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Accepted papers to appear in an upcoming issue

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Self-eclipsing: alignment-free vortex coronagraphy

Artur Aleksanyan and Etienne Brasselet

Doc ID: 284554 Received 11 Jan 2017; Accepted 23 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: We report on a self-induced strategy to achieve high-contrast optical imaging without a need of any man-made optical masks, which relies on the self-induced spin-to-orbital angular momentum conversion phenomenon. This is experimentally demonstrated by realizing a laboratory demonstration of self-eclipsing of a light source following the generation of a self-adapted vectorial optical vortex transmission mask. The proposed concept, namely the realization of an alignment-free optical vortex coronagraph, may inspire the development of future generations of smart astronomical imaging instruments.

Dielectric metasurfaces solve differential and integro-differential equations

Sajjad AbdollahRamezani, Ata Chizari, Ali Eshaghian Dorche, mohammad vahid jamali, and Jawad Salehi

Doc ID: 285699 Received 27 Jan 2017; Accepted 23 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: Leveraging subwavelength resonant nanostructures, plasmonic metasurfaces have recently attracted much attentions as a breakthrough concept for engineering optical waves both spatially and spectrally. However, inherent Ohmic losses concomitant with low coupling efficiencies pose fundamental impediments over their practical applications. Not only could all-dielectric metasurfaces tackle such substantial drawbacks, but also their CMOS- compatible configurations support both Mie resonances that are invariant to the excitation angle. Here, we report on a transmittive metasurface comprising arrayed silicon nanodisks embedded in a homogeneous dielectric medium to manipulate phase and amplitude of incident light locally and almost independently. By taking advantage of the interplay between the electric/magnetic resonances and employing general concepts of spatial Fourier transformation, a highly efficient metadevice is proposed to perform mathematical operations including solution of ordinary differential and integro-differential equations with constant coefficients. Our findings furthersubstantiate dielectric metasurfaces as promising candidates for miniaturized, two-dimensional, and planar optical analog computing systems that are much thinner than their conventional lens-based counterparts.

Ultra-low threshold polariton condensation

Mark Steger, Brian Fluegel, Kirstin Alberi, David Snoke, Loren Pfeiffer, Kenneth West, and Angelo Mascarenhas

Doc ID: 286973 Received 20 Feb 2017; Accepted 21 Feb 2017; Posted 23 Feb 2017  View: PDF

Abstract: We demonstrate condensation of microcavity polaritons with a very sharp threshold occurring at two orders of magnitude lower pump intensity than previous demonstrations of condensation. The long cavity-lifetime and trapping and pumping geometries are crucial to the realization of this low threshold. Polariton condensation, or ``polariton lasing' has long been proposed as a promising source of coherent light at lower threshold than traditional lasing, and these results indicate some considerations for optimizing designs for lower thresholds.

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

Phase noise analysis of swept-source optical coherence tomography systems

Yuye Ling, Yu Gan, Xinwen Yao, and Christine Hendon

Doc ID: 285433 Received 26 Jan 2017; Accepted 20 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: We proposed a new model to characterize the phase noise in swept-source optical coherence tomography (SS-OCT). It is discovered that the phase stability of SS-OCT is not only determined by signal-to-noise ratio. The model was validated by using both Monte Carlo methods and experiments.

Improvement of the beam quality of a high-pulseenergymid-infrared fractional-image-rotationenhancementZnGeP2 optical parametric oscillator

Martin Schellhorn, Gerhard Spindler, and Marc Eichhorn

Doc ID: 283071 Received 16 Dec 2016; Accepted 20 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: The beam quality of a high-energy mid-infrared ZnGeP2(ZGP) optical parametric oscillator (OPO) has beenimproved by use of a negative lens inside the nonplanarfractional-image-rotation enhancement (FIRE) resonatorcompensating for thermal lensing and gain guidingeffects. With a f = -0.9 m CaF2 lens the beam quality is 1.5and ~ 2 for the resonant signal beam and the nonresonantidler beam, respectively. Up to 33 mJ of midinfraredpulse energy in the 3-5 μm wavelength range isobtained with 94 mJ of pump energy on crystal. This is animprovement of the beam quality by a factor 3 for thesignal beam and ~ 2 for the idler beam compared withoutusing a lens inside the FIRE resonator.

Single-longitudinal-mode ring diamond Raman laser

Ondrej Kitzler, Jipeng Lin, Helen Pask, Richard Mildren, Stephen Webster, Nils Hempler, Graeme Malcolm, and David Spence

Doc ID: 285833 Received 31 Jan 2017; Accepted 20 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: We demonstrate a single-longitudinal-mode ring diamond Raman laser, pumped by a tunable single-mode Ti:sapphire laser. Two methods to acheive unidirectional operation have been demonstrated: increasing gain for one direction using a reinjecting mirror, and increasing loss for one direction using sum-frequency mixing in BBO. Both methods result in a stable single-longitudinal-mode operation.

Phase noise characterization of sub-hertz line-width lasers via digital cross correlation

Xiaopeng Xie, Romain Bouchand, Daniele Nicolodi, Michel Lours, Christophe Christophe ALEXANDRE, and Yann Le Coq

Doc ID: 283242 Received 20 Dec 2016; Accepted 19 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: Phase noise or frequency noise is a key metrics to evaluate the short term stability of a laser. This property is of a great interest for the applications but delicate to characterize, especially for narrow line-width lasers. In this letter, we demonstrate a digital cross correlation scheme to characterize the absolute phase noise of sub-hertz line-width lasers. Three 1,542 nm ultra-stable lasers are used in this approach. For each measurement two lasers act as references to characterize a third one. Phase noise power spectral density from 0.5 Hz to 1 MHz Fourier frequencies can be derived for each laser by a mere change of the lasers configuration. This is the first time showing the phase noise of sub-hertz line-width lasers with no reference limitation. We also present an analysis of the laser phase noise performance.

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.

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.

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.

Simple and seamless broadband optical frequency comb generation using an InAs/InP quantum dot laser

Li Liu, Xiupu Zhang, Tiefeng Xu, ZHENXIANG DAI, Shixun Dai, and Taijun Liu

Doc ID: 284476 Received 13 Jan 2017; Accepted 16 Feb 2017; Posted 23 Feb 2017  View: PDF

Abstract: A simple and seamless broadband optical frequency comb (OFC) generator is proposed and experimentally demonstrated using a C-band Fabry-Perot quantum dot mode-locked laser combined with a dual-driven LiNbO3 Mach–Zehnder modulator. It is demonstrated that 10-dB seamless bandwidth of the OFC is 8.2 nm (1.02 THz), which has 62 and 40 comb lines for frequency spacing of 16.56 and 24.84 GHz respectively. The single-sideband phase noise is as low as -112 dBc/Hz and -108 dBc/Hz at an offset of 10 kHz, respectively for the photodetector-converted 16.56 and 24.84 GHz frequency carrier. Correspondingly, the RF linewidth of the 16.56 and 24.84 GHz frequency carrier is about 251 to 263 Hz, respectively. This suggests that a high-quality OFC is obtained using a simple configuration

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Femtosecond-laser written Tm:KLu(WO4)2 waveguide lasers

Xavier Mateos, Esrom Kifle, Javier Vazquez de Aldana, Airan Rodenas, Pavel Loiko, Sun Young Choi, Fabian Rotermund, Uwe Griebner, Valentin Petrov, Magdalena Aguilo, and Francesc Diaz

Doc ID: 282633 Received 12 Dec 2016; Accepted 02 Feb 2017; Posted 24 Feb 2017  View: PDF

Abstract: Depressed-index channel waveguides with a circular and photonic-crystal-like cladding designs are fabricated in a bulk monoclinic Tm:KLu(WO4)2 crystal by 3D direct femtosecond laser writing. The channel waveguide structures are characterized and laser operation is achieved using external mirrors. In the continuous-wave mode, the maximum output power of 46 mW is achieved at 1912 nm corresponding to a slope efficiency of 15.2% and a laser threshold of only 21 mW. Passive Q-switching of a waveguide with a circular cladding is realized using single-walled carbon nanotubes. Stable 7 nJ/50 ns pulses are achieved at a repetition rate of 1.48 MHz. This first demonstration of ~2 μm fs-laser written waveguide lasers based on monoclinic double tungstates is promising for further lasers of this type doped with Tm3+ and Ho3+ ions.

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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