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Accepted papers to appear in an upcoming issue

OSA now posts prepublication articles as soon as they are accepted and cleared for production. See the FAQ for additional information.

Compact wavelength add-drop multiplexers using Bragg gratings in coupled dielectric-loaded plasmonic waveguides

Ilya Radko, Giulio Biagi, Kjeld Pedersen, Sergey Bozhevolnyi, Horst-Gunter Rubahn, and Jacek Fiutowski

Doc ID: 232970 Received 26 Jan 2015; Accepted 30 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We report a novel design of a compact wavelength add-drop multiplexer utilizing dielectric-loaded surface plasmon-polariton waveguides (DLSPPWs). The DLSPPW-based configuration exploits routing properties of directional couplers and filtering abilities of Bragg gratings. We present practical realization of a 20-μm-long device operating at telecom wavelengths that can reroute optical signals separated by approximately 70 nm in the wavelength band. We characterize the performance of the fabricated structures using scanning near-field optical microscopy as well as leakage-radiation microscopy and support our findings with numerical simulations.

Yb-fiber-laser-based, 1.8 W-average-power picosecond ultraviolet source at 266 nm

Suddapalli Chaitanya Kumar, Josep Canals Casals, Enrique Sánchez Bautista, Kavita Devi, and Majid Ebrahim-Zadeh

Doc ID: 235836 Received 10 Mar 2015; Accepted 30 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We report a compact, stable, high-power, picosecond ultraviolet (UV) source at 266 nm based on simple single-pass two-step fourth harmonic generation (FHG) of a mode-locked Yb-fiber laser at 79.5 MHz in LiB3O5 (LBO) and β-BaB2O4 (BBO). Using a 30-mm-long LBO crystal for single-pass second harmonic generation (SHG), we achieve up to 9.1 W of average green power at 532 nm for 16.8 W of Yb-fiber power at a conversion efficiency of 54% in 16.2 ps pulses with TEM00 spatial profile and passive power stability better than 0.5% rms over 16 h. The generated green radiation is then used for single-pass FHG into the UV, providing as much as 1.8 W of average power at 266 nm under the optimum focusing condition in the presence of the spatial walk-off, at an overall FHG conversion efficiency of ~11%. The generated UV output exhibits passive power stability better than 4.6% rms over 1.5 h and a beam pointing stability better than 84 µrad over 1 h. The UV output beam has a circularity>80% in high beam quality with TEM00 mode profile. To the best of our knowledge, this is the first report of picosecond UV generation at 266 nm at MHz repetition rates.

Dual Light Field and Polarization Imaging Using CMOS Diffractive Image Sensors

Suren Jayasuriya, Sriram Sivaramakrishnan, Ellen Chuang, Debashree Guruaribam, Albert Wang, and Alyosha Molnar

Doc ID: 236226 Received 17 Mar 2015; Accepted 30 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: In this Letter, we present the first integrated CMOS image sensor that can simultaneously perform light field and polarization imaging without the use of external filters or additional optical elements. Previous work has shown how photodetectors with two stacks of integrated metal gratings above them (called Angle Sensitive Pixels) diffract light in a Talbot pattern to capture 4D light fields. We show, in addition to diffractive imaging, these gratings polarize incoming light and characterize the response of these sensors to polarization and incidence angle. Finally we show two applications of polarization imaging: imaging stress-induced birefringence and identifying specular reflections in scenes to improve light field algorithms for these scenes.

Variable two-crystal cascade for conical refraction

Viktor Peet

Doc ID: 236327 Received 18 Mar 2015; Accepted 30 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: The cascade conical refraction occurs when collimated light beam is passed consequently along the optic axes of several biaxial crystals arranged in series. For commonly used optical arrangements the general structure of light emerging from such a cascade is rigorously determined by the used crystals leaving few possibilities for the variations of the established light pattern. A simple modification of two-crystal arrangement is reported. This modification adds an extreme versatility to the effect and allows one to tune continuously the actual cascade parameters. As a result, practically any pattern of two-crystal cascade conical refraction can be obtained for any pair of biaxial crystals.

Enhancing the heralded single photon rate from a silicon nanowire by time and wavelength division multiplexing pump pulses

Chunle Xiong, Xiang Zhang, Iman Jizan, Jiakun He, Alex Clark, Duk-Yong Choi, Chang Chae, and Benjamin Eggleton

Doc ID: 234924 Received 23 Feb 2015; Accepted 30 Apr 2015; Posted 01 May 2015  View: PDF

Abstract: Heralded single photons produced on a silicon chip represent an integrated photon source solution for scalable photonic quantum technologies. The key limitation of such sources is their non-deterministic nature introduced by the stochastic spontaneous four-wave mixing (SFWM) process. Active spatial and temporal multiplexing can improve this by enhancing the single photon rate without degrading the quantum signal to noise ratio. Here taking advantage of the broad bandwidth of SFWM in a silicon nanowire, we experimentally demonstrate heralded single photon generation from a silicon nanowire pumped by time and wavelength division multiplexed pulses. We show a 90±5% enhancement on the heralded photon rate at the cost of only 14±2% reduction to the signal to noise ratio, close to the performance found using only time division multiplexed pulses. As single photon events are distributed to multiple wavelength channels, this new scheme overcomes the saturation limit of avalanche single photon detectors and will improve the ultimate performance of such photon sources.

Degenerate band edge resonances in periodic silicon ridge waveguides

Ronald Reano, Michael Wood, and Justin Burr

Doc ID: 236363 Received 18 Mar 2015; Accepted 30 Apr 2015; Posted 01 May 2015  View: PDF

Abstract: We experimentally demonstrate degenerate band edge resonances in periodic Si ridge waveguides that are compatible with carrier injection modulation for active electro-optical devices. The resonant cavities are designed using a combination of the planewave expansion method and the finite difference time domain technique. Measured and simulated quality factors of the first band edge resonances scale to the fifth-power of the number of periods. Quality factor scaling is determined to be limited by fabrication imperfections. Compared to resonators based on a regular transmission band edge, degenerate band edge devices can achieve significantly larger quality factors in the same number of periods. Applications include compact electro-optical switches, modulators, and sensors that benefit from high quality factor and large distributed electric fields.

Design of novel N-dimensional CAP filters for 10 Gb/s CAP-PON system

Lei Deng, Jiale He, Lu Shi, Mengfan Cheng, Ming Tang, Songnian Fu, Minming Zhang, Ping Shum, and Dengming Liu

Doc ID: 237160 Received 31 Mar 2015; Accepted 30 Apr 2015; Posted 01 May 2015  View: PDF

Abstract: We propose a novel method to design N-dimensional carrierless amplitude and phase modulation (CAP) filters. Theoretical analysis and experimental results show that by using the proposed method, the required iteration steps for filters design are significantly decreased, and the orthogonality between CAP filters could be maintained even with lower cut-off frequency compared with the existing methods. Furthermore, we successfully demonstrate a 10 Gb/s 4-dimensinal CAP data transmission experiment over 25 km standard single mode fiber. The results show that the proposed N-dimensional CAP filter design method has potential applications in low-cost and high speed CAP-PON systems.

Reverse bistable effect in ferroelectric liquid crystal devices with ultra-fast switching at low driving voltage

qi guo, Xiaojin Zhao, huijie zhao, and Vladimir Chigrinov

Doc ID: 237542 Received 03 Apr 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: In this paper, reverse bistable effect with deep-sub-millisecond switching time is first reported in ferroelectric liquid crystal (FLC) devices using planer photo-alignment technique. It is indicated by our experimental results that both the anchoring energy and the dielectric property of the FLC’s alignment layer is critical for the existence of the reverse bistable effect. In addition, with the derived criteria of the reverse bistable effect, we quantitatively analyze the switching dynamics of the reverse bistable FLC and the transition condition between the traditional bistability and our presented reverse bistability. Moreover, the fabricated FLC device exhibits an ultra-fast switching of ~160μs and a high contrast ratio of 1000:1, both of which were measured at a low driving voltage of 11V. The featured deep-sub-millisecond switching time is really advantageous for our presented reverse bistable FLC devices, which enables a significant quality improvement of the existing optical devices as well as a wide range of new applications in photonics and display areas.

Dual-color three-dimensional STED microscopy with a single high-repetition-rate laser

Kyu Young Han and Taekjip Ha

Doc ID: 236124 Received 12 Mar 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We describe a dual-color three-dimensional stimulated emission depletion (3D-STED) microscopy employing a single laser source with a repetition rate of 80 MHz. Multiple excitation pulses synchronized with a STED pulse were generated by a photonic crystal fiber and the desired wavelengths were selected by an acousto-optic tunable filter with high spectral purity. Selective excitation at different wavelengths permits simultaneous imaging of two fluorescent markers at a nanoscale resolution in three dimensions.

Broad spectral excitation of opsin for enhanced stimulation of cells

Samarendra Mohanty, Sarmishtha Satpathy, Subrata Batabyal, Kamal Dhakal, John Lin, and Young-tae Kim

Doc ID: 236809 Received 24 Mar 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: Optical stimulation of cells expressing light-sensitive proteins (opsins) has allowed targeted activation with cellular specificity. However, since narrow-band light has been used for excitation of these optogenetic probes, only active stimulation strategies are being attempted for clinical applications such as restoration of vision. Here, we report use of broad spectral excitation (white light) for optogenetic stimulation of opsin-sensitized cells. We found that ReaChR is optimally excited with white light offering significantly higher photocurrents compared to spectrally-filtered narrow-band light stimulation. Our findings open up the possibility of passive stimulation strategy by use of natural sunlight for retinal stimulation, which could have benefits for ambient light stimulated vision restoration.

Miniaturized fiber-coupled confocal fluorescence microscope with an electrowetting variable focus lens using no moving parts

Emily Gibson, Juliet Gopinath, Victor Bright, Baris Ozbay, Justin Losacco, Richard Weir, Robert Cormack, and Diego Restrepo

Doc ID: 236814 Received 24 Mar 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We report a miniature, lightweight fiber-coupled confocal fluorescence microscope that incorporates an electrowetting variable focus lens to provide axial scanning for full three-dimensional (3D) imaging. Lateral scanning is accomplished by coupling our device to a laser-scanning confocal microscope through a coherent imaging fiber-bundle. The optical components of the device are combined in a custom 3D-printed adapter with an assembled weight of <2 g that can be mounted onto the head of a mouse. Confocal sectioning provides an axial resolution of ~12 µm and an axial scan range of ~80 µm. The lateral field-of-view is 300 µm and the lateral resolution is 1.8 µm. We determined these parameters by imaging fixed sections of mouse neuronal tissue labeled with green fluorescent protein (GFP) and fluorescent bead samples in agarose gel. To demonstrate viability for imaging intact tissue, we resolved multiple optical sections of ex vivo mouse olfactory nerve fibers expressing yellow fluorescent protein (YFP).

Wavefront reconstruction in digital off-axis holography via sparse coding of amplitude and absolute phase

Nikolay Petrov, Vladimir Katkovnik, Karen Egiazarian, and Igor Shevkunov

Doc ID: 233776 Received 04 Feb 2015; Accepted 29 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: This work presents the new method for wavefront reconstruction from digital holograms recorded in off-axis configuration. The main features of the proposed algorithm are good ability for noise filtration due to the original formulation of the problem taking into account the presence of noise in the recorded intensity distribution and the sparse phase and amplitude reconstruction approach (SPAR) with data-adaptive block-matching 3D (BM3D) technique. Basically, the sparsity assumes that low dimensional models can be used for phase and amplitude approximations. This low dimensionality enables strong suppression of noisy components and accurate revealing of the main features of the signals of interest. The principal point is that dictionaries of these sparse models are not known in advance and reconstructed from given noisy observations in multiobjective optimization procedure. We show experimental results demonstrating effectiveness of our approach.

Self-referenced sensor utilizing extra-ordinary optical transmission from metal nanoslits array

Sachin Srivastava and Ibrahim Abdulhalim

Doc ID: 235893 Received 11 Mar 2015; Accepted 28 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We report the first self referenced sensor based on the extra-ordinary optical transmission (EOT) of metal-nanoslits array in the near infra-red (NIR) telecommunication window of the electromagnetic spectrum. The nanoslits array shows two enhanced transmission peaks, out of which one shows a red shift with an increase in the refractive index of the analyte medium, while the other remains fixed. We demonstrate the detection of small amounts of water in ethanol using the nanoslits array chip. The present study might be useful in developing ultra-small biosensor chips integrated to optical fibers for online monitoring and remote sensing applications.

Achromatization of retarder for broadband polarimetric system

Tingkui Mu, Chunmin Zhang, Qiwei Li, and Rongguang Liang

Doc ID: 235765 Received 10 Mar 2015; Accepted 28 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: Broadband polarimetric system with enhanced performance is highly desired in many applications, such as remote sensing. However the wavelength-dependent retardance of a simple retarder limits the system performance over a broadband spectrum. To achromatize retarder by combining a stack of plates made of same materal with different azimuths, in this letter we propose a new approach to optimize the achromatic retarder by using the condition number k2 based on 2-norm or the equally weighted variance EWV, two figures of merit for the polarimetric system, as the merit function. The variations of azimuthal angle and retardance can be well coordinated with more degree of freedom. Our study within the frame of a optimized full-Stokes polarimeter shows that, for the combination with seven Quartz plates, the root-mean-square error of the k2 and EWV are smaller than 0.5% and 0.07% respectively over the waveband of 0.4 - 0.7 micrometers. The maximum deviation of the equivalent retardance and azimutal angle are approximately 0.33% of 131.8 deg and 0.66% of 90 deg respectively.

Deep UV microsphere projection lithography

Alireza Bonakdar, Hooman Mohseni, Robert Brown, Sung Jun Jang, Mohsen Rezaei, Eric Dexheimer, and Vala Fathipour

Doc ID: 236973 Received 01 Apr 2015; Accepted 28 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: In this letter, we present a single-exposure deep-UV projection lithography at 254-nm wavelength that produces nanopatterns in a scalable area with a feature size of 80 nm. In this method, a macroscopic lens projects a pixelated optical mask on a monolayer of hexagonally arranged microspheres that reside on the Fourier plane and image the mask’s pattern into a photoresist film. Our macroscopic lens shrinks the size of the mask by providing an imaging magnification of ~1.86×10^4, while enhancing the exposure power. On the other hand, microsphere lens produces a sub-diffraction limit focal point – a so-called photonic nanojet – based on the near-surface focusing effect, which ensures an excellent pattering accuracy against the presence of surface roughness. Ray-optics simulation is utilized to design the bulk optics part of the lithography system while a wave-optics simulation is implemented to simulate the optical properties of the exposed regions beneath the microspheres. We characterize the lithography performance in terms of the proximity effect, lens aberration, and interference effect due to refractive index mismatch between photoresist and substrate.

Diffractive broadband coupling into high-Q resonant cavities

Hongtao Lin, Xiaochen Sun, Jifeng Liu, and Juejun Hu

Doc ID: 236514 Received 19 Mar 2015; Accepted 28 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: Optical resonators with high quality factors (Q-factor) constitute the main building block for many photonic devices capitalizing on light-matter interactions, ranging from light emitters to biochemical sensors. While high Q-factor enhances light-matter interactions, it also limits the device operation bandwidth. Here we propose and numerically analyze a generic coupling scheme to overcome the apparent trade-off. By using an orthogonal grating, broadband optical coupling into high-Q cavities of diverse geometric configurations can be achieved. As an example, the approach is applied to demonstrate over 28-fold optical absorption enhancement across a 150 nm band around 900 nm wavelength in single-layer graphene embedded inside a Fabry-Perot cavity.

Azimuthal multiple beam interference effects with combinations of vortex beams

Ignacio Moreno, Jeffrey Davis, Taylor Womble-Dahl, and Don Cottrell

Doc ID: 236906 Received 26 Mar 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We create a series of vortex beams consisting of positive and negative charges and develop a geometry where they interfere creating azimuthal multiple beam interference effects. Usually the combination of two beams with opposite charges creates an azimuthal two-beam interference effect where the intensity varies sinusoidally with azimuthal angle. We combine several of these beams to create patterns where the interference becomes more sharply defined in the azimuthal direction and where destructive interference eliminates some of the intensity peaks. The process is complicated by the fact that the radii of the different vortex beams depend on the charge and the focal length of the Fourier lens. We generate a series of patterns where the different charges are focused with different focal lengths such that their radii agree. However to encode these, we encode patterns from the larger charges that have been Fresnel diffracted to the plane of the lowest charge. These complicated patterns are encoded onto a liquid crystal display (LCD). Experimental results agree well with theory

Tunable all-optical plasmonic diode based on Fano resonance in nonlinear cavities-coupled waveguide

Yihang Chen, Cairong Fan, Fenghua Shi, and Hongxing Wu

Doc ID: 234909 Received 17 Feb 2015; Accepted 27 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: Tunable all-optical plasmonic diode is proposed based on the Fano resonance in an asymmetric and nonlinear system, comprising metal-insulator-metal waveguides coupled with nanocavities. The spatial asymmetry of the system gives rise to the nonreciprocity of the field localizations at the nonlinear gap between the coupled cavities and to the nonreciprocal nonlinear response. Nonlinear Fano resonance, originating from the interference between the discrete cavity mode and the continuum traveling mode, is observed and effectively tuned by changing the input power. By combining the unidirectional nonlinear response with the steep dispersion of the Fano asymmetric line shape, a transmission contrast ratio up to 41.46 dB was achieved between forward and backward transmission. Our all-optical plasmonic diode with compact structure can find important applications in integrated optical nanocircuits.

Modeling and analysis of polarization effects in Fourier domain mode-locked lasers

Christian Jirauschek and Robert Huber

Doc ID: 234560 Received 13 Feb 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We develop a theoretical model for Fourier domain mode-locked (FDML) lasers in a non-polarization maintaining configuration, which is the most widely used type of FDML source. This theoretical approach is applied to analyze a widely wavelength-swept FDML setup, as used for picosecond pulse generation by temporal compression of the sweeps. We demonstrate that good agreement between simulation and experiment can only be obtained by including polarization effects due to fiber bending birefringence, polarization mode dispersion and cross-phase modulation into the theoretical model. Notably, the polarization dynamics is shown to have a beneficial effect on the instantaneous linewidth, resulting in improved coherence and thus compressibility of the wavelength-swept FDML output.

High-quality ultraviolet beam generation in multimode photonic crystal fiber through non-degenerate four-wave mixing at 532~nm

Benoit Sevigny, Geraud Bouwmans, Andy Cassez, Olivier Vanvincq, and Yves Quiquempois

Doc ID: 236665 Received 24 Mar 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: All-fiber ultraviolet (UV) light sources are of great practical interest for a multitude of applications spanned across different sectors, from industrial to biomedical to name a few. However, production of UV light sources with high beam quality has been a problem to this day as the fiber designs required to reach UV wavelengths by four-wave mixing with widely available pumps (i.e. 532 nm) are challenging because of their small size and increased risk of material damage. In this paper, a specific pumping scheme is presented that allows the conversion of two pump photons in different modes to UV light in the fundamental mode and the corresponding idler in a higher-order mode. The process has also been shown to work experimentally and UV light at 390.5 nm in the fundamental mode was successfully generated.

1120nm Diode-Pumped Bi-doped Fiber Amplifier

Naresh Kumar Thipparapu, Saurabh Jain, Andrey Umnikov, Pranabesh Barua, and Jayanta Sahu

Doc ID: 236673 Received 23 Mar 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: Bismuth-doped aluminosilicate fiber has been fabricated by the MCVD-solution doping method and characterized for its unsaturable loss and gain. The amplifier performance has been compared for a novel pumping wavelength of 1120nm with the conventional pumping wavelength region of 1047nm. Unsaturable loss was 65% and 35% at 1047nm and 1120nm, pump wavelengths respectively. A maximum gain of about 8dB at 1180nm for a fiber length of 100m was observed with 1120nm pumping. Gain enhancement of 70% was achieved with the 1120nm pump as compared to 1047nm pump. A further 3.5dB gain was obtained on simultaneous pumping at 1047nm and 1120nm.

Generation of elliptically-polarized attosecond pulse trains

Dejan Milosevic

Doc ID: 236711 Received 24 Mar 2015; Accepted 27 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: Stimulated by recent demonstration of the first bright source of circularly-polarized high harmonics we examine the attosecond pulse trains generated by a group of such harmonics. For the $s$ ground state of atom the polarization of generated pulses is close to linear with three different orientation per cycle. However, for the $p$ ground state of the inert gases used in the experiments, the polarization of the attosecond pulses is close to elliptic. We show that this is caused by the different intensity of the high harmonics of the opposite helicity.

Low photobleaching and high emission depletion efficiency: the potential of AIE luminogen as fluorescent probe for STED microscopy

Jun Qian, Jia Yu, fuhong cai, Zhen Zhu, Xian Sun, An Qin, Ben Tang, and Sailing He

Doc ID: 235015 Received 19 Feb 2015; Accepted 25 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We present a preliminary study, which explores the potential of aggregation-induced emission (AIE) luminogen as a new fluorescent probe for STED microscopy. Compared with Coumarin 102, which is a commonly used organic fluorophore in STED microscopy, HPS, a typical AIE luminogen, is more resistant to photobleaching. In addition, HPS doped nanoparticles have higher emission depletion efficiency than Coumarin 102 in organic solution. These two advantages of AIE luminogen can facilitate the improvement of spatial resolution, as well as long-term imaging, in STED microscopy. AIE luminogen will be a promising candidate for STED microscopy in the future.

Arrays of resonant nano-pillars for biochemical sensing

MIGUEL HOLGADO, Ana Hernandez, Rafael Casquel, Iñaki Cornago, Francisco Javier Sanza, Beatriz Santamaría, María Victoria Maigler, Fátima Fernandez, Alavaro Lavin, and María Fé Laguna

Doc ID: 235285 Received 27 Feb 2015; Accepted 25 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: In this article we demonstrate for the first time the experimental capability for biochemical sensing of resonant nano-pillars (RNPs) arrays. These arrays are fabricated over a glass substrate and are optically interrogated from the backside of this substrate. The reflectivity profile of the RNPs arrays are measured by infiltrating different ethanol fractions in water in order to evaluate the optical response for the different refractive indexes ranging from 1.330 to 1.342. A linear fit of the resonant modes shift is observed as function of the bulk refractive index of the liquid infiltrated. For the type of transducer analyzed, a relevant sensitivity of 10017 cm-1/Refractive Index Unit (RIU) is achieved allowing reaching a competitive Limit of Detections (LoD) in the order of 1x10-5 RIU.

Fiber-based dual-focus time-demultiplexed SHG microscopy

Juergen Popp, Sandro Heuke, Fisseha Bekele Legesse, Adrian Lorenz, Torbjoern Pascher, Denis Akimov, Matthias Jaeger, and Michael Schmitt

Doc ID: 237299 Received 01 Apr 2015; Accepted 25 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We present a dual-focus SHG microscopy approach based on stable, compact and inexpensive fiber technology. One-tenth of the fiber laser output is coupled into a 100 m ($\hat{=}$ 500 ns) long single mode fiber and further amplified to achieve two separately guided beams with time-alternating pulse trains. SHG detection is performed sequentially generating two individual images in one scan. Thus, the configuration allows for imaging of distinct areas within the field of view at twice the repetition rate of the fiber laser but is readily extended to a multiple of the repetition rate with tens of foci.

Third-order nonlinearity and passive Q-switching of Cr4+:YGG garnet crystal

Huaijin Zhang, Shuxian Wang, Yuxia Zhang, Kui Wu, Rui Zhang, Haohai Yu, Guanghui Zhang, and Xiong Qihua

Doc ID: 235379 Received 27 Feb 2015; Accepted 24 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: We demonstrate the third-order nonlinear optical properties of Cr4+:Y3Ga5O12 (Cr4+:YGG) and Q-switched lasers with Cr4+:YGG as the saturable absorber for the first time to our knowledge. The third-order nonlinear properties, including the optical Kerr nonlinearity and saturable absorption, were systematically measured and analyzed in detail by using a Z-scan technique. The measured data show that Cr4+:YGG has a large nonlinear refractive index, ground-state absorption cross section and excited-state absorption cross section in contrast to Cr4+:Y3Al5O12 (Cr4+:YAG). With a Nd:YGG crystal as the gain medium and a Cr4+:YGG crystal as the saturable absorber, the passively Q-switched laser was performed. The shortest pulse width and largest pulse energy were achieved at the absorbed pump power of 8 W with the values of 9.1 ns and 26.1 μJ, respectively, corresponding to the average output power of 0.87 W and peak power of 2.9 kW. The results indicate that Cr4+:YGG is an available and promising optical switcher for the pulsed lasers.

Single-order diffraction with trapezoidal transmission grating

Quanping Fan, wei Liu, Ke Wang, hua yang, lai Wei, Xiaoli Zhu, Changqing Xie, Qiangqiang Zhang, Feng Qian, Yang Yan, Yuqiu Gu, Min Zhou, leifeng cao, and Gang Jiang

Doc ID: 236521 Received 20 Mar 2015; Accepted 24 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: Diffraction grating is a widely used dispersion element in spectral analysis from infrared to X-ray region. Traditionally, it has square wave transmission function, suffering from high-order diffraction contamination. Single-order diffraction can be achieved by sinusoidal amplitude transmission grating, but the fabrication is difficult. Here, we propose a novel idea to design grating based on trapezoidal transmission function, which makes traditional grating as a special case. Grating designed by this idea can not only suppress higher-order diffraction by several orders of magnitude as sinusoidal amplitude grating does, but also greatly reduce the fabrication difficulty to the level of processing for traditional grating. It offers a new opportunity for fabrication of grating with single-order diffraction and measurement of spectrum without contamination of high order harmonic components. This idea can easily extend to varied-line-space grating, concave grating with single order diffraction or zone plates with single foci and will bring great changes in the field of grating applications.

Experimental analysis of BRDF cross section conversion term in direction cosine space

Samuel Butler, Stephen Nauyoks, and Michael Marciniak

Doc ID: 233703 Received 04 Feb 2015; Accepted 24 Apr 2015; Posted 30 Apr 2015  View: PDF

Abstract: Of the many classes of BRDF models, two popular classes of models are the microfacet model and the linear systems diffraction model. The microfacet model has the benefit of speed and simplicity, as it uses geometric optics approximations, while linear systems theory uses a diffraction approach to compute the BRDF, at the expense of greater computational complexity. In this letter, non-grazing BRDF measurements of rough and polished surface-reflecting materials at multiple incident angles are scaled by the microfacet cross section conversion term, but in the linear systems direction cosine space, resulting in great alignment of BRDF data at various incident angles in this space. This results in a predictive BRDF model for surface-reflecting materials at non-grazing angles, while avoiding some of the computational complexities in the linear systems diffraction model.

Highly directional emission from a quantum emitter embedded in a hemispherical cavity

Yong Ma, Guillem‎ Ballesteros, Joanna Zajac, Jining Sun, and Brian Gerardot

Doc ID: 235393 Received 04 Mar 2015; Accepted 24 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We report a solid-state, micron-sized hemispherical cavity which yields significantly enhanced extraction efficiency with modest Purcell enhancement from embedded quantum emitters. A simple analytical model provides a guideline for the design and optimization of the structure while finite-difference time-domain simulations are used for full analysis of the optimum structure. Cavity modes with up to 90% extraction efficiency, a Purcell enhancement factor > 2, and a quality factor of 50 are achieved. In addition, Gaussian-like far-field beam profiles with low divergence are exhibited for several modes. These monolithic cavities are promising for solid-state emitters buried in a high dielectric environment, such as self-assembled quantum dots and optically active defects in diamond.

Design of multifold Ge/Si/Ge composite quantum-dot heterostructures for visible to near-infrared photodetection

Pei-Wen Li, Ming-Hao Kuo, Wei-Ting Lai, Sheng-Wei Lee, Yen-Chun Chen, Chia-Wei Chang, Wen-Hao Chang, and Tzu-Min Hsu

Doc ID: 235478 Received 04 Mar 2015; Accepted 24 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We demonstrated an effective approach to grow high-quality thin film (>1 μm) of multifold Ge/Si/Ge composite quantum dots (CQDs) stacked heterostructures for near infrared photodetection and optical interconnect applications. An otherwise random, self-assembly of variable-fold Ge/Si CQDs has been grown on Si through the insertion of Si spacer layers to produce micron-scale-thick, stacked Ge/Si CQD layers with desired QD morphology and composition distribution. The high crystalline quality of the multifold Ge CQD heterostructures is evidenced by an extremely low dark current density of 3.68 pA/μm², superior photoresponsivity of 267 and 220 mA/W under 850 and 980 nm illumination, respectively, and very fast temporal response time of 0.24 ns of the Ge/Si CQD photodetectors.

High-power Yb:YAG single-crystal fiber amplifiers for femtosecond lasers in cylindrical polarization

Fabien Lesparre, Jean-Thomas Gomes, Xavier Delen, Igor Martial, Julien Didierjean, Wolfgang Pallmann, Bojan Resan, Thomas Graf, Marwan Abdou Ahmed, Frederic Druon, Francois Balembois, Patrick Georges, and Michael Eckerle

Doc ID: 236780 Received 25 Mar 2015; Accepted 24 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We demonstrate a three-stage diode-pumped Yb:YAG single-crystal-fiber amplifier to generate femtosecond pulses at high average powers with linear or cylindrical (i.e. radial or azimuthal) polarization. At a repetition rate of 20MHz, 750fs pulses were obtained at an average power of 85W in cylindrical polarization and at 100W in linear polarization. The report includes investigations on the use of Yb:YAG single-crystal-fibers with different length/doping ratio and the zero-phonon pumping at a wavelength of 969nm in order to optimize the performance.

Coherent combination of two Tm-doped fiber amplifiers

Christian Gaida, Marco Kienel, Michael Müller, Arno Klenke, Martin Gebhardt, Fabian Stutzki, Cesar Jauregui, Jens Limpert, and Andreas Tünnermann

Doc ID: 235506 Received 06 Mar 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: The efficient coherent combination of two ultrafast Tm-doped fiber amplifiers in the 2 μm wavelength region is demonstrated. The performance of the combined amplifiers is compared to the output characteristics of a single amplifier being limited by the onset of detrimental nonlinear effects. Nearly transform-limited pulses with 830 fs duration, 22 μJ pulse energy and 25 MW peak power have been achieved with a combining efficiency greater than 90%. Based on this result it can be expected that 2 μm-ultrafast-fiber-laser-systems will enter new performance realms in the near future.

400 W near diffraction-limited single-frequency all-solid photonic bandgap fiber amplifier

Iyad Dajani, Benjamin Pulford, Thomas Ehrenreich, Roger Holten, Fanting Kong, Thomas Hawkins, and Liang Dong

Doc ID: 235545 Received 04 Mar 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: An ytterbium-doped large mode area photonic bandgap fiber is used to demonstrate 400 W of single-frequency output at 1064 nm with excellent beam quality and minimal stimulated Brillouin scattering. The fiber possesses all-solid microstructures embedded in the cladding and a core composed of phosphosilicate with a diameter of ~50 µm. As the signal power is pushed beyond 450 W, there is degradation in the beam quality due to the modal instability. We briefly discuss techniques to alleviate this problem in future designs. To the best of our knowledge, the 400 W single-frequency near diffraction-limited output far exceeds the current state-of-the-art from such type of fiber amplifier.

Gain-assisted critical coupling for high-performance coherent perfect absorbers

Seok Ho Song, Jae Woong Yoon, and MyoungJin Jung

Doc ID: 237351 Received 01 Apr 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Critical coupling of an optical resonator is necessary for coherent perfect light absorption in many active device applications. We propose a gain-assisted method for exact access to critical coupling conditions without altering any structure parameters. In a coherent absorber with additional internal gain media, critical coupling with arbitrarily high coherent signal extinction can be obtained by continuously tuning optical pumping density. Assuming a surface-plasmon resonance grating covered by a gain layer as a promising architecture, we numerically demonstrate gain-assisted continuous access to its critical coupling point with experimentally probable settings. In addition, the gain tuning further introduces switching of the coherent-absorber’s functionality to a conventional lossless beam splitter.

Raman Stokes--anti-Stokes Correlations in Diamond

Lukas Novotny, Mark Kasperczyk, Ado Jorio, Elke Neu, and Patrick Maletinsky

Doc ID: 236585 Received 23 Mar 2015; Accepted 23 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We investigate the arrival statistics of Stokes (S) and anti-Stokes (aS) Raman photons generated in thin diamond crystals. Strong quantum correlations between the S and aS signals are observed, which implies that the two processes share the same phonon, that is, the phonon excited in the S process is consumed in the aS process. We show that the intensity cross-correlation, which describes the simultaneous detection of Stokes and anti-Stokes photons, increases steadily with decreasing laser power and saturates at very low pump powers, implying that the number of Stokes-induced aS photons is comparable to the number of spontaneously generated aS photons. Furthermore, the coincidence rate shows a quadratic plus cubic power dependence, indicating the generation of multiple S photons per pulse at high powers.

Ultrafast all-optical modulation using a photonic-crystal Fano structure with broken symmetry

Yi Yu, Hao Hu, Leif Oxenlowe, Kresten Yvind, and Jesper Mork

Doc ID: 234224 Received 12 Feb 2015; Accepted 23 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We experimentally demonstrate ultrafast all-optical modulation using an ultra-compact InP photonic-crystal Fano structure. In contrast to symmetric configurations previously considered, the use of a structure with broken symmetry in combination with a well-engineered Fano resonance is shown to suppress patterning effects as well as lowering the energy consumption. These properties enable the achievement of error-free 10 Gbit/s modulation with low pump energy using realistic pseudo-random binary sequence patterns. At 20 Gbit/s, the bit-error-ratio remains well below the limit for forward error correction.

Optimization of the split-spectrum amplitude-decorrelation angiography algorithm on a spectral optical coherence tomography system

Simon Gao, Yali Jia, Gangjun Liu, and David Huang

Doc ID: 235085 Received 23 Feb 2015; Accepted 22 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: The split-spectrum amplitude-decorrelation angiography (SSADA) algorithm was optimized on a spectral optical coherence tomography system using a flow phantom. The number of times the spectrum was split and the bandwidth of each split were adjusted to maximize the flow phantom decorrelation signal-to-noise ratio. The improvement in flow detection was then demonstrated with en face retinal angiograms. The optimized algorithm increased the detectable retinal microvascular flow and decreased the variability of the quantified vessel density in OCT retinal angiograms of healthy human subjects.

Optimizing Mode Instability in Low NA Fibers by Passive Strategies

Nicoletta Haarlammert, Bettina Sattler, Andreas Liem, Maximilian Strecker, Johannes Nold, Thomas Schreiber, Ramona Eberhardt, Andreas Tünnermann, Klaus Ludewigt, and Markus Jung

Doc ID: 235223 Received 24 Feb 2015; Accepted 21 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Systematic experimental investigations towards the mode instability (MI) threshold in low NA fibers are performed. By testing several fibers with varying V-parameters drawn from the same preform a high degree of reproducibility of the experimental conditions could be achieved. This allows for systematic investigations on isolated parameters influencing the complex behavior of MI. A maximum MI threshold of 2 kW presenting a power record for narrow linewidth fiber amplifiers could be demonstrated for the tested fibers. The MI threshold was found to sensitively depend on the V-parameter for large V-parameters (> 2), but to be robust for smaller V-parameters. Furthermore, the fiber bending diameter and the seed excitation conditions were identified to sensitively influence the MI threshold.

First Demonstration of OFDM ECDMA for Low Cost Optical Access Networks

Xuhan Guo, Qi Wang, Xin Li, lei zhou, Liming Fang, Adrian Wonfor, Jinlong Wei, Johannes von Lindeiner, Richard Penty, and Ian White

Doc ID: 236249 Received 18 Mar 2015; Accepted 21 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We demonstrate for the first time an analogue orthogonal frequency division multiplexing (OFDM) based electrical code division multiplexing access (ECDMA) passive optical network (PON) for the next-generation access applications. Advantages of the system include low cost, high capacity and enhanced spectral efficiency. A proof-of-principal 16 QAM ECDMA PON downlink experiment is used to show the transmission of an aggregate data rate of 24.8 Gb/s within a 8-user system. Transmission is achieved over 25 km of SMF with negligible dispersion and crosstalk penalties.

Simultaneous omnidirectional zero-n and zero-phi non-Bragg gaps in metamaterial-polaritonic photonic superlattices

Edwin Moncada, Jorge Mejía-Salazar, and Juan Granada

Doc ID: 233990 Received 06 Feb 2015; Accepted 21 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Present study shows that the inclusion of single negative polaritonic-like layers in one-dimensional metamaterial photonic superlattices may lead to new effects, such as the simultaneous existence of omnidirectional zero-n and zero-phi non-Bragg gaps for both, transversal electric (TE) and transversal magnetic (TM) polarizations, which as shown at the end, are also robust to uniaxial anisotropic effects. Such omnidirectional behavior, in the case of the zero-n gap, occurs within the same frequency range for both polarizations, which is not allowed in the case of DNG metamaterial-air superlattices, suggesting a route to design and develop omnidirectional optical filters for all polarizations. Furthermore, present results show that, when polaritonic inclusions are considered, the long wavelength approximation is not ever suitable to describe the non-Bragg gaps edges.

Localized Photonic jets from flat 3D dielectric cuboids in the reflection mode

Miguel Beruete, Víctor Pacheco-Peña, Igor Minin, and Oleg Minin

Doc ID: 235082 Received 23 Feb 2015; Accepted 21 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: A photonic jet (terajet at THz frequencies) commonly denotes a specific spatially localized region in the near-field at the front side of a dielectric particle with diameter comparable with wavelength illuminated with a plane wave from its backside (i.e., the jet emerges from the shadow surface of a dielectric particle). In this paper the formation of photonic is demonstrated using the recently proposed 3D dielectric cuboids working in “reflection" mode when the specific spatially localized region is localized towards the direction of incidence wavefront. The results of simulations based on Finite Integration Technique are discussed. All dimensions are given in wavelength units so that all results can be scaled to any frequency of interest including optical frequencies, simplifying the fabrication process compared with spherical dielectrics. The results here presented may be of interest for novel applications including microscopy techniques and sensors.

Coherence experiments in single-pixel digital holography

Jung-Ping Liu, Chia-Hao Guo, Wei-Jen Hsiao, Ting-Chung Poon, and Peter Tsang

Doc ID: 234767 Received 16 Feb 2015; Accepted 20 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: In optical scanning holography (OSH), the coherence properties of the acquired holograms depend on the single-pixel size, i.e., the active area of the photo-detector. For the first time, we have demonstrated coherent, partial coherent and incoherent three-dimensional (3-D) imaging by experiment in such a single-pixel digital holographic recording system. We have found, for the incoherent-mode of OSH, in which the detector of the largest active area is applied, the 3-D location of a diffusely reflecting object can be successfully retrieved without speckle noise. For partial coherent mode employing a smaller pixel size of the detector, significant speckles and randomly distributed bright spots appear among the reconstructed images. For the coherent-mode of OSH when the size of the pixel is vanishing small, the bright spots disappear. However, the speckle remains and the signal-to-noise ratio is low.

Generation of 8-nJ pulses from a normal dispersion thulium doped fiber laser

Yuxing Tang, Andy Chong, and Frank Wise

Doc ID: 235043 Received 25 Feb 2015; Accepted 20 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: We report a study of a mode-locked thulium (Tm) fiber laser with varying normal dispersion. It is difficult to reach the high-energy dissipative-soliton regime due to the anomalous dispersion of most fibers at 2 m. With large normal dispersion, the laser exhibits elements of self-similar pulse evolution, and is the first Tm fiber laser to achieve the performance benefits of normal-dispersion operation. The laser generates 7.6-nJ pulses, which can be dechirped to 130 fs duration. The resulting peak power is 4 times higher than that of previous Tm fiber lasers.

Computational illumination based motion deblurring with an LED array microscope

Chenguang Ma, Laura Waller, Lei Tian, Ziji Liu, and Qionghai Dai

Doc ID: 232709 Received 20 Jan 2015; Accepted 20 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Motion blur, which results from time-averaging a signal over the camera's exposure time, is a common problem when imaging fast moving objects in microscope. In this paper, we demonstrate linear motion deblurring in an LED array microscope, based on computational illumination. By illuminating moving objects with a well-designed temporal coded sequence during each single camera exposure, the resulting motion blur is invertible and can thus be computationally removed. With programmable LEDs, the coded illumination pattern in our system has the benefit of being continuous, fast, and adaptive, which leads to high quality deblur performance and a flexible implementation. The proposed method is demonstrated experimentally for fast moving targets in a fluidic environment with simple, inexpensive optics and no moving parts.

A phase locked MHz pulse selctor for X-ray sources

Karsten Holldack, Alexander Föhlisch, Daniel Förster, Bernd Lindenau, Marko Leyendecker, Franz Janssen, Carsten Winkler, Jürgen Kirschner, and Frank Schumann

Doc ID: 237792 Received 09 Apr 2015; Accepted 19 Apr 2015; Posted 21 Apr 2015  View: PDF

Abstract: Picosecond X-ray pulses are extracted with a phase locked X-ray pulse selector at 1.25 MHz repetition rate from the pulse trains of the accelerator driven multiuser X-ray source BESSY II preserving the peak brilliance at high pulse purity. The system consists of a specially designed in-vacuum chopper wheel rotating with 1 kHz angular frequency. The wheel is driven in an ultrahigh vacuum and is levitated on magnetic bearings being capable of withstanding high centrifugal forces. Pulses are picked by 1252 high precision slits of 70 μm width on the outer rim of the wheel corresponding to a temporal opening window of the chopper of 70 ns. We demonstrate how the electronic phase stabilization of ±2 ns together with an arrival time jitter of the individual slits of the same order of magnitude allows us to pick short single bunch x-ray pulses out of a 200 ns ion clearing gap in a multibunch pulse train as emitted from a synchrotron facility at 1.25 MHz repetition rate with a pulse purity below the shot noise detection limit. The approach is applicable to any high repetition pulsed radiation source, in particular in the X-ray spectral range up to 10 keV. The opening window in a real X-ray beamline, its stability as well as the limits of mechanical pulse picking techniques in the MHz range are discussed.

Wide Operation Range In-Phase Coherently Coupled Vertical Cavity Surface Emitting Laser Array Based on Proton Implantation

Meng Xun, Chen Xu, Yiyang Xie, Jun Deng, Guoqing Jiang, jun wang, Kun Xu, and Hongda Chen

Doc ID: 235381 Received 06 Mar 2015; Accepted 19 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: In-phase coherently coupled vertical cavity surface emitting laser (VCSEL) hexagonal arrays based on proton implantation were produced. The near-field profiles, far-field profiles and emission spectra of the arrays under different injection currents were tested and analyzed. The arrays can maintain in-phase single mode in a considerably wide current range from 10mA (Ith) to 35mA (3.5×Ith), exhibiting excellent beam quality. The far-field divergence angular of the in-phase coupled array is 2.5 degrees. Approximately 29% of total power is localized in central lobe. Compared to square structure arrays, hexagonal arrays can maintain a more stable in-phase single mode because of stronger coupling among the elements. The maximum output power of the array is 4.9mW under pulse wave condition. Simulation of far field profile was carried out to match the in-phase operation test results. The performance enhancement of the array is accessible if the condition of heat dissipation is better. The process procedure of proton implantation is relatively simple and low cost. It can be used as an alternative to coherently coupled array implementations.

Hard X-ray single crystal bi-mirror

Irina Snigireva, Anatoly Snigirev, Michail Lyubomirskiy, Vecheslav Yunkin, and Serguei Kuznetsov

Doc ID: 233954 Received 06 Feb 2015; Accepted 19 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: We report a novel hard X-ray interferometer consisting of two parallel channels manufactured in the single Si crystal by means of the microfabrication technology. The sidewall surfaces of the channels, analogous to mirrors, are used at very small incident angles acting equivalently to narrow micrometre size slits. The proposed interferometer design allows to arrange mirrors at different split distances. Experimental tests of the interferometer were performed at the ESRF ID06 beamline in the energy range from 12 keV to 16 keV. The interference patterns at different grazing incidence angles were recorded in the near- and far-field. Evaluation the influence of the channel surface roughness on the visibility of interference fringes was performed.

Dielectric-loaded surface plasmon polariton crossing waveguides using multimode interference

Masashi Ota, Masashi Fukuhara, Asahi Sumimura, Motoki Ito, Takuma Aihara, Yuya Ishii, and Mitsuo Fukuda

Doc ID: 235310 Received 26 Feb 2015; Accepted 18 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A low-loss low-crosstalk multimode interference (MMI) crossing design for dielectric-loaded surface plasmon polariton waveguides (DLSPPWs), which are SiO₂ stripes on Au films, is demonstrated numerically and experimentally. DLSPPWs are compatible with strong surface plasmon polariton (SPP) field confinement and maintain relatively low propagation losses. Unlike simpler crossings without MMI structures, low insertion loss of 0.65 dB and low crosstalk of −20.27 dB is confirmed numerically at a crossing angle of 10° when using tilted mirror-imaged MMI crossings. Similar insertion losses were also confirmed experimentally. The proposed structure will be beneficial for plasmonic device miniaturization and flexible patterning of optical interconnections.

Spectral shifts of evanescent waves generated by the scattering of polychromatic light in the near field

Jia Li, Liping Chang, Jingjing Chen, and wu pinghui

Doc ID: 235642 Received 06 Mar 2015; Accepted 18 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Evanescent waves generated by the scattering of polychromatic light using a spatially deterministic medium and their near-zone spectral properties, to the best of our knowledge, have not been addressed in the literature. On the basis of the Born approximation, we formulate expressions for the near-zone scattered wave by assuming that the scattering potential of the medium is of the Gaussian profile. The dependence of the spectral shift on effective sizes of the scattering potential (ESSP) is shown using numerical simulations. It is indicated that the increase of either ESSP or near-field diffraction length can induce spectral shifts in scattered evanescent waves.

Tunable control of electromagnetically induced transparency analogue in a compact graphene-based waveguide

Wei Li, Lin Wang, and Xunya Jiang

Doc ID: 238034 Received 16 Apr 2015; Accepted 17 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: An easily-integrated compact graphene-based waveguide structure is proposed to achieve an analogue of electromagnetically induced transparency(EIT) effect at terahertz frequencies. The structure is composed of a graphene waveguide and two identical-shape graphene ribbons paralleled located on the same side of the waveguide at different distances, in which the closer and the farther ribbons behave as the bright and the dark resonators respectively. The EIT-like effect is caused by the destructive interference of the two resonators. By shifting the Fermi energy levels of ribbons, the transparency window can be dynamically tuned. The structure may offer another way for tunable integrated optical devices.

An analog photonic link based on the Aulter-Townes splitting induced dual-band filter for OCS and the SOI signal processor

Hongchen Yu, Minghua Chen, Hongwei Chen, Sigang Yang, Shizhong Xie, and Pengxiao Li

Doc ID: 232555 Received 16 Jan 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: Analog photonic link (APL) is attractive for its potential high performance of larger dynamic range, tunability and EMI. An APL based on the Aulter-Townes splitting (ATS)-effect induced dual-band filter for optical carrier suppression (OCS) and the SOI signal processor has been proposed and experimentally demonstrated. The bandwidths of the two passbands are approximate 780 MHz and the interval could be tuned from 8 GHz to more than 80 GHz in simulation. The extinction ratio is larger than 20 dB which can provide a 20 dB suppression of the optical carrier and higher order sidebands to obtain clean optical carrier and local oscillator (LO) for modulation and down-conversion. The down-conversion APL based on the proposed dual-band OCS filter at X-band has been presented and the spurious free dynamic range (SFDR) of the link is measured to as high as 102.2 dB-Hz2/3.

Wideband Doppler frequency shift measurement and direction ambiguity resolution using optical frequency shift and optical heterodyning

Xihua Zou, Bing Lu, Wei Pan, Lianshan Yan, Bin Luo, and Xianglei Yan

Doc ID: 235203 Received 24 Feb 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A photonic approach for both wideband Doppler frequency shift (DFS) measurement and direction ambiguity resolution is proposed and experimentally demonstrated. In the proposed approach, a light wave from a laser diode is split into two paths. In one path, the DFS information is converted into an optical sideband close to the optical carrier by using two cascaded electro-optic modulators, while in the other path the optical carrier is up-shifted by a specific value (e.g., from several MHz to hundreds of MHz) using an optical frequency shift module. Then the optical signals from the two paths are combined and detected by a low-speed photodetector (PD), generating a low-frequency electronic signal. Through a subtract between the specific optical frequency shift and the measured frequency of the low-frequency signal, the value of DFS is estimated from the derived absolute value and the direction ambiguity is resolved from the derived sign (i.e., + or -). In the proof-of-concept experiments, DFSs from -90 to 90 kHz are successfully estimated for microwave signals at 10, 15, and 20GHz, where the estimation errors are lower than ±60Hz. The estimation errors can be further reduced via the use of a more stable optical frequency shift module.

Impact of mirror spider legs on imaging quality in Mirau micro-interferometry

Justine Lullin, Stephane Perrin, Maciej Baranski, Sylwester Bargiel, Luc Froehly, Nicolas Passilly, Jorge Albero, and Christophe Gorecki

Doc ID: 235230 Received 24 Feb 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: We report the impact on imaging quality of mirror suspensions, referred to as spider legs, used to support the reference mirror in a Mirau micro-interferometer which requires the vertical alignment of lens, mirror and beamsplitter. Because the light goes from the microlens to the beamsplitter through the mirror plane, the spider legs are a source of diffraction. This impact is studied as a function of different parameters of the spider legs design. Imaging criteria, such as the resolution as well as the symmetry of the imaging system, are determined using the point spread function and the modulation transfer function of the pupil. These imaging criteria are used to determine the optimum radius of curvature, thickness and number of legs of the spider structure. We show that 3 curved legs give performances similar to a suspension-free mirror.

A quantum cascade laser-based mid-IR frequency metrology system with ultra-narrow linewidth and ultra-high 1×10^-13-level absolute frequency stability

Michael Hansen, Stephan Schiller, Qun-Feng Chen, Evangelos Magoulakis, and Ingo Ernsting

Doc ID: 234932 Received 20 Feb 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: Abstract We demonstrate a powerful tool complete system for high-resolution mid-IR spectroscopy and frequency metrology with quantum cascade lasers (QCLs). We have implemented frequency stabilization of a QCL to an ultra-low expansion (ULE) reference cavity, via upconversion to the near-IR spectral range, at a level of 1×10^{-13}. The absolute frequency of the QCL is measured relative to a hydrogen maser, with instability <1×10^{-13} and inaccuracy 5×10^{-13}, using a frequency comb phase-stabilized to an independent ultrastable laser. We demonstrate that sub-10 Hz (FWHM) QCL linewidth is achievable. The QCL linewidth is observed in real time.

Quadriwave lateral shearing interferometer based on a randomly encoded hybrid grating

Yongying Yang, Tong Ling, Dong Liu, Xiumei Yue, Yibing Shen, and Jian Bai

Doc ID: 236118 Received 16 Mar 2015; Accepted 17 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A compact quadriwave lateral shearing interferometer (QWLSI) with strong adaptability and high precision is proposed based on a novel randomly encoded hybrid grating (REHG). By performing the inverse Fourier transform of the desired ±1 Fraunhofer diffraction orders, the amplitude and phase distributions of the ideally calculated quadriwave grating can be obtained. Then a phase chessboard is introduced to generate the same phase distribution, while the amplitude distribution can be achieved using randomly encoding method by quantizing the radiant flux on the ideal quadriwave grating. As the Faunhofer diffraction of the REHG only contains the ±1 orders, no order selection mask is ever needed for the REHG-LSI. The simulations and the experiments show that the REHG-LSI exhibits strong adaptability, nice repeatability and high precision.

Quantitative retinal blood flow mapping from fluorescein videoangiography using tracer kinetic modeling

Kenneth Tichauer, Micah Guthrie, Logan Hones, Lagnojita Sinha, Keith St. Lawrence, and Jennifer Kang-Mieler

Doc ID: 229166 Received 05 Dec 2014; Accepted 17 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: Abnormal retinal blood flow (RBF) has been associated with numerous retinal pathologies, yet existing methods for measuring RBF predominantly provide only relative measures of blood flow and are unable to quantify volumetric blood flow, which could allow direct patient to patient comparison. This work presents a methodology based on linear systems theory and an image-based arterial input function to quantitatively mapping volumetric blood flow from standard fluorescein videoangiography data, and is therefore directly translatable to the clinic. Application of the approach to fluorescein retinal videoangiography in rats (4 control, 4 diabetic) demonstrated significantly higher RBF in 4-5 week diabetic rats as expected from the literature.

Two-photon absorption and all-optical modulation in germanium-on-silicon waveguides for the mid-infrared

Anna Peacock, Li Shen, Noel Healy, Colin Mitchell, Jordi Soler Penades, Milos Nedeljkovic, and Goran Mashanovich

Doc ID: 235426 Received 03 Mar 2015; Accepted 17 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: The nonlinear absorption properties of a germanium-on-silicon waveguide have been characterized across the two-photon absorption (TPA) transmission window. The results show that the TPA parameters in germanium waveguides are much stronger than the peak values in silicon, in good agreement with selected measurements conducted in bulk materials. Exploiting the large nonlinear absorption near the bandedge, efficient all-optical modulation is achieved with a modulation depth of ~8 dB and a response time <5 ps.

All bismuth fiber system for femtosecond pulse generation, compression and energy scaling

Teppo Noronen, Oleg Okhotnikov, Evgeny Dianov, Mikhail Melkumov, Vladimir Khopin, and Dmitrii Stolyarov

Doc ID: 235665 Received 06 Mar 2015; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: We demonstrate a 1.44 µm bismuth-doped master oscillator–power amplifier (MOPA) system for generating femtosecond pulses. The cavity of master oscillator comprises dispersion compensating fiber for detuning the total dispersion to the normal regime and a carbon nanotube saturable absorber for triggering the mode-locked operation. The described multi-function bismuth fiber amplifier performs energy scaling, large spectral broadening and pulse compression. The results show that the large chirp superimposed on the pulses in the bismuth oscillator with normal dispersion can be effectively suppressed in a subsequent bismuth power amplifier with anomalous dispersion and high nonlinearity, resulting in high-quality pulses with record duration of 240 fs. An all-fiber design provides practical solution that avoids the need for supplementary pulse stretching and compression.

Long-range photonic crystal surface waves designed for semiconductor light-emitting devices

V. Konopsky

Doc ID: 237543 Received 03 Apr 2015; Accepted 16 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: A one-dimensional (1D) semiconductor photonic crystal (PC) structure with a terminal metal nanofilm, supporting propagation of long-range surface plasmons (LRSPs), is considered as an LRSP amplifier with current pumping. Current is injected to an active region through the metal nanofilm from one side and doped semiconductor layers from the other side. The propagation length of LRSP waves in such 1D PC structures reaches several millimeters, and therefore, a gain as low as 10 1/cm is enough to compensate for attenuation and amplify LRSPs. A unique advantage of this structure is that the refractive index of LRSP wave is very close to unity. As a result, no return reflection to semiconductor occurs during the edge-emission of LRSP to air, and this enhances the light extraction efficiency from semiconductor light sources such as edge-emitting superluminescent diodes and light-emitting diodes (LEDs). Optical feedback may be incorporated in this LRSP amplifier by grating deposition on the external side of the metal nanofilm and LRSP lasing (i.e. long-range SPASER) may be realized without the use of complicated "etch-and-regrow" processes.

Efficient scheme for generation of photonic NOON states in circuit QED

Chui-Ping Yang, Shao-Jie Xiong, Tong Liu, Jin-Ming Liu, and Zhe Sun

Doc ID: 230994 Received 19 Dec 2014; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: We propose an efficient scheme for generating photonic NOON states of two resonators coupled to a four-level superconducting flux device (coupler). This proposal operates essentially by employing a technique of a coupler resonantly interacting with two resonators simultaneously. As a consequence, the NOON-state preparation requires only N+1 operational steps and thus is much faster when compared with a recent proposal [Q. P. Su et al., Scientific Reports 4, 3898 (2014)] requiring 2N steps of operation. Moreover, due to the use of only two resonators and a coupler, the experimental setup is much simplified when compared with previous proposals requiring three resonators and two superconducting qubits/qutrits.

Mid-infrared supercontinuum generation in suspended core tellurite microstructured optical fibers

Mohammad Belal, Lin Xu, Peter Horak, Li Shen, Xian Feng, Mohammad Ettabib, David Richardson, Periklis Petropoulos, and Jonathan Price

Doc ID: 234390 Received 11 Feb 2015; Accepted 16 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: We report the fabrication of a Tellurite optical fiber with a suspended core design, formed on a 220 nm wide membrane of glass. The fiber was pumped at two different wavelengths (1500 nm and 2400 nm) using femtosecond pulses generated from an optical parametric oscillator in order to produce mid-infrared supercontinuum (SC). We observed that SC spectra extending to 3 µm were readily generated. To further optimize the design detailed numerical study was performed which revealed how the fiber structural characteristics dramatically influence the spectral broadening because of the changes in the dispersion profile and in turn, the interplay of nonlinear effects that give rise to SC generation. We found that an accurate control of the core shape can be employed to contain the generated SC spectra within well-defined spectral regions or to provide a broad extension of the continuum to beyond 4 µm.

Prescribed intensity design for extended sources in three-dimensional rotational geometry

Hong Hua, Rengmao Wu, Yi Qin, Youri Meuret, Pablo Benitez, and Juan Carlos Miñano

Doc ID: 235801 Received 10 Mar 2015; Accepted 16 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Regulating the intensity distribution of an extended source to produce a prescribed illumination in three-dimensional (3D) rotationally symmetric geometry remains a challenging issue in illumination design. In this letter, we present an effective method focusing on creating prescribed intensity designs for extended sources. By this method, a prescribed 3D intensity design is first converted into a two-dimensional intensity design for the extended source, a new approach is used to calculate the initial patch to generate a more stable design and then a feedback strategy is employed to improve the performance of the aspherical lens in 3D rotational geometry. Three examples are presented to demonstrate the effectiveness of the proposed method in terms of performance and capacity for tackling complex designs. © 2015 Optical Society of America

Bayesian-based aberration correction and numerical diffraction for improved lensfree on-chip microscopy of biological specimens

Alexander Wong, Farnoud Kazemzadeh, Chao Jin, and Xiao Yu Wang

Doc ID: 235351 Received 02 Mar 2015; Accepted 15 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Lensfree on-chip microscopy is an emerging imaging technique that can be used to visualize and study biological specimens without the need for imaging lens systems. Important issues that can limit the performance of lensfree on-chip microscopy include interferometric aberrations, acquisition noise, and image reconstruction artifacts. In this study, we introduce a Bayesian-based method for performing aberration correction and numerical diffraction that accounts for all three of these issues to improve the effective numerical aperture (NA) and signal-to-noise ratio (SNR) of the reconstructed microscopic image. The proposed method was experimentally validated using the USAF resolution target as well as real waterborne Anabaena flos-aquae samples, demonstrating improvements in NA by ~25% over the standard method, and improvements in SNR of 2.3 dB and 3.8 dB in the reconstructed image when compared to the reconstructed images produced using the standard method and a maximum likelihood estimation method, respectively.

Tomographic reconstruction in soft x-ray microscopy using focus-stack back-projection

Mårten Selin, Emelie Fogelqvist, Stephan Werner, and Hans Hertz

Doc ID: 235733 Received 09 Mar 2015; Accepted 15 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: Tomographic reconstruction in soft x-ray microscopy is a powerful technique for obtaining high-resolution 3D images of biological samples. However, the depth of focus of such zone-plate-based microscopes is typically shorter than the thickness of many relevant biological objects, challenging the validity of the projection assumption used in conventional reconstruction algorithms. In order to make full use of the soft x-ray microscopes’ high resolution, the tomographic reconstruction needs to take the depth of focus into account. Here we present a method to achieve high resolution in the full sample when the depth of focus is short compared to the sample thickness. The method relies on the back-projection of focus-stacked image data from x-ray microscopy. We demonstrate the method on theoretical and experimental data.

Soliton annihilation into dispersive waves

Alexandre Kudlinski, Arnaud Mussot, Matteo Conforti, and Shaofei Wang

Doc ID: 236903 Received 25 Mar 2015; Accepted 15 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: We investigate the propagation of a soliton in an axially-varying optical fiber with a progressive change from anomalous to normal dispersion regimes. Spectral and temporal measurements provide evidence for a complete annihilation of the soliton, which explodes into a polychromatic dispersive wave. This interpretation is confirmed by numerical solution of the generalized nonlinear Schr\"{o}dinger equation.

Single shot, time-resolved measurement of the coherence properties of OCT swept source lasers.

Thomas Butler, Svetlana Slepneva, Ben O'Shaughnessy, Bryan Kelleher, David Goulding, Stephen Hegarty, Maciej Wojtkowski, Karol Karnowski, H.-C. Lyu, and Guillaume Huyet

Doc ID: 235171 Received 24 Feb 2015; Accepted 15 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: A novel, time-resolved interferometric technique is presented which allows the reconstruction of the complex electric field output of a swept source laser in a single-shot measurement. The power of the technique is demonstrated by examining a short cavity swept source designed for OCT applications with a spectral width of over 100 nm. The novel analysis allows a time-resolved real-time characterisation of the roll-off, optical spectrum, linewidth and coherence properties of a dynamic, rapidly swept laser source.

Exploiting Non-Reciprocity in BOTDA systems

Alexia Lopez-Gil, Xabier Angulo-Vinuesa, Alejandro Dominguez-Lopez, Sonia Martin Lopez, and Miguel Gonzalez Herraez

Doc ID: 235166 Received 27 Feb 2015; Accepted 15 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: In this paper, we present and demonstrate a novel technique for distributed measurements in Brillouin Optical Time-Domain Analysis (BOTDA) based on the use of the nonlinear phase-shift induced by stimulated Brillouin scattering (SBS). Employing a Sagnac Interferometer (SI), the position-resolved Brillouin Phase-shift Spectrum (BPS) along the fiber can be obtained, benefiting from the sensitivity to non-reciprocal phase-shifts of the SI scheme. This proposal simplifies the existing methods to retrieve the BPS distribution along an optical fiber since no phase modulation, no filtering and no high-bandwidth detectors are required. The fundamentals of the technique are described theoretically and validated through numerical simulations and experimental measurements.

Multiplexed recording with uncorrelated computer-generated reference patterns in coaxial holographic data storage

Teruyoshi Nobukawa, Takanori Nomura, and Yotaro Wani

Doc ID: 235321 Received 02 Mar 2015; Accepted 14 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: A computer-generated reference pattern (CGRP) allows improvement in light efficiency and the quality of a reconstructed data in coaxial holographic data storage. In this Letter, a multiplexed recording method with uncorrelated CGRPs is proposed. With this method, crosstalk from adjacent holograms is suppressed without shifting a medium. To confirm the feasibility of the proposed method experimentally, shift selectivity is investigated and then multiplexed recording is performed. Experimental results show that the proposed method enables high-density recording compared with conventional shift multiplexing. In addition, a theoretical analysis implies that at least 100 uncorrelated CGRPs can be designed and used for multiplexing recording.

Enhancement cavities for zero-offset-frequency pulse trains

Simon Holzberger, Nikolai Lilienfein, Michael Trubetskov, Henning Carstens, Fabian Lücking, Vladimir Pervak, Ferenc Krausz, and Ioachim Pupeza

Doc ID: 236663 Received 24 Mar 2015; Accepted 14 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: The optimal enhancement of broadband optical pulses in a passive resonator requires a seeding pulse train with a specific carrier-envelope offset frequency. Here, we control the phase of the cavity mirrors to tune the offset frequency for which a given comb is optimally enhanced. This enables the enhancement of a zero-offset-frequency train of sub-30-fs pulses to multi-kW average powers. The combination of pulse duration, power and zero-phase slip constitutes a crucial step towards the generation of attosecond pulses at multi-10-MHz repetition rates. In addition, this control affords the enhancement of pulses generated by difference-frequency mixing, e.g., for mid-infrared spectroscopy.

An Untethered Photonic Sensor for Wall Pressure Measurement

Tindaro Ioppolo and maurizio manzo

Doc ID: 236304 Received 18 Mar 2015; Accepted 13 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: In this paper we study a novel untethered photonic wall pressure sensor that uses as sensing element a dome shaped micro-scale laser. Since the sensor does not require any optical or electrical cabling, it allows measurements where cabling tends to be problematic. The micro-laser is made by a mixture Trimethylolpropan Tri(3-mercaptopropionate), commercial name THIOCURE and Polyethylene (glycol) Diacrylate (PEGDA) mixed with a solution of rhodamine 6G. Two different volume ratios between the THIOCURE and the PEGDA are studied, since different ratios lead to different mechanical properties. In addition, two different sensor configurations are presented: (i) sensor coupled to a membrane, that allows differential wall pressure measurement and (ii) sensor without membrane that allows absolute wall pressure measurement. The sensitivity plots are presented in the paper for both sensor configurations and polymer ratios.

Fabrication and characterization of an all-solid tellurite- phosphate photonic bandgap fiber

Tonglei Cheng, Sakai Yukiko, Takenobu Suzuki, and Yasutake Ohishi

Doc ID: 236748 Received 25 Mar 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We present an all-solid tellurite–phosphate photonic bandgap fiber (PBGF) with two layers of high-index rods (TeO2–Li2O–WO3–MoO3–Nb2O5, TLWMN) in the cladding (TeO2-ZnO-Li2O-K2O-Al2O3-P2O5, TZLKAP). TLWMN and ZLKAP glasses have good compatibility for fabricating the all-solid PBGF. Photonic bandgap (PBG) properties are calculated by the plane wave expansion method (PWM), and the results agree well with the measured transmission spectrum. Furthermore, the modal field patterns are measured at 1300 and 1520 nm, respectively. The light is confined to the core at 1300 nm and lost in the cladding at 1520 nm, which match well with the calculated modal field intensities.

Plastic fiber design for THz generation through wavelength translation

Ajanta Barh, R varshney, Govind Agrawal, Azizur Rahman, and Bishnu Pal

Doc ID: 236779 Received 25 Mar 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We report on an all-fiber Terahertz (THz) radiation source by exploiting nonlinear parametric process in a theoretically designed microstructured-core double clad plastic fiber (MC-DCPF). The required phase-matching condition is satisfied through suitable tailoring of the fiber dispersion and nonlinear properties at the pump wavelength of a high power CO2 laser, with a CO laser of much lower power acting as a seed concomitantly. Our simulated results reveal that a THz radiation source at the frequency of ~ 3 THz could be realized with a 3-dB phase-matching band-width of 2.13 GHz in a 65 m long optimized MC-DCPF. Maximum power conversion efficiency >1% is realizable even after including the material loss.

Laser damage density measurement of optical components in the sub-picosecond regime

Martin Sozet, Jerome Neauport, Eric Lavastre, Nadja Roquin, Laurent Gallais, and Laurent Lamaignère

Doc ID: 234218 Received 11 Feb 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: A rasterscan procedure adapted to the sub-picosecond regime is set to determine laser-induced damage densities as function of fluences. Density measurement is carried out on dielectric high-reflective coatings operating at 1053 nm. Whereas laser-induced damage is usually considered deterministic in this regime, damage events occur on these structures for fluences significantly lower than their intrinsic damage threshold. Scanning Electron Microscope observations of these “under threshold” damage sites evidence ejections of defects, embedded in the dielectric stack. This method brings a new viewpoint for the qualification of optical components and their optimization for a high resistance in the sub-picosecond regime.

Control of laser-induced frequency shift in ultracold cesium molecules by an external magnetic field

Jie Ma, Jizhou Wu, Yuqing Li, Guosheng Feng, Wenliang Liu, Liantuan Xiao, and Suotang Jia

Doc ID: 234503 Received 17 Feb 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We investigate an effective control of the laser-induced frequency shift of ultracold cesium molecules formed by photoassociation in a magnetic levitated crossed dipole trap via an external magnetic field. A series of molecular photoassociation spectra have been measured with increasing the PA laser intensity at different bias fields. We find that the laser-induced frequency shift rate is strongly dependent on the external magnetic field, namely the rate can be increased by a maximum of s6 times comparing with the rate without an external magnetic field. A qualitatively theoretical explanation has been offered by considering the external magnetic field that can be used to manipulate the interaction between ultracold atoms.

Engineering wavefront caustics trajectories in ${\cal PT}$-symmetric lattices

Tsampikos Kottos, Nicholas Bender, and Hamidreza Ramezani

Doc ID: 236128 Received 16 Mar 2015; Accepted 13 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We utilize caustic theory in ${\cal PT}-$symmetric lattices to design focusing and curved beam dynamics. We show that the gain and loss parameter in these systems provides an addition degree of freedom which allows for the design of the same caustics trajectories with different intensity distribution in the individual waveguides. Moreover we can create aberration-free focal points at any paraxial distance $z_f$, with anomalously large focal intensity.

Linear negative dispersion with a gain doublet via optomechanical interactions

JIAYI QIN, chunnong zhao, Yiqiu Ma, li ju, and David Blair

Doc ID: 235138 Received 25 Feb 2015; Accepted 13 Apr 2015; Posted 23 Apr 2015  View: PDF

Abstract: Optical cavities containing a negative dispersion medium have been proposed as a means of improving the sensitivity of laser interferometric gravitational wave (GW) detectors through the creation of white light signal recycling cavities. Here we demonstrate that negative dispersion can be realized using an optomechanical cavity pumped by a blue detuned doublet. We used an 85mm cavity with an intra-cavity silicon nitride membrane. Tunable negative dispersion is demonstrated, with a phase derivative $d\varphi/df$ from $-0.14$ Deg$\cdot$Hz$^{-1}$ to $-4.2\times10^{-3}$ Deg$\cdot$Hz$^{-1}$.

Transverse single mode edge-emitting lasers based on coupled waveguides

Nikita Gordeev, Mikhail Maximov, Alexey Payusov, Yuri Shernyakov, Nikolay Kalyuzhnyy, Sergey Mintairov, and Marina Kulagina

Doc ID: 234979 Received 19 Feb 2015; Accepted 12 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We report on the transverse single mode emission from InGaAs/GaAs quantum well edge-emitting lasers with broadened waveguide. The lasers are based on coupled large optical cavity (CLOC) structures where high-order vertical modes of the broad active waveguide are suppressed due to their resonant tunneling into a coupled single mode passive waveguide. The CLOC lasers have shown stable Gaussian shaped vertical far-field profiles with the divergence as low as 21.4° FWHM (full width at half maximum) in CW (continuous-wave) operation.

Multiple plasmonic-photonic couplings in the Au nanobeaker arrays: enhanced robustness and wavelength tunability

Yuebing Zheng and Linhan Lin

Doc ID: 236389 Received 18 Mar 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: Diffractive coupling in the plasmonic nanoparticle arrays introduces the collective plasmon resonances with high scattering efficiency and narrow linewidth. However, the collective behavior is often limited to the arrays embedded in a homogeneous refractive index environment. The collective plasmon resonances can be suppressed when the arrays are supported on the solid-state substrates with different superstrates, as required for many applications, because of the different dispersion relations between the substrate and the superstrate. Herein, we develop a general concept, which seeks to synergize the sub-nanoparticle engineering of “hot spots” with the far-field coupling behavior, for the versatile control of plasmonic-photonic couplings in an asymmetric environment. To demonstrate our concept, we choose as an example the Au nanobeaker arrays (NBAs), which are the conformally coated Au thin layers on the interior sidewalls and bottoms of nanohole arrays in SiO2 substrates. Using the finite-difference time-domain simulations, we show that engineering the plasmonic “hot spots” in the NBAs by simply controlling the depth-to-diameter aspect ratio of individual units enables multiple plasmonic-photonic couplings in an asymmetric environment. These couplings are robust with a wide range of resonance wavelengths from visible to infrared. Furthermore, the angle-dependent transmission spectra of the arrays reveal a transition from band-edge to propagating state for the orthogonal coupling and a splitting of diffraction waves in the parallel coupling. The proposed NBAs will find enhanced applications in plasmonic lasers and bio-sensing.

Enhanced spectral response of π-phase shifted fiber Bragg gratings in closed-loop configuration

Pietro Malara, Carlo Edoardo Campanella, Francesco De Leonardis, Antonio Giorgini, Saverio Avino, vittorio Passaro, and Gianluca Gagliardi

Doc ID: 234919 Received 17 Feb 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: By integrating a π-shifted fiber Bragg grating (π-FBG) in a ring resonator, a spectral feature shows in the transmission spectrum in correspondence of the Bragg wavelength, that is much sharper than the π-FBG resonance. This feature can be detected with a simple integrated cavity output technique. The resolution of any sensor based on the fitting of the π-FBG spectral profile can thus be largely improved at no additional fabrication costs and without altering the sensor robustness. A theoretical model shows that the resolution improvement attainable in the closed-loop geometry depends on the grating symmetry and the ring resonator quality factor. With a commercial grating in a medium-finesse ring, a spectral feature 12 times sharper than the π-FBG resonance is experimentally demonstrated. A much larger enhancement is expected in an optimized, low-loss setup.

Self-induced transparency and coherent population trapping of ⁸⁷Rb vapor in a mode-locked laser

Jean-Claude Diels, Ladan Arissian, Koji Masuda, Gaetano Mileti, and Christoph Affolderbach

Doc ID: 234389 Received 11 Feb 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: Simultaneous self-induced transparency and a dark line resonance are observed inside a mode-locked laser. The circulating pulse, tuned to the 795 nm optical resonance of intracavity rubidium, has sufficient intensity to create at each passage a population inversion — return to ground state, typical of self-induced transparency. A drop in fluorescence (dark line resonance), is observed as the repetition rate is tuned to a submultiple of the hyperfine ground-state splitting.

Microwave controlled efficient Raman sub-harmonic generation

Pankaj Jha, Rajitha V, Tarak Dey, and Sumanta Das

Doc ID: 232628 Received 19 Jan 2015; Accepted 11 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: We propose a novel scheme for efficient Raman sub-harmonic generation in a system of homogeneously broadened atomic vapor with atoms in a closed three level -configuration. The key feature of our scheme is the microwave induced atomic coherence of the two lower level metastable states. We show explicitly that by manipulating these coherence via the amplitude and phase of the microwave field, we can control the generation of different Raman sub-harmonics. Our scheme is viable in currently available atomic vapour cells thereby opening the way for efficient sub-harmonic generation in standard experimental setups.

Ground-plane-less bidirectional terahertz absorber based on omega resonators

Alexei Balmakou, Maxim Podalov, Sergei Khakhomov, Doekele Stavenga, and Igor Semchenko

Doc ID: 236100 Received 12 Mar 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We present a new ultrathin metamaterial which acts as a frequency-selective absorber of terahertz radiation. The absorber is a square array of pairs of omega-shaped micro-resonators made of high ohmic loss metal. The metamaterial provides significant suppression of transmitted and reflected radiation in a bidirectional regime (that is, for both forward and backward propagating radiation). The absorber is efficient in a wide range of angles of incidence. The absence of a ground plane makes the absorber unique in comparison with numerous analogs with a ground plane that operate in a unidirectional regime. The novel metamaterial potentially enables controllable transmission of terahertz radiation in imaging systems. Analytical calculations as well as finite-element electromagnetic modeling are presented for an exemplary case with peak absorption at ~3 THz.

Flexible compensation of dispersion-induced power fading for multi-service RoF links based on phase-coherent orthogonal lightwave generator

Beilei Wu, Ming Zhu, Mu Xu, Jing Wang, Muguang Wang, Fengping Yan, Shuisheng Jian, and Gee-Kung Chang

Doc ID: 236292 Received 18 Mar 2015; Accepted 11 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: A novel technique to simultaneously compensate dispersion-induced power fading for multi-service radio-over-fiber (RoF) links is proposed. At the central office (CO), phase-coherent orthogonal lightwave generator (POLG) consisting of a polarization rotator (PR) and a single-driver Mach-Zehnder modulator (MZM) is used. By adjusting a polarization controller (PC) in the base station (BS), the phase difference between the orthogonal polarization carrier and two sidebands can be controlled, and the frequency response can be flexibly shifted for individual radio frequency (RF) service. We experimentally shift the destructive interference to the constructive interference at various frequencies for 25-km and 30-km fiber links. The performances of two services carrying 1-Gb/s on-off keying (OOK) data at 9 GHz and 16.6 GHz over 30-km fiber in the proposed system show receiver sensitivity improvement of ~12-dB at the bit error rate (BER) of 10−3 compared with the conventional double sideband (DSB) modulation case.

Turbulence Compensation of an Orbital-Angular-Momentum and Polarization Multiplexed Link Using a Data-Carrying Beacon on a Separate Wavelength

Yongxiong Ren, Guodong Xie, Hao Huang, Long Li, Nisar Ahmed, Yan Yan, Martin Lavery, Moshe Tur, Mark Allen Neifeld, Robert Boyd, Jeffrey Shapiro, and Alan Willner

Doc ID: 233828 Received 27 Feb 2015; Accepted 11 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: We investigate sensing of a data-carrying Gaussian beacon on a separate wavelength as a means to provide the information needed to compensate for the effects of atmospheric turbulence on orbital angular momentum (OAM) and polarization multiplexed beams in a free-space optical link. The influence of the Gaussian beacon's wavelength on the compensation of OAM beams at 1560 nm is studied experimentally. It is found that the compensation performance degrades slowly with the increase in the beacon's wavelength offset, in the 1520-1590 nm band, from the OAM beams. Using this scheme, we experimentally demonstrate a 1-Tbit/s OAM-and polarization-multiplexed link through emulated dynamic turbulence with a data-carrying beacon at 1550 nm. Experimental results show that turbulence effects on all 10 data channels each carrying a 100-Gbit/s signal, are mitigated efficiently and the power penalties after compensation are below 5.9 dB for all channels. The results of work might be helpful to the future implementation of a high-capacity OAM, polarization and wavelength multiplexed free-space optical link affected by atmospheric turbulence.

Beam deformation within an acousto-optic lens

Shaoqun Zeng, Zhenqiao Zhou, Longhui Li, Jianchun Wang, and Qinglei Hui

Doc ID: 235374 Received 02 Mar 2015; Accepted 11 Apr 2015; Posted 16 Apr 2015  View: PDF

Abstract: The acousto-optic lens (AOL) is becoming a popular tool in the neuroscience field. Here we analyzed the deformation of the diffraction beam after passage through an AOL consisting of a pair of acousto-optic deflectors using both theoretical and experimental data. The results showed that, because of the high sensitivity of optical spatial frequencies of acousto-optic deflectors, the boundary strength of the diffraction beam of the AOL decreases significantly. When the focal length of AOL diminishes, the deformation of the diffraction beam becomes more serious with a smaller beam size. This deformation of the diffraction beam finally leads to a decreased illuminative numerical aperture, which worsens the image’s spatial resolution.©

Imaging and sensing based on dual-pulse nonlinear photoacoustic contrast: a preliminary study on fatty liver

Chao Tian, Xueding Wang, Zhixing Xie, and Mario Fabiilli

Doc ID: 234793 Received 17 Feb 2015; Accepted 11 Apr 2015; Posted 20 Apr 2015  View: PDF

Abstract: The feasibility of diagnostic imaging and tissue characterization based on a new contrast realized by dual-pulse photoacoustic measurement was studied. Unlike current photoacoustic methods which are mostly focused on the measurement of tissue optical absorption, this contrast revealed by a dual-pulse laser excitation process takes advantage of the temperature dependence of Grüneisen parameter of tissue. The first laser pulse heats the sample and causes a temperature rise in the target tissue, which leads to the change of Grüneisen parameter and the amplitude of the photoacoustic signal from the second laser pulse. This new contrast is then quantified by percentile change in the second pulse signal as a result of the first laser pulse. Since the temperature-dependent Grüeneisen parameter is tissue specific and closely relevant to chemical and molecular properties of the sample, the dual-pulse photoacoustic measurement is able to differentiate various tissue types and conditions. The preliminary study on phantoms and a mouse model has suggested the capability of the proposed contrast in characterization of fatty livers and the potential for future clinical diagnosis of liver conditions.

Visible-to-near-infrared octave spanning supercontinuum generation in a silicon nitride waveguide

Haolan Zhao, Roel G. Baets, Gunther Roelkens, Stephane Clemmen, Philippe Helin, Simone Severi, François Leo, Ananth Subramanian, Edouard Brainis, Bart Kuyken, and Ashim Dhakal

Doc ID: 234835 Received 25 Feb 2015; Accepted 10 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: The generation of an octave spanning supercontinuum covering 488 nm to 978 nm (at -30 dB) is demonstrated for the first time on-chip. This result is achieved by dispersion engineering a 1 cm long Si₃N₄ waveguide and pumping it with an 100 fs Ti:Sapphire laser emitting at 795 nm. This work offers a bright broadband source for biophotonic applications and frequency metrology.

In situ study of two interacting femtosecond filaments in sapphire

Andrius Melninkaitis, Audrius Dubietis, and Nerijus Siaulys

Doc ID: 232577 Received 02 Feb 2015; Accepted 10 Apr 2015; Posted 13 Apr 2015  View: PDF

Abstract: Interaction dynamics of two co-propagating femtosecond light filaments in sapphire crystal is studied by means of time-resolved off-axis digital holographic and shadowgraphic microscopy with 22 fs temporal and 1 μm spatial resolution. In particular, we demonstrate that filament interaction originates from instantaneous modification of the refractive index resulting from Kerr effect. Fusion, splitting and even suppression of the resulting plasma channels induced by interacting filaments was observed by varying time delay between the input pulses. Free electron channels were reconstructed in the form of the time-lapse movie with unprecedented spatial and temporal resolution.

Molecular decay rate near nonlocal plasmonic particles

Christian Girard, Aurélien Cuche, Erik Dujardin, Arnaud Arbouet, and Adnen Mlayah

Doc ID: 233146 Received 28 Jan 2015; Accepted 10 Apr 2015; Posted 10 Apr 2015  View: PDF

Abstract: When the size of metal nanoparticles is smaller than typically 10 nm, their optical response becomes sensitive to both spatial dispersion and quantum size effects associated with the confinement of the conduction electrons inside the particle. In this Letter, we propose a nonlocal scheme able to compute molecular decay rates near spherical nanoparticles which includes the electron--electron interactions through a simple model of electronic polarizabilities. The plasmonic particle is schematized by a dynamic dipolar polarizability and the quantum system is characterized by a two--level--system. In this scheme, the light--matter interaction is described in term of classical field--susceptibilities. This theoretical framework could be extended to address the influence of nonlocality on the dynamics of quantum systems placed in the vicinity of nano-objects of arbitrary morphologies.

Ultracompact and broadband polarization beam splitter based on polarization dependent critical guiding condition

Guanghui Wang, Xuping Zhang, Zhoufeng Ying, Ho-pui Ho, and Ying Huang

Doc ID: 234489 Received 11 Feb 2015; Accepted 09 Apr 2015; Posted 10 Apr 2015  View: PDF

Abstract: An ultracompact and broadband polarization beam splitter (PBS) based on the polarization dependent critical guiding condition of an asymmetrical directional coupler is proposed. The device consists of a pair of silicon waveguides with different height and width. Due to the different cutoff conditions for the TE and TM polarization modes, it is possible to have the TM mode guided in one waveguide, while the TE mode is supported in both. Therefore, only the phase-matching condition for the cross-coupling of TE mode needs to be considered. This approach not only simplifies the design procedures, but also significantly improves device performance, with smaller total length and larger bandwidth. Finally, regardless of the contribution of S-bend waveguides, our proposed PBS has a coupling region as short as 0.2µm, which is the shortest reported until now. The simulation result shows that the extinction ratios for TE and TM polarization are 13.5dB and 16.6dB at their respective output ports, and their insertion losses are 0.29dB and 0.13dB, respectively. Numerical simulations also show that the device offers a very large bandwidth (~140nm) with large extinction ratio (>10dB) and low insertion loss (<1dB).

Imaging and characterizing shear wave and shear modulus under orthogonal acoustic radiation force excitation using OCT Doppler variance method

Jiang Zhu, Yueqiao Qu, Teng Ma, RUI LI, Yongzhao Du, shenghai huang, Kirk Shung, Qifa Zhou, and Zhongping Chen

Doc ID: 234982 Received 19 Feb 2015; Accepted 09 Apr 2015; Posted 10 Apr 2015  View: PDF

Abstract: We report on a system for imaging and quantifying shear wave and shear modulus under orthogonal acoustic radiation force (ARF) excitation using optical coherence tomography (OCT) Doppler variance method. The ARF perpendicular to the OCT beam is produced by a remote ultrasonic transducer. A shear wave induced by ARF excitation propagates parallel to the OCT beam. The OCT Doppler variance method, which is sensitive to the transverse vibration, is used to measure the ARF induced vibration. For analysis of the shear modulus, the Doppler variance method is utilized to visualize shear wave propagation instead of Doppler OCT method and the propagation velocity of the shear wave is measured at different depths of one location with the M scan. In order to quantify shear modulus beyond the OCT imaging depth, we move ARF to a deeper layer at a known step and measure the time delay of the shear wave propagating to the same OCT imaging depth. We also quantitatively map the shear modulus of a cross-section in a tissue-equivalent phantom after employing the B scan.

Diamagnetic Cavitization of laser produced barium plasma in transverse magnetic field

Pramod Gopinath, MAKARAJU RAJU, R K Singh, and Ajai Kumar

Doc ID: 235592 Received 04 Mar 2015; Accepted 09 Apr 2015; Posted 10 Apr 2015  View: PDF

Abstract: Influence of uniform transverse magnetic field and ambient Ar pressure on the plasma plume produced by Nd:YAG laser ablation of barium has been investigated by time-of-flight optical emission spectroscopy. Experiments were carried out with laser pulse energy of 150 mJ and 0.45 Tesla magnetic field. The time-of-flight profiles showed ambient pressure independent behaviour at 6 mm distance from the target which is attributed to the diamagnetic behavior of the laser plasma. We have explained the compression of temporal profiles of ionic lines using a theoretical model and correlated to estimated magnetic diffusion time.

Concept for a transmissive, large angle, light steering device with high efficiency

HsienHui Cheng, Achintya Bhowmik, and Philip Bos

Doc ID: 232106 Received 12 Jan 2015; Accepted 09 Apr 2015; Posted 09 Apr 2015  View: PDF

Abstract: A device concept is presented to allow very large angle deflection of light passing through a transmissive device. Deflection of light, switchable between angles larger than +-60 degrees, is shown to be possible with efficiency approaching 100%

Effect of Blood Vessels on Light Distribution on Optogenetic Stimulation of Cortex

Ramin Pashaie, Mehdi Azimipour, and Farid Atry

Doc ID: 230883 Received 17 Dec 2014; Accepted 09 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: In this article, the impact of blood vessels on light distribution during photostimulation of cortical tissue in small rodents is investigated. Brain optical properties were extracted using a double-integrating sphere setup and optical coherence tomography was used to image cortical vessels and capillaries to generate three-dimensional angiogram of the cortex. By combining these two datasets, a complete volumetric structure of the cortical tissue was developed and linked to a Monte Carlo code which simulates light propagation in this inhomogeneous structure and illustrates the effect of blood vessels on the penetration depth and pattern preservation in optogenetic stimulation.

Electrooptic millimeter-wave harmonic downconversion and vector demodulation using cascaded phase-modulation and optical filtering

Vincent Pagan and Thomas Murphy

Doc ID: 235035 Received 23 Mar 2015; Accepted 09 Apr 2015; Posted 28 Apr 2015  View: PDF

Abstract: We describe and demonstrate an electrooptic technique to simultaneously downconvert and demodulate vector modulated millimeter-wave signals. The system uses electrooptic phase-modulation and optical filtering to perform harmonic downconversion of the RF signal to an intermediate frequency (IF) or to baseband. We demonstrate downconversion of RF signals between 7-70 GHz to IFs below 20 GHz. Furthermore, we show harmonic downconversion and vector demodulation of 2.5 Gbps 4-QAM and 5 Gbps 16-QAM signals at carrier frequencies of 40 GHz to baseband.

Beyond the current noise limit in imaging through turbulent medium

Aleksander Kurek, Adam Popowicz, Bogdan Smolka, and Agnieszka Pollo

Doc ID: 230482 Received 11 Feb 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: Shift-and-add is an approach employed to mitigate the phenomenon of resolution degradation in images acquired through a turbulent medium. Using this technique, a large number of consecutive short exposures is registered below the coherence time of the atmosphere or other blurring medium. The acquired images are shifted to the position of the brightest speckle and stacked together to obtain high-resolution and high signal-to-noise frame. In this Letter, we present a highly efficient method for determination of frames shifts, even if in a single frame the object cannot be distinguished from the background noise. The technique utilizes our custom genetic algorithm, which iteratively evolves a set of image shifts. We used the maximal energy of stacked images as an objective function for shifts estimation and validate the efficiency of the method on simulated and real images of simple and complex sources. Obtained results validated, that our proposed method allows for the recovery of spatial distribution of objects even only 2% brighter than their background. The presented approach extends significantly current limits of image reconstruction with the use of shift-and-add method. The applications of our algorithm include both the optical and the infrared imaging. Our method may be also employed as a digital image stabilizer in extremely low light level conditions in professional and consumer applications.

Background-free 3D chemical imaging based on polarization coherent Raman holography

Kebin Shi, Yonggang Lv, ziheng ji, Hong Yang, and Qihuang Gong

Doc ID: 231548 Received 05 Jan 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: We report on a holographic coherent anti-Stokes Raman scattering imaging by using polarization discrimination for non-resonant background suppression. With reduced polarization scrambling effect under weakly focused excitation, non-resonant background free coherent Raman imaging is demonstrated. A fast chemically selective imaging is achieved in a three-dimensional volume of 70um x70um x100um in 2 seconds.

Four-wave mixing in silicon coupled-cavity resonators with port-selective, orthogonal supermode excitation

Milos Popovic, Xiaoge Zeng, and Cale Gentry

Doc ID: 234778 Received 09 Mar 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: We propose coupled-cavity triply-resonant systems for degenerate-pump four-wave mixing (FWM) applications that support strong nonlinear interaction between distributed pump, signal and idler modes, and allow independent coupling of the pump mode and signal/idler modes to separate ports based on non-uniform supermode profile. We demonstrate seeded FWM using this scheme with wavelength conversion efficiency of -54dB at input pump power of 3.5dBm, and discuss applications of such orthogonal supermode coupling.

Surface second harmonic generation from silicon pillar arrays with strong geometrical dependence

Bikash Choudhury, Srinivasan Anand, Reza Sanatinia, Pankaj Sahoo, Marcin Swillo, and Guillermo Andler

Doc ID: 235502 Received 03 Mar 2015; Accepted 07 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: We present experimental demonstration and analysis of enhanced surface second harmonic generation (SHG) from hexagonal arrays of silicon pillars. Three sets of Si pillar samples with truncated-cone shaped pillar arrays having periods of 500, 1000 and 2000 nm and corresponding average diameters of 200, 585 and 1550 nm, respectively, are fabricated by colloidal lithography and plasma dry etching. We have observed strong dependence of SHG intensity on the pillar geometry. Pillar arrays with 1000 nm period and 585nm average diameter gives more than one order magnitude higher SHG signal compared to the other two samples. We theoretically verified the dependence of SHG intensity on pillar geometry by finite difference time domain (FDTD) simulations in terms of the surface normal E-field component. The enhanced surface SHG light can be useful for nonlinear silicon photonics, surface/interface characterization and optical biosensing.

Modeling crater formation in femtosecond-pulse laser damage from basic principles

Robert Mitchell, Douglass Schumacher, and Enam Chowdhury

Doc ID: 235343 Received 06 Mar 2015; Accepted 06 Apr 2015; Posted 17 Apr 2015  View: PDF

Abstract: We present the first fundamental simulation method for the determination of crater morphology due to femtosecond-pulse laser damage. To this end we have adapted the particle-in-cell (PIC) method commonly used in plasma physics for use in the study of laser damage, and developed the first implementation of a pair-potential for PIC codes. We find that the PIC method is a complementary approach to modeling laser damage, bridging the gap between fully ab-initio molecular dynamics approaches and empirical models. We demonstrate our method by modeling a femtosecond-pulse laser incident on a flat copper slab, for a range of intensities.

Imaging arbitrary acoustic whispering-gallery modes in the GHz range with ultrashort light pulses

Sylvain MEZIL, Paul Otsuka, Shogo Kaneko, Oliver Wright, Motonobu Tomoda, and O. Matsuda

Doc ID: 235769 Received 11 Mar 2015; Accepted 05 Apr 2015; Posted 14 Apr 2015  View: PDF

Abstract: Using an ultrafast optical technique with enhanced frequency control we image surface-acoustic whispering-gallery-like modes in a microscopic disk at various frequencies up to 1~GHz, allowing experimental determination of their dispersion. This is made possible by intensity-modulated optical pumping and probing with a periodic femtosecond light source. Spatiotemporal Fourier transforms of the two-dimensional acoustic fields measured to micron resolution allow us to isolate individual whispering-gallery modes of first and second radial order as well as their mode patterns and Q factors to unprecedented frequency resolution. We thereby demonstrate arbitrary-frequency ultrafast control and imaging of a micro-acoustic system with an optical time-resolved technique. Applications include quality control of surface acoustic wave filters in telecommunications.

TE-polarized graphene modes sustained by photonic crystal structures

Iterio Degli-Eredi, John Sipe, and Nathalie Vermeulen

Doc ID: 235727 Received 09 Mar 2015; Accepted 01 Apr 2015; Posted 08 Apr 2015  View: PDF

Abstract: We present the design of a supporting photonic crystal structure that would allow for the excitation of the predicted transverse electric (TE) polarized excitation in a single layer of graphene. We show that it is possible to measure this excitation at room temperature, and that adding an extra layer of dielectric material on top of the structure would further facilitate the experimental observation of the graphene mode.

Off-axis interferometer with adjustable fringe contrast based on polarization encoding

Sharon Karepov, Tal Ellenbogen, and Natan Shaked

Doc ID: 232118 Received 12 Jan 2015; Accepted 01 Apr 2015; Posted 03 Apr 2015  View: PDF

Abstract: We propose a compact, close-to-common-path, off-axis interferometric system for low polarizing samples based on a spatial polarization encoder that is placed at the Fourier plane of a conventional transmission microscope. The polarization encoder erases the sample information from one polarization state and maintains it on the orthogonal polarization state, while retaining the low spatial frequencies of the sample, and thus enabling quantitative phase acquisition. In addition, the interference fringe visibility can be controlled by polarization manipulations. We demonstrate this concept experimentally by quantitative phase imaging of a USAF 1951 phase test target and human red blood cells with optimal fringe visibility and single-exposure phase reconstruction.

8E-18 fractional laser frequency instability with a long room-temperature cavity

Uwe Sterr, Stephan Falke, Christian Grebing, Stefan Vogt, Thomas Legero, Mikko Merimaa, Christian Lisdat, and Sebastian Häfner

Doc ID: 233886 Received 04 Feb 2015; Accepted 30 Mar 2015; Posted 01 Apr 2015  View: PDF

Abstract: We present a laser system based on a 48 cm long optical glass resonator. The large size requires a sophisticated thermal control and optimized mounting design. A self balancing mounting was essential to reliably reach sensitivities to acceleration of below Δν/ν < 2E-10 /g in all directions. Furthermore, fiber noise cancellations from a common reference point near the laser diode to the cavity mirror and to additional user points (Sr clock and frequency comb) are implemented. Through comparison to other cavity-stabilized lasers and to a strontium lattice clock an instability of below 1E-16 at averaging times from 1 s to 1000 s is revealed.

In- and out-of-plane tissue micro-displacement measurement by correlation coefficients of optical coherence tomography

Yoshiaki Yasuno, Shuichi Makita, Kazuhiro Kurokawa, and Youngjoo Hong

Doc ID: 226715 Received 11 Nov 2014; Accepted 27 Mar 2015; Posted 31 Mar 2015  View: PDF

Abstract: We propose a method to measure the in-plane and out-of-plane displacements of tissue using the correlation coefficients of optical coherence tomography (OCT) signals. The displacements are determined by the local correlation coefficients between digitally-shifted reference OCT images and a target image. The method achieves sub-micron displacement measurement with an accuracy better than 0.32 μm and repeatability better than 0.36 μm. The feasibility of the method was examined by measuring the displacement field of a laser-irradiated porcine retina. This method successfully visualized the dynamic change of the displacement field during laser irradiation.

Subterawatt mid-infrared-to-mid-ultraviolet supercontinuum enhanced by third-to-fifteenth odd-order harmonics

Aleksei Zheltikov, Andrius Baltuska, Audrius Pugzlys, Aleksandr Voronin, Andrey Fedotov, Dmitry Sidorov-Biryukov, Alexander Mitrofanov, Sergey Mitryukovsky, Giedrius Andriukaitis, Tobias Flöry, and Evgeny Stepanov

Doc ID: 232712 Received 26 Jan 2015; Accepted 26 Mar 2015; Posted 31 Mar 2015  View: PDF

Abstract: A high-energy supercontinuum spanning 4.7 octaves, from 250 to 6500 nm, is generated using a 0.25-TW, 3.9-μm output of a mid-infrared optical parametric chirped-pulse amplifier as a driver inducing a laser filament in the air. The high-frequency wing of the supercontinuum spectrum is enhanced by odd-order optical harmonics of the mid-infrared driver. Optical harmonics up to the 15th order are observed in supercontinuum spectra as overlapping, yet well-resolved peaks broadened, as verified by numerical modeling, due to spatially nonuniform ionization-induced blue shift.

*****Comment-Null-field radiationless sources

Iver Brevik

Doc ID: 234840 Received 09 Mar 2015; Accepted 26 Mar 2015; Posted 17 Apr 2015  View: PDF

Abstract: We elaborate upon a recent paper of E. Hurwitz and G. Gbur [Opt. Lett. {\bf 39}, 6529 (2014)], dealing with null-field sources. After commenting on their theory in Minkowski space, we show how the theory can be conveniently generalized to the case of curvilinear space when the latter is restricted to be time-independent and time-orthogonal.

Single-pass UV generation at 222.5 nm based on high-power GaN external cavity diode laser

Norman Ruhnke, André Mueller, Bernd Eppich, Reiner Güther, Martin Maiwald, Bernd Sumpf, Goetz Erbert, and Guenther Traenkle

Doc ID: 235205 Received 24 Feb 2015; Accepted 24 Mar 2015; Posted 13 Apr 2015  View: PDF

Abstract: We demonstrate a compact system for single-pass frequency doubling of high-power GaN diode laser radiation. The deep UV laser light at 222.5 nm is generated in a β-BaB2O4 (BBO) crystal. A high-power GaN external cavity diode laser (ECDL) system in Littrow configuration with narrowband emission at 445 nm is used as pump source. At a pump power of 680 mW a maximum UV power of 16 μW in continuous-wave operation at 222.5 nm is achieved. This concept enables a compact diode laser based system emitting in the deep ultraviolet spectral range.

A burst-train generator of high energy femtosecond laser pulses for driving heat accumulation effect during Micromachinig

Saeid Rezaei, Peter Herman, and Jianzhao Li

Doc ID: 228535 Received 26 Nov 2014; Accepted 12 Feb 2015; Posted 08 Apr 2015  View: PDF

Abstract: A new method for generating high repetition rate (12.7 to 38.2 MHz) burst-trains of femtosecond laser pulses has been demonstrated for the purpose of tailoring ultrashort laser interactions in material processing that can harness the heat accumulation effect amongst pulses separated by short internal (i.e. 26 ns). Computer-controlled time-delays were applied to synchronously trigger the high frequency switching of a high voltage Pockels Cell to specify distinctive values of polarization rotation for each round trip of a laser pulse cycling within a passive resonator. Polarization dependent output coupling facilitated the flexible shaping of the burst envelope profile to provide burst trains of up to ~1 mJ burst energy divided over a selectable number (1 to 25) of pulses. Individual pulses of energy variable up to 150 μJ energy and with pulse duration tunable over 70 fs to 2 ps were applied in burst trains to generate deep and high aspect ratio holes that were not possible to form with low-repetition rate laser pulses.

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