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Accepted papers to appear in an upcoming issue

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Random bit generation at tunable rates using a chaotic semiconductor laser under distributed feedback

Sze-Chun Chan, Xiao-Zhou Li, Song-Sui Li, and Jun-Ping Zhuang

Doc ID: 245485 Received 07 Jul 2015; Accepted 30 Jul 2015; Posted 30 Jul 2015  View: PDF

Abstract: A semiconductor laser with distributed feedback from a fiber Bragg grating (FBG) is investigated for random bit generation (RBG). The feedback perturbs the laser to emit chaotically with the intensity sampled periodically. The samples are then converted into random bits by a simple postprocessing of self-differencing and selecting bits. Unlike a conventional mirror that provides localized feedback, the FBG provides distributed feedback which effectively suppresses the information of the round-trip feedback delay time. Randomness is ensured even when the sampling period is commensurate with the feedback delay between the laser and the grating. Consequently, in RBG, the FBG feedback enables continuous tuning of the output bit rate, reduces the minimum sampling period, and increases the number of bits selected per sample. RBG is experimentally investigated at a sampling period continuously tunable from over 16 ns down to 50 ps, while the feedback delay is fixed at 7.7 ns. By selecting 5 least significant bits per sample, output bit rates from 0.3 Gbps to 100 Gbps are achieved with randomness examined by the National Institute of Standards and Technology test suite.

PROUD-based method for simple real-time in-line characterization of propagation-induced distortions in NRZ Data Signals

Hugo Martins, Juan Pastor Graells, Luis Romero Cortés, Daniel Piote, Sonia Martin-Lopez, Jose Azana, and Miguel Gonzalez Herraez

Doc ID: 242195 Received 15 Jun 2015; Accepted 29 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: A simple, in-line method for real-time full characterization (amplitude and phase) of propagation distortions arising due to group velocity dispersion and self-phase modulation on 10-20 Gbps transmitted NRZ optical signals is reported. It is based on phase reconstruction using optical ultrafast differentiation (PROUD), a linear and self-referenced technique. The flexibility of the technique is demonstrated by characterizing different data stream scenarios. Experimental results were modelled using conventional propagation equations, showing good agreement with the measured data.

Lensfree Spectral Light-field Fusion Microscopy for Contrast- and Resolution-enhanced Imaging of Biological Specimens

Farnoud Kazemzadeh, Chao Jin, Sara Molladavoodi, Yu Mei, Monica Emelko, Maud Gorbet, and Alexander Wong

Doc ID: 242295 Received 04 Jun 2015; Accepted 29 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: A lensfree spectral light-field fusion microscopy (LSLFM) system is presented for enabling contrast- and resolution-enhanced imaging of biological specimens. LSLFM consists of a pulsed multispectral lensfree microscope for capturing interferometric light-field encodings at different wavelengths, and Bayesian-based fusion to reconstruct a fused object light-field from the encodings. By fusing unique object detail information captured at different wavelengths, LSLFM can achieve improved resolution, contrast, and signal-to-noise ratio (SNR) over a single-channel lensfree microscopy system. A five-channel LSLFM system was developed and quantitatively evaluated to validate the design. Experimental results demonstrated that the LSLFM system provided SNR improvements of 6.81-16.55 dB, as well as a six-fold improvement in the dispersion index (DI), over that achieved using a single-channel lensfree deconvolution microscopy system at individual wavelengths. Furthermore, the LSLFM system achieved an increase in numerical aperture (NA) of > 3 times over a single-channel lensfree deconvolution microscopy system at the highest-resolution wavelength used in the study. Samples of Staurastrum paradoxum, a waterborne algae, and human corneal epithelial cells were imaged using the system to illustrate its potential for enhanced imaging of biological specimens.

Performance of a dual Fabry-Perot refractometer

Patrick Egan, Jack Stone, Jay Hendricks, Jacob Ricker, Gregory Scace, and Gregory Strouse

Doc ID: 240818 Received 12 May 2015; Accepted 28 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: We have built and characterized a refractometer that utilizes two Fabry-Perot cavities formed on a dimensionally stable spacer. In the typical mode of operation, one cavity is held at vacuum and the other cavity is filled with nitrogen gas. The differential change in length between the cavities is measured as the difference in frequency between two helium-neon (633 nm) lasers, one locked to the resonance of each cavity. This differential change in optical length is a measure of the gas refractivity. Using the known values for the molar refractivity and virial coefficients of nitrogen, and accounting for cavity length distortions, the device could be used as a high-resolution, multi-decade pressure sensor. We describe the performance of the refractometer and also present the equations needed to calculate pressure from gas refractivity.

Tunable plasmonic resonances based on elliptical annular aperture arrays on conducting substrates for advanced biosensing

Wei Peng, Yuzhang Liang, Lixia Li, Siyu Qian, and qiao Wang

Doc ID: 241415 Received 25 May 2015; Accepted 28 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: Introducing a conducting metal layer and the structural asymmetry to an elliptical annular aperture arrays, multiple plasmonic coupled resonant modes are generated under normal incidence in the visible light range. The electromagnetic fields can be strongly enhanced at resonant modes in this device, which increases the interaction volume of the detected analyte and optical fields, therefore, multiple plamonic coupled modes exhibit higher refractive index sensitivity than as large as 610 nm/RIU. The distinct Fano-like resonance around a wavelength of 681 nm originates from the interference between bonding dipolar and the quadrupolar modes. Due to the excitation of sharp spectral features, as narrow as 7 nm, high figure of merits of 94 at the Fano-like dip is obtained in a wide refractive index range of 1.33~1.40. Furthermore, to generate strong Fano-like resonance, the geometric shape of ellipse is selected, which is less dependent on structural asymmetry and requires less fabrication accuracy and tolerance compared to the circle shape. This device is promising for biosensing applications with high-sensitivity and low limit of detection.

Effect of spherical aberration on Laser Beam Self-Focusing in the Atmosphere

Xiaoling Ji, Hanling Deng, Xiaoqing Li, and Xianqu Wang

Doc ID: 242659 Received 09 Jun 2015; Accepted 28 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: The effect of spherical aberration on the laser beam self-focusing in the atmosphere to assist delivering powerful laser beams from orbit to the ground is studied. It is found that for the small orbital mirror size, a Gaussian beam with negative spherical aberration might be stronger compressed without filamentation than that without spherical aberration, and its spot size on the ground can be reduced well below the diffraction limit. However, for the large orbital mirror size, spherical aberration will result in an increase of receiver size on the ground.

Low-temperature Cross-talk Magnetic Field Sensor Based on Tapered All-solid Waveguide-array Fiber and Magnetic Fluids

Miao Yinping, xixi ma, jixuan wu, binbin song, bo liu, and Jian-Quan Yao

Doc ID: 243915 Received 03 Jul 2015; Accepted 28 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: A compact fiber-optic magnetic-field sensor based on tapered all-solid waveguide-array fiber (WAF) and magnetic fluid (MF) has been proposed and experimentally demonstrated. The tapered all-solid WAF is fabricated by using a fusion splicer and the sensor is formed by immersing the tapered all-solid WAF into the MF. The transmission spectra have been measured and analyzed under different magnetic field intensities. Experimental results show that the acquired magnetic field sensitivity is 44.57 pm/Oe for a linear magnetic field intensity range from 50 Oe to 200 Oe. All solid WAF has very similar thermal expansion coefficient for high and low refractive index glasses, so mode profile is not affected by thermal drifts. Also, magnetically induced refractive index changes into the ferrofluid are of the order of ~5×10-2, while the corresponding thermally induced refractive index changes into the ferrofluid are expected to be lower. The temperature response has also been detected and the temperature-induced wavelength shift perturbation is less than 0.3 nm from temperature of 26.9 ℃ to 44 ℃. The proposed magnetic field sensor has such advantages as low temperature sensitivity, simple structure and easy of fabrication. It also indicates that the magnetic field sensor based on tapered all-solid WAF and MF is helpful to reduce temperature cross-sensitivity for the measurement of magnetic field.

Spectroscopic sensing of reflection optical activity in achiral AgGaS2

Oriol Arteaga

Doc ID: 242980 Received 16 Jun 2015; Accepted 28 Jul 2015; Posted 30 Jul 2015  View: PDF

Abstract: Optical activity is a fundamental effect of electrodynamics that was discovered more than 200 years ago. While optical activity is typically recognized by the rotation of the polarization of light as it propagates through a bulk medium, in certain configurations, the specular reflection of light on the surface of a material is also sensitive to its optical activity. Here we show that the ellipsometric analysis of the light reflected at the surface of a gyrotropic but achiral crystal of AgGaS2 allows the spectroscopic determination of its optical activity above the bandgap, where transmission methods are not applicable. This is the first clear spectroscopic determination of reflection optical activity in a crystal and we have measured the largest optical activity ever reported for a natural material. We also demonstrate that normal incidence transmission and reflection measurements probe different aspects of optical activity.

Low-DMD few-mode fiber with distributed long-period grating

Jian Fang, An Li, and William Shieh

Doc ID: 245693 Received 09 Jul 2015; Accepted 27 Jul 2015; Posted 30 Jul 2015  View: PDF

Abstract: We propose a distributed grating-assisted few-mode fiber (DG-FMF) to reduce the differential mode delay (DMD). By introducing asymmetric long-period fiber gratings with random exposure directions in a step-index few-mode fiber during fiber manufacture process, the strong random mode coupling is generated along the entire length of the fiber. Simulation results show that mean DMD in the DG-FMF can be reduced to less than 12 ns at a distance of 100 km with a period of 514 μm and grating strength of 1×10¯⁶. The DMD reduction in our DG-FMF is guaranteed within the entire C-band, and in a wide temperature range from −20 °C to +60 °C.

Nonlinear Raman-Nath diffraction of femtosecond laser pulses in a 2D nonlinear photonic crystal

Andrey Vyunishev, Vasily Arkhipkin, Vitaly Slabko, Ivan Baturin, Andrey Akhmatkhanov, Vladimir Shur, and Anatoly Chirkin

Doc ID: 243548 Received 24 Jun 2015; Accepted 27 Jul 2015; Posted 27 Jul 2015  View: PDF

Abstract: We study second harmonic (SH) generation of femtosecond laser pulses in a rectangular two-dimensional nonlinear photonic crystal (NLPC). Multiple SH beams were observed in the vicinity of the propagation direction of the fundamental beam. It has been verified that the angular positions of these beams obey the conditions of nonlinear Raman-Nath diffraction (NRND). The measured SH spectra of specific NRND orders consist of narrow peaks that experience a high-frequency spectral shift as the order grows. These results can be interpreted as high-order quasi-phase-matched second harmonic generation under nonlinear Raman-Nath diffraction. We derive an analytical expression for the process studied and find the theoretical results to be in good agreement with the experimental data. We estimate the enhancement factor of nonlinear Raman-Nath diffraction in 2D NLPC to be 70.

Plasmonic random nanostructures on fiber tip for trapping live cells and colloidal particles

Jiajie Chen, Zhiwen Kang, Sui-Kai Kong, and Ho-pui Ho

Doc ID: 238121 Received 08 May 2015; Accepted 27 Jul 2015; Posted 28 Jul 2015  View: PDF

Abstract: We demonstrate optical trapping on a gold-coated single-mode fiber tip as excited by 980 nm laser radiation. The trapping force here is not due to common plasmonic localization, but dominated by the combined effect of thermophoresis and thermal convection. The reported scheme only requires simple thin film deposition. More importantly, efficient broadband plasmonic absorption of the gold random nanostructures, aided by purely Gaussian excitation profile from the fiber core, has led to very low trapping power threshold typically in hundreds of microwatts. This highly versatile fiber based trapping scheme clearly offers many potential application possibilities in life sciences as well as engineering disciplines.

Computational Modeling of Optical Properties in Aluminum Nanolayers Inserted in ZnO for Solar Cell Electrodes

Winston Soboyejo, Egidius Rwenyagila, Benjamin Agyei-Tuffour, Keyna Onogu, Omololu Akin-Ojo, Martiale Zebaze Kana, and Terry Alford

Doc ID: 241653 Received 25 May 2015; Accepted 27 Jul 2015; Posted 28 Jul 2015  View: PDF

Abstract: Numerical simulations were used to study the transmittances (Ts) of ZnO/Al/ZnO (ZAZ) films with Al thicknesses between ~ 1 – 40 nm. The simulations are also validated using previously reported experimental results. Multilayers with Al layer thicknesses between ~ 1 – 10 nm are shown to have average Ts between ~ 75 and 90%, which decreased further to ~ 63 and 41% for the mid-layer Al thicknesses of 20 and 40 nm, respectively. Variations in the ZnO thickness between ~ 10 – 100 nm are shown to have little effects on the optical properties of the model multilayers, for a given Al thickness. The reliability of the simulations is tested by comparing them with experimental measurements on films produced using similar interlayer thicknesses. These are also shown to be comparable to the performance characteristics of indium tin oxide (ITO) anodes that are used currently in organic solar cells and light emitting devices.

Far-infrared quasimonochromatic perfect absorption in a thin GaAs film on Au

Shun-Tung Yen and Pei-Kang Chung

Doc ID: 242037 Received 02 Jun 2015; Accepted 27 Jul 2015; Posted 28 Jul 2015  View: PDF

Abstract: We study the far-infrared absorption properties of a thin GaAs film on Au. We show that a 1.2 μm GaAs film on Au can absorb completely an electromagnetic wave of 7.9 THz and totally reflect the waves of frequencies not very close to 7.9 THz. The uniformity of the layered structure enables observation of a quasimonochromatic, nearly perfect absorption of 96% in a 1.4 µm GaAs film. The absorption can be high for a wide range of incident angle.

Control of lateral thickness gradients of Mo/Si multilayer on curved substrates using genetic algorithm

BO YU, Chun-shui Jin, Shun Yao, Hui Wang, FENG ZHOU, Benyin Guo, Yao Xie, Yu Liu, Li-ping Wang, and Chun Li

Doc ID: 242205 Received 08 Jun 2015; Accepted 27 Jul 2015; Posted 28 Jul 2015  View: PDF

Abstract: An inversion method based on genetic algorithm has been developed to control the lateral thickness gradients of Mo/Si multilayer deposited on curved substrates by planar magnetron sputtering. At first, the sputtering distribution of target is inversed from coating thickness profiles of flat substrates at different heights. Then the speed profiles of substrates sweeping across the target are optimized according to the desired coating thickness profiles of the primary and secondary mirrors in a two-bounce projection system. The measured coating thickness profiles show that the non-compensable added figure error is below 0.1 nm rms and the wavelength uniformity across each mirror surface is within ±0.2% P-V. The inversion method introduced here exhibits its convenience in obtaining sputtering distribution of target and efficiency in coating iterations during process development.

Paths correlation matrix

Qian Weixian, Xiaojun Zhou, Yingcheng Lu, and Jiang Xu

Doc ID: 242939 Received 17 Jun 2015; Accepted 27 Jul 2015; Posted 28 Jul 2015  View: PDF

Abstract: Both the Jones and Mueller matrices encounter difficulties when physically modelling mixed materials or rough surfaces due to the complexity of light-matter interactions. To address these issues, we derived a matrix called the paths correlation matrix (PCM), which is a probabilistic mixture of Jones matrices of every light propagation paths. Because PCM is related to actual light propagation paths, it is well suited for physical modeling. Experiments were performed, and the reflection PCM of a mixture of granite and aluminum was measured. The PCM of the mixed sample was accurately decomposed into pure granite’s single reflection, pure aluminum’s single reflection, and depolarization caused by multiple reflections, which is consistent with the theoretical derivation. Reflection parameters of both smooth and rough surface can be calculated from PCM decomposition, and the results fit well with the theoretical calculations provided by the Fresnel equations. These theoretical and experimental analyses verify that PCM is an efficient way to physically model light-matter interactions.

Determination of recombination coefficients for nanocrystalline silicon embedded in hydrogenated amorphous silicon

Andre Kaplan, Igor Yurkevich, Wei He, Thomas Roger, and Ammar Zakar

Doc ID: 243471 Received 01 Jul 2015; Accepted 27 Jul 2015; Posted 28 Jul 2015  View: PDF

Abstract: Using the spectroscopic pump-probe reflectance method we investigated recombination kinetics in the samples of nano crystalline silicon embedded in the matrix of the hydrogenated amorphous silicon. We found that the kinetics is governed by two competing processes of the bimolecular and three-particle Auger recombinations. We determined the values of the recombination coefficients for these processes and showed that they are carrier density dependent but having opposite trends: the coefficient for the bimolecular process increases while that for the Auger process decreases as a function of the initial carrier concentration.

Vertical optical ring resonators fully integrated with nanophotonic waveguides on silicon-on-insulator substrates

Abbas Madani, Moritz Kleinert, David Stolarek, Lars Zimmermann, Libo Ma, and Oliver Schmidt

Doc ID: 243899 Received 29 Jun 2015; Accepted 25 Jul 2015; Posted 27 Jul 2015  View: PDF

Abstract: We demonstrate full integration of vertical optical ring resonators with silicon nanophotonic waveguides on silicon-on-insulator substrates to accomplish a significant step towards 3D photonic integration. The on-chip integration is realized by rolling up 2D differentially strained TiO2 nanomembranes into 3D microtube cavities on a nanophotonic microchip. The integration configuration allows for out of plane optical coupling between the in-plane nanowaveguides and the vertical microtube cavities as a compact and mechanically stable optical unit, which could enable refined vertical light transfer in 3D stacks of multiple photonic layers. In this vertical transmission scheme, resonant filtering of optical signals at telecommunication wavelengths is demonstrated based on subwavelength thick walled microcavities. Moreover, an array of microtube cavities is prepared and each microtube cavity is integrated with multiple waveguides which opens up interesting perspectives towards parallel and multi-routing through a single cavity device as well as high-throughput optofluidic sensing schemes.

Poly-periodic hole arrays for angle-invariant plasmonic filters

Kyung Cheol Choi and Yun Seon Do

Doc ID: 245413 Received 06 Jul 2015; Accepted 25 Jul 2015; Posted 27 Jul 2015  View: PDF

Abstract: We suggest a plasmonic filter with novel hole arrays for an angle-invariant optical response. The suggested patterns consist of randomly distributed polycrystalline domains in which nano sized holes are arranged with the same period. While the microscopic area of periodicity determines the center wavelength and transmission intensity, the broken periodicity of each domain contributes to restrain the angle dependency. The results increase the possible use of nanohole-based filters in practical area.

Reconfigurable semiconductor laser networks based on diffractive coupling

Daniel Brunner and Ingo Fischer

Doc ID: 242821 Received 12 Jun 2015; Accepted 24 Jul 2015; Posted 27 Jul 2015  View: PDF

Abstract: Networks of optical emitters are highly sought-after, both for fundamental investigations as well as for various technological applications. We introduce and implement a novel scheme, based on diffractive optical coupling, allowing for the coupling of large numbers of optical emitters with adjustable weights. We demonstrate its potential by coupling emitters of a 2D array of semiconductor lasers with significant efficiency.

Microfiber Bragg gratings with negative index modulation

Bai-Ou Guan, Yang Ran, Long Jin, Shuai Gao, Li-Peng Sun, Yunyun Huang, and Jie LI

Doc ID: 242264 Received 04 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: In this paper, Bragg gratings with negative index modulation are inscribed into microfibers. The larger germanium-doped core region of the multimode fiber provides the necessary photosensitivity to form type IIa grating when it is drawn down to the micro-scale. The formation of type IIa grating can be accelerated by reducing the diameter of the microfiber due to the lower saturate modulation and the amplified tension-strain transformation effect. This provides a highly efficient way for the fabrication of fiber gratings with 800 oC temperature resistance

Look-back-upon tree recurrence method for Geiger-mode avalanche photodiode performance prediction

Peng Zhao, Yan ZHANG, YuMing Hua, and WeiPing Qian

Doc ID: 242396 Received 12 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: Based on the Poisson signal distribution, this paper for the first time proposes the look-back-upon tree recurrence method under discrete time to predict the performance of Geiger-mode avalanche photodiodes with short dead time. The results of method proposed correspond to the results of previous methods for diverse input flux. The look-back-upon tree recurrence method possesses dramatically low time complexity and space complexity to realize real-time analysis of Geiger-mode avalanche photodiode performance among all the range of dead time and input diversity.

In situ fabrication of tunable microlens

Lei Zhang, Limin Tong, Wei Fang, zhiyuan Wang, Yichuan Wang, and Rui Qiu

Doc ID: 242547 Received 09 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We demonstrate an optofluidic variable-focus microlens formed by solid polydimethylsiloxane (PDMS) meniscus channel wall and tunable liquid lens body. A novel method for in situ fabrication of meniscus channel wall is developed by introducing liquid PDMS prepolymer into a microchannel followed by curing. Three light manipulation techniques including tunable optical focusing, collimating and diverging are realized by varying the refractive index (RI) of liquid lens body. Also, we present an absorption measurement of methylene blue (MB) with a collimated probing light, achieving a detection limit of 0.25 μM by using a 5 mm long detection cell.

High-power, widely tunable, room-temperature picosecond optical parametric oscillator based on cylindrical 5%MgO:PPLN

Suddapalli Chaitanya Kumar, Wei Junxiong, Jérôme Debray, Vicent Kemlin, Benoit Boulanger, Hideki Ishizuki, Takunori Taira, and Majid Ebrahim-Zadeh

Doc ID: 242954 Received 12 Jun 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We report a high-power picosecond optical parametric oscillator (OPO) based on cylindrical MgO:PPLN synchronously pumped by a Yb-fiber laser. The singly-resonant OPO is tunable in the near-infrared signal across 1413-1900 nm together with a mid-infrared idler coverage of 2418-4307 nm by angle tuning of the MgO:PPLN crystal at room temperature. With non-optimized output coupling of ~10%, the OPO simultaneously delivers 2.4 W of signal at 1664 nm and 1.7 W of idler at 2950 nm at an overall extraction efficiency of ~45% with high beam pointing stability <30 µrad and <14 µrad for the signal and idler, respectively. The generated signal and idler exhibit passive power stability better than 1% rms and 0.8% rms over 15 h, measured simultaneously at 1638 nm and 3036 nm, respectively, in high beam quality with TEM00 mode profile. The extracted signal pulses from the OPO have duration of 15.2 ps with a spectral bandwidth of 0.7 nm, corresponding to a time-bandwidth product of ΔυΔτ~1.2.

Polarization-sensitive optical coherence tomography system tolerant to fiber disturbances using a line camera

Manuel Marques, Sylvain Rivet, Adrian Bradu, and Adrian Podoleanu

Doc ID: 241308 Received 20 May 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: This Letter presents a spectral-domain, polarization-sensitive optical coherence tomography (PS-OCT) system where the light collection from the two arms of the interferometer is performed exclusively using single-mode fibers and couplers, and the two orthogonal polarization components are sequentially detected by a single line camera. Retardance measurements can be affected by polarimetric effects due to fiber birefringence and diattenuation in fiber couplers. This configuration bypasses such issues by performing polarization selection before the collection fiber, through the combination of a polarization rotator and a linear polarizer. Retardance calibration is achieved with a Berek compensator. Similar net retardance maps of a birefringent phantom are obtained for two different settings of induced fiber birefringence, effectively demonstrating the tolerance of the configuration to fiber-based disturbances.

Diode-end-pumped single-mode mid-infrared laser operation in a single Er:GGG microchip

you zhenyu, Jinglong Xu, Yan wang, Zhaojie Zhu, Jianfu Li, Hongyan Wang, and Chaoyang Tu

Doc ID: 241552 Received 28 May 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We reported on a diode-end-pumped single-mode microchip laser using a 600-μm-thick monolithic Er:GGG at ~2.7 μm, generating a maximum output power of 50.8 mW and the maximum pulsed energy of 0.306 mJ with repetition rates of pumping light of 200 Hz and 100 Hz, respectively. The maximum slope efficiency of the laser was 20.1%. The laser was operated in a single longitudinal mode centered at about 2704 nm with a FWHM of 0.42 nm. The laser had a fundamental beam profile that that the beam quality parameter M2 was measured as 1.46. These results indicate that the Er:GGG microchip laser is a potential compact mid-infrared laser source.

Femtosecond Mode-locked Nd3+-doped Ba(Zr,Mg,Ta)O3 Ceramic Laser

Yuki Higashi, Hiroaki Nakao, Akira Shirakawa, Ken-ichi Ueda, Alexander Kaminskii, Satoshi Kuretake, Yuji Kintaka, Koji Murayama, and Nobuhiko Tanaka

Doc ID: 239827 Received 29 Apr 2015; Accepted 23 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: We have demonstrated continuous wave (CW) laser operation and first sub-200 fs mode-locked laser operation of Nd3+-doped Ba(Zr,Mg,Ta)O3 ceramic. Its disordered crystalline nature exhibits a broad gain bandwidth of 30 nm with high emission cross section. It also has higher thermal and mechanical properties than Nd:glass. In CW operation, the maximum output power of 1.5 W under 6.2 W of absorbed pump power was obtained. In mode-locked operation, the pulse duration of 196 fs with the average power of 60 mW was successfully achieved. The laser spectrum straddled both fluorescence peaks of A-site and B-site Nd3+ ions.

Optimal generation of high harmonics in the water-window region by synthesizing 800-nm and mid-infrared laser pulses

Cheng Jin, Kyung-Han Hong, and Chii Dong Lin

Doc ID: 242536 Received 11 Jun 2015; Accepted 22 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We propose a method to optimally synthesize a strong 800-nm Ti:sapphire laser pulse and a relatively weak mid-infrared laser pulse to enhance harmonic yields in the water-window region. The required wavelength of the mid-infrared laser is varied from about 2.0 to 3.2 μm. The optimized waveforms generate comparable harmonic yields as the waveforms proposed in [Sci. Rep. 4, 7067 (2014)], but with much weaker intensity for the mid-infrared laser. This method provides an alternative scheme, based on the available laser technology, to help realize tabletop light source in the water-window region by high-order harmonic generation.

Highly stable digital holographic microscope using Sagnac interferometer

Arun Anand, Vismay Trivedi, Bahram Javidi, Vani Chhaniwal, Priyanka Vora, and Swapnil mahajan

Doc ID: 236217 Received 17 Mar 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: Interferometric microscopy has grown into a very potent tool for quantitative phase imaging of biological samples. Among the interfermetric methods, microscopy by digital holography is one of the most effective techniques especially for studying dynamics of cells. Imaging of cell fluctuations requires digital holographic setups with high temporal stability. Common path setups in which the object and the reference beam encounters the same set of optical elements provides better temporal stability compared to two beam setups. Here we present a compact, easy to implement, common path digital holographic microscope based on Sagnac interferometer geometry. The microscope is implemented using a diode laser module employing a CCD array or a webcam sensor to record holograms. The system was tested for three dimensional imaging capability, numerical focusing ability and temporal stability. Sub nanometer temporal stability without external vibration isolation components were obtained in both cases. The higher temporal stability makes the microscope compatible to image cell fluctuations, which is demonstrated by imaging the oscillation of cell membrane of human red blood cells.

A new method to evaluate afterpulsing probability in single-photon avalanche diodes

Sheng-Di Lin, Jau-Yang Wu, Yi-Shan Lee, and Bo-Wei Tzou

Doc ID: 239665 Received 23 Apr 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We propose and demonstrate a new method for evaluating afterpulsing effect in single-photon avalanche photodiodes (SPADs). By analyzing the statistical property of dark count rate, we can quantitatively characterize afterpulsing probability of a SPAD. In experiment, the temperature-dependent DCR distribution becomes non-Poissonian at lower temperature and higher excess bias as the afterpulsing effect becomes significant. Our work provides a flexible way to examine afterpulsing probability in either single-device or circuit level.

High reflectance La/B based multilayer mirror for 6.x nm wavelength

Dmitry Kuznetsov, Andrey Yakshin, Marko Sturm, Robbert van de Kruijs, Eric Louis, and Fred Bijkerk

Doc ID: 240794 Received 21 May 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We report a hybrid thin film deposition procedure to significantly enhance the reflectivity of La/B based multilayer structures. This is of relevance for applications of multilayer optics at 6.7 nm wavelength and beyond. Such multilayers showed a reflectance of 64.1% @ 6.65 nm measured at 1.5 degrees off-normal incidence at PTB (BESSY-II). This was achieved by a special scheme of La passivation. The La layer was nitridated to avoid formation of the optically unfavorable LaBx compound at the B-on-La interface. To avoid the also undesired BN formation at the La-on-B interface, a time-dosed nitridation at the initial stage was applied. This research revealed a good potential for further increase in the reflectivity of multilayer structures at 6.7 nm.

Interferometric velocity measurements through a fluctuating phase boundary using a Fresnel guide star

Hannes Radner, Lars Buettner, and Juergen Czarske

Doc ID: 241500 Received 22 May 2015; Accepted 21 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: Laser optical techniques are widely used for flow measurements as they offer a high spatial and velocity resolution. However, an undisturbed optical access to the measurement volume is desired. In order to measure through a fluctuating phase boundary, we present the use of adaptive optics. In an experiment we prove, that the Fresnel reflex of a phase boundary can be used as a proper guide star for adaptive velocity measurements with a single optical access. Interferometric flow measurements through a fluctuating phase boundary have been accomplished by a Mach-Zehnder interferometer.

In-fiber whispering gallery mode resonator fabricated by femtosecond laser micromaching

Tao Zhu, leilei shi, Dongmei huang, Min Liu, Ming Deng, and Wei Huang

Doc ID: 240530 Received 07 May 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: An in-fiber whispering gallery mode resonator fabricated by femtosecond laser micromaching is demonstrated. The cylinder resonator cavity is fabricated by scanning the D-fiber cladding with infrared femtosecond pulses along a cylindrical trace with radius of 25 μm and height of 20 μm. Quality factor on the order of 103 is achieved by smoothing the cavity surface with ultrasonic cleaner, which is mainly limited by the surface roughness of hundreds nanometers. Resonant characteristics and polarization dependence of the proposed resonator is also studied in detail. Our method takes a step forward to the integration of whispering gallery mode resonators.

Giant Thermo-Optical Relaxation Oscillations in mm-size Whispering Gallery Mode Disk-Resonators

Yanne Chembo, Souleymane DIALLO, and Guoping Lin

Doc ID: 240828 Received 12 May 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: In this letter, we show that giant thermo-optical oscillations can be triggered in mm-size whispering-gallerymode disk-resonators when they are pumped by a resonant continuous-wave laser. Our resonator is a ultra-high Q barium fluoride cavity which features a positive thermo-optic coefficient and a negative thermoelastic coefficient. We demonstrate for the first time that the complex interplay between these two thermic coefficients and the intrinsic Kerr nonlinearity yields very sharp slow-fast relaxation oscillations with a slow timescale that can be exceptionally large, typically of the order of one second. We use a time-domain model in order to gain understanding into this instability, and we find that both the experimental and theoretical results are in excellent agreement. The understanding of these thermal effects is an essential requirement for every WGM-related applications and our study demonstrates that even in the case of mm-size resonators, such effects can still be accurately analyzed using nonlinear time-domain models.

High-beam quality, high-efficiency laser based on fiber with heavily Yb3+-doped phosphate core and silica cladding

Olga Egorova, Sergey Semjonov, Oleg Medvedkov, Maxim Astapovich, Andrey Okhrimchuk, Boris Galagan, Boris Denker, Sergei Sverchkov, and Evgeny Dianov

Doc ID: 241424 Received 22 May 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We have fabricated and tested a composite fiber with an Yb3+-doped phosphate glass core and silica cladding. Oscillation with a slope efficiency of 74% was achieved using core pumping at 976 nm with fiber lengths of 48-80 mm in a simple laser configuration, where the cavity was formed by a high-reflectivity Bragg grating and the cleaved fiber end. The measured M2 factors were as low as 1.05-1.22 even though the fiber was multimode at the lasing wavelength.

High Energy Non-collinear Optical Parametric Amplifier Producing 4-fs Pulses in the Visible Seeded by a Gas Phase Filament

Robert Levis and Johanan Odhner

Doc ID: 239705 Received 24 Apr 2015; Accepted 21 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We report on the design and characterization of a short-pulse-pumped, single-stage non-collinear optical parametric amplifier (NOPA) that achieves high pulse energies in the few-cycle pulse regime. Optimal pulse front-tilting and temporal compression of the short (35 fs) pump pulse are achieved using a 4-\textit{f} grating compressor, while spatial chirp at the NOPA crystal is eliminated with proper imaging using a pair of reflective telescopes. Gas-phase filamentation in an open-ended argon-filled cell provides a bright, stable seed source with little residual chirp that is suitable for temporal overlap with the short pump pulse without dispersion pre-compensation. Two seeding geometries are explored, and pulses as short as 3.5 fs are obtained by seeding with the entire filament bandwidth. Fourier transform-limited 4 fs pulses are obtained by filtering the IR portion of the spectrum

Ultrafast Tm-doped fiber laser mode-locked with black phosphorus

Grzegorz Sobon, Jaroslaw Sotor, Wojciech Macherzynski, Krzysztof Abramski, Maciej Kowalczyk, and Piotr Pałetko

Doc ID: 242066 Received 02 Jun 2015; Accepted 21 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: We report, for the first time to our knowledge, the usage of black phosphorus (BP) as saturable absorber for mode-locking of a Thulium-doped fiber laser. We have experimentally shown, that BP exhibits saturable absorption in the 2 μm wavelength range and supports ultrashort pulse generation. The saturable absorber was based on mechanically exfoliated BP deposited on a fiber connector tip. The laser was capable of generation 739-fs pulses centered at 1910 nm. Our results show, that BP might be considered as an universal, broadband saturable absorber, which might successfully compete with graphene or other low-dimensional nanomaterials.

Cosine light-trapping nanostructures for thin film solar cells

Guo Xiaowei, Bang Liu, Yi Li, and Young Zhou

Doc ID: 242634 Received 10 Jun 2015; Accepted 20 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: In this paper, we present a cosine light-trapping texture for thin film silicon solar cells. The surface texture was numerically demonstrated to exhibit comparable light trapping performance to the inverted pyramid one which is classic high efficiency light trapping structure. The cosine texture can be directly formed by interference lithography while the inverted pyramid needs more complicate processing. The proposed structure has the potential to play a key role in thin film solar cells.

Integrated remotely-tunable optical delay line for millimeter-wave beam steering fabricated in an InP generic foundry

Cao Zizheng, Netsanet Tessema, Sylwester Latkowski, Valentina Moskalenko, Kevin Williams, xinran zhao, zhongbiao chen, Eduward Tangdiongga, A. Koonen, and Henrie Boom

Doc ID: 241358 Received 22 May 2015; Accepted 20 Jul 2015; Posted 30 Jul 2015  View: PDF

Abstract: A compact and fabrication-tolerant integrated remotely-tunable optical delay line is proposed for millimeter-wave beam steering and is fabricated in an InP generic foundry. The proposed delay line is based on a spectrally-cyclic arrayed waveguide grating feedback loop. Its major features include the tolerant architecture with reduced chip size, and bi-directional operation with simplified remote tuning. Moreover, its cyclic feature guarantees further cascaded operations either for 2-D radio beam steering or for high resolution delay generation. The experimental results show less than 6.5dB insertion loss of the integrated delay line. Five different delays from 0ps to 71.6ps are generated with less than 0.67ps delay errors.

Quasi-3D Plasmonic Coupling Scheme for Nearfield Optical Lithography and Imaging

Liang Pan, Yuan Wang, Zhidong Du, Chen Chen, Yongshik Park, and Xiang Zhang

Doc ID: 241707 Received 26 May 2015; Accepted 20 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: Near-field optical imaging and lithography rely on achieving both high resolution and efficient coupling. Particularly conventional Nearfield Scanning Optical Microscopy (NSOM) suffers from the tradeoff between resolution and efficiency. Planar plasmonic lens schemes can partially solve this issue utilizing plasmonic resonances but the performance is not robust over a large range of sample materials. In this work we show a novel quasi-3D plasmonic scheme to focus light into the extreme subwavelength region in the near field with an efficiency orders higher than NSOM. The superb performance comes from the strong coupling between the localized mode with an off-plane E field component and the sample being processed. Our scheme can efficiently focus light to a spot with a diameter down to 1/20 of its wavelength and the coupling efficiency can be as high as 10%. Theoretically, we demonstrate that the FWHM of the focus spot can be 7 nm with an enhancement of 800 at UV region. The focusing performance is constantly good over a large variety of materials and the illumination and collection imaging scheme has been demonstrated by simulation. An example design of this quasi-3D coupling scheme is fabricated and its imaging performance is characterized by the apertureless optical nearfield measurement. The high coupling efficiency at extreme subwavelength resolution of this quasi-3D coupling scheme opens the door to many applications such as optical lithography, nanoscale imaging, heat assisted magnetic recording, plasmon enhanced Raman spectroscopy, etc.

Second harmonic generation interferometry in magnetic dipole metamaterials

Irina Kolmychek, Anton Bykov, Evgeniy Mamonov, and Tatiana Murzina

Doc ID: 242893 Received 12 Jun 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We present the experimental studies on optical second harmonic generation from meta-surfaces exhibiting magnetic dipole resonances in the visible spectral range. The structure consists of a square lattice of 'nano-burgers' of the composition Au/MgF$_2$/Au with the average disk diameter of 140 nm and the period of the structure of 400 nm. We show that at normal incidence, the intensity of the second harmonic (SH) wave generated by the metasurface increases by an order of magnitude as the excitation wavelength approaches the magnetic dipole resonance, while the phase of the SH wave experiences a shift up to 330$^\circ$. Based on the phenomenological description of the SH process, the observed effects indicate the dominant role of the nonlinear magnetic dipole polarization driven by the $\hat{\chi}^{emm}$ susceptibility in second harmonic generation in 'nano-burgers'.

1.1 μm InAs/GaAs quantum-dot light-emitting transistors grown by molecular beam epitaxy

Chao-Hsin Wu, Cheng-Han Wu, Hsuan-An Chen, and Shih-Yen Lin

Doc ID: 243132 Received 17 Jun 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: In this letter, we report the enhanced radiative recombination output from an AlGaAs/GaAs heterojunction bipolar transistor with InAs quantum dots embedded in the base region to form a quantum-dot light-emitting transistor (QDLET) grown by molecular beam epitaxy systems. For the device with a 100×100 μm² emitter area, we demonstrate the dual output characteristics with an electrical output and an optical output when the device operating in the common-emitter configuration. The quantum-dot light-emitting transistor exhibits a base recombination radiation in the near-infrared spectral range with a dominant peak at λ of 1100 nm.

Optical injection and spectral filtering of high-power UV laser diodes

Vera Schäfer, Christopher Ballance, Calvin Tock, and David Lucas

Doc ID: 242223 Received 04 Jun 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We demonstrate injection-locking of 120mW laser diodes operating at 397nm. We achieve stable operation with injection powers of ~100 μW and a slave laser output power of up to 110mW. We investigate the spectral purity of the slave laser light via photon scattering experiments on a single trapped Ca40 ion. We show that it is possible to achieve a scattering rate indistinguishable from that of monochromatic light by filtering the laser light with a diffraction grating to remove amplified spontaneous emission.

Arbitrary state of polarization with customized degree of polarization generator

Angel Lizana, Irene Estévez, F. A. Torres-Ruiz, Alba Peinado, Claudio Ramírez, and Juan Campos Coloma

Doc ID: 234146 Received 06 Feb 2015; Accepted 20 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: An optical set-up able to generate arbitrary states of polarization with customized degree of polarization is presented in this work. Compared with the few alternatives existing in literature, it presents an easy-to-built optical set-up and leads to a superior performance. In fact, experimental results are presented, providing an accurate control for the generation of states of polarization (maximum error of 1.7% and 3.3% for ellipticity and azimuth, respectively) as well as for the associated degree of polarization (full experimental variation from 1 up to 0.003, with a 1.7% maximum error). The system proposed may be useful for different applications, as for polarimeters testing, speckle metrology, and biological applications as example.

Whispering gallery modes in optical fibers based on reflectionless potentials

Sergey Suchkov, Misha Sumetsky, and Andrey Sukhorukov

Doc ID: 241332 Received 21 May 2015; Accepted 19 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We consider an optical fiber with nanoscale variation of the effective fiber radius supporting whispering gallery modes slowly propagating along the fiber, and reveal that the radius variation can be designed to support reflectionless propagation of these modes. We show that reflectionless modulations can realize control of transmission amplitude and temporal delay, while enabling close packing due to the absence of cross-talk, in contrast to conventional potentials.

Degree of polarization (uniformity) and depolarization index: Unambiguous depolarization contrast for optical coherence tomography

Martin Villiger, Brett Bouma, and Norman Lippok

Doc ID: 239767 Received 24 Apr 2015; Accepted 19 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: The degree of polarization (uniformity) has attracted increased interest as a functional contrast in optical coherence tomography (OCT). However, its computation from a single polarization state suggests an ambiguity that is strongly dependent on a sample's orientation. We here propose an improved metric to present depolarization with respect to the optical system rather than the propagating field. Using numerical simulations and optical frequency domain imaging, we evaluate the conventional DOP(U) for different polarization states and compare its performance with the unambiguous depolarization index.

Ultra-compact Broadband Higher-Order-Mode Pass Filter fabricated in a Silicon Waveguide for Multimode Photonics

Xiaowei Guan, Yunhong Ding, and Lars Frandsen

Doc ID: 245566 Received 08 Jul 2015; Accepted 19 Jul 2015; Posted 29 Jul 2015  View: PDF

Abstract: An ultra-compact and broadband higher-order-mode pass filter in a 1D photonic crystal silicon waveguide is proposed and experimentally demonstrated. The photonic crystal is designed for the lower-order mode to work in the photonic band gap while the higher-order mode is located in the air band. Consequently, light on the lower-order mode is prohibited to pass through the filter while light on a higher-order mode can be converted to a Bloch mode in the photonic crystal and pass through the filter with low insertion loss. As an example, we fabricate a ~15μm-long first-order-mode pass filter which filters out the fundamental mode with a measured insertion loss of ~1.8 dB. The extinction ratio is measured to be around 50 dB (with a variation of +/-10 dB due to the detection limitation of the measurement setup) in the measured wavelength range from 1480 nm to 1580 nm. Additionally, calculations predict the extinction ratio to be larger than 50 dB in a 170 nm broad bandwidth.

Spin-dependent asymmetric diffraction of evanescent waves by subwavelength gratings

Guo Ping Wang and Kedi Wu

Doc ID: 242143 Received 02 Jun 2015; Accepted 18 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We present a robust way to observe spin-to-orbital conversion phenomenon. A spinning evanescent wave can be asymmetrically transformed into propagation waves through one certain diffraction order by a periodical subwavelength grating. By detecting diffraction field distribution behind the grating, we observed spin-dependent mirror symmetry breaking of diffraction light. Furthermore, we can also simultaneously observe multiple order diffraction of a spin evanescent wave by a Fibonacci grating. In this case, the diffraction lights can interfere to each other behind the quasi-periodical grating to from an asymmetric interference patterns. Our work provides another way towards the realization of spin-to-orbital conversion of light.

Trapping light into fiber tapers

Dmitry Strekalov, Anatoliy Savchenkov, Ekaterina Savchenkova, and Andrey Matsko

Doc ID: 241213 Received 18 May 2015; Accepted 17 Jul 2015; Posted 17 Jul 2015  View: PDF

Abstract: A tapered cylindrical dielectric optical waveguide acts as a high quality factor white-light cavity providing high field concentration as well as long optical group delay. It is possible to optimize shape of a lossless taper to suppress reflection of the input light and achieve infinitely high field concentration. These tapers can be used in sensing and opto-electronics applications instead of conventional microvacities.

Versatile, carrier-envelope phase-stable spatiotemporal light bullets

Audrius Dubietis, Ieva Gražulevičiūtė, Rosvaldas Suminas, Gintaras Tamosauskas, and Arnaud Couairon

Doc ID: 241561 Received 25 May 2015; Accepted 17 Jul 2015; Posted 17 Jul 2015  View: PDF

Abstract: We present an extensive experimental investigation of self-focusing and filamentation of intense 90 fs, 1.8 µm, carrier-envelope phase-stable laser pulses in fused silica in the anomalous group velocity dispersion region. Spectral measurements in a wedge-shaped sample uncover dynamics of the spectral broadening, which captures the evolution of third harmonic, resonant radiation and supercontinuum spectra as a function of propagation distance with unprecedented detail. The relevant events of spectral broadening are linked to formation and propagation dynamics of spatiotemporal light bullets as measured by three dimensional imaging technique. We also show that at higher input power the light bullet splits into two bullets, which retain characteristic O-shaped spatiotemporal intensity distributions and propagate with different Group velocities. Finally, we demonstrate that the light bullets have stable carrier-envelope phase, which is preserved even after the bullet splitting event, as verified by f-2f interferometric measurements.

Optimization of acquisition systems for low light level robustness in space optical communications

Bai Shuai, Jia Qiang, Liang Zhang, and Jianyu Wang

Doc ID: 240509 Received 08 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: The channel establishment in space optical communications relies on the ATP (Acquisition, Tracking, and Pointing) systems to initially acquire and then stably track the beacon beam. However, insufficient optical power may lead to unstable acquisition or even acquisition failure. In this letter, we analyze the mechanisms causing the instability, and then propose an approach to constrain the acquisition velocity. The approach is based on velocity prediction obtained from the light spot centroids and angle measurement data. Theoretical and experimental results show that the acceptable minimum optical power for acquisition decreases by 5.5 dB after optimization, which effectively enhances the acquisition system’s robustness under low light level conditions. This approach improves the adaptability of satellite–ground optical communications and also has practical value for deep space optical communications.

Theoretical treatment of the interaction between two-level atoms and periodic waveguides

Xiaorun Zang and Philippe Lalanne

Doc ID: 241270 Received 20 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: Light transport in periodic waveguides coupled to a two-level atom is investigated. By using optical Bloch equations and a photonic modal formalism, we derive semi-analytical expressions for the scattering matrix of one atom trapped in a periodic waveguide. The derivation is general, as the expressions hold for any periodic photonic or plasmonic waveguides. It provides a basic building block to study collective effects arising from photon-mediated multi-atom interactions in periodic waveguides.

UV-curable silicate phosphor planar films printed on glass substrate for white light-emitting diodes

Yong Soo Cho, Jin Woo Jang, Jun Sik Kim, Oh Hyeon Kwon, and Tae Hyeon Lee

Doc ID: 241629 Received 27 May 2015; Accepted 17 Jul 2015; Posted 20 Jul 2015  View: PDF

Abstract: We suggest a simple way of forming a nonconventional remote phosphor layer for white light-emitting diodes. A printing technology using a paste consisting of yellow (Ba,Sr,Ca)2SiO4:Eu2+ silicate phosphor and UV-curable polymer is applied to form solid planar films on a common soda lime silicate glass substrate through UV-radiation. Relative content of the phosphor was adjusted for best dispersion of the phosphor particles in the polymer matrix with better emission and luminescence performance. As a result, the 70 wt% phosphor-embedded film has a luminous efficacy of ~70.1 lm/W at 200 mA.

Anharmonic propagation of two-dimensional beams carrying orbital angular momentum in a harmonic potential

Yiqi Zhang, Milivoj Belic, Xing Liu, Wei-Ping Zhong, wen feng, and Yanpeng Zhang

Doc ID: 242661 Received 23 Jun 2015; Accepted 17 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: We analytically and numerically investigate an anharmonic propagation of two-dimensional beams in a harmonic potential. We pick non-centrosymmetric beams of common interest that carry orbital angular momentum. The examples studied include superposed Bessel-Gauss (BG), Laguerre-Gauss (LG) and circular Airy (CA) beams. For the BG beams, periodic inversion, phase transition, and rotation with periodic angular velocity are demonstrated during propagation. For the LG and CA beams, periodic inversion and variable rotation are still there but not the phase transition. On the whole, the ``center of mass' and the orbital angular momentum of a beam exhibit periodic motion, but that motion is subject to external torques and forces and, depending on the intensity distribution, may not be harmonic. Our results are applicable to other superpositions of finite circularly asymmetric beams.

Local excitation of surface plasmon polaritons using nitrogen-vacancy centers

Cesar Garcia-Ortiz, Sergey Bozhevolnyi, and S Kumar

Doc ID: 245679 Received 09 Jul 2015; Accepted 17 Jul 2015; Posted 27 Jul 2015  View: PDF

Abstract: Surface plasmon polaritons (SPPs) are locally excited at silver surfaces using (~100) nm-sized nanodiamonds (NDs) with multiple nitrogen-vacancy (NV) centers (~400). The fluorescence from an externally illuminated (at 532 nm) ND and from nearby NDs, which are not illuminated but produce out-of-plane scattering of SPPs excited by the illuminated ND, exhibit distinctly different wavelength spectra, showing short-wavelength filtering due to the SPP propagation loss. The results indicate that NDs with multiple NV centers can be used as efficient sub-wavelength SPP sources in planar integrated plasmonics for various applications.

Phase derivative estimation from a single interferogram using Kalman smoothing algorithm

Pramod Rastogi and Rishikesh Kulkarni

Doc ID: 242277 Received 09 Jun 2015; Accepted 16 Jul 2015; Posted 22 Jul 2015  View: PDF

Abstract: We report a technique for the direct phase derivative estimation from a single recording of a complex interferogram. In this technique, the interference field is represented as an autoregressive model with spatially varying coefficients. The estimates of these coefficients are obtained using the Kalman filter implementation. The RTS smoothing algorithm further improves the accuracy of the coefficient estimation. These estimated coefficients are utilized to compute the spatially-varying phase derivative. The stochastic evolution of the coefficients is considered which allows to estimate the phase derivative with any type of spatial variation. The simulation and experimental results are provided to substantiate the noise robustness and applicability of the proposed method in phase derivative estimation.

Tailoring of Spectral Response and Spatial Field Distribution with Corrugated Photonic Crystal Slab

raanan gad, Ofer Levi, Iliya Sigal, Costa Nicolaou, Wah Tung Lau, and Soroosh Ahmadi

Doc ID: 240098 Received 01 May 2015; Accepted 15 Jul 2015; Posted 16 Jul 2015  View: PDF

Abstract: We report a new physical mechanism for simultaneous tuning of quality factors, spectral responses, and field distributions in photonic crystal slabs through removal of polarization mode degeneracy using a lattice of elliptical nano-holes. The quality factors in these structures can become higher than those obtained with much smaller circular nano-holes. Furthermore, the modes can be superimposed by either rotating or morphing the elliptical nano-holes into a corrugated grating. These findings will enable improved radiation-matter interaction in optical, microwave and THZ frequencies along with enhanced opto-acoustic coupling.

Laguerre-Gauss beams vs Bessel beams showdown: peer comparison

Job Mendoza Hernandez, Maximino Arroyo Carrasco, Marcelo Iturbe-Castillo, and Sabino Chavez-Cerda

Doc ID: 243706 Received 25 Jun 2015; Accepted 12 Jul 2015; Posted 13 Jul 2015  View: PDF

Abstract: We present for the first time a comparison in similitude of circumstances between Laguerre-Gauss beams and Bessel beams showing that the former can be a better option for many applications that have been attributed to Bessel beams. By solving the Laguerre-Gauss differential equation in the asymptotic limit of large radial index we find the parameters to perform a peer comparison showing that Laguerre-Gauss beams can propagate quasi-nondiffracting within the same region of space where the corresponding Bessel beams do. We also demonstrate that Laguerre-Gauss beams having the property of self-healing are more robust in the sense that can propagate further than Bessel beams under similar initial conditions.

Towards a new radiative-transfer-based model for remote sensing of terrestrial surface albedo

Shengcheng Cui, Xiaobing Zheng, Zhen Wang, Shizhi Yang, Xuebin Li, Heli Wei, Honghua Huang, and wenyue zhu

Doc ID: 240111 Received 04 May 2015; Accepted 10 Jul 2015; Posted 24 Jul 2015  View: PDF

Abstract: This letter formulates a simple yet accurate radiative-transfer-based theoretical model to characterize the fraction of radiation reflected by terrestrial surfaces. Emphasis is placed on the concept of inhomogeneous distribution of diffuse sky radiation function (DSRF) under real atmosphere conditions. Multiple surface-atmosphere interaction effects are considered when coupling surface anisotropic reflectance field with diffuse sky radiation field for the land surface albedo (LSA) model construction. The advantage of the presented model is that it can well elucidate the impact of DSRF on the surface volume scattering and geometry-optical scattering components respectively, especially for slant illuminations with zenith angle larger than 50 degrees. In addition, the consistency and convergence of our model is evaluated using the limit theory of radiative transfer equation. Intercomparisons between satellite and ground measurements indicate that our model is accurate and promising for land-atmosphere interactions study.

Experimental demonstration of laser damage caused by coupling effect of subsurface defects and coating layers

Yingjie Chai, Meiping Zhu, Kui Yi, Weili Zhang, Hu Wang, Zhou Fang, Zhengyuan Bai, cui yun, and Jianda Shao

Doc ID: 239785 Received 27 Apr 2015; Accepted 08 Jul 2015; Posted 09 Jul 2015  View: PDF

Abstract: The laser damage resistance of coatings for high power laser systems depends greatly on the surface quality of the substrate. In our work, experimental approaches were employed to understand the coupling effect of subsurface defects and coatings on the laser resistance of coatings. 1064 nm (1ω) anti-reflection coating was deposited by e-beam coater on fused silica with and without micro-scale pits (structural defects). The micro-scale pits were precisely fabricated by femtosecond laser processing to prevent the emergence of subsurface cracks. Different deposition temperatures and substrate cleaning methods were characterized in order to verify the intensity of the coupling effect of substrate and coating layers. Our experimental results indicate that impurities, introduced in the finishing process, shifted to the substrate surface, and aggregated during the heating process, play a much more crucial role than structural defects (Length: ~7μm; Width: ~3μm; Depth: ~0.8μm) in the laser-induced damage process. A comparative study on the deposition methods indicated that combination of relatively low coating temperature and HF substrate etching tend to decrease the coupling effect, resulting in higher laser-induced damage resistance .

Extended tunability of Nd-doped fiber lasers operating at 872-936nm

Mathieu Laroche, Baptiste Leconte, Hervé Gilles, Sylvain Girard, Benoit Cadier, and thierry Robin

Doc ID: 238408 Received 21 Apr 2015; Accepted 06 Jul 2015; Posted 21 Jul 2015  View: PDF

Abstract: Efficient high-power operation of a Nd-doped fiber laser operating in a wavelength-tunable configuration using volume Bragg grating (VBG) is reported in this letter. High power operation on the 4F3/2-4I9/2 transition of Nd3+ at short wavelengths below 900 nm is demonstrated for the first time in silica fibers. A high efficiency (47 % laser conversion), output power up to 22 W and a narrow linewidth of 0.035 nm are achieved. This configuration is compared with a more conventional fiber laser setup using band-pass filter and dichroic high reflecting mirror.

How planar optical waves can be made to climb dielectric steps

Manfred Hammer, Jens Förstner, and Andre Hildebrandt

Doc ID: 240068 Received 23 Mar 2015; Accepted 02 Jul 2015; Posted 08 Jul 2015  View: PDF

Abstract: We show how to optically connect guiding layers at different elevations in a 3-D integrated photonic circuit. Transfer of optical power carried by planar, semi-guided waves is possible without reflections, without radiation losses, and over large vertical distances. This functionality is realized through simple step-like folds of high-contrast dielectric slab waveguides, in combination with oblique wave incidence, and fulfilling a resonance condition. Radiation losses vanish, and polarization conversion is being suppressed, for TE wave incidence beyond certain critical angles. This can be understood by fundamental arguments resting on a version of Snell's law. The two 90-degree corners of a step act as identical partial reflectors in a Fabry-Perot-like resonator setup. By selecting the step height, i.e. the distance between the reflectors, one realizes resonant states with full transmission. Rigorous quasi-analytical simulations for typical silicon/silica parameters demonstrate the functioning. Combinations of several step junctions can lead to other types of optical on-chip connects, e.g. u-turn- or bridge-like configurations.

Mid-IR femtosecond frequency conversion by soliton-probe collision in phase-mismatched quadratic nonlinear crystals

Morten Bache, Xing Liu, Binbin Zhou, and Hairun Guo

Doc ID: 241572 Received 25 May 2015; Accepted 29 Jun 2015; Posted 30 Jun 2015  View: PDF

Abstract: We show numerically that ultrashort self-defocusing temporal solitons colliding with a weak pulsed probe in the near-IR can convert the probe to the mid-IR. A near-perfect conversion efficiency is possible for a high effective soliton order. The near-IR self-defocusing soliton can form in a quadratic nonlinear crystal (beta-barium borate) in the normal dispersion regime due to cascaded (phase-mismatched) second-harmonic generation, and the mid-IR converted wave is formed in the anomalous dispersion regime between λ=2.2-2.4 μm as a resonant dispersive wave. This process relies on non-degenerate four-wave mixing mediated by an effective negative cross-phase modulation term caused by cascaded soliton-probe sum-frequency generation.

>200W incoherently combined supercontinuum source using a 3×1 broadband fiber power combiner

Zilun Chen, Hang Zhou, Aijun Jin, Xuanfeng Zhou, Bin Zhang, Sheng-Ping Chen, Jing Hou, and Jinbao Chen

Doc ID: 237223 Received 31 Mar 2015; Accepted 23 Jun 2015; Posted 25 Jun 2015  View: PDF

Abstract: We report an incoherently combined near-infrared SC source with >200 W output power using a 3×1 broadband fiber power combiner. A broadband fiber power combiner is designed and theoretically investigated. The power transmission efficiencies of light at different wavelengths of the combiner are calculated and the combiner is verified to be capable of combining broadband sources efficiently. Then a combiner is fabricated. Three ~70 W near infrared SC sources are constructed and then using the combiner a >200 W near infrared SC source is obtained. Conclusively, using incoherently combining method we can obtain a high power SC source and the thermo-management can be realized easily. We believe that this is a suitable method to obtain higher power SC source.

Spontaneous creation and annihilation of temporal cavity solitons in a coherently-driven passive fiber resonator

Miro Erkintalo, Stephane Coen, Kathy Luo, Jae Jang, and Stuart Murdoch

Doc ID: 240910 Received 13 May 2015; Accepted 19 Jun 2015; Posted 13 Jul 2015  View: PDF

Abstract: We report on the experimental observation of spontaneous creation and annihilation of temporal cavity solitons (CSs) in a coherently-driven, macroscopic optical fiber resonator. Specifically, we show that CSs are spontaneously created when the frequency of the cavity driving field is tuned across a resonance, and that they can individually disappear at different stages of the scan. In contrast to previous experiments in monolithic microresonators, we are able to identify these dynamics in real time, thanks to the macroscopic dimensions of our resonator. Our experimental observations are in excellent agreement with numerical simulations. We also discuss the mechanisms responsible for the one-by-one disappearance of CSs.

A simple method to enhance terahertz radiation from femtosecond laser filament array with a step phase plate

Jiayu Zhao, Lanjun Guo, Wei Chu, Bin Zeng, Hui Gao, Weiwei Liu, and Ya Cheng

Doc ID: 236756 Received 24 Mar 2015; Accepted 08 Jun 2015; Posted 24 Jul 2015  View: PDF

Abstract: In this work, we experimentally demonstrate a 200% enhancement of terahertz (THz) wave amplitude generated by femtosecond laser filamentation in air. The experimental setup simply uses a semicircular phase plate to generate two parallel filaments. Temporally overlapped THz pulses from two filaments coherently add up, giving rise to significant enhancement of the THz pulse amplitude. It has been foreseen that further enhancement would be achieved if the design of phase plates could be optimized to generate filament array. This simple method makes full use of the laser energy and might potentially open a new approach to remotely enhance the THz emission in air.

Comment on Asymmetric optical cryptosystem based on coherent superposition and equal modulus decomposition

Xiaopeng Deng

Doc ID: 240236 Received 12 May 2015; Accepted 08 Jun 2015; Posted 21 Jul 2015  View: PDF

Abstract: I comment on the recent Letter by Jianjun Cai et al. [Opt. Lett.40, 475(2015)], in which the authors claimed that the method can achieve high robustness against the special attack based on iterative Fourier transform. However, according to my analysis and simulation results, the asymmetric optical cryptosystem cannot resist the special attack based on iterative Fourier transform. So, I think their attack analysis and algorithm are ill-considered and worth discussing.

Comment on "Single-shot speckle reduction in numerical reconstruction of digitally recorded holograms"

Jonathan Maycock, Bryan Hennelly, and John McDonald

Doc ID: 238333 Received 23 Apr 2015; Accepted 19 May 2015; Posted 28 Jul 2015  View: PDF

Abstract: We comment on a recent Letter by Hincapie et al. [Opt. Lett. 40, 1623 (2015)] in which the authors proposed a method to reduce the speckle noise in digital holograms. This method was previously published by us in Maycock [PhD Thesis, 2012] and Maycock and Hennelly [Book, LAP LAMBERT, Academic Publishing, 2014]. We also wish to highlight an important limitation of the method resulting from the superposition of different perspectives of the object/scene, which was not addressed in their paper.

Room-temperature magnetic gradiometry with fiber-coupled nitrogen--vacancy centers in diamond

Aleksei Zheltikov, Ilya Fedotov, Sean Blakley, and Sergey Kilin

Doc ID: 237633 Received 07 Apr 2015; Accepted 12 May 2015; Posted 01 Jul 2015  View: PDF

Abstract: Differential optical detection of a magnetic resonance induced in nitrogen--vacancy (NV) centers in diamond is shown to enable a high-spatial-resolution room-temperature magnetic field gradiometry on a fiber platform. An ultracompact design of this fiber-based solid-state magnetic gradiometer is achieved by integrating an NV-diamond magnetic sensor with a two-fiber opto--microwave interface, which couples NV centers to microwave and optical fields, used to resonantly drive and interrogate the spin of NV centers.

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