally, a Maltab-based user friendly GUI is developed to control the whole system and perform tomographic reconstruction using both a multiplicative and inverse radon based techniques.

Aspect Ratio Engineering of Microlens Arrays in Thin-Film Flip-Chip Light-Emitting Diodes

Peifen Zhu, Nelson Tansu, Wei Sun, and Chee-Keong Tan

Doc ID: 250602 Received 21 Sep 2015; Accepted 09 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: The light extraction efficiency of thin-film flip-chip InGaN-based light-emitting diodes (LEDs) with TiO2 microlens arrays was calculated by employing finite-difference time-domain (FDTD) method. The microlens arrays formed by embedding hexagonal close packed TiO2 sphere arrays in polystyrene (PS) layer were placed on top of the InGaN LED to serve as an intermediate medium for the light extraction. By tuning the thickness of PS layer, both of the in-coupling and out-coupling efficiencies were optimized to achieve maximum light extraction efficiency. Thicker PS layer resulted in higher in-coupling efficiency while thinner PS layer led to higher out-coupling efficiency. Thus the maximum light extraction efficiency becomes a tradeoff between in-coupling efficiency and out-coupling efficiency. In addition, the cavity formed by PS layer also affects the light extraction from the LED. Our study reveals that the maximum light extraction efficiency of 86% was achievable by tuning PS thickness to 75 nm with maximized in-coupling and out-coupling efficiency accompanied by the optimized resonant cavity condition.

Fabry Perot Based Strain Insensitive PCF Modal Interferometer for Inline Sensing of Refractive Index and Temperature

Rajan Jha and Jitendra Dash

Doc ID: 250627 Received 22 Sep 2015; Accepted 09 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: We report a highly stable, compact strain insensitive inline microcavity based PCF modal interferometer for the determination of RI of analyte and temperature. The interferometer is fabricated by splicing one end of solid core PCF (SCPCF) with SMF and other end with Hollow core PCF (HCPCF). This is followed by cleaving the possible part of the solid glass portion present after the microcavity. The formation of the cavities at the end face of SCPCF results in reduction of the period of the interference pattern that helps in achieving distinctiveness in the measurement. Three sensor heads have been fabricated and each has different length of collapsed region formed by splicing SMF with SCPCF. The response of the sensor is found to be sensitive to the length of this collapsed region between SMF and SCPCF with a sensitivity of 53 nm/RIU and resolution of 1.8 × 10-4 RIU. The temperature response of the sensor is found to be linear having a temperature sensitivity of 12 pm/°C. In addition to these, the effect of strain on the proposed structure is analyzed in both wavelength and intensity interrogation.

Optical strain for monitoring of concrete failure mechanism with discontinuity

Sudipta Bhattacharjee and Debasis Deb

Doc ID: 250813 Received 25 Sep 2015; Accepted 09 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: Finite element based digital image correlation (FEM-DIC) is one of the most widely used non-contact techniques in the field of experimental mechanics for measurement of deformation/strain. In this paper, FEM-DIC method is refined by introducing concept of multilevel extended digital image correlation (X-DIC) which can also capture deformation across discontinuity planes if those exist in images. Using regular and enhanced displacements at each node, strain tensors are estimated by applying the concept of Smooth Particle Hydrodynamics (SPH). Numerical works are carried out to check the accuracy level of the developed algorithm by considering discrete discontinuity on the surface of a sample. Work is further extended to determine displacements and strains developed at the surface of several cubical concrete samples under uniaxial loading conditions. The tests are conducted until fractures are developed in the post-failure region. Using the concept of cumulative effective strain, a parameter is identified which can be used as a precursor in the object failure process.

Retina-like sensor based on lens array with large field of view

Qun Hao, Fan Fan, and Xuemin Cheng

Doc ID: 251117 Received 29 Sep 2015; Accepted 09 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: This paper puts forward a new kind of retina-like sensor based on lens array, which can be used in conventional optical system. This sensor achieves log-polar mapping by dividing imaging optical system’s image plane using lens array. In this paper the mathematical model has been set up with the relative structural parameters. Also, the simulation experiments and parameter analysis have been discussed to verify the reliability of this system. From the experiment results, it can be seen that this sensor realized the log-polar mapping with the transformed image outputted. Each lens corresponded to a circular region in the image plane with no crossover between different fields of view of adjacent lenses. When the number of rings changes, the relative error did not significantly change and this error could be reduced to 1% when lenses in each ring increased. The work widely enlarged the application of this kind of sensor, which will lay a theoretical foundation to retina-like sensor.

Analysis of buried interfaces in multilayers mirrors using grazing incidence EUV reflectometry near resonance edges

Mewael SERTSU, Marco Nardello, Angelo Giglia, Alain Corso, Chiara Maurizio, Larissa Juschkin, and Piergiorgio Nicolosi

Doc ID: 245667 Received 20 Jul 2015; Accepted 09 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: Accurate measurements of optical properties of multilayer mirrors (MLs) and chemical compositions of inter-diffusion layers are particularly challenging to date. In this work, an innovative and non-destructive experimental characterization method for multilayers is discussed. It is based on Extreme Ultraviolet (EUV) reflectivity measurements performed on a wide grazing incidence angular range at energy near resonance edges of low-Z elements in the ML components. This experimental method combined with the underlying physical phenomenon of abrupt changes of optical constants near EUV resonance edges enables to characterize optical and structural properties of multilayers with high sensitivity. Major advantage of the method is to perform detailed quantitative analysis of buried interfaces of multilayer structures in a non-destructive and non-imaging setup. Coatings of Si/Mo multilayers on Si substrate with period d=16 .4 nm, number of bilayers N=25 and different capping structures are investigated. Stoichiometric compositions of Si-on-Mo and Mo-on-Si interface diffusion layers derived. Effects of surface oxidation reactions and Carbon contaminations on the optical constants of capping layers and impact of neighboring atoms’ interactions on optical responses of Si and Mo layers are discussed.

Fiber Optic Hydrogen Sensor Based on an Etched Bragg Grating Coated with Palladium

Luis Coelho, Jose Luis Santos, Diana Viegas, and Jose Almeida

Doc ID: 248617 Received 25 Aug 2015; Accepted 09 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: A study of a sensor for hydrogen (H2) detection based on fiber Bragg gratings coated with palladium (Pd) with self-temperature compensation is presented. The cladding around the gratings was reduced down to 50 µm diameter by chemical etching process. One of the gratings was left uncoated and the other was coated with 150 nm of Pd. It was observed that palladium hydride has unstable behavior in environments with high humidity level. A simple solution to overcome this problem based on a Teflon tape is presented. The sensing device studied was able to respond to H2 concentrations in the range 0-1 % (v/v) at room temperature and atmospheric pressure, achieving sensitivities larger than 20 pm/% (v/v). Considering H2 concentrations in nitrogen up to 1%, the performance of the sensing head was characterized for different thicknesses of Pd coating ranging from 50 to 200 nm.

Traceable methods for characterization of dynamic stroboscopic scanning white light interferometer measurements

Ville Heikkinen, Ivan Kassamakov, Jeremias Seppä, Tor Paulin, Anton Nolvi, Antti Lassila, and Edward Hæggström

Doc ID: 249666 Received 09 Sep 2015; Accepted 09 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: Stroboscopic scanning white light interferometry (SSWLI) can be used for 3D imaging of oscillating samples. It allows measurement of µm to mm size samples with nm vertical precision. Unlike coherent light source systems the SSWLI can measure unambiguously samples with vertical steps. Traceability of the vertical displacement measurement is important with SSWLI since the height measurement is not related to any specific monochromatic light wavelength. For static measurements SSWLI can be calibrated using e.g. step height standards, but to characterize dynamic measurements traceable samples with accurate motion are needed due to error sources related to the frequency response of the SSWLI. In the presented method SSWLI measurements are performed on dynamic transfer standards which are characterized using a laser interferometer traceable to the SI-meter. In this work dynamic SSWLI measurements at sub-kHz to 10.7 kHz frequencies with µm range displacement are characterized. The expanded uncertainty (k=2) was 9.6 nm for a measured displacement of 766 nm at 10.7 kHz. The methodology can be used up to the frequency limits of the SSWLI using suitable samples.

Scattering by a conductive half-screen between isorefractive media

Yusuf Umul

Doc ID: 250113 Received 15 Sep 2015; Accepted 08 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: The scattering process of electromagnetic waves by a conductive half-plane, located between isorefractive media, is investigated. First of all the conductive sheet at the interface of isorefractive media is considered. The reflection and transmission coefficients of the plane are evaluated. The diffracted fields by the half-plane are obtained with the aid of a relation between the diffracted and scattered geometrical optics waves. The resultant field expressions are examined numerically.

Recent progress in see-through 3D displays using holographic optical element [Invited]

Byoungho Lee, Changwon Jang, Chang-Kun Lee, Jinsoo Jeong, Gang Li, Seungjae Lee, Jiwoon Yeom, and Keehoon Hong

Doc ID: 249272 Received 01 Sep 2015; Accepted 08 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: The principles and characteristics of the see-through 3D displays are presented. Especially, we focus on the integral imaging display system using holographic optical element (IDHOE), which is able to display 3D images and satisfy the see-through property at the same time. The technique has its advantage of the high transparency and capability of displaying autostereoscopic 3D images. We have analyzed optical properties of IDHOE for both recording and displaying stages. Furthermore, various studies of new applications and system improvements for IDHOE are introduced. Thanks to the characteristics of a holographic volume grating, it is possible to implement a full color lens-array HOE, conjugated reconstruction, and as well as 2D/3D convertible IDHOE. Studies on the improvements of viewing characteristics including a viewing angle, fill factor, and resolution are also presented. Lastly, essential issues and its possible solutions are discussed as a future work.

Influence of size, proportion, and absorption coefficient of spherical scatterers on the degree of light polarization and the grain size of speckle pattern

Christelle Abou Nader, rana nassif, Fabrice Pellen, Bernard Le Jeune, Guy Le Brun, and Marie Abboud

Doc ID: 247912 Received 13 Aug 2015; Accepted 08 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: In this paper, we present the evolution of speckle pattern polarimetric parameters in response to controlled changes in scatterer sizes, proportions and the absorption coefficient in media. The experimental study was performed on mixtures of polystyrene microspheres with dye in order to ensure biological medium-like properties. The speckle grain sizes and degrees of polarization for linear and circular light were monitored. We observed helicity flipping in the degree of circular polarization for small scatterer proportion around 25%. Furthermore linear depolarization decreased slightly for media containing more small particles. Good agreement was shown with numerical results computed using a Monte Carlo simulation of polarized light taking into account our experimental configuration. Speckle grain size also evolves with the increase of small scatterers as well as the media absorption coefficient. Such variations of properties are encountered during fruit maturation, in tissues in precancerous stages and any transformation that causes a modification in particle proportions and absorption coefficient in biological media. The computed parameters proved to be sensitive to these changes.

Hyperbolic tangential function based progressive addition lens design

xdong cui and qiu gufeng

Doc ID: 248344 Received 21 Aug 2015; Accepted 08 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: The diopter distribution is key to the successful design of a progressive addition lens. A hyperbolic tangential function is then introduced to well describe the desired diopter distribution on the lens. Simulation and fabrication show that the astigmia on the whole surface is very close to the addition, exhibiting superior performance than that of currently used high-order polynomials and cosine functions. Our investigations found that once the diopter distribution design is reasonable, both the direct and indirect methods of constructing a progressive addition lens can give consistent results. With this function we are able to effectively control the design of critical areas, the position, sizes of far-view and near-view zones, as well as the channel of the lens. This study would provide an efficient way to customize different progressive lenses not only for presbyopia, but also for anti-fatigue, office progressive usages etc.

Effects of cloud on GLOW performance and error analysis

Tulu Bacha and Belay Demoz

Doc ID: 247707 Received 10 Aug 2015; Accepted 08 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: The wind measurement by the Goddard Lidar Observatory for Wind (GLOW) is compared with that of radiosonde launched from the same station. In clear sky region, the two measurements are in agreement [Vermeesch et al. 2011]. However, in the cloudy region of atmosphere the GLOW measurement deviates from the radiosonde measurement. In this paper, the GLOW measurement error relative to the radiosonde measurement has been compared with aerosol backscatter ratio measured by Howard University Raman Lidar (HURL) which operated at the same station. The wind speed error of GLOW and cloud optical depth calculated from HURL data were related. The relation is useful in correcting wind measurement error due to cloud in Goddard Lidar Observatory for Wind (GLOW) and for future space based Doppler wind lidar measurements. The averaged wind speed error measured by GLOW in the cloud region was plotted as a function of cloud optical depth. The plot shows that the error induced by the presence of cloud is directly related to the cloud optical depth.

Wavelength-Dependent Femtosecond Pulse Amplification in Wide Band Tapered-Waveguide Quantum Well Semiconductor Optical Amplifiers

Hooshang Ghafouri-Shiraz and Mingjun Xia

Doc ID: 249890 Received 10 Sep 2015; Accepted 08 Nov 2015; Posted 10 Nov 2015  View: PDF

Abstract: In this paper, we have studied the wavelength-dependent amplification in three different wide-band quantum well semiconductor optical amplifiers (QWA) having conventional, exponentially tapered and linearly tapered active region waveguide structures. A new theoretical model for tapered-waveguide QWAs considering the effect of lateral carrier density distribution and the strain effect in quantum well is established based on quantum well transmission line modelling method. The temporal and spectral characteristics of amplified femtosecond pulse are analyzed for each structure. It was found that, for the amplification of a single femtosecond pulse, the taperedwaveguide QWA provides higher saturation gain and the output spectra of amplified pulse in all the three structures exhibit an apparent red shift and bandwidth narrowing due to the reduction of carrier density however, the output spectrum in the tapered-waveguide amplifier is less distorted and exhibits smaller bandwidth narrowing. For the simultaneous amplifications of two femtosecond pulses with different central frequencies, in all the three structures, two peaks appear in the output spectra while the peak at the frequency closer to the peak frequency of the QWA gain spectrum receives higher amplification due to the frequency (wavelength) dependent of the QWA gain. At a low peak power level of the input pulse, the bandwidth of each window in the tapered structure is larger than that of the conventional waveguide structure, which aggravates the spectrum alias in the amplification of femtosecond pulses with different central frequencies. As the peak powers of the two pulses increase, the spectrum alias in the conventional waveguide becomes more serious while there are small changes in the tapered structures. Also, we have found that in the amplification of femtosecond pulse train, the linear tapered QWAs exhibit the fastest gain recovery as compared with the conventional and exponentially tapered QWAs.

Theoretical considerations on aperiodic sinusoidal fringes in comparison to phase-shifted sinusoidal fringes for high-speed three-dimensional shape measurement

Stefan Heist, Peter kuehmstedt, Andreas Tünnermann, and Gunther Notni

Doc ID: 249913 Received 11 Sep 2015; Accepted 07 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: The demand for optically reconstructing the three-dimensional (3-D) surface shape of moving objects or deformation processes makes the development of high-speed projectors necessary. Our 3-D sensor containing an array projector can achieve frame rates of several 10 kHz and is based on the projection of aperiodic sinusoidal fringes. This approach is compared with phase-shifting fringe projection as probably the most widely used technique. Theoretical considerations as well as extensive simulations are conducted to derive criteria for the design of optimal sequences of aperiodic sinusoidal fringes and to compare the number of patterns of both approaches necessary for comparable accuracies.

A high efficiency microchip laser with self-injection seeding

Sha Wang, Yan-biao Wang, Xianheng Yang, Guoying Feng, and Shouhuan Zhou

Doc ID: 249757 Received 09 Sep 2015; Accepted 07 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: In this paper, we use a small bandwidth 808 nm cw Ti:Sapphire laser as pump source to pump a picosecond microchip laser. Different focal length pump focus lenses have been tested to improve the laser efficiency. The maximum slope efficiency of 19.84% is obtained by a 30 mm focal length lens. The pump threshold is only 13 mW. In order to reduce the timing jitter, we explored self-injection seeding method by adding a seeding cavity to the microchip laser. A maximum reduction factor of 23 is obtained at the output power of 8 mW. From the experiments, we also found out that higher seeding pulse energy will help to reduce the jitter more.

Robust modeling and performance analysis of high power Diode side-pumped solid state Laser Systems

tamer elkashif, samy ghoniemy, and ayman mokhtar

Doc ID: 243503 Received 26 Jun 2015; Accepted 07 Nov 2015; Posted 12 Nov 2015  View: PDF

Abstract: In this paper, we present an enhanced high power extrinsic diode side-pumped solid state laser (DPSSL) model to accurately predict the dynamic operations and pump distribution under different practical conditions. We introduce a new implementation technique for the proposed model that provides a compelling incentive for the performance assessment and enhancement of high power diode side-pumped Nd:YAG lasers using cooperative agents relying on MATLAB, GLAD and Zemax ray tracing software packages. A large signal laser model including thermal effects, a modified laser gain formulation and incorporating the geometrical pump distribution for three radially arranged arrays of laser diodes is presented. The design of a customized prototype diode side-pumped high power laser head is fabricated for the purpose of testing is discussed. A detailed comparative experimental and simulation study of the dynamic operation and the beam characteristics that are used to verify the accuracy of the proposed model for analyzing the performance of the high power DPSS lasers under different conditions are discussed. The simulated and measured results of power, pump distribution, beam shape and slope efficiency under different conditions and for a specific case where the targeted output power is 140 W while an input pumping power is 400 W and 95% output coupler reflectivity showed a good agreement with slope efficiency approximately 35%. This assures the robustness of the proposed model to accurately predict the design parameters a practical high power DPSS lasers.

Non-uniformity Correction of Imaging Systems with a Spatially Non-homogeneous Radiation Source

Berndt Gutschwager and Joerg Hollandt

Doc ID: 249825 Received 09 Sep 2015; Accepted 05 Nov 2015; Posted 09 Nov 2015  View: PDF

Abstract: We present a novel method of non-uniformity correction of imaging systems in a wide optical spectral range by applying a radiation source with an unknown and spatially non-homogeneous radiance or radiance temperature distribution. The benefit of this method is that it can be applied with radiation sources of arbitrary spatial radiance or radiance temperature distribution and only requires the sufficient temporal stability of this distribution during the measurement process. The method is based on the recording of several (at least three) images of a radiation source and a purposeful row- and line-shift of these sequent images in relation to the first primary image. The mathematical procedure is explained in detail. Its numerical verification with a source of a predefined nonhomogenous radiance distribution and a thermal imager of a predefined non-uniform FPA responsivity is presented.

Fast CGH Generation by Radial Symmetric Interpolation and Sampling Analysis

Seok Lee, Hyunsung Chang, Hocheon Wey, and Dongkyung Nam

Doc ID: 249216 Received 01 Sep 2015; Accepted 05 Nov 2015; Posted 05 Nov 2015  View: PDF

Abstract: In this paper, we present an fast hologram pattern generation method by radial symmetric interpolation which exploits concentric redundancy of point hologram pattern to reduce computational complexity in hologram pattern calculation and analyze the quality degradation sources in proposed method. Compared to analytic method in which directly calculates phase and amplitude information from wave equation, in our method Fresnel zone plate is periodically sampled along diagonal line and the wave information of point hologram is calculated by linear interpolation. During this sampling and interpolation process, the wave information can be modified from the original signal and degrade the reconstruction quality compared to analytic pattern calculation method. The effect of sampling and linear interpolation is investigated in spatial and frequency domains.

Use of diffraction grating for measuring the focal length and distortion of optical systems

Petr Pokorny and Antonin Miks

Doc ID: 248855 Received 27 Aug 2015; Accepted 04 Nov 2015; Posted 04 Nov 2015  View: PDF

Abstract: The paper presents experimentally simple, accurate and inexpensive method for measuring the focal length and distortion of optical systems using a diffraction grating. The proposed approach does not require any special components or any expensive equipment. The detailed theoretical analysis is performed, and the estimation of uncertainties is studied as well. Afterwards, the method is demonstrated on a computer simulated situation, exemplified on an experimental measurement, and compared with commercially available measurement devices. It is shown that the method provides sufficiently accurate results for many practical applications; therefore, it is appropriate for a laboratory testing and for an industrial application.

Human Skin Detection in the Visible and Near Infrared

Michael Mendenhall, Abel Nunez, and Richard Martin

Doc ID: 247950 Received 14 Aug 2015; Accepted 03 Nov 2015; Posted 03 Nov 2015  View: PDF

Abstract: Skin detection is a well-studied area in color imagery and is useful in a number of scenarios to include search and rescue and computer vision. Most approaches focus on color imagery due to cost and availability. Many of the visible-based approaches do well at detecting skin (above 90%), they tend to have relatively high false alarm rates (8-15%). This article presents a novel feature space for skin detection in visible and near infrared portions of the electromagnetic spectrum. The features are derived from known spectral absorption of skin constituents: hemoglobin, melanin, and water. Fitting a Gaussian mixture to skin and background distributions and using a likelihood ratio test detector, the features presented here show dominating performance when comparing receiver operating characteristic curves (ROCs) and statistically significant improvement when comparing equal error rates and area under the ROC (AUC). A detection/false alarm probability of 98.1%/2.1% is achieved for the averaged equal error rate (EER). EER values for the proposed feature space show a 3-8.5 percentage point increase in detection probability with a 3.8-8.4 percentage point decrease in false alarm probability. The AUC shows a 0.017-0.169 increase in total area under the curve compared to well performing color-based features.

Characterizations of transparent particle scattering properties in near field holography using Debye series

Xuecheng Wu, Yingchun WU, Longchao Yao, Marc Brunel, Sebastien Coetmellec, Renxian Li, Denis Lebrun, Hao Zhou, Gerard Grehan, and Kefa Cen

Doc ID: 248580 Received 25 Aug 2015; Accepted 01 Nov 2015; Posted 03 Nov 2015  View: PDF

Abstract: The effects of individual scattering process on the formations of both the particle hologram and its corresponding reconstructed 3D particle image are investigated using Debye series. A particle hologram model using Debye series, decomposes the object wave into different scattering modes, and thus permits evaluating the effects of individual scattering process (diffraction, reflection, transmission, refractions with (p-1) internal reflections) on the particle holography quantitatively. In the Gabor inline holography of a transparent droplet, the transmission light causes the small discrepancies between the hologram fringes of an opaque particle (diffraction) and a transparent particle near the zero point of the Bessel-like modulation function, and eventually gives rise to the glory spot in the center of the reconstructed dark particle image. For the off-axis holography, effects of reflection particularly the total reflection by the bubble, transmission, and refractions with (p-1) internal reflections of the scattered light on the formation and reconstructed glory spot images of both the typical forward and backward off-axis holography are revealed.

Extinction efficiencies for metallic fibers in the infrared: Orientational average correction

sharhabeel alyones and Charles Bruce

Doc ID: 250699 Received 23 Sep 2015; Accepted 01 Nov 2015; Posted 03 Nov 2015  View: PDF

Abstract: In this article, a correction of a previously computed extinction spectrum of a sample of silver fibers in the infrared is reported. The spectrum was inaccurately computed through use of an approximation relating the E-field aligned values to those of the orientationally averaged extinction efficiency. This approximation is very close for spectral points in the vicinity of the primary resonance but not necessarily for those well away from this resonance. Here, the exact theory has been used to produce the spectra.

Real-time depth controllable integral imaging pickup and reconstruction method with a light field camera

Byoungho Lee, Youngmo Jeong, Jonghyun Kim, Jiwoon Yeom, and Chang-Kun Lee

Doc ID: 245452 Received 07 Jul 2015; Accepted 01 Nov 2015; Posted 03 Nov 2015  View: PDF

Abstract: A light field camera is considered as an effective tool to capture three-dimensional information of objects. We propose a depth controllable integral imaging pickup system with a real-time light field camera setup. According to the focal plane of light field camera, the objects in virtual and real space are recorded simultaneously. With a high frame rate camera and a focus controllable lens, light field can be captured at various focal plane. The captured light field information is analyzed by geometrical optics and four-dimensional light field analysis. We adapt an F-number matching method at capture and display stage to record more accurate light field and solve depth distortion, respectively. To convert the captured light field into the proper elemental image, a real-time pixel mapping algorithm considering pseudoscopic problem and depth distortion is used. The proposed system can provide real and virtual elemental images simultaneously and one can control the focal plane for a given scene. The elemental image can be reconstructed to 3D image in real-time.

Interference-type time lens based on temporal hologram in a loop configuration

Xiao Hu and Honggen Li

Doc ID: 247739 Received 12 Aug 2015; Accepted 01 Nov 2015; Posted 03 Nov 2015  View: PDF

Abstract: An alternative scheme is proposed to implement the time lens based on the temporal hologram concept. Instead of using an edge-pass filtering (EPF), this scheme achieves keeping only the time-lens (quadratic phase-modulation) term of interest by interference of two modulated component beams. In this scheme, additional linear frequency component is not required to be added to the electronic drive signal to avoid the overlapping of the target frequency component and its conjugate of the modulated signal. Thus the proposed hologram based time lens is not only able to relax the limitation of the bandwidth and sampling rate of the arbitrary waveform generator (AWG) on the time-bandwidth product (TBP) and resolution to some extent, but also capable to process shorter input pulse signal. These advantages make the proposed interference type hologram time lens especially suitable to be used in a loop configuration where it can be reused when the signal pulse circulates in the loop. This promises significantly enhanced time-bandwidth product and resolution, and the temporal aperture size can be designed as large as desired theoretically.

Synthetic aperture in terahertz in-line digital holography for resolution enhancement

Haochong Huang, Lu Rong, Dayong Wang, Weihua Li, Qinghua Deng, Li bin, Yunxin Wang, Zhiqiang Zhan, Xuemin Wang, and Weidong Wu

Doc ID: 247238 Received 10 Aug 2015; Accepted 29 Oct 2015; Posted 02 Nov 2015  View: PDF

Abstract: Terahertz digital holography is a combination of terahertz technology and digital holography. In digital holography, the imaging resolution is the key parameter in determining the detailed quality of a reconstructed wavefront. In the paper, the synthetic aperture method is used in terahertz digital holography, and the in-line arrangement is built to perform the detection. The resolved capability of previous terahertz digital holographic systems restricts this technique to meet the requirement of practical detection. In contrast, the experimental resolved power of the present method can reach 125 μm, which is the best resolution of terahertz digital holography to date. Furthermore, the basic detection of a biological specimen is conducted to show the practical application. In all, the results of the proposed method demonstrate the enhancement of experimental imaging resolution, and that the amplitude and phase distributions of the fine structure of samples can be reconstructed by using terahertz digital holography.

An Optofluidic Bio-imaging platform for Quantitative Phase Imaging of Lab on a Chip Devices

Renu John and Vimal Prabhu Pandiyan

Doc ID: 248758 Received 26 Aug 2015; Accepted 29 Oct 2015; Posted 02 Nov 2015  View: PDF

Abstract: We demonstrate a versatile 3-D phase imaging microscope platform for real time imaging of opto-microfluidic devices based on the principle of digital holographic microscopy (DHM). Lab-on-Chip microfluidic devices fabricated on transparent polydimethylsiloxane (PDMS) and glass substrates have attained wide popularity in biological sensing applications. However, 3-D volumetric visualization, monitoring and characterization of microfluidic devices and flows, and biochemical kinetics happening in these devices are not feasible using traditional bright field microscopy. The traditional bright field microscopic techniques fail in such applications where the fluids carrying biological samples are transparent and not visible in bright light. Phase-based microscopy techniques only can image the phase of a microfluidic channel and changes in refractive indices due to various fluids and biological samples present in the channel. This paper demonstrates three dimensional phase imaging of a microfluidic device with nanometric depth precisions and high SNR. We demonstrate imaging of microelectrodes of nanometric thickness patterned on glass substrate and the microfluidic channel. Three dimensional imaging of a transparent polydimethylsiloxane (PDMS) opto-microfluidic channel, fluid flow and live Yeast cells flowing in this channel has been demonstrated using DHM. We also quantify the average velocity of fluid flow through the channel. In contrast to conventional bright field microscope, the 3-D depth information in the images illustrated in this work carry much information about the biological system under observation. The results demonstrated in this paper prove the high potential of DHM in imaging optofluidic devices, detection of pathogens, cells and bioanalytes on Lab-on Chip devices and also in studying microfluidic dynamics in real time based on phase changes that are not possible under bright field microscope.

Estimation of parameters for evaluating subsurface microcracks in glass with in-line digital holographic microscopy

Xiupin Wu, Wanrong Gao, and Yong He

Doc ID: 248817 Received 27 Aug 2015; Accepted 29 Oct 2015; Posted 02 Nov 2015  View: PDF

Abstract: In this work, a new method for imaging subsurface damage is proposed, which is, to the best of our knowledge, the first application of the in-line digital holographic microscopy (IDHM) to the reconstruction of the subsurface damage in glass. By combination of the in-line arrangement and an objective lens to image the hologram on the CCD surface, the method is characterized by its high resolution in both the lateral and depth directions. Then the three dimensional reconstruction of the micro cracks within the glass was realized by numerically focusing en-face images at different depths, and the sizes of SSD along the transversal and depth directions were estimated. Based on the experimental results, the cracks can be divided to two categories: one is that the cracks begin from the surface of optical elements, the other is totally within the components. To indicate the propagation or development trajectory of the cracks and predict the magnitude of the laser induced damage threshold (LIDT), the relative intensity distributions of the light scattered by the cracks compared with the ones without cracks were also reconstructed. In this case all the required parameters for evaluating SSD are obtained with our IDHM system, so that the SSD produced in the manufacturing process can be reduced or removed more easily to optimize the performance of the optical component and extend its lifetime. These results provide the guidance for the optical system design of precision measurements.

Dual wavelength digital holography for 3D Particle Image Velocimetry: experimental validation

Stanislas Grare, Daniel Allano, Sebastien Coetmellec, Gaele Perret, Frédéric Corbin, Brunel Marc, Gerard Grehan, and Denis Lebrun

Doc ID: 248860 Received 28 Aug 2015; Accepted 29 Oct 2015; Posted 02 Nov 2015  View: PDF

Abstract: A multi-exposure digital in-line hologram of a particle field is recorded by two successive pulses of different wavelengths. During the reconstruction step, each recording can be independently analyzed by selecting a given wavelength. This procedure enables avoiding the superimposition of particle images that may be close to each other.

Design of metallic nanoparticles gratings for filtering properties in the visible spectrum

Yoann Brûlé, Guillaume Demesy, Anne-Laure Fehrembach, Boris Gralak, Evgeny Popov, Gerard Tayeb, Matthias Grangier, David Barat, Philippe Gogol, and Beatrice Dagens

Doc ID: 247470 Received 06 Aug 2015; Accepted 27 Oct 2015; Posted 02 Nov 2015  View: PDF

Abstract: Plasmonic resonances in metallic nanoparticles are exploited to create efficient optical filtering functions. A Finite Element Method is used to model metallic nanoparticles gratings. The accuracy of this method is shown by comparing numerical results with measurements on a two-dimensional grating of gold nanocylinders with elliptic cross section. Then a parametric analysis is performed in order to design efficient filters with polarization dependent properties together with high transparency over the visible range. The behavior of nanoparticle gratings is also modelled using the Maxwell-Garnett homogenization theory and analyzed by comparison with the diffraction by a single nanoparticle. The proposed structures are intended to be included in optical systems which could find innovative applications.

LIBS determination of toxic metals in fresh fish

TERESA FLORES, Luis Ponce, FERNANDO ALVIRA, and M. Gabriel Bilmes

Doc ID: 248878 Received 28 Aug 2015; Accepted 27 Oct 2015; Posted 28 Oct 2015  View: PDF

Abstract: A method based on Laser Induced Plasma Spectroscopy for monitoring lead and copper accumulation in edible fish, particularly “tilapia del Nilo” (Oreochromis niloticus) is presented. The capability of this analytical method is compared with results obtained by atomic absorption spectrometry (AAS). Detection limits by LIBS are 25 ppm for Pb and 100 ppm for Cu, values that are below of the maximum permissible levels of some international standards. Application of LIBS detection allows the development of portable instruments for contamination control of edible fish.

Underwater gas pipeline leakage source localization by distributed fiber-optic sensing based on PSO tuning of the SVM

Yue Huang, Qiang Wang, Qihua Yang, and Lilian Shi

Doc ID: 246401 Received 21 Jul 2015; Accepted 23 Oct 2015; Posted 24 Nov 2015  View: PDF

Abstract: Accurate underwater gas pipeline leak localization requires particular attention due to the sensitivity of environmental conditions. Experiments were performed to analyze the localization performance of a distributed optical fiber sensing system based on the hybrid Sagnac and Mach-Zehnder interferometer.The traditional null frequency location method dose not allow accurate location of the leakage points easily. To improve the positioning accuracy, the particle swarm optimization algorithm (PSO) tuning of the support vector machine (SVM) was used to predict the leakage points based on gathered leakage data . The PSO is able to optimize the support vector machine (SVM) parameters. For 10 km range chosen, the results show the PSO+SVM the average absolute error of the leakage points predicted is 66.731 m. The prediction accuracy of leakage points is 98.25% by PSO tuning of the SVM processing. For 20 leakage test data points, the average absolute error of leakage point location is 124.8 m. The leakage position predicted by the PSO algorithm after optimization of the parameters is more accurate.

An adjustable hollow cone output X-ray beam from an ellipsoidal mono-capillary with a combination of a pinhole and a beam stop

Xuepeng Sun, Zhiguo Liu, Longtao Yi, weiyuan Sun, fangzuo Li, Bowen Jiang, yongzhong Ma, and Tianxi Sun

Doc ID: 241353 Received 26 May 2015; Accepted 22 Oct 2015; Posted 23 Oct 2015  View: PDF

Abstract: A combined shading system (CSS) consisting of a beam stop and a pinhole is proposed for use between an ellipsoidal mono-capillary (EM) and a conventional laboratory X-ray source to obtain an adjustable hollow cone output beam for different experiments with no need for changing the EM. The CSS can change the incident X-ray beam on the EM by adjusting the position of the beam stop and the pinhole, with the corresponding change of the output beam of the EM. In this study, the adjustable hollow cone output X-ray beam of an 80-mm long EM with a CSS was studied in detail with a laboratory Cu X-ray generator with a focal spot diameter of 50 μm. The adjustable range of the focal spot size of the EM was from 8.6 to 58.7 μm. The adjustable range of the gain of the focal spot of the EM was from 0 to1350. The beam divergence of the hollow cone output beam of the EM ranged from 6 to16.75 mrad. The illumination angle of the hollow cone output beam of the EM ranged from 0 to 5.95 mrad. In addition, the potential application of the proposed adjusting method in testing the performance of the EM is briefly discussed.

High-speed dithering-based three-dimensional data compression algorithms by phase correction

Yajun Wang and Lianxin Zhang

Doc ID: 247503 Received 26 Aug 2015; Accepted 19 Oct 2015; Posted 25 Nov 2015  View: PDF

Abstract: The Holoimage technique can substantially reduce the three-dimensional (3D) shape data sizes by converting the 3D shape data into regular 24-bit 2D images. And the dithering-based compression algorithm was recently proposed to further reduce the data size by only utilizing 3 bits to represent 3D shape data. However, our research finds that the recovery accuracy of the dithering-based algorithm is not very high due to the loss of information in the dithering process. Besides, we find that the final 3D recovery accuracy is highly related with the phase information. To address the low accuracy problem, in this paper, we propose two different phase-correction methods to store the phase error information and retrieve the absolute phase with higher accuracy. Both methods can provide recovered 3D results with much better quality. Experimental results are presented to verify the performance of the proposed methods.

Reply to comment on the “Calibration method for highaccuracy measurement of long focal length with Talbot interferometry”

Jia Luo and Jian Bai

Doc ID: 251306 Received 01 Oct 2015; Accepted 16 Oct 2015; Posted 22 Oct 2015  View: PDF

Abstract: Thanks to Sukmock Lee for the attention to our paper [Appl. Opt. 51, 2407 (2012)], and also for the comment [Appl. Opt. XX, xxx (2015)]. Two numerical mistakes were pointed out by Sukmock Lee and they are corrected in this paper. However, these numerical mistakes do not affect the feasibility and precision of this calibration method. Therefore it cannot be made a conclusion that it is difficult to agree with the calibration method for the long focal length measurements.

Comparison of two methodologies for calibrating satellite instruments in the visible and near-infrared

Steven Brown, Robert Barnes, Keith Lykke, Bruce Guenther, James Butler, Thomas Schwarting, Kevin Turpie, David Moyer, Frank Deluccia, and Chris Moeller

Doc ID: 242454 Received 05 Jun 2015; Accepted 09 Oct 2015; Posted 06 Nov 2015  View: PDF

Abstract: Traditionally, satellite instruments that measure Earth-reflected solar radiation in the visible and near infrared wavelength regions have been calibrated for radiance responsivity in a two-step method. In the first step, the relative spectral response (RSR) of the instrument is determined using a nearly monochromatic light source such as a lamp-illuminated monochromator. These sources do not typically fill the field-of-view of the instrument nor act as calibrated sources of light. Consequently, they only provide a relative (not absolute) spectral response for the instrument. In the second step, the instrument views a calibrated source of broadband light, such as a lamp-illuminated integrating sphere. The RSR and the sphere absolute spectral radiance are combined to determine the absolute spectral radiance responsivity (ASR) of the instrument. More recently, a full-aperture absolute calibration approach using widely tunable monochromatic lasers has been developed. Using these sources, the ASR of an instrument can be determined in a single step on a wavelength-by-wavelength basis. From these monochromatic ASRs, the responses of the instrument bands to broadband radiance sources can be calculated directly, eliminating the need for calibrated broadband light sources such as integrating spheres. In this work, the traditional broadband source-based calibration of the Suomi National Preparatory Project (SNPP) Visible Infrared Imaging Radiometer Suite (VIIRS) sensor is compared with the laser-based calibration of the sensor. Finally, the impact of the new full-aperture laser-based calibration approach on the on-orbit performance of the sensor is considered.

Optical description and design method with annularly stitched aspheric surface

Dewen Cheng, xujiao chen, Chen Xu, yuan hu, and Yongtian Wang

Doc ID: 247555 Received 10 Aug 2015; Accepted 02 Oct 2015; Posted 20 Oct 2015  View: PDF

Abstract: The relentless pressure for new optical functions, small volume, and light weight has greatly increased the importance of aspheric surfaces. In this paper, we propose an annularly stitched aspheric surface (ASAS) description method to increase the freedom and flexibility of imaging system design. The rotationally symmetric ASAS consists of circular central zone and one or more annular zones, two neighbor zones are constrained to have the same derivatives on their joint curve, and this means the ASAS is C1 continuous. This finding is proved and verified by the mathematical deduction of the surface formulas. Two optimization strategies and two design methods with the C1 continuous constraints are also discussed. It can greatly facilitate the design and even achieve some impossible designs without increasing the fabrication difficulty. Two different systems with the proposed ASAS are optimized and the results are presented. The design results verified the practicability of the ASAS.

Comment on the “Calibration method for high-accuracy measurement of long focal length with Talbot interferometry”

Sukmock Lee

Doc ID: 243814 Received 25 Jun 2015; Accepted 13 Aug 2015; Posted 22 Oct 2015  View: PDF

Abstract: In a recent paper [Appl. Opt. 51, 2407 (2012)], the authors presented a calibration method for the long focal length Moiré fringe measurements to reduce the relative error to less than 0.02%, which was based on two presented results. We tried to reproduce the same results with the information and equations provided, but were unsuccessful.

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