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Accepted papers to appear in an upcoming issue

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Measuring anisotropy ellipse of atmospheric turbulence by intensity correlations of laser light

Fei Wang, Italo Toselli, Jia Li, and Olga Korotkova

Doc ID: 282552 Received 09 Dec 2016; Accepted 21 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: The experimental study of a laser beam propagating through near-ground atmosphere on the grassy field in University of Miami (UM) has been performed. The average intensity, scintillation index and the intensity correlation in the receiver plane is measured at three different channels. Our results reveal that only the intensity correlation function displays the anisotropic information of turbulence, corresponding to the refractive index anisotropy ellipse of the atmospheric turbulence fluctuations. In addition, we also report an interesting phenomenon relating to turbulence eddy orientation near the ground. The experimental results are demonstrated by the numerical simulation using multi-phase screen method. Our findings provide an efficient way to determine the anisotropic parameters of atmospheric turbulence.

Diode-pumped Nd:YVO4 laser with discrete multi-wavelength tunability and high efficiency

Tanant Waritanant and Arkady Major

Doc ID: 282468 Received 12 Dec 2016; Accepted 20 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: Selectable and discretely tunable multi-wavelength diode-pumped Nd:YVO4 laser operating at 1064.0, 1073.1, and 1085.2 nm was demonstrated using a single intracavity birefringent plate. Under 11.2 W of absorbed pump power, the maximum output power of more than 3.8 W for any of the three wavelengths was achieved with slope and optical-to-optical efficiencies of more than 45% and 35%, respectively.

Direct measurement of the negative Goos-Hänchen shift of single reflection in two dimensional photonic crystal with negative refractive index

Jiang Qiang, Jiabi Chen, liang ming, Yan Wang, bing hu, and Songlin Zhuang

Doc ID: 286741 Received 14 Feb 2017; Accepted 20 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: The negative Goos-Hänchen shift on two dimensional photonic crystal with effective negative refractive index is investigated by simulation and experiment. The measured refractive index of the fabricated photonic crystal is nearly -0.44. The difference between Goos-Hänchen shift of TE wave GTE and that of TM wave GTM (DGHS) in the height direction of silicon rod is measured at three incident angles. The result shows that DGHS is always smaller than -GTM, thus GTE<0; therefore, the negative GHS does occur on the surface of the photonic crystal with negative refractive index

Passive near-field imaging with pseudo-thermal sources

Gustavo Cancado, Roxana Rezvani Naraghi, and Aristide Dogariu

Doc ID: 282554 Received 12 Dec 2016; Accepted 17 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: We demonstrate experimentally that spurious effects caused by interference can be eliminated in passive near-field imaging by implementing a simple random illumination. We show that typical imaging artifacts are effectively eliminated when the radiation emitted by a pseudo-thermal source illuminates the sample and the scattered field is collected by an aperture probe over essentially all angles of incidence. This novel pseudo-thermal source can be easily implemented and significantly enhances the performance of passive near-field imaging.

III-V-on-silicon three-section DBR laser with over 12 nm continuous tuning range

Sören Dhoore, Gunther Roelkens, and Geert Morthier

Doc ID: 284159 Received 24 Jan 2017; Accepted 17 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: Device and tuning characteristics of a novel heterogeneously integrated III-V-on-silicon three-section distributed Bragg reflector laser are presented. The laser exhibits a continuous wavelength tuning range of more than 12 nm. Thermal tuning is achieved through carrier injection in the passive tuning layer of a III-V tunable twin-guide membrane. Single-mode lasing with a side-mode suppression ratio larger than 30 dB over the entire tuning range is realised through implementation of a sidewall-corrugated silicon-on-insulator waveguide grating as one of the laser mirrors.

Self-referenced Temperature Sensing with a Lithium Niobate Microdisk Resonator

Rui Luo, HAOWEI JIANG, Hanxiao Liang, Yuping Chen, and Qiang Lin

Doc ID: 284481 Received 12 Jan 2017; Accepted 17 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: Self-referenced temperature sensing based on thermo-optic birefringence is demonstrated on a Z-cut lithium niobate microdisk resonator. Due to the significant difference between thermo-optic coefficients of ordinary and extraordinary light, quasi-transverse magnetic and quasi-transverse electric modes in the microdisk show relative cavity resonance shift upon temperature change, which acts as a robust self-reference for temperature sensing. Temperature sensitivity of 0.834 GHz/K and measurement uncertainty of 0.8 mK are demonstrated with an optical input power of only 1.5 μW.

Optofluidic tunable mode-locked fiber laser using long-period grating integrated microfluidic chip

Jie Wang, Mian Yao, Chengzhi Hu, A. Ping Zhang, Yonghang Shen, Hwa Yaw Tam, and Ping Kong Wai

Doc ID: 282604 Received 09 Dec 2016; Accepted 17 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: An optofluidic tunable mode-locked fiber laser using a microfluidic chip integrated with long-period grating (LPG) is presented. The microfluidic chip enables ultra-fine adjustment of the liquid’s refractive index (RI) and thus LPG’s spectrum via tuning the mixing ratio of the microfluidic flows. With such an optofluidic spectrum-tunable filter, the central wavelength of the mode-locked laser can be tuned continuously, while the mode-locking state is steadily maintained. The mode-locked pulses are measured with pulse duration of 0.9 ps and repetition rate of 12.14 MHz, respectively. Moreover, bound solitons with variable soliton separations are experimentally demonstrated.

83.4 W, 17.69 kHz spectral bandwidth, continuous-wave, beam densely folded Innoslab amplifier

Jian Ning, Han KeZhen, Jingliang He, yiran wang, hongkun nie, Haikun Zhang, Baitao Zhang, Kejian Yang, and ruihua Wang

Doc ID: 282642 Received 12 Dec 2016; Accepted 16 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: Combined with the advantages of the narrow bandwidth of non-planar ring oscillator (NPRO) seed laser and the structure of direct pumped Innoslab amplifier, a high efficiency and high power continuous-wave (CW) single-frequency laser was obtained by densely folding the seed laser beam in an Innoslab amplifier with a wedged multi-folded configuration. A maximum output power of 83.4 W of a single-frequency amplifier with a bandwidth of 17.69 kHz was obtained under a pump power of 4 W, corresponding to an optical-to-optical conversion efficiency of 33.2%. The beam quality factor M² at the maximum output power in horizontal and vertical direction was measured to be 1.15 and 1.24, respectively. The long-term power instability in 2 hours was less than 1.63%.

Cyclic spectra for wavelength-routed optical networks

Bill Corcoran, Zihan Geng, Valery Rozental, and Arthur Lowery

Doc ID: 284931 Received 17 Jan 2017; Accepted 16 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: We propose occupying guard-bands in closely-spaced WDM systems with redundant signal spectral components, to increase tolerance to frequency misalignment and channel shaping from multiplexing elements. By cyclically repeating the spectrum of a modulated signal, we show improved tolerance to impairments due to add/drop multiplexing with a commercial wavelength selective switch, in systems using 5-20\% guard bands on a 50-GHz DWDM grid.

Ultracompact X-ray dosimeter based on scintillators coupled to a nano-optical antenna.

Zhihua Xie, Hichem Maradj, Miguel Suarez, Lydie Viau, Virginie Moutarlier, Claudine Filiatre, Carole Fauquet, Didier Tonneau, and Thierry Grosjean

Doc ID: 284167 Received 05 Jan 2017; Accepted 15 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: We show that nano-optical antennas are capable of controlling the luminescence induced by the absorption of X-rays into matter. The X-ray excited luminescence from a tiny scintillation cluster coupled to a horn nano-optical antenna is highly directed and determined by the antenna geometrical parameters. Directionality is sufficiently high to efficiently outcouple the X-ray excited luminescence to a narrow single mode fiber, thus enabling ultracompact fiber-integrated X-ray sensors. Our nano-optically driven approach offers the possibility of X-ray profiling and dosimetry in ultra-confined environments, opening up new avenues in the fields of X-ray imaging, as well as medical and industrial endoscopy. With this study, nano-optical antennas make a first key contribution to the development of X-ray sensing protocols and architectures.

Fabrication of concave microlens arrays by local fictive temperature modification of fused silica

Chuanchao Zhang, wei liao, Ke Yang, Taixiang Liu, Yang Bai, Lijuan Zhang, Xiaolong Jiang, jing chen, yilan jiang, Haijun Wang, xiaoyu luan, Hai Zhou, Xiaodong Yuan, and Wanguo Zheng

Doc ID: 284626 Received 13 Jan 2017; Accepted 15 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: A simple and convenient means of fabricating concave microlens arrays direct on silica glass by using the local fictive temperature modification of fused silica is presented. This method is based on the fact that an increased fictive temperature results in a much higher HF acid etching rate of fused silica. Combining the abrupt local fictive temperature enhancement by the CO2 laser pulse and the subsequent etching by the HF acid solution, concave microlens arrays with high fill-factor, excellent smoothness and optical performance are generated on fused silica.

Encoding and Display with Stereo Split-Ring Resonator Arrays

Zheng-Han Wang, Yuan-Sheng Hu, Xiang Xiong, Ruwen Peng, and Mu Wang

Doc ID: 283733 Received 28 Dec 2016; Accepted 15 Feb 2017; Posted 15 Feb 2017  View: PDF

Abstract: In this letter, we report on encoding and display based on stereo standing U-shaped resonator (SUSR) arrays. The SUSR serves as a perfect absorber at a structure-dependent frequency when the polarization of incident light is parallel to the bottom rim of the SUSR. When the incidence polarization is rotated for 90o (perpendicular to the bottom rim of the SUSR), SUSR turns to a perfect reflector at all frequencies. Further, the resonant frequency sensitively depends on the height of the arms of SUSR. By introducing SUSRs with different arm height, resonant absorption state may occur at different frequencies. By defining the resonant absorption state as “Dark” and the reflection state as “Bright”, we can encode and display binary patterns. Besides, when SUSR rotates with the direction of the standing arms as axis, different reflectivity, hence different shade will be generated. In this way we may realize gray scale display. Experimentally we demonstrate that this encoding and display scheme indeed works.

Measuring the complex orbital angular momentum spectrum of light with mode matching method

Peng Zhao, Shikang li, Xue Feng, Kaiyu Cui, Fang Liu, Wei Zhang, and Yidong Huang

Doc ID: 284420 Received 10 Jan 2017; Accepted 15 Feb 2017; Posted 15 Feb 2017  View: PDF

Abstract: The relative phase shift among different components in the superposition of orbital angular momentum (OAM) states contains significant information. However, with existing methods of measuring OAM spectrum, the phase term of the spectrum coefficient is hard to obtain. In this work, a mode matching method is proposed to identify the complex OAM spectrum with a Mach-Zender interferometer and a charge coupled device camera. It is potential to extend the applications of OAM in scenarios sensitive to the phase factor, for instance, in imaging and quantum manipulation.

Contrast-transfer-function phase retrieval based on compressed sensing

Pablo Villanueva-Perez, Filippo Arcadu, Peter Cloetens, and Marco Stampanoni

Doc ID: 279978 Received 08 Nov 2016; Accepted 15 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: We report on a new contrast-transfer-function (CTF) phase-retrieval method based on the alternatingdirection method of multipliers (ADMM-CTF), which allows to exploit any compressed sensing regularization scheme reflecting the sparsity of the investigated object.The proposed iterative algorithm retrieves accurate phase maps from highly noisy single-distance projection microscopy data andis characterized by a stable convergence, not bounded to the prior knowledge of the object support or to the initialization strategy.Experiments on simulated and real datasets show that ADMM-CTF yields reconstructions with a substantial lower amountof artifacts and enhanced signal-to-noise ratio compared to the standard analytical inversion.

Extracting an accurate model for permittivity from experimental data: Hunting complex poles from the real line.

Mauricio Garcia-Vergara, Guillaume Demesy, and Frederic Zolla

Doc ID: 282601 Received 13 Dec 2016; Accepted 14 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: In this letter, we describe a very general procedure to obtain a causal fit of the permittivity of materials from experimental data with very few parameters. Unlike other closed forms proposed in the literature, the particularity of this approach lies in its independence towards the material or frequency range at stake. Many illustrative numerical examples are given and the accuracy of the fitting is compared to other expressions in the literature.

Zeonex-PMMA microstructured polymer optical FBGs for simultaneous humidity and temperature sensing

Getinet Woyessa, JENS PEDERSEN, Andrea Fasano, Kristian Nielsen, Christos Markos, Henrik Rasmussen, and Ole Bang

Doc ID: 282886 Received 26 Dec 2016; Accepted 14 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: In this work, we report for the first time the fabrication and characterization of a Zeonex/PMMA microstructured polymer optical fiber (mPOF) Bragg grating sensor for simultaneous monitoring of relative humidity (RH) and temperature. The sensing element (probe) is based on two separate in-line fiber Bragg gratings (FBGs) inscribed in the fabricated mPOF. A root mean square deviation of 0.8 % RH and 0.6 °C in the range of 10 to 90 % RH and 20 to 80 ᵒC was found. The developed mPOFBG sensor constitutes an efficient route towards low cost, easy to fabricate and compact multi-parameter sensing solution.

Discrete tuning concept for fiber-integrated lasers based on tailored FBG arrays and a theta cavity layout

Tobias Tieß, Martin Becker, Manfred Rothhardt, Hartmut Bartelt, and Matthias Jäger

Doc ID: 284337 Received 11 Jan 2017; Accepted 14 Feb 2017; Posted 22 Feb 2017  View: PDF

Abstract: We demonstrate a novel tuning concept for pulsed fiber-integrated lasers with a fiber Bragg grating (FBG) array as discrete and tailored spectral filter as well as a modified laser design. Based on a theta cavity layout, the structural delay lines originating from the FBG array are balanced enabling now a constant repetition rate and stable pulse properties over the full tuning range. The emission wavelength is electrically tuned with respect to the filter properties based on an adapted temporal gating scheme using an acousto-optic modulator. This concept has been investigated with an Yb-doped fiber laser demonstrating excellent emission properties with high signal contrast (>35 dB) and narrow linewidth (<150 pm) over a tuning range of 25 nm.

Sensitivity evaluation of quantitative phase imaging: a study of wavlength shifting interferometry

Shichao Chen, Chengshuai Li, and Yizheng Zhu

Doc ID: 285025 Received 18 Jan 2017; Accepted 13 Feb 2017; Posted 17 Feb 2017  View: PDF

Abstract: Sensitivity is a critical figure of merit to quantify measurement performance in quantitative phase imaging. It is affected by various noise sources in the system and by signal processing algorithms as well. Here, we propose a three-level framework for sensitivity evaluation, including Cramér-Rao bound (CRB), algorithmic sensitivity and experimental sensitivity. Comparing the first two determines the theoretical efficiency of an algorithm, whilst inspecting the gap between the latter two reveals system efficiency. As an example, we apply this framework to wavelength shifting interferometry, an important category of quantitative phase imaging techniques. In shot noise-limited regime, CRB is derived and the performance of 4-step Carré algorithm is studied in simulations and experiments. Importantly, the proposed procedure allows the algorithmic sensitivity to be conveniently estimated from a single set of measurement data, which serves as a basis for system efficiency evaluation.

Excess carrier-envelope phase noise generation in saturable absorbers

Nils Raabe, Tianli Feng, Mark Mero, Haochen Tian, Youjian Song, Wolfgang Hänsel, Ronald Holzwarth, Alexander Sell, Armin Zach, and Gunter Steinmeyer

Doc ID: 283436 Received 22 Dec 2016; Accepted 13 Feb 2017; Posted 15 Feb 2017  View: PDF

Abstract: Attosecond spectroscopy and precision frequency metrology depend on stabilization of the carrier-envelope phase (CEP) of mode-locked lasers. Unfortunately, the phase of only a few types of lasers can be stabilized to jitters in the few-hundred mrad range. In a comparative experimental study, we analyze a femtosecond Ti:sapphire laser and three mode-locked fiberlasers. We numerically demodulate recorded time series of the free-running carrier-envelope beat note. Our analysis indicates a correlation between amplitude and frequency fluctuations at low Fourier frequencies for essentially all lasers investigated. While this correlation typically rolls off at frequencies beyond 100 kHz, we see clear indications for a broadband coupling mechanism in one of the fiber lasers. We suspect that the observedcoupling mechanism acts to transfer intracavity power fluctuations into excess phase noise. This coupling mechanism is related to the mode-locking mechanism employed and not to the gain medium itself. We further verify this hypothesis by numerical simulations, which identify resonances of the saturable absorber mirror as a possible explanation for the couplingmechanism. Finally, we discuss how to avoid a detrimental influence of such resonances.

Characterization of spatiotemporal chaos in Kerr optical frequency comb and in all fiber cavities

Saliya Coulibaly, Zheng Liu, Mardia Ouali, Marcel Clerc Gavilán, Mustapha Tlidi, and Abdelmajid Taki

Doc ID: 283776 Received 28 Dec 2016; Accepted 13 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: Complex spatiotemporal dynamics have been a subject of recent experimental investigations in optical frequency comb microresonators and in driven fiber cavities with a Kerr-type media. We show that this complex behavior has a spatiotemporal chaotic nature. We determine numerically the Lyapunov spectra, allowing to characterize different dynamical behavior occurring in these simple devices. The Yorke-Kaplan dimension is used as an order parameter to characterize the bifurcation diagram. We identify a wide regime of parameters where the system exhibits a coexistence between the spatiotemporal chaos, the oscillatory localized structure, and the homogeneous steady state. The destabilization of an oscillatory localized state through radiation of counter propagative fronts between the homogeneous and the spatiotemporal chaotic states is analyzed. To characterize better the spatiotemporal chaos, we estimate the front speed as a function of the pump intensity.

Secure key distribution based on chaos synchronization of VCSELs subject to symmetric random-polarization optical injection

Ning Jiang, Chenpeng Xue, Ding Liu, Yunxin Lv, and Kun Qiu

Doc ID: 283029 Received 16 Dec 2016; Accepted 12 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: We propose and demonstrate a secure key distribution based on the dynamic chaos synchronization of two external cavity vertical cavity surface emitting lasers (VCSELs) subject to symmetric random polarization injections. By exchanging the random parameters that control the polarization angles of driving injection, Alice and Bob can identify the time slots in which high quality private chaos synchronization is achieved, and independently generate a shared key from the synchronized polarization differential signals of their local VCSELs with dual threshold sampling technology and post processing. The results show that Gb/s key distribution with good randomness and low bit error ratio can be achieved. In the proposed scheme, the exchange messages do not contain any information about the key generation, which affords a high level security for key distribution.

First experimental demonstration of faster-than-Nyquist PDM-16QAM transmission over SSMF

Fu Songnian, Xiao Zhuopeng, Li Borui, Lei Deng, Ming Tang, and Deming Liu

Doc ID: 283165 Received 20 Dec 2016; Accepted 12 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: We demonstrate faster-than-Nyquist (FTN) transmission with a novel mitigation scheme of inter-carrier-interference (ICI). To the best of our knowledge, it is the first experimental demonstration of FTN PDM-16QAM transmission over standard single mode fibers (SSMF). Due to the use of maximum likelihood sequence detection (MLSD) and multi-input multi-output (MIMO) processing for severely overlapped Nyquist-PDM-16QAM carriers, 5.4-dB OSNR improvement is experimentally observed under the scenario of 2×16-GBd PDM-16QAM back-to-back (BTB) transmission with a carrier spacing of 15-GHz. A net SE up to 7.68-b/s/Hz is achieved with transmission of 15-GHz spaced dual-carrier superchannel over 960-km SSMF, with hard decision forward error correction (HD-FEC) taken into account. Furthermore, FTN superchannels transmission with carrier spacing of 14-GHz and 15-GHz are successfully realized over 960-km and 1920-km SSMFs, respectively.

Bulk second-harmonic generation from thermally-evaporated indium selenide thin films

Abdallah Slablab, Kalle Koskinen, Divya S, Robert Czaplicki, Semen Chervinskii, Kailasnath M, P Radhakrishnan, and Martti Kauranen

Doc ID: 283997 Received 03 Jan 2017; Accepted 12 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: We investigate bulk second-order nonlinear optical properties of amorphous indium selenide thin films fabricated by thermal evaporation. Such films are shown to exhibit strong and photostable second-harmonic generation (SHG). We report strong thickness-dependence of the second-harmonic signals as characterized by the Maker-fringe method. The absolute value of the nonlinear susceptibility tensor of the film is addressed by analyzing the interference of SHG signals from the film and the glass substrate. The value of the joint non-diagonal component of the susceptibility is found to be 4 pm/V, which is comparable to that of widely used second-order nonlinear materials.

Propagation of Optical Vortices in a Nonlinear Atomic Medium with Photonic Band Gap

Yiqi Zhang, zhaoyang zhang, Danmeng Ma, Mingtao Cao, Zhongfeng xu, and Yanpeng Zhang

Doc ID: 284769 Received 13 Jan 2017; Accepted 10 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: We experimentally generate a vortex beam through a four-wave mixing (FWM) process after satisfying the phase-matching condition in a rubidium atomic vapor cell with photonic band gap (PBG) structure. The observed FWM vortex can also be viewed as the reflected part of the launched probe vortex from the PBG. Further, we investigate the propagation behaviors including the spatial shift and splitting of probe and FWM vortices in the medium with enhanced Kerr nonlinearity induced by electromagnetically induced transparency. The study can be useful for better understanding and manipulating the applications involving the interactions between optical vortices and medium.

A digitally controlled chirped pulse laser for sub-terahertz-range fiber structure interrogation

Tao Wei, ZHEN CHEN, and Gerald Hefferman

Doc ID: 282912 Received 18 Dec 2016; Accepted 10 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: This letter reports a sweep velocity-locked laser pulse generator (SV-LLPG) controlled using a digital phase locked loop (DPLL) circuit. This design is used for the interrogation of sub-terahertz-range fiber structures for sensing applications that require real-time data collection with mm-level spatial resolution. A distributed feedback laser (DFB) was employed to generate chirped laser pulses via injection current modulation. A DPLL circuit was developed to lock the optical frequency sweep velocity. A high-quality linearly chirped laser pulse with a frequency excursion of 117.69 GHz at optical communication band was demonstrated. The system was further adopted to interrogate a continuously distributed sub-THz-range fiber structure (Sub-THz-FS) for sensing applications. A strain test was conducted in which the Sub-THz-FS showed a linear response to longitudinal strain change with predicted sensitivity. Additionally, temperature testing was conducted in which a heat source was used to generate a temperature distribution along the fiber structure to demonstrate its distributed sensing capability. A Gaussian temperature profile was measured using the described system and tracked in real-time as the heat source was moved.

Optofluidic biomolecule sensors based on a-Si:H microrings embedded in silicon-glass microchannels

Timo Lipka, Lennart Moldenhauer, Lennart Wahn, and Hoc Khiem Trieu

Doc ID: 285523 Received 24 Jan 2017; Accepted 10 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: The large-scale and low-cost fabrication of high-sensitivity sensors for the real-time detection of bio-chemicals and molecular substances opens up new opportunities in the areas of bioanalytic screening and medical diagnostics. Planar integrated photonic resonators that can be fabricated with low-footprint, in spatial and wavelength multiplexed arrangement, andwhich enable the integration with microfluidics on wafer-scale have emerged as a promising sensing platform for these application fields. We realized a novel optofluidic and label-free biosensor that is based onlow-loss hydrogenated amorphous silicon microring resonators embedded in silicon/glassmicrofluidic channels for the analyte injection and biomolecule immobilization. The optofluidic sensor merits for refractive index and biomolecule sensing are evaluated by sensitivity and detection limit simulations, whereas, a proof-of-concept is demonstrated by real-time protein immobilization experiments of functionalized resonators.

Two-photon Shack-Hartmann wavefront sensor

Fei Xia, David Sinefeld, Bo Li, and Chris Xu

Doc ID: 283968 Received 20 Jan 2017; Accepted 10 Feb 2017; Posted 21 Feb 2017  View: PDF

Abstract: We introduce a simple wavefront sensing scheme for aberration measurement of pulsed laser beams in near-infrared wavelengths (< 2200 nm), where detectors are not always available or are very expensive. The method is based on two-photon absorption in silicon detector array for longer wavelengths detection. We demonstrate the simplicity of such implementations with a commercially available Shack-Hartmann wavefront sensor and discuss the detection sensitivity of this method.

Ellipticity-tunable attosecond XUV pulse generation with a rotary bicircularly polarized laser field

Peixiang Lu, Xiaofan Zhang, Xiaosong Zhu, Qingbin Zhang, Dian Wang, Pengfei Lan, and Xi Liu

Doc ID: 282413 Received 09 Dec 2016; Accepted 09 Feb 2017; Posted 10 Feb 2017  View: PDF

Abstract: We propose and theoretically demonstrate a method to generate attosecond XUV pulses with tunable ellipticity from aligned molecules irradiated by a bichromatic counterrotating circularly polarized (BCCP) driving laser field. By rotating the BCCP field, the attoseond XUV pulse varies from left-elliptically polarized to right-elliptically polarized. The rotation of the BCCP field can be easily achieved by adjusting the relative phases between the two circularly polarized components. This scheme will benefit a broad range of applications, including exploration of chiral-sensitive properties of the light-matter interaction and time-resolved imaging of magnetic structures.

Tailoring frequency generation in uniform and concatenated multimode fibers

Zeinab Sanjabi Eznaveh, Mohammad Amin Eftekhar, Jose Antonio-Lopez, Miroslav Kolesik, Axel Schulzgen, Frank Wise, Demetrios Christodoulides, and Rodrigo Amezcua Correa

Doc ID: 281710 Received 01 Dec 2016; Accepted 09 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: We demonstrate that frequency generation in multimode parabolic-index fibers can be precisely engineered through appropriate fiber design. This is accomplished by exploiting the onset of a geometric parametric instability that arises from resonant spatiotemporal compression. By launching the output of an amplified Q-switched microchip laser delivering 400 ps pulses at 1064 nm, we observe a series of intense frequency sidebands that strongly depend on the fiber core size. The nonlinear frequency generation is analyzed in three fiber samples with 50 μm, 60 μm and 80 μm core diameters. We further demonstrate that by cascading fibers of different core-sizes, a desired frequency band can be generated from the frequency lines parametrically produced in each section. The observed frequency shifts are in excellent agreement with analytical predictions and numerical simulations. Our results suggest that core scaling and fiber concatenation can provide a viable avenue in designing optical sources with tailored output frequencies.

Active pulse-shaping for end-pumped Nd:YVO4 amplifier with high gain

Mingming Nie, Qiang Liu, Encai Ji, Xuezhe Cao, Xing Fu, and mali gong

Doc ID: 282146 Received 05 Dec 2016; Accepted 09 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: We demonstrated the active-shaping for a solid-state Nd:YVO4 amplifier with high average gain of 39.2dB. Interesting pulse shapes based on the Second Gate of Tsinghua University was produced with pulse distortion compensated. The average output power was 8.3 W with respect to the input power of 1 mW. In addition, a very flat square pulse was produced with Root-Mean-Square (RMS) less than 3 % in amplitude. A numerical method was proposed to realize active-shaping without an experimental test for the Nd:YVO4 amplifier, showing great potential for the design of lasers with both high peak power (>100 kW) and desired pulse shape.

Optical alignment of oval graphene flakes

Ehsan Mobini, aso rahimzadegan, Rasoul Alaee, and Carsten Rockstuhl

Doc ID: 283856 Received 02 Jan 2017; Accepted 09 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Patterned graphene, as an atomically thin layer, supports localized surface plasmon-polaritons (LSPPs) at mid-infrared or far-infrared frequencies. This provides a pronounced optical force/torque in addition to large optical cross sections and will make it an ideal candidate for optical manipulation. Here, we study the optical force and torque exerted by a linearly polarized plane wave on circular and oval graphene flakes. Whereas the torque vanishes for circular flakes, the finite torque allows rotating and orienting oval flakes relative to the electric field polarization. Depending on the wavelength, the alignment is either perpendicular or parallel. In our contribution, we rely on full-wave numerical simulation but also on an analytical model that treats the graphene flakes in dipole approximation. The presented results reveal a good level of control on the spatial alignment of graphene flakes subjected to far-infrared illumination.

Extended Depth-of-Field Microscopy with a High-Speed Deformable Mirror

William Shain, Nicholas Vickers, Bennett Goldberg, Thomas Bifano, and Jerome Mertz

Doc ID: 284343 Received 09 Jan 2017; Accepted 09 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Wide-field fluorescence microscopy is generally limited to either small volumes or low temporal resolution. We present a microscope add-on that provides fast, light-efficient extended depth-of-field (EDOF) using a deformable mirror of update rate 20kHz. Out-of-focus contributions in the raw EDOF imagesare suppressed with a deconvolution algorithm derived directly from the microscope 3D optical transfer function. Demonstrations of the benefits of EDOF microscopy are shown with GCaMP-labeled mouse brain tissue.

Whispering gallery mode single nano-particle detection and sizing: the validity of the dipole approximation

Matthew Foreman, David Keng, Eshan Treasurer, Jehovani Lopez, and Stephen Arnold

Doc ID: 281750 Received 29 Nov 2016; Accepted 08 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Interactions between whispering gallery modes (WGMs) and small nanoparticles are commonly modelled by treating the particle as a point dipole scatterer. This approach is assumed to be accurate as long as the nanoparticle radius, a, is small compared to the WGM wavelength λ. In this article, however, we show that the large field gradients associated with the evanescent decay of a WGM causes the dipole theory to significantly underestimate the interaction strength, and hence induced WGM resonance shift, even for particles as small as a ~ λ/10. To mitigate this issue we employ a renormalized Born approximation to more accurately determine nanoparticle induced resonance shifts and hence enable improved particle sizing. The domain of validity of this approximation is investigated and supporting experimental results are presented.

The role of beam waist in Laguerre-Gauss expansion of vortex beams

Giuseppe Vallone

Doc ID: 282608 Received 12 Dec 2016; Accepted 08 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Laguerre-Gauss (LG) modes represent an orthonormal basis set of solutions of the paraxial wave equation.LG are characterized bytwo integer parameters $n$ and $\ell$ that are related to the radial and azimuthal profile of the beam. The physical dimension of the mode is instead determined by the beam waist parameter $w_0$: only LG modes with the same $w_0$ satisfy the orthogonality relation. Here, we derive the scalar product between two LG modes with different beam waists and show how this result can be exploited to derive different expansions of a generic beam in terms of LG modes. In particular, we apply our results to the recently introduced Circular Beams, by deriving a previously unknown expansion. We finally show how the waist parameter must be chosen in order to optimize such expansion.

Terahertz modulation induced by filament interaction

Heping Zeng, Boqu He, Junyi Nan, Shuai Yuan, and Min Min

Doc ID: 282714 Received 13 Dec 2016; Accepted 07 Feb 2017; Posted 07 Feb 2017  View: PDF

Abstract: We experimentally demonstrated that nonlinear filament interaction could spectrally modulate terahertz (THz) radiation generated from asymmetric two-color filaments. It was the spatial plasma density modulation in plasma channels that induced the THz spectral modulation. As a result of optical manipulation of electron density in the filamentary plasma gratings, the generated THz was enhanced at high-frequency spectra while suppressed at low-frequency spectra, indicating that increase of free electron density in the filamentary plasma grating brought about THz frequency upshifts.

Polarization-basis tracking scheme for quantum key distribution using revealed sifted key bits

Wei Chen, Ding YuYang, Hua Chen, Zhengfu Han, Zhen-Qiang Yin, Li Yaping, Chao Wang, Shuang Wang, and Guang-can Guo

Doc ID: 280490 Received 15 Nov 2016; Accepted 07 Feb 2017; Posted 10 Feb 2017  View: PDF

Abstract: Calibration of the polarization basis between the transmitter and receiver is an important task in quantum key distribution (QKD). An effective and continuously working polarization-basis tracking (CWPBT) scheme will promote the efficiency of the system and reduce the potential secure risk when switching between the transmission and calibration modes. In this paper, we proposed a CWPBT scheme using only sifted key bits revealed during error correction procedure, without introducing additional reference light or interrupting the transmission of quantum signals. We applied the scheme to a polarization-encoding BB84 QKD system in a 50km fiber channel, and obtained an average quantum bit error rate (QBER) of 2.32% and a standard derivation of 0.87% during 24 hours of continuous operation. The stable and relatively low QBER validates the effectiveness of the scheme.

On the application of principal component analysis to the calculation of the bulk integral optical properties for radiation parameterizations in climate models

Anthony Baran and Stuart Newman

Doc ID: 281125 Received 25 Nov 2016; Accepted 07 Feb 2017; Posted 10 Feb 2017  View: PDF

Abstract: Rigorous electromagnetic computations required for the calculation of high-resolution monochromatic bulk integral optical properties of irregular atmospheric particles are onerous in memory and in time. Here, it is shown that from a set of 145 monochromatic bulk integral ice optical properties, it is possible to reduce the set to 8 hinge wavelengths by using the method of principal component analysis (PCA) regression. From the 8 hinge wavelengths the full set can be reconstructed to within root mean square errors of <<1%. To obtain optimal reconstruction, the training set must cover as wide a range of parameter space as possible. Rigorous electromagnetic methods can now be routinely applied to represent accurately the integral optical properties of atmospheric particles in climate models.

High-directional Vortex Beam Emitter Based on Archimedean Spiral Adiabatic Waveguides

shimao li, en yu, Laura Meriggi, Qingsheng Xiao, Zhichao Nong, Xinlun Cai, Marc Sorel, and Siyuan Yu

Doc ID: 283339 Received 21 Dec 2016; Accepted 07 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Integrated devices that emit light beams with orbital angular momentum (OAM) are becoming key components for wide-ranging applications. Here, we propose and demonstrate a highly directional silicon photonic vortex beam emitter based on a 3-turn Archimedean spiral adiabatic waveguide integrated with an angular grating. Such compact emitter is capable of generating vortex beams with small divergence angles and high directivity. Various order OAM modes can be selectively generated by the emitter at different wavelength with side-mode suppression ratio as large as 13.6 dB.

Spatial Light Structuring Using a Combination of Multiple Orthogonal Orbital Angular Momentum Beams with Complex Coefficients

Guodong Xie, Cong Liu, Long Li, Yongxiong Ren, Zhe Zhao, Yan Yan, Nisar Ahmed, Zhe Wang, Asher Willner, Changjing Bao, Yinwen Cao, Peicheng Liao, Morteza Ziyadi, Ahmed Almaiman, Solyman Ashrafi, Moshe Tur, and Alan Willner

Doc ID: 283602 Received 26 Dec 2016; Accepted 07 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Analogous to time signals that can be composed of multiple frequency functions, we use uniquely structured orthogonal spatial modes to create different beam shapes. We tailor the spatial structure by judiciously choosing a weighted combination of multiple modal states within an orthogonal orbital angular momentum (OAM) basis set, creating desired beam intensity “shapes”. The weights of the OAM beams to be combined forms a Fourier pair with the spatial intensity distribution in the azimuthal direction of the resultant beam. As an example, we simulate and experimentally create various beam shapes by designing the weights of the combined OAM beams. We also find that 6X higher localized power as compared to traditional beam combining could be achieved by coherently combining 9 orthogonal OAM beams. Besides, we show that the combination of OAM beams with different radial indices allows intensity manipulation in the radial direction of the resultant beam.

Carrier Envelope Offset Frequency Detection and Stabilization of a Diode-Pumped Mode-locked Ti:Sapphire Laser

Kutan Gurel, Valentin Wittwer, SARGIS HAKOBYAN, Stephane Schilt, and Thomas Sudmeyer

Doc ID: 284991 Received 17 Jan 2017; Accepted 07 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: We demonstrate the first diode-pumped Ti:Sapphire laser frequency comb. It is pumped by two green laser diodes with a total pump power of 3 W. The Ti:Sapphire laser generates 250 mW of average output power in 61-fs pulses at a repetition rate of 216 MHz. We generated an octave-spanning supercontinuum spectrum in a photonic-crystal fiber and detected the carrier envelope offset (CEO) frequency in a standard f-to-2f interferometer setup. We stabilized the CEO-frequency through direct current modulation of one of the green pump diodes. We achieved a reduction of the CEO phase noise power spectral density by 140 dB at 1 Hz offset frequency. An advantage of diode pumping is the ability for a high bandwidth modulation of the pump power via direct current modulation. We studied the modulation capabilities and noise properties of green pump laser diodes. The current-to-output-power modulation transfer function shows a bandwidth of up to 2 MHz, limited by the used current driver.

Second harmonic generation in multimodegraded-index fibers: spatial beam cleaning andmultiple harmonic sideband generation.

Daniele Modotto, Davide Ceoldo, Katarzyna Krupa, Alessandro Tonello, Vincent COUDERC, Umberto Minoni, Guy Millot, and Stefan Wabnitz

Doc ID: 282909 Received 15 Dec 2016; Accepted 06 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: We study experimentally and numerically the spectral and spatial dynamics of second harmonic generation in an all-optically poled multimode graded-index fiber. In contrast with poled single-mode fibers, in a multimode graded-index fiber a pump can generate a series of sharp sidebands around its second harmonic that originate from the sub-millimetric periodic evolution of the intensity at the fundamental frequency. The mutual interaction between the fundamental and its second harmonic may also strongly affect the spatial distribution of guided light for both colors: when increasing the pump power, both fundamental and second harmonic output beams evolve from disordered multimode speckles into two self-organized bell-shaped beams.

Functional optoacoustic neuro-tomography of calcium fluxes in adult zebrafish brain in-vivo

Xose Luis Dean Ben, Sven Gottschalk, gali sela, shy shoham, and Daniel Razansky

Doc ID: 280563 Received 11 Nov 2016; Accepted 06 Feb 2017; Posted 06 Feb 2017  View: PDF

Abstract: Genetically encoded calcium indicators (GECIs) have revolutionized neuroimaging by enabling mapping the activity of entire neuronal populations in vivo. Visualization of these powerful activity sensors has so far been limited to depth-restricted microscopic studies due to intense light scattering in the brain. We demonstrate, for the first time, real-time volumetric optoacoustic monitoring of calcium transients in a scattering brain of a living adult transgenic zebrafish expressing GCaMP5G calcium indicator. Fast changes in optoacoustic traces associated to GCaMP5G activity were detectable in the presence of other strongly absorbing endogenous chromophores, such as hemoglobin. The new functional optoacoustic neuroimaging method can visualize neural activity at penetration depths and spatio-temporal resolution scales not covered with the existing neuroimaging techniques.

Reduction of speckle noise in holographic images using spatial jittering in numerical reconstructions

Pascal Picart, haouat mohamed, Jorge Garcia-Sucerquia, and Abelhamid Kellou

Doc ID: 283319 Received 21 Dec 2016; Accepted 06 Feb 2017; Posted 06 Feb 2017  View: PDF

Abstract: This paper presents an easy, fast and efficient single-shot method to reduce speckle noise in digital Fresnel holography. In this method, several images from a single hologram are reconstructed by introducing spatial displacements in the Fresnel kernel. Spatial jitters produce images with different speckle positions. Averaging the set of numerically produced images leads to a strong reduction of speckle noise in both amplitude and phase difference images. Experimental results show the suitability of the proposed approach and confirm its applicability to digital holographic interferometry.

Optoacoustic reconstruction using fast sparse representation

Yiyong Han, Lu Ding, Xose Luis Dean Ben, Daniel Razansky, Jaya Prakash, and Vasilis Ntziachristos

Doc ID: 278984 Received 08 Nov 2016; Accepted 06 Feb 2017; Posted 07 Feb 2017  View: PDF

Abstract: Optoacoustic tomography based on insufficient spatial sampling of ultrasound waves leads to loss of contrast and artifacts on the reconstructed images. Compared to reconstructions based on L2-norm regularization, sparsity-based reconstructions may improve contrast and reduce image artifacts but at a high computational cost, which has so far limited their use to 2D optoacoustic tomography. Here we propose a fast, sparsity-based reconstruction algorithm for 3D optoacoustic tomography, based on gradient descent with Barzilai-Borwein line search (L1-GDBB). Using simulations and experiments, we show that L1-GDBB offers 4-fold faster reconstruction than previously reported L1-norm regularized reconstruction based on gradient descent with backtracking line search. Moreover, the new algorithm provides higher-quality images with fewer artifacts than non-sparsity-based L2-norm regularized reconstruction.

Taper Resistant Subwavelength Grating Micro Lens

Mao Ye and Y. Yi

Doc ID: 283164 Received 23 Dec 2016; Accepted 06 Feb 2017; Posted 10 Feb 2017  View: PDF

Abstract: Subwavelength grating micro lens has attracted much attention due to its variety of potential applications. Instead of vertical sidewall profile normally considered by most of recent works, a tapered side wall profile is often obtained during the fabrication with current etching processes, especially during the fabrication of high aspect ratio structures. In this work, we have discovered that a tapered side wall profile may have a significant destructive effect on the concentration properties of emerging subwavelength concentrating lenses/metasurfaces. This is caused by the phase shift resulting from the tapered profile that affects each individual phase shifter. More interestingly, we have further discovered that there exist some period/fill-factor combinations for phase shifters that “resist” the phase shift caused by the tapered structure. This study will provide an important avenue for the design of subwavelength concentrating lenses/metasurfaces to overcome the limit from practical nanofabrication processes when dealing with the tapered side wall profile.

Measuring extinction with digital holography: Nonspherical particles and experimental validation

Matthew Berg, Nava Subedi, and Peter Anderson

Doc ID: 283540 Received 23 Dec 2016; Accepted 06 Feb 2017; Posted 13 Feb 2017  View: PDF

Abstract: Through simulations and a simple experiment, this letter shows how a particle's extinction cross section can be extracted from a digital hologram. Spherical and nonspherical particles are considered covering a range of cross section values of nearly five orders of magnitude. The extracted cross sections are typically less than 10% in error from the true values. It is also shown that holograms encompassing a sufficiently large angular range of scattered light yield an estimate for the absorption cross section.

Monoclinic Tm3+:MgWO4: A novel crystal for continuous-wave and passively Q-switched lasers at 2 μm

Xavier Mateos, Pavel Loiko, Josep Maria Serres, Magdalena Aguilo, Francesc Diaz, lizhen zhang, zhoubin lin, Haifeng Lin, Zhang Ge, Konstantin Yumashev, Valentin Petrov, Uwe Griebner, Yicheng Wang, Sun Young Choi, Fabian Rotermund, and Weidong Chen

Doc ID: 284649 Received 13 Jan 2017; Accepted 06 Feb 2017; Posted 14 Feb 2017  View: PDF

Abstract: Monoclinic thulium-doped magnesium monotungstate, Tm3+:MgWO4, is promising for efficient power-scalable continuous-wave (CW) and passively Q-switched lasers at >2 μm. Under diode-pumping at 802 nm, a compact CW laser based on Z-cut Tm:MgWO4 generated 3.09 W at 2022-2034 nm with a slope efficiency of 50% which represents the highest output power ever achieved with this type of laser host. Stable passive Q-switching of the Tm:MgWO4 laser is demonstrated for the first time using single-walled carbon nanotubes (SWCNTs), graphene and Cr2+:ZnS saturable absorbers. Using the latter best performance are achieved with 16.1 μJ / 13.6 ns pulses at 2017.8 nm with to a maximum average output power of 0.87 W and a peak power of 1.18 kW.

Voltage-induced waveguides in lithium niobate films on silicon substrates

Mathieu Chauvet, Pierrick Thoa, and Florent Bassignot

Doc ID: 283927 Received 09 Jan 2017; Accepted 05 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: Tunable channel waveguides have been fabricated by domain inversion of a LiNbO3 thin film bonded to a silicon wafer. The electro-optic effect is used to induce the waveguides and to alter its guiding properties. A low amplitude electric signal can tune the voltage-induced structure from an efficient waveguide to an anti-guide giving a waveguide transmission that varies over more than 25dB. Frequency response of the components is given.

Time-multiplexed structured illumination using a DMD for optical diffraction tomography

KyeoReh Lee, Kyoohyun Kim, Geon Kim, Seungwoo Shin, and YongKeun Park

Doc ID: 285225 Received 20 Jan 2017; Accepted 05 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: We present a time-multiplexing structured illumination control technique for optical diffraction tomography (ODT). Instead of tilting the angle of llumination, time-multiplexed sinusoidal illumination is exploited using a digital micromirror device (DMD). Present method effectively eliminates unwanted diffracted beams from binary DMD patterns, which deteriorates the image quality of the ODT in previous binary Lee hologram method. We experimentally show the feasibility and advantage of present method by reconstructing three-dimensional refractive index (RI) distributions of various samples, and comparing with conventional Lee hologram method.

Modified timing characteristic of a scintillation detection system with photonic crystal structures

Jinliang Liu, Bo Liu, Zhichao Zhu, Liang Chen, JING HU, mengxuan xu, Chuanwei Cheng, Xiaoping Ouyang, Zhongbing Zhang, Jinlu Ruan, Shiyi He, Mu Gu, Hong Chen, and Linyue Liu

Doc ID: 284191 Received 10 Jan 2017; Accepted 04 Feb 2017; Posted 09 Feb 2017  View: PDF

Abstract: It is intuitively expected that an enhanced light extraction of scintillator can be easily achieved by photonic crystal structures. Here, we demonstrate a modified timing characteristic for a detection system induced by enhanced light extraction with photonic crystal structures. Such improvement is due to the enhanced light extraction which can been clearly proven by the independent measurements of the light output and the timing resolution. The present investigation is advantageous to promote the development of scintillation detection system performance based on the time-of-flight measurement.

Fabrication of a centimeter-long cavity on a nanofiber for cavity QED

Kali Prasanna Nayak, Kohzo Hakuta, and Jameesh Keloth

Doc ID: 285517 Received 24 Jan 2017; Accepted 04 Feb 2017; Posted 10 Feb 2017  View: PDF

Abstract: We report the fabrication of a 1.2 cm long cavity directly on a nanofiber using femtosecond laser ablation. The cavity modes with finesse value in the range 200-400 can still maintain the transmission between 40-60%, which can enable “strong-coupling” regime of cavity QED for a single atom trapped 200 nm away from the fiber surface. For such cavity modes, we estimate the one-pass intra-cavity transmission to be 99.53%. Other cavity modes, which can enable high cooperativity in the range 3-10, show transmission over 60-85% and are suitable for fiber-based single photon sources and quantum nonlinear optics in the “Purcell”regime.

High extinction ratio terahertz wire-grid polarizers with connecting bridges on quartz substrates

John Cetnar, Weidong Zhang, Carl Pfeiffer, Elliott Brown, Shivashankar Vangala, and Junpeng Guo

Doc ID: 281859 Received 01 Dec 2016; Accepted 31 Jan 2017; Posted 31 Jan 2017  View: PDF

Abstract: A THz wire-grid polarizer with metallic bridges on a quartz substrate was simulated, fabricated, and tested. The device functions as a wide-band polarizer to incident THz radiation. In addition, the metallic bridges permit the device to function as a transparent electrode when a DC bias is applied across it. Three design variations of the polarizer with bridges and a polarizer without bridges were studied. Results show the devices with bridges have average s-polarization transmittance less than -6 dB and average extinction ratios of approximately 40 dB across a frequency range of 220 to 990 GHz and thus are comparable to the polarizer without bridges.

A high numerical aperture (NA = 0.92) objective lens for imaging and addressing of cold atoms

Carsten Robens, Stefan Brakhane, Wolfgang Alt, Felix Kleißler, Dieter Meschede, Geol Moon, Gautam Ramola, and Andrea Alberti

Doc ID: 280118 Received 08 Nov 2016; Accepted 24 Jan 2017; Posted 30 Jan 2017  View: PDF

Abstract: We have designed, built, and characterized a high-resolution objective lens that is compatible with an ultra-high vacuum environment. The lens system exploits the principle of the Weierstrass-sphere solid immersion lens to reach a numerical aperture (NA) of 0.92. Tailored to the requirements of optical lattice experiments, the objective lens features a relatively long working distance of 150 μm. Our two-lens design is remarkably insensitive to mechanical tolerances in spite of the large NA. Additionally, we demonstrate the application of a tapered optical fiber tip, as used in scanning near-field optical microscopy, to measure the point spread function of a high NA optical system. From the point spread function, we infer the wavefront aberration for the entire field of view of about 75 μm. Pushing the NA of an optical system to its ultimate limit enables novel applications in quantum technologies such as quantum control of atoms in optical microtraps with an unprecedented spatial resolution and photon collection efficiency.

Dark-field Brillouin microscopy

Giuseppe Antonacci

Doc ID: 283328 Received 21 Dec 2016; Accepted 20 Jan 2017; Posted 23 Jan 2017  View: PDF

Abstract: Brillouin microscopy is a non-contact and label-free technique for mapping fundamental micro-mechanical properties in the volume of biological systems. Specular reflections and elastic scattering easily overwhelm the weak Brillouin spectra due to the limited extinction of virtually imaged phased array (VIPA) spectrometers, thereby affecting the image acquisition. In this Letter, we demonstrate a dark-field method to reject the elastic background light using an annular illumination and a confocal detection. To validate our method, images of polystyrene and liquid samples were obtained using both a confocal and the dark-field system. An extinction ratio of 30 dB was readily achieved.

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