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Accepted papers to appear in an upcoming issue

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Initial observations of the femtosecond timing jitter at the European XFEL

Henry Kirkwood, Romain Letrun, Takanori Tanikawa, Jia Liu, Motoaki Nakatsutsumi, Moritz Emons, Tomasz Jezynski, Guido Palmer, Max Lederer, Richard Bean, Jens Buck, Samuele di dio cafiso, Rita Graceffa, Jan Gruenert, Sebastian Goede, Hauke Hoeppner, Yoonhee Kim, Zuzana Konopkova, Grant Mills, Mikako Makita, Alexander Pelka, Thomas Preston, Marcin Sikorski, Cedric Takem, Klaus Giewekemeyer, Matthieu Chollet, Patrik Vagovic, Henry Chapman, Adrian Mancuso, and tokushi sato

Doc ID: 358067 Received 30 Jan 2019; Accepted 14 Feb 2019; Posted 14 Feb 2019  View: PDF

Abstract: Intense, ultrashort, and high repetition rate x-ray pulses, combined with a femtosecond optical laser, allow pump-probe experiments with fast data acquisition and femtosecond time resolution. However, the relative timing of the x-ray pulses and the optical laser pulses can be controlled only to a level of the intrinsic error of the instrument which, without characterization, limits the time resolution of experiments. This limitation inevitably calls for a precise determination of relative arrival time, which can be used after measurement for sorting and tagging the experimental data to a much finer resolution than it can be controlled to. The observed root-mean-square timing jitter between x-ray and the optical laser at the SPB/SFX instrument at European XFEL was 308 fs. This first measurement of timing jitter at the European XFEL provides an important step in realizing ultrafast experiments at this novel x-ray source. A method for determining the change in complex refractive index of samples is also presented.

Characterizing pump line phase offset of a single-soliton Kerr comb by dual comb interferometry

Ziyun Kong, chengying bao, Oscar Sandoval, Bohao Liu, Cong Wang, Jose Jaramillo-Villegas, Minghao Qi, and Andrew Weiner

Doc ID: 356985 Received 07 Jan 2019; Accepted 13 Feb 2019; Posted 14 Feb 2019  View: PDF

Abstract: We report phase retrieval of a single-soliton Kerr comb using electric field cross-correlation implemented via dual-comb interferometry. The phase profile of the Kerr comb is acquired through the heterodyne beat between the Kerr comb and an electro-optical comb with a precharacterized phase profile. The soliton Kerr comb has a nearly flat phase profile, and the pump line is observedto show a phase offset which depends on the pumping parameters. The experimental results are in agreement with numerical simulations.

Tm-doped Crystals for mid-IR Optical Cryocoolers and Radiation Balanced Lasers

Saeid Rostami, Alexander Albrecht, Azzurra Volpi, Markus Hehlen, Mauro Tonelli, and Mansoor Sheik-Bahae

Doc ID: 358329 Received 23 Jan 2019; Accepted 13 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: We report the complete characterization of various cooling grade Tm-doped crystals including the first demonstration of optical refrigeration in Tm:YLF crystals. Room temperature laser cooling efficiencies of 1% and 2% (mol) Tm:YLF, and 1% Tm:BYF crystals at different excitation polarizations are measured and their external quantum efficiency and background absorption are extracted. By performing detailed low-temperature spectroscopic analysis of the samples, global minimum achievable temperatures of 160 K to 110 K are estimated. The potential of Tm-doped crystals to realize mid-IR optical cryocoolers and radiation balanced lasers (RBL) in the eye-safe region of the spectrum is discussed, and a promising 2-tone RBL in a tandem structure of Tm:YLF and Ho:YLF crystals is proposed.

Relative intensity noise of continuous-wave interband cascade laser at room temperature

Yu Deng, Binbin Zhao, Yitian Gu, and Cheng Wang

Doc ID: 357406 Received 11 Jan 2019; Accepted 12 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: This work investigates the relative intensity noise (RIN) characteristics of a continuous-wave 3.4 μm interband cascade laser operated at room temperature. The RIN decreases with increasing pump current and reaches down to -130 dB/Hz at a frequency of 450 MHz. In addition, it is proved that the current noise of the laser pump source dominates the RIN for frequencies below 100 MHz. The measured RIN is quantitatively in agreement with the theoretical analysis, from which the gain coefficient and the transparent carrier number of the ICL are extracted.

On collective Rabi splitting in nanolasers and nano-LEDs

Emil Andrè, Igor Protsenko, Alexander Uskov, Jesper Mork, and Martijn Wubs

Doc ID: 355768 Received 20 Dec 2018; Accepted 12 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: We analytically calculate the optical emission spectrum of nanolasers and nano-LEDs based on a model of many incoherently pumped two-level emitters in a cavity. At low pump rates we find two peaks in the spectrum for large coupling strengths and numbers of emitters. We interpret the double-peaked spectrum as a signature of collective Rabi splitting, and discuss the difference between the splitting of the spectrum and the existence of two eigenmodes. We show that an LED will never exhibit a split spectrum, even though it can have distinct eigenmodes. For systems where the splitting is possible we show that the two peaks merge into a single one when the pump rate is increased. Finally, we compute the linewidth of the systems, and discuss the influence of inter-emitter correlations on the lineshape.

On the theory of an adiabatic pulse compressor in theKerr medium with distributed gain and dispersion

Sergei Turitsyn

Doc ID: 355970 Received 28 Dec 2018; Accepted 12 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: A general theory is presented for an optical pulse compressorbased on the adiabatic field evolution in a nonlinearKerr-medium with distributed amplification andvarying dispersion. Analytical expression is derivedlinking parameter of the adiabaticity, gain distributionand dispersion profile.

Lifetime-filtered laser-induced exciplex fluorescence for crosstalk-free liquid-vapor imaging

Terrence Meyer, Alber Douglawi, venkatasubramanian athmanathan, Mikhail Slipchenko, and James Gord

Doc ID: 354806 Received 17 Dec 2018; Accepted 12 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: Laser-induced exciplex fluorescence is a well-established technique for liquid-vapor imaging in evaporating sprays that offers phase-dependent spectrally separated emission. However, the accuracy of this approach is limited by substantial crosstalk from the liquid to vapor phase signals. This work shows the use of a combination of spectral and temporal filtering to reduce this crosstalk by three orders of magnitude and eliminate the need for temperature-dependent crosstalk corrections in the N,N-diethylmethylamine/fluorobenzene system. The relative decay rates of the liquid and vapor signals are quantified and show crosstalk-free imaging for monodisperse evaporating droplets over a wide range of exciplex tracer concentrations.

Development of an X-ray imaging detector to resolve 200 nm line-and-space patterns by using transparent ceramics layers bonded by solid-state diffusion

Takashi Kameshima, Akihisa Takeuchi, Kentaro Uesugi, Togo Kudo, Yoshiki Kohmura, Kenji Tamasaku, Katsuhiro Muramatsu, Takagimi Yanagitani, Makina Yabashi, and Takaki Hatsui

Doc ID: 354814 Received 11 Dec 2018; Accepted 11 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: A high-resolution lens-coupled X-ray imaging detector equipped with a thin-layer transparent ceramics scintillator has been developed. The scintillator consists of a 5 μm thick Ce-doped Lu3Al5O12 layer (Ce:LuAG) bonded onto the support substrate of the non-doped LuAG ceramics by using a solid-state diffusion technique. Secondary electron microscopy (SEM) of the bonded interface indicated that the crystal grains were densely packed without any pores in the optical wavelength scale, indicating a quasi-uniform refraction index across the interface. This guarantees high transparency and minimum reflection, which are essential properties for X-ray imaging detectors. The Ce:LuAG scintillator was incorporated into an X-ray imaging detector coupled with an objective lens with a numerical aperture of 0.85 and an optical magnification of 100. The scintillation lights were imaged onto a CMOS image sensor. The effective pixel size on the scintillator plane was 65 nm. X-ray transmission images of 200 nm line-and-space patterns were successfully resolved. The high spatial resolution was demonstrated by X-ray transmission images of large integrated circuits with the wiring patterns clearly visualized.

Stimulated Brillouin Scattering in layered media: nanoscale enhancement of silicon

Michael Smith, Christian Wolff, Chris Poulton, and C. Martijn de Sterke

Doc ID: 353028 Received 29 Nov 2018; Accepted 11 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: We report a theoretical study of Stimulated Brillouin Scattering (SBS) in general anisotropic media, incorporating the effects of both acoustic strain and local rotation in all calculations. We apply our general theoretical framework to compute the SBS gain for layered media with periodic length scales smaller than all optical and acoustic wavelengths, where such composites behave like homogeneous anisotropic media. We theoretically predict that a layered medium comprising nanometre-thin layers of silicon and As2S3 glass possesses a bulk SBS gain of 1.28 × 10−9 W−1 m. This is more than 500 times larger than the gain coefficient of silicon, and substantially larger than the gain of As2S3. The enhancement is due to a combination of roto-optic, photoelastic, and artificial photoelastic contributions in the composite structure.

Generation of deep ultraviolet sub-2 fs pulses

MARA GALLI, Vincent Wanie, Diogo Pereira Lopes, erik månsson, Andrea Trabattoni, Lorenzo Colaizzi, Krishna Saraswathula, Andrea Cartella, Fabio Frassetto, Luca Poletto, François Légaré, Salvatore Stagira, Mauro Nisoli, REBECA MARTINEZ VAZQUEZ, Roberto Osellame, and Francesca Calegari

Doc ID: 357022 Received 07 Jan 2019; Accepted 11 Feb 2019; Posted 11 Feb 2019  View: PDF

Abstract: We demonstrate the generation of few-cycle deep ultraviolet pulses via frequency upconversion of 5-fs nearinfrared pulses in argon using a laser-fabricated gas cell. The measured spectrum extends from 210 to 340 nm, corresponding to a transform-limited pulse duration of 1.45 fs. We extract from a dispersion-free second order cross-correlation measurement a pulse durationof 1.9 fs, defining a new record in the deep ultraviolet spectral range.

Spatial location of correlations in a random distributed feedback Raman fiber laser

Ilya Vatnik, Oleg Gorbunov, Srikanth Sugavanam, Dmitry Churkin, and Evgeny Podivilov

Doc ID: 356242 Received 11 Jan 2019; Accepted 11 Feb 2019; Posted 14 Feb 2019  View: PDF

Abstract: Nonlinear interactions between different components of multiwavelength radiation is one of the main processes shaping properties of quasi-CW fiber lasers. In random fiber lasers nonlinear influence may be more complicated as there are no distinct longitudinal modes in radiation because of random nature of the feedback. In the present paper, we uncover underlying nonlinear interactions between different spectral components of the random fiber laser radiation by using a multiwavelength random distributed feedback fiber laser. We experimentally characterize nonlinear interactions by cross-correlating intensity dynamics from separate generation lines. Analysis of Pearson correlation functions allows us to spatially locate the area over the fiber laser length in which correlations more likely to occur. This in turn leads us to the conclusion about the main mechanism of spectral correlations – relative intensity noise transfer from the pump wave.

THz-bandwidth switching of heralded single photons

Connor Kupchak, Jennifer Erskine, Duncan England, and Benjamin Sussman

Doc ID: 357896 Received 22 Jan 2019; Accepted 10 Feb 2019; Posted 14 Feb 2019  View: PDF

Abstract: Optically induced ultrafast switching of single photons is demonstrated by rotating the photon polarization via the Kerr effect in a commercially available single mode fiber. A switching efficiency of 97\% is achieved with a $\sim1.7$\,ps switching time, and signal-to-noise ratio of $\sim800$. Preservation of the single photon properties is confirmed by measuring no significant increase in the second-order autocorrelation function $g^{(2)}(0)$. These values are attained with only nanojoule level pump energies that are produced by a laser oscillator with 80\,MHz repetition rate. The results highlight a simple device capable of both high-bandwidth operations and preservation of single-photon properties for applications in photonic quantum processing and ultrafast time-gating or switching.

Silica microsphere cavity based microwave photonic notch filter with ultra-narrow bandwidth and high peak rejection

Bei Yu, Yongchao Chen, Jingshun Pan, Bin Zhang, Fan Li, Lei Wan, Xiaojie Guo, Jianping Li, and Zhaohui Li

Doc ID: 356548 Received 03 Jan 2019; Accepted 10 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: We propose and experimentally demonstrate a microwave photonic (MWP) notch filter based on a silica microsphere cavity. By using high-Q factor (~ 1e7) cavity with diameter of 132um, the filter bandwidth can be easily decreased down to 15 MHz in terms of simple fabrication and flexible coupling. Then we use the advanced modulation technique based on a dual parallel Mach Zehnder modulator (DP-MZM) to further improve the peak rejection (PR). The experimental results show that the MWP notch filter with its PR beyond 55 dB and frequency tunability range over 8 GHz has been achieved in combination of the double sideband (DSB) modulation. To the best of our knowledge, this is a record of PR and bandwidth considered simultaneously for an MWP filter based on a silica microcavities. Thus, the proposed MWP filter will be useful in the fields of microwave photonic signal processing and radar systems etc.

Broadband extended source imaging Mueller-matrix polarimeter

Juan Lopez-Tellez, Russell Chipman, Lisa Li, Scott McEldowney, and Matthew Smith

Doc ID: 359718 Received 07 Feb 2019; Accepted 10 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: An imaging Mueller-matrix polarimeter, named the RGB950, takes images of medium size (tens of cm) objects by using a very bright source, large polarization state generator, and very high quality camera. Its broadband extended light source switches between red, green, blue, and near-infrared light to allow taking polarimetric images for comparison with RGB camera images. The large diffuse source makes shadow transitions gradual and spreads out the specular reflected spot into a larger less conspicuous area.

Measuring nonclassicality with Silicon photomultipliers

Giovanni Chesi, Luca Malinverno, Alessia Allevi, Romualdo Santoro, Maria Bondani, and Massimo Caccia

Doc ID: 341271 Received 05 Oct 2018; Accepted 09 Feb 2019; Posted 11 Feb 2019  View: PDF

Abstract: Detectors' imperfections are expected to be so detrimental in quantum optics applications to prevent the measurement and the exploitation of true quantum properties of light especially in the mesoscopic regime where photon-number resolution is required. We demonstrate that, by a proper analysis of the output signal, nonclassicality of twin-beam states can be detected and exploited with commercial and cost effective silicon-based photon-number-resolving detectors.

Non-invasive measurement of the refractive index of cell-organelles using surface plasmon resonance microscopy

Eva Kreysing and Hossein Hassani

Doc ID: 354421 Received 03 Dec 2018; Accepted 09 Feb 2019; Posted 11 Feb 2019  View: PDF

Abstract: The health of a eucariotic cell depends on the proper functioning of its cell organelles. Characterizing these nanometer to micrometer scaled specialized subunits without disturbing the cell is challenging but can also provide valuable insights regarding the state of a cell. We show, that objective-based scanning surface plasmon resonance microscopy can be used to analyze therefractive index of cell organelles quantitatively in a non-invasive and label-free manner with a lateral resolution at the diffraction limit.

Efficient high-power dual-wavelength yellow-green Nd:YVO4 lasers

Yung-Fu Chen, Yu Cheng Liu, Y. Y. Pan, D. Y. Gu, Hao-Ping Cheng, C. H. Tsou, and Hsing-Chih Liang

Doc ID: 359335 Received 31 Jan 2019; Accepted 08 Feb 2019; Posted 11 Feb 2019  View: PDF

Abstract: An efficient high-power dual-wavelength yellow-green Nd:YVO4 self-Raman laser is inventively developed by using two different lithium triborate (LBO) crystals. The first and second LBO crystals are employed to generate the 559-nm yellow and 532-nm green lasers, respectively. The temperature of the first LBO crystal is fixed at the optimal phase-matching, whereas the temperature of the second LBO crystal is tuned to flexibly control the relative strengths between the 532-nm and 559-nm waves. When the temperature of the second LBO crystal is set for the maximal total output power, the 532-nm and 559-nm output powers are respectively 7.1 W and 2.9 W at a pump power of 31.6 W, corresponding to a conversion efficiency of 31.6%. When the temperature is controlled for the balanced output, the 532-nm and 559-nm powers are respectively 4.3 W and 4.2 W at a pump power of 31.6 W, corresponding to a conversion efficiency of 26.9%.

Digital holographic phase imaging based on phase iteratively enhanced compressive sensing

Zhenpeng Luo, Jianshe Ma, Ping Su, and Liangcai Cao

Doc ID: 353207 Received 30 Nov 2018; Accepted 08 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: Digital holography has been widely applied in quantitative phase imaging (QPI) for monolayer objects within a limited depth. For multilayer imaging, compressive sensing is employed to eliminate defocused image but missing phase information. An phase iteratively enhanced compressive sensing (PIE-CS) algorithm is proposed to achieve phase imaging and eliminate defocused image simultaneously. Linear filtering is firstly applied to the off-axis hologram in spatial domain, and an intermediate reconstructed complex image is obtained. A periodic phase mask is then superimposed on the intermediate reconstructed image to iteratively eliminate the defocused images and recover the object with phase information. The experimental recovery of amplitude and phase of a two-layer sample with as little as 7% of random measurement is demonstrated. The average phase error of the PIE-CS algorithm is analyzed and the results show the feasibility for QPI.

Iterative Wavefront Correction for Complex Spectral Domain Optical Coherence Tomography

Jonas Kanngießer, Maik Rahlves, and Bernhard Roth

Doc ID: 355206 Received 21 Dec 2018; Accepted 08 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: We propose a compact setup for optical wavefront manipulation in a spectral domain OCT system. The system can easily be implemented into existing OCT setups through modification of the source path only. We demonstrate complex-valued OCT signal acquisition and iterative optical wavefront shaping, which allows to locally enhance the OCT signal acquired from within a scattering sample. To our knowledge this combination is presented for the first time. The system lends itself for future imaging studies in strongly scattering media such as biological tissue.

Terahertz Generation Measurements of Multi-layered GeTe-Sb2Te3 Phase Change Materials

Kotaro Makino, Kosaku Kato, Yuta Saito, Paul Fons, Alexander Kolobov, Junji Tominaga, Takashi Nakano, and Makoto Nakajima

Doc ID: 357834 Received 16 Jan 2019; Accepted 08 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: Multi-layered structures of GeTe and Sb₂Te₃ phase change material, also referred to as interfacial phase- change memory (iPCM), provide superior performance for non-volatile electrical memory technology in which the atomically controlled structure plays an important role in memory operation. Here, we report on Tera- hertz (THz) wave generation measurements. 3- and 20- layer iPCM samples were irradiated with a femtosec- ond laser and the generated THz radiation was ob- served. It was found that the THz field from the 20- layer sample was weaker than that from 3-layer sample. This result indicates that the structure of the 20-layer sample was disordered in the successive stacking of lay- ers while 3-layer sample possesses an aligned atomic structure compared with 20-layer sample. We propose that THz generation measurements can be used as an evaluation technique for iPCM.

Overcoming the speckle correlation limit to achieve a fiber wavemeter with attometer resolution

Graham Bruce, Laura O'Donnell, Mingzhou Chen, and Kishan Dholakia

Doc ID: 358352 Received 23 Jan 2019; Accepted 08 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: The measurement of the wavelength of light using speckle is a promising tool for the realization of compact and precise wavemeters and spectrometers. However, the resolution of these devices is limited by strong correlations between the speckle patterns produced by closely-spaced wavelengths. Here, we show how principal component analysis of speckle images provides a route to overcome this limit. Using this, we demonstrate a compact wavemeter which measures wavelength changes of a stabilized diode laser of 5.3 am, eight orders of magnitude below the speckle correlation limit.

Emergence of an optical vortex shaping via a phase jump factor

Hai Ma, Xinzhong Li, Zhang Hao, Jie Tang, Hehe Li, Miaomiao Tang, Jingge Wang, and Yangjian Cai

Doc ID: 356725 Received 03 Jan 2019; Accepted 08 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: Topological charge (TC) of an optical vortex (OV) is a crucial parameter. Through unwrapping the TC definition integral, the parameter of TC is replaced by two factors, namely the phase gradient factor and the phase jump factor. Based on these two factors, we report on a novel OV, referred to as the remainder-phase optical vortex (ROV). The properties of the ROV are studied in depth by adjusting these two factors. Results show that the phase gradient factor determines the total orbital angular momentum (OAM), whereas the phase jump factor decides the number of split unit vortices and reshapes the structure of the OAM distribution. This work provides a novel OV with controllable OAM distribution, which will open up new applications such as particle manipulation, beam shaping and micro-fabrication.

Real-time cross-sectional and en face OCT angiography guiding high-quality scan acquisition

Yali Jia, Xiang Wei, Acner Benech, Shaohua Pi, Tristan Hormel, William Cepurna, David Huang, and John Morrison

Doc ID: 357181 Received 09 Jan 2019; Accepted 08 Feb 2019; Posted 14 Feb 2019  View: PDF

Abstract: Defocusing, vignetting, and bulk motion degrade the image quality of optical coherence tomography angiography (OCTA) more significantly than structural OCT. Assessment of focus, alignment conditions, and the stability of imaging subjects in commercially available OCTA systems are currently based on OCT signal quality alone, without knowledge of OCTA signal quality. This results in low yield rates for further quantification. In this study, we developed a novel OCTA platform based on a graphics processing unit (GPU) for real-time, high refresh rate, B-san-by-B-scan split-spectrum amplitude-decorrelation angiography (SSADA). The GPU provides a real-time display of both cross-sectional and en face images to assist operators during scan acquisition and ensure OCTA scan quality.

A novel polarization beam splitter based on silicon nitride-silica-silicon horizontal slot waveguide

Yang Liu, limin chang, zezheng Li, Lei Liu, huan guan, and Zhi-Yong Li

Doc ID: 356574 Received 02 Jan 2019; Accepted 07 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: A novel compact polarization beam splitter (PBS) based on silicon nitride-silica-silicon horizontal slot waveguide is numerically proposed. In the slot waveguide, the TE mode propagates through the silicon layer while the TM mode is confined in the slot region. By utilizing asymmetric directional coupler (DC) and bent directional coupler (bent DC) consisting of a slot waveguide and a thin silicon waveguide, PBSs with 14.6 μm (DC) and 5.2 μm (bent DC) coupling region are obtained. Without cascading other structures, the DC PBS shows low insertion loss (IL) of 0.4 (0.2) dB and high extinction ratio (ER) of 31.56 (24.61) dB for TE (TM) port around 1.55 mm. While the IL and ER of bent DC PBS are 0.4 (0.15) dB and 35.83 (21.74) dB. The proposed PBSs also have a good fabrication tolerance and broad bandwidth (>40 nm) for extinction ratio of >20 dB.

Femtosecond filamentation and supercontinuum generation in bulk silicon

Agne Marcinkeviciute, Vytautas Jukna, Rosvaldas Suminas, Nail Garejev, Gintaras Tamosauskas, and Audrius Dubietis

Doc ID: 356842 Received 04 Jan 2019; Accepted 07 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: We experimentally study filamentation and supercontinuum generation in bulk silicon crystal using femtosecond mid-infrared pulses with carrier wavelengths in the range of 3.25 - 4.7 μm, in the presence of three, four and five photon absorption. Spectral measurements show a fairly stable blue-shifted cut-off in the 2.5 - 2.7 μm range and gradual increase of the longwave extent with increasing wavelength of the incident pulses, eventually yielding an octave-spanning supercontinuum, covering the wavelength range from 2.5 to 5.8 μm with the input pulses at 4.7 μm. The recorded spatiotemporal intensity distributions of a single filament revealed pulse splitting after the nonlinear focus, in line with the pulse splitting-based filamentation scenario inherent to normally dispersive dielectric nonlinear media.

Bloch oscillations of multidimensional dark soliton wave packets and light bullets

Rodislav Driben, Xuekai Ma, Stefan Schumacher, and Torsten Meier

Doc ID: 355366 Received 14 Dec 2018; Accepted 07 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: The robust propagation of dark solitonic waves featuring Bloch oscillations (BOs) in media with a Kerr nonlinearity is demonstrated. The models considered have a discrete refractive index gradient in one dimension and are continuous in the orthogonal direction or directions. Such systems can be realized in photonic systems, where temporal dispersion of normal type is able to support dark solitons. The demonstrated effects may also appear in the dynamics of Bose-Einstein condensates (BEC) where dark solitons appear due to the joint action of diffraction and a self-defocusing nonlinearity. Our analysis shows furthermore that a periodic variation of the refractive index gradient in the propagation direction allows to realize the spatial analogue of dynamical localization. In addition, we demonstrate that dark solitons serve as excellent carriers for light bullets of peculiar dark-bright type that can also feature robust BOs.

Wavelength scaling of terahertz pulse energies delivered by two-color air plasmas

Alisee Nguyen, Korbinian Kaltenecker, Jean-Christophe Delagnes, Binbin Zhou, Eric Cormier, Nikita Fedorov, Rodrigue Bouillaud, Dominique Descamps, Illia Thiele, Stefan Skupin, Peter Jepsen, and Luc Berge

Doc ID: 355083 Received 12 Dec 2018; Accepted 07 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: We address the long-standing problem of the anomalous growth observed in the terahertz (THz) energy yield of air plasmas created by two-color laser pulses, as the fundamental wavelength λ₀ is increased. In order to ensure reproducibility, we used two distinct optical parametric amplifier (OPA) systems. We report THz energies scaling like λ₀^α with large exponents 5.6≤α≤14.3, which departs from the growth in λ₀² expected from the photocurrent theory. By means of comprehensive 3D simulations, we demonstrate that the changes in the laser beam size, pulse duration and phase matching conditions in the second harmonic generation process when tuning the OPA's carrier wavelength can lead to these high scaling powers. The value of the phase angle between the two colors reached at the exit of the doubling crystal turns out to be crucial and even explains non-monotonic behaviors in the measurements.

Laser fabrication of graphene-based electrothermal actuators enabling predicable deformation

Lin Zhu, Yuan-Yuan Gao, Bing Han, Yonglai Zhang, and Hong-Bo Sun

Doc ID: 355166 Received 13 Dec 2018; Accepted 07 Feb 2019; Posted 11 Feb 2019  View: PDF

Abstract: Electrothermal actuators (ETAs) that can convert electric energy into mechanical works have been extensively studied for their great potential in artificial muscles and robotics. However, the production of ETAs that enable complex and predictable deformation are still challenging. In this paper, an ETA based on reduced graphene oxide (RGO) and polyethylene (PE) bimorph is developed through a facile laser-scribing method. Since the laser-scribing technology permits flexible patterning, conductive RGO electrodes with complex circuit patterns can be readily produced on a thermally active PE film, forming an ETA capable of fast and reversible deformation. In addition, the laser scribed ETA demonstrated orientation-defined bending performance, enabling more sophisticated deformation control. The laser-scribing of GO has opened up a new way to produce ETAs towards cutting-edge applications such as soft robotics and intelligent systems.

High-Speed Waveguide Integrated Silicon Photodetector on SiN-SOI Platform for Short Reach Datacom

Avijit Chatterjee, Saumitra Saumitra, Sujit Kumar Sikdar, and Shankar Kumar Selvaraja

Doc ID: 357170 Received 09 Jan 2019; Accepted 07 Feb 2019; Posted 11 Feb 2019  View: PDF

Abstract: We present waveguide integrated high-speed Si photodetector integrated with silicon nitride (SiN) waveguide on SOI platform for short reach data communication in 850 nm wavelength band. We demonstrate a waveguide couple Si pin photodetector responsivity of 0.44 A/W at 25 V bias. The frequency response of the photodetector is evaluated by coupling of a femtosecond laser source through SiN grating coupler of the integrated photodetector. We estimate a 3dB bandwidth of 14 GHz at 20 V bias, highest reported bandwidth for a waveguide integrated Si photodetector. We also present detailed optoelectronic DC and AC characterisation of the fabricated devices. The demonstrated integrated photodetector could enable an integrated solution for scaling of short reach data communication and connectivity.

A high dynamic range and wavelength-reused bidirectional radio-over-fiber link

Jianping Yao and Nianqiang Li

Doc ID: 355803 Received 20 Dec 2018; Accepted 06 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: We propose and experimentally demonstrate a bidirectional radio-over-fiber (RoF) link based on a Sagnac loop incorporating a polarization modulator (PolM) to generate simultaneously a polarization-modulated optical signal and an unmodulated optical signal for wavelength reuse and for increasing the dynamic range. Thanks to the travelling-wave nature of the PolM, a polarization-modulated optical signal and an unmodulated optical signal are generated at the output of the Sagnac loop, which are combined at a polarizer and detected at a photodetector (PD). By controlling the powers of the two optical signals, the third order intermodulation distortion (IMD3) terms can be fully suppressed, to increase the dynamic range for downstream transmission. The unmodulated optical signal is reused for upstream transmission. A bidirectional RoF link to transmit a 2.5 Gb/s 16QAM downstream and upstream signals, and a 3.5 Gb/s 128 subcarrier orthogonal frequency division multiplexing (OFDM) QPSK downstream and upstream signals using a single wavelength over 10.5 km single-mode fiber are experimentally demonstrated. The transmission performance versus the dynamic range is also studied.

High-efficiency high-repetition-rate gain-switched operation around 3 µm in Cr2+:CdSe single-crystal laser pumped by fiber-laser-pumped Ho3+:YAG laser

Oleg Antipov, Ilya Eranov, M. Frolov, Yuriy Korostelin, Vladimir Kozlovsky, and Yan Skasyrsky

Doc ID: 356029 Received 26 Dec 2018; Accepted 06 Feb 2019; Posted 06 Feb 2019  View: PDF

Abstract: We report the efficient gain-switched high-repetition-rate Cr2+:CdSe single-crystal laser operating around 3 µm and pumped at 2.09 µm by a fiber-laser-pumped Ho3+:YAG laser. Average power of up to 6 W with optical-to-optical efficiency of 67% at 2.65-2.85 µm was achieved in the low-quantum-defect pumped Cr2+:CdSe laser with nanosecond pulses at 8 kHz repetition rate. Wavelength tunability from 2.5 µm to 3.15 µm was demonstrated using a set of cavity mirrors and an intracavity Lyot filter.

Compact snapshot optically replicating and remapping imaging spectrometer (ORRIS) using a focal plane continuous variable filter

Tingkui Mu, Feng Han, Donghao Bao, Chunmin Zhang, and Rongguang Liang

Doc ID: 356576 Received 03 Jan 2019; Accepted 05 Feb 2019; Posted 06 Feb 2019  View: PDF

Abstract: Snapshot spectral imaging is a cutting-edge parallel acquisition technique to acquire the three-dimensional (3D) datacube (x, y, λ) in real time. In this letter, a novel snapshot spectral imaging technique, Optically Replicating and Remapping Imaging Spectrometer (ORRIS), is presented. It is based on the combination of the shifting of subimages replicated by a specially designed lenslet array (LA) and the filtering of each subimage by a focal plane continuous variable filter (CVF). The 3D datacube is recovered just using a simple image remapping process. The use of the LA and the focal plane CVF makes the system compact and miniature, and achieves hyperspectral imaging. A handheld proof-of-principle prototype is built. The ORRIS prototype covers a Vis/NIR wavelength region 380 to 860 nm with 80 spectral channels with a spatial resolution of 400 × 400 pixels. The prototype is validated by measuring outdoor static and dynamic scenes.

Construction of cascaded Fabry-Perot interferometers by four in-fiber mirrors for high temperature sensing

Dongning Wang and Jun Deng

Doc ID: 357492 Received 11 Jan 2019; Accepted 05 Feb 2019; Posted 06 Feb 2019  View: PDF

Abstract: An optical fiber high temperature sensor is proposed and demonstrated by use of cascaded Fabry-Perot interferometers based on four in-fiber mirrors fabricated by femtosecond laser inscription. The output fringe pattern exhibits dominant/highly distinguishable dip wavelength, which helps in unambiguous measurement beyond the free spectral range. The device has an excellent thermal stability in high temperature up to 1100°C and the temperature sensitivity obtained is 9.91 pm/°C, within the temperature range between 100 and 400°C, and 15.88 pm/℃, within the temperature range between 400 and 1100℃, respectively. The device is featured with compact size, simple fabrication and convenient operation, which makes it attractive for monitoring of extreme environment.

Giant-pulse generation in diode-pumped cesium vapor laser using the cavity dumping technique

Masamori Endo

Doc ID: 353201 Received 29 Nov 2018; Accepted 04 Feb 2019; Posted 08 Feb 2019  View: PDF

Abstract: Cavity dumping has been demonstrated in a diode-pumped alkali laser (DPAL) using a Pockels cell. We generated a 14 ns FWHM pulse with a peak power of 77 W from a 3.1 W continuous wave (CW) cesium DPAL. Due to the limitation of the high-voltage power supply, the pulse repetition rate is restricted to 100 Hz. Periodic spikes contained in the temporal profile of the pulse were observed, presumably due to interference between the two longitudinal modes. As a result, the peak power of the pulse was enhanced from the average power stored in the optical resonator. To the best of our knowledge, this is the first demonstration of giant-pulse generation in DPALs.

A Picosecond Slab Regenerative Amplifier Using a large fundamental mode Stable-unstable Hybrid Cavity

qinjun peng, Ke Liu, Zhao Liu, Xiao-Jun Wang, Bo Yong, Jing Yang, Li He, yang yu, Fengliang Xu, Da Cui, and Xu Zuyan

Doc ID: 356578 Received 02 Jan 2019; Accepted 04 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: Slab gain mediums with large aspect ratio were difficult to be adopted in ultrafast regenerative amplifiers due to the obstacle of mode matching with the seed beam. We proposed that an unstable cavity could be employed to solve this difficulty by taking the advantage of its large fundamental mode volume. In this way, An Nd:YVO4 slab based picosecond regenerative amplifier have been successfully demonstrated using a stable-unstable hybrid cavity. The maximum average output power of 10.5 W was achieved at the repetition rate of 10 kHz. The beam quality factor M2 was measured to be 1.54 in the stable direction and 2.26 in the unstable direction.

Distributed vibration measurement based on coherent multi-slope assisted BOTDA with large dynamic range

Hua Zheng, Dan Qi Feng, Jingdong Zhang, Tao Zhu, Yongzhong Bai, Dingrong Qu, Xianbin Huang, and FENG QIU

Doc ID: 356377 Received 28 Dec 2018; Accepted 04 Feb 2019; Posted 05 Feb 2019  View: PDF

Abstract: We propose a novel technique to enhance the dynamic range of coherent slope assisted BOTDA. A multi-tone probe and a reference wave are launched into the fiber under test (FUT), after interacting with pump pulse, the Brillouin gain as well as Brillouin phase shift of each tone can be demodulated simultaneously. In light of this, the strain information can be determined by the Brillouin phase-gain ratio (BPGR) of each tone. In the experiment, a three-tone probe with 60 MHz interval is used, effective measurement frequency span larger than 180 MHz is verified in ~2km single mode fiber with 2.5 m spatial resolution and 1.5 kHz sampling rate to strain. Vibration signal with 41 Hz frequency and 2546 με amplitude is successfully demodulated.

Applicability of the constitutive equations for the determination of the material properties of optically active materials

Chris Sturm, Vitaly Zviagin, and Marius Grundmann

Doc ID: 354711 Received 07 Dec 2018; Accepted 04 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: For the description of the optical response of optically active media, different constitutive equations have been proposed in the literature. However, the validity of these different sets of equation is still under debate. Here, we demonstrate on potassium titanyl phosphate (KTiOPO₄, KTP) by means of ellipsometry that only the symmetric constitutive equation describes the observed spectra properly and allows the unique determination of the gyration tensor.

Precise in vivo Tissue Micro-Raman Spectroscopy with Simultaneous Reflectance Confocal Microscopy Monitoring Using a Single Laser

Zhenguo Wu, Liwei Jiang, Wenbo Wang, Jianhua Zhao, Harvey Lui, and Haishan Zeng

Doc ID: 356897 Received 21 Jan 2019; Accepted 04 Feb 2019; Posted 14 Feb 2019  View: PDF

Abstract: Raman spectroscopy provides molecular finger-printing of biological tissues. To achieve high spatial resolution, confocal Raman spectroscopy (micro-Raman) has been developed. To guide where micro-Raman is acquired, imaging guidance is necessary, especially for high scattering biological tissue. reflectance confocal microscopy (RCM) has been integrated with micro-Raman. However Existing systems do not allow point of interest micro-Raman measurement with simultaneous RCM guidance. Here we demonstrate how a single laser can be used to localize and acquire micro-Raman signals within tissue with simultaneous real-time RCM imaging. Applications of this RCM-guided micro-Raman system for ex vivo samples and in vivo skin measurements are presented.

No-prior single-shot scattering imaging beyond memory effect

Xiaoyu Wang, Xin Jin, Junqi Li, xiaocong lian, xiangyang ji, and Qionghai Dai

Doc ID: 358010 Received 17 Jan 2019; Accepted 03 Feb 2019; Posted 13 Feb 2019  View: PDF

Abstract: Imaging beyond the memory effect is critical to seeing through the scattering media. Methods proposed before are suffered from invasive point spread functions measurement or availability of prior information of the imaging targets. In this letter, we propose a prior-free single shot scattering imaging method to exceed the memory effect range. The autocorrelation of each imaging target is separated blindly from the autocorrelation of the recorded dual-target speckle via Fourier spectrum guessing and iterative energy constrained compensation. Working together with phase retrieval, dual targets exceeding the memory effect range can be reconstructed via single shot. The effectiveness of the algorithm is verified by simulated experiments and real imaging system.

Artifact-free imaging through a bone-like layer by using an ultrasonic-guided photoacoustic microscopy

Chao Tao, XiaoJun Liu, and Wentian Chen

Doc ID: 354740 Received 07 Dec 2018; Accepted 03 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: Reflection artifacts caused by a bone-like layer badly degrade the quality of photoacoustic image in many biomedical applications, e.g., in vivo brain imaging through skull. We proposed an ultrasonic-guided photoacoustic microscopy (UG-PAM) to remove the reflection artifacts. This system is developed from a dual-mode microscopy, integrating a scanning acoustic microscopy with a conventional PAM. Based on similar propagation characteristics of photoacoustic signal and ultrasonic echo in a bone-like layer, we employ the ultrasonic echo as a filter to remove the multiple-reflected artifacts in photoacoustic signals and obtain artifact-free images. An experiment of imaging a phantom below a bone-like film is used to demonstrate the performance of this method. The results suggest that this method can achieve an artifact-free image of the phantom under the film successfully, whereas the conventional PAM fails to achieve clean images of the vessel-like absorbers. This study might improve the imaging quality of PAM in many biomedical applications.

Anomalous blue-shift of terahertz whispering-gallery modes via dielectric and metallic tuning

Dominik Vogt, Angus Jones, Harald Schwefel, and Rainer Leonhardt

Doc ID: 355328 Received 14 Dec 2018; Accepted 03 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: The vast majority of resonant systems show a red-shift for the resonance frequency when a perturbation, e.g. losses, are introduced to the system. In contrast, here we report for the first time the experimental demonstration of both red- and anomalous blue-shifting of whispering-gallery modes (WGMs) using dielectric and metallic substrates. The maximum blue-shift is more than three times as large as the expected red-shift, proving that the anomalous blue-shift is more than a peculiar curiosity. The experiments are performed in the terahertz (THz) frequency range with coherent continuous-wave spectroscopy. The results establish dielectric and metallic tuning as a novel, and viable approach to tune high quality (high-Q) WGMs, and provide valuable insights into the anomalous blue-shift of WGM cavity systems. The tuning capabilities for these compact monolithic resonators is of significant interest for fundamental science and technological applications alike.

Parametric Amplification in Large-Aperture Diffusion Bonded Periodically Poled Crystals

Eli Sobolev, Pavel Komm, Salman Noach, and Gilad Marcus

Doc ID: 357109 Received 08 Jan 2019; Accepted 01 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: With conventional poling techniques of pyroelectric crystals, the thickness of the periodically poled crystals is typically limited to 0.5–1 mm. Such a small crystal’s aperture limits the amount of energy/power that this device may deliver. Here we discuss diffusion bonding as an alternative method to achieve a wider periodically poled crystal, with virtually unlimited width. It is shown that the amplified signal preserved a good beam profile despite a possible phase-shift between the stitched crystals. This technique may be extended to larger aperture optical parametric amplifiers and allows for high-energy output from periodically poled crystals.

Low-loss and low-crosstalk triplexer on silicon

Dajian Liu, Ming Zhang, and Daoxin Dai

Doc ID: 356625 Received 03 Jan 2019; Accepted 01 Feb 2019; Posted 06 Feb 2019  View: PDF

Abstract: A low-loss and low-crosstalk silicon triplexer is proposed and realized for wavelength-division-multiplexed optical systems with the wavelength-channels of 1310 nm, 1490 nm and 1550 nm. The proposed on-chip triplexer is composed of three cascaded multimode-waveguide-grating-based (MWG) filters, which consist of a multimode waveguide grating and a two-mode (de)multiplexer. For all the three wavelength-channels, flattop spectral responses are achieved experimentally and their 3-dB bandwidths are 89 nm, 19 nm and 7 nm, respectively. The excess losses are less than 1 dB. The crosstalks are −36~−27 dB and −30 dB for channels 1490 nm and 1550 nm, respectively.

High-power Faraday isolator on a uniaxial CeF3 crystal

Alexey Starobor, Evgeniy Mironov, and Oleg Palashov

Doc ID: 353038 Received 28 Nov 2018; Accepted 01 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: We have created the first high-power Faraday isolator on an anisotropic magneto-optical element. The isolator is based on one magneto-optical element of a uniaxial CeF3 crystal and ensures an isolation degree of 30 dB at a record high average laser radiation power of 700 W. The limitations due to the anisotropic nature of the crystal do not impose significantly more stringent requirements either for the beam or the magneto-optical element

Single-shot Compressed Optical-Streaking Ultra-high-speed Photography

Xianglei Liu, Jingdan Liu, Cheng Jiang, Fiorenzo Vetrone, and Jinyang Liang

Doc ID: 354435 Received 05 Dec 2018; Accepted 01 Feb 2019; Posted 04 Feb 2019  View: PDF

Abstract: Single-shot ultra-high-speed imaging is of great significance to capture transient phenomena in physics, biology, and chemistry in real time. Existing techniques, however, have a restricted application scope, a low sequence depth, or a limited pixel count. To overcome these limitations, we developed single-shot compressed optical-streaking ultra-high-speed photography (COSUP) with an imaging speed of 1.5 million frames per second, a sequence depth of 500 frames, and an (x,y) pixel count of 0.5 megapixels per frame. COSUP’s single-shot ultra-high-speed imaging ability was demonstrated by recording single laser pulses illuminating through transmissive targets and by tracing a fast-moving object. As a universal imaging platform, COSUP is capable of increasing imaging speeds of a wide range of CCD and CMOS cameras by four orders of magnitude. We envision COSUP to be applied in widespread applications in biomedicine and materials science.

Single-pixel imaging with sampling distributed over simplex vertices

Krzysztof Czajkowski, Anna Pastuszczak, and Rafal Kotynski

Doc ID: 352772 Received 23 Nov 2018; Accepted 31 Jan 2019; Posted 01 Feb 2019  View: PDF

Abstract: We propose a method of reduction of experimental noise in single-pixel imaging by expressing the subsets of sampling patterns as linear combinations of vertices of a multidimensional regular simplex. This method may be also directly extended to complementary sampling.The modified sampling consists only of non-negative patterns. The measurement becomes theoretically independent of the ambient illumination, and in practice becomes more robust to the varying conditions of the experiment. We show how the optimal dimensionality of the simplex depends on the level of measurement noise. We present experimental results of single-pixel imaging using binarized sampling and a real-time reconstruction with the Fourier domain regularized inversion method.

Live electrooptic imaging with a low coherence optical LO signal source for suppression of interference noises

Masahiro Tsuchiya, Shinji Fukui, and Muneo Yorinaga

Doc ID: 356902 Received 04 Jan 2019; Accepted 31 Jan 2019; Posted 01 Feb 2019  View: PDF

Abstract: Reported in this paper is the first application of a low coherence optical local oscillator signal source to the live electrooptic imaging (LEI) scheme, where high frequency electric field (EF) distributions are visualized in real time. A fiber-optic super luminescent diode (SLD) in conjunction with a LiNbO₃ Mach-Zehnder modulator (MZM) was found to work well for the real-time imaging of GHz-rang EF distributions with high suppression of interference pattern image noises (IPINs), which have been long a problem to be solved. While the SLD-based LEI system works up to the MZM bandwidth (10 GHz), IPINs caused by microscopic defects in an electrooptic sensor appear suggesting a limitation given by the SLD coherence length.

Non-linear target count rate estimation in single photon lidar due to first photon bias

Rory Barton-Grimley, Jeffrey Thayer, and Matthew Hayman

Doc ID: 355700 Received 20 Dec 2018; Accepted 31 Jan 2019; Posted 31 Jan 2019  View: PDF

Abstract: The use of time-tagging single photon lidar for high resolution ranging and backscattered count rate measurements requires special attention to mitigate biases and distortions typically not seen in full-waveform lidar sensors. Specifically, sub-pulse sampling and the presence of non-zero receiver dead-time generates an effect named First Photon Bias (FPB). FPB manifests itself as an intensity induced ranging offset, previously documented, and a non-linear count rate with integrated distribution distortions. These combined effects require special attention when integrating lidar point clouds to accurately estimate backscattered signal strength and true range. The presented work indicates that correcting solely for the introduced range bias does not address the non-linear shape distortions in the accumulated photon distribution. Analyses of distribution widths and estimated signal strengths must consider both effects. We present an analysis that demonstrates the cause and effect of the FPB on photon time-tagging integrated photon distributions using the Monte-Carlo method, relates the modeled results to previously published data and statistics, and provides a framework for interpreting range and backscattered signal strength measurements from these sensors.

Differential method for freeform optics applied to two-mirror off-axis telescope design

Jean-Baptiste Volatier and Guillaume Druart

Doc ID: 357770 Received 15 Jan 2019; Accepted 31 Jan 2019; Posted 31 Jan 2019  View: PDF

Abstract: In this letter we present a method to design the freeform surfaces of an off-axis unobscured two-mirror telescope by integration of a system of differential equations. The system is derived from the differentiation of the Fermat path's principle and is integrated as an ordinary differential equation problem. The method is used to design the freeform surfaces of a telescope whose performance is verified in off-the-shelf optical design software (Zemax).

High Extinction Electro-optic Modulation on Lithium Niobate Thin Film

Mingwei Jin, jiayang chen, Yong Meng Sua, and Yuping Huang

Doc ID: 355544 Received 18 Dec 2018; Accepted 30 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: Integrated nanophotonics using lithium niobate on insulator promises much-awaited solutions for scalable photonics techniques. One of its core functions is electro-optic modulation, which currently suffers limited extinction (<30 dB) due to inevitable fabrication errors. To compensate for them, we exploit a cascaded Mach-Zehnder interferometry design to achieve 50 dB modulation extinction on chip for a wide range of wavelengths. Together, its favorable features of chip-integration, high extinction, broadband, and good stability may prove valuable in many flourishing photonics applications.

Large scale piston error detection technology for segmented optical mirrors via convolutional neural networks

Dequan Li, Shuyan Xu, Dong Wang, and Dejie Yan

Doc ID: 358119 Received 18 Jan 2019; Accepted 30 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: In the cophasing of the segmented optical mirrors, the Shack-Hartmann wavefront sensor is not sensitive to the submirrors piston error, and the large range piston errors beyond the cophasing detection range of phase diversity(PD) algorithm. It is necessary to introduce specific sensors (e.g., curvature sensors), but they greatly increase the complexity of the optical system. In this paper, we introduce the convolutional neural network (CNN) to distinguish the piston error range of each submirror. To get rid of the dependence of the CNN dataset on the imaging target, We construct the feature vector by the in-focal and the defocused images. The method surpass the fundamental limit of the detection range by using different wavelengths. The simulation results show that the CNN recognition accuracy of the corresponding submirror piston error range are around 100%, indicating that the method is effective.

High-transmittance double-layer frequency-selective surface based on interlaced multi-ring metallic mesh

Xi Lu, Yeshu Liu, Lu Zhengang, Yilei Zhang, He yan Wang, Ruidong Ji, and Jiubin Tan

Doc ID: 354978 Received 18 Dec 2018; Accepted 30 Jan 2019; Posted 01 Feb 2019  View: PDF

Abstract: In this work, we proposed an optically transparent double-layer frequency-selective surface (FSS) based on interlaced multi-ring metallic mesh. By changing the large metal area of a conventional double-layer FSS into triangular-orthogonal distributed basic rings and nested rotated sub-rings, we achieved an FSS with high optical transmittance and low normalized high-order diffraction intensity while maintaining a flat passband and steep transition band. The results showed that our fabricated FSS had a normalized visible transmittance of 90.31%, stable filtering passband of ~33.9 GHz, 3-dB bandwidth of 13.4 GHz, and uniform diffraction distribution, which are favorable characteristics for optically transparent FSS applications.

Confocal fluorescence microscopy for geometry parameter measurements of submerged micro-structures

Merlin Mikulewitsch, Andreas Fischer, and Axel von Freyberg

Doc ID: 355899 Received 21 Dec 2018; Accepted 29 Jan 2019; Posted 01 Feb 2019  View: PDF

Abstract: Due to the challenging environment of micro-manufacturing techniques where the workpiece is submerged in a fluid, a contactless in situ capable measurement is required for quality control. However, the in situ conditions and the small specimen dimensions hinder the use of conventional metrology. Confocal fluorescence microscopy is shown to enable step height measurements of a specimen submerged in a 2.6 mm thick fluid layer with an uncertainty of 8.8 μm by fitting a model of the fluorescence intensity to the measured signal. To ascertain the potential of the proposed measurement approach, the minimal achievable uncertainty of 0.07 μm for a shot noise limited signal is derived.

A Highly Sensitive Liquid Crystal Optically Addressed Spatial Light Modulator for Infrared to Visible Image Up-Conversion

Asi Solodar, Hadar Manis‐Levy, Gabby Sarusi, and Ibrahim Abdulhalim

Doc ID: 349632 Received 13 Nov 2018; Accepted 29 Jan 2019; Posted 01 Feb 2019  View: PDF

Abstract: A liquid crystal optically addressed spatial light modulator (LC-OASLM) based on InGaAs photodiodes array operating at low light levels, is investigated in the short wavelength infrared (SWIR) spectral band to serve as SWIR to visible imaging up-conversion device. It consists of InGaAs/InP heterojunction photodetectors array sandwiched with nematic LC layer. The photodiodes array composed of a 640×512 InGaAs/InP heterojunctions, grown on InP substrate with a 15μm pitch. A full up-converted visible image in stills and video modes were demonstrated with SWIR light intensities as low as 70nW/cm2 or less than pW/pixel. The influence of operation frequency on the performance of the device was found theoretically and experimentally to be crucial for a proper operation of the device. The optimum sensitivity and contrast of the device are found to be at certain frequency around 70Hz. To the best of our knowledge this is the first time that such a high performance upconversion device is presented and actual visible images are obtained

Generation of multiple solitons using competing nonlocal nonlinearities

Alessandro Alberucci, Jisha Pannian, Stefan Nolte, Jeroen Beeckman, Kristiaan Neyts, and Frederik Van Acker

Doc ID: 355466 Received 14 Dec 2018; Accepted 29 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: We discuss the dynamics of fundamental Gaussian beams launched in saturable and nonlocal nonlinear media. Solely in the presence of a self-focusing saturable nonlinearity, the breathing solitons undergo strong deformation. The addition of a defocusing nonlinearity leads to the generation of couples of solitons. Experimentally we demonstrate in nematic liquid crystals the formation of multiple spatial solitons starting from a bell-shaped input, with both direction and number of filaments depending on the input power, confirming the theoretical predictions.

Artifacts in speckle-tracking and multi-aperture Doppler OCT imaging of lateral motion

Hendrik Spahr, Clara Pfäffle, Gereon Hüttmann, and Dierck Hillmann

Doc ID: 343038 Received 28 Jan 2019; Accepted 29 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: Optical coherence tomography can detect lateral motion by either tracking the speckle pattern or by multi-aperture Doppler-OCT. Both methods are commonly used, but lead to valid results only if either the sample is exactly focused and imaged without any aberrations or axial motion is identical in the entire field of view. Though the former condition can only be fulfilled for one depth, speckle tracking and multi-aperture Doppler OCT have often been applied to entire B-scans or volumes. A numerical simulation of the artifact, which is induced by a certain defocus, reveals a surprisingly large effect. The physical origin of this artifact is explained by mathematical descriptions of the imaging process.

Real-time Electrical Tuning of an Optical Spring on a Monolithically integrated Ultrahigh Q Lithium Nibote Microresonator

Zhiwei Fang, Sanaul Haque, Jintian Lin, Rongbo Wu, Jianhao Zhang, Min Wang, Junxia Zhou, Muniyat Rafa, Tao Lu, and Ya Cheng

Doc ID: 356656 Received 02 Jan 2019; Accepted 29 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: We report an ultrahigh quality (Q~10^7) factor lithium niobate (LN) whispering gallery microresonator monolithically integrated with in-plane microelectrodes. With the fabricated device, coherent regenerative optomechanical oscillation with an effective mechanical quality (Q_m) factor as high as 2.86×10^8 is observed in air. We demonstrate real-time electrical tuning of the optomechanical frequency with an electro-mechanical tuning efficiency around -134 kHz/100V.

Weak randomness impacts the security of reference-frame-independent quantum key distribution

Hong-Wei Li, Chunmei Zhang, Qin Wang, and Wen-Bo Wang

Doc ID: 356742 Received 03 Jan 2019; Accepted 29 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: Perfect randomness is of great significance in various quantum key distribution (QKD) protocols. In this Letter, we investigate the effect of weak randomness on the state preparation in reference-frame-independent QKD (RFI-QKD), which may be implemented with imperfect random numbers or quantum state encoding devices. In the scenario of weak randomness, the maximal amount of information the eavesdropper can acquire should be carefully evaluated. With practical experimental parameters, we demonstrate that even a small proportion of weak randomness will impact the security of RFI-QKD seriously. Furthermore, we briefly study the side-effect of weak randomness on RFI measurement-device-independent QKD (RFI-MDI-QKD), and simulation results show that weak randomness damages the performance of RFI-MDI-QKD more critically than that of RFI-QKD.

Far-field thermal emission from a semiconductor hyperbolic metamaterial

Patrick Sohr, Chi Ian Ip, and Stephanie Law

Doc ID: 357030 Received 07 Jan 2019; Accepted 28 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: This paper investigates the far-field thermal emission of a Si:InAs/AlSb semiconductor hyperbolic metamaterial (HMM). Understanding the thermal emission of HMMs could result in advancements in thermophotovoltaics and thermal emission management. In recent years, there has been controversy about whether the large wavevector volume plasmon polariton (VPP) modes that exist in HMMs could be outcoupled into the far field using a grating and give rise to super-Planckian thermal emission. In this experiment, gold gratings with varying periods were applied to the surface of the HMM to out-couple the VPP modes into free space. The sample was heated to 185C, and the polarized thermal emission was measured using Fourier transform infrared spectroscopy. The HMM showed minimal angle sensitivity up to 50. The sample showed multiple peaks in emissivity which corresponded to the resonant wavelengths of the VPP modes, demonstrating out-coupling from these modes. Although these modes showed increases in the emissivity, super-Planckian emission was not observed. Emission from VPP modes could be leveraged to create materials with designer emissivity profiles.

Laser-processed diffractive lenses for the frequency range of 4.7 THz

Simonas Indrišiūnas, Heiko Richter, Ignas Grigelionis, Vytautas Janonis, Linas Minkevicius, Gintaras Valusis, Gediminas Raciukaitis, Till Hagelschuer, Heinz-Wilhelm Hübers, and Irmantas Kašalynas

Doc ID: 354497 Received 06 Dec 2018; Accepted 28 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: The development of diffractive lenses for the upper terahertz (THz) frequency range above 1 THz was successfully demonstrated by employing a direct laser ablation (DLA) technology. Two types of samples such as the Soret zone plate lens (SZPL) and the multi-level phase-correcting Fresnel lens (MPFL) were fabricated of a metal foil and crystalline silicon, respectively. The focusing performance along the optical axis of a 4.745 THz quantum cascade laser (QCL) beam with respect to the positioning angle of the sample was studied by using a real-time micro-bolometric camera. A binary-phase profile sample demonstrated values of the focusing gain and focused-beam size up to 25 dB and 0.15 mm (2.4 lambda), respectively. The increase of the phase quantization level to eight led to higher (up to 29 dB) focusing gain values without a measurable increase of optical losses. All the samples were tolerant to misalignment as large as 10 degree of oblique incidence with a focusing power drop not larger than 10 %. The results pave the way for new applications of industry-ready DLA technology in the entire THz range.

Reservoir Computing based on Transverse Modes in a Single Optical Waveguide

Charis Mesaritakis and Dimitris Syvridis

Doc ID: 355898 Received 20 Dec 2018; Accepted 28 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: In this work, a passive reservoir computing scheme is presented, that relies on the excitation and guiding of transverse modes in a large cross-section photonic waveguide. The optical modes act similar to conventional waveguide based reservoir nodes, whereas random defects act as the operational equivalent of inter-node connections. Therefore, the proposed scheme’s number of nodes and connection can scale with the waveguide’s volume, contrary to planar implementations. The principle of operation, alongside the role of modes-defects to performance is validated through a numerical model, whereas the classification of time-dependent, 2D analog/digital image streams, is used as an application relevant benchmark test

Purely Kerr nonlinear models admitting flat-topsolitons

Liangwei Zeng, Jianhua Zeng, Yaroslav Kartashov, and Boris Malomed

Doc ID: 348649 Received 19 Oct 2018; Accepted 28 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: We elaborate one- and two-dimensional (1D and 2D) models of media withself-repulsive cubic nonlinearity, whose local strength is subject tospatial modulation that admits the existence of flat-top (FT) solitons ofvarious types, including fundamental ones, 1D multipoles, and 2D vortices.Previously, solitons of the FT type were only produced by models withcompeting nonlinearities. The present setting may be implemented in opticsand Bose-Einstein condensates. The 1D version gives rise to an exact analytical solution for a stable FT soliton, and generic families may be predicted by means of the Thomas-Fermi approximation. In an accurate form, solitons and their stability are obtained as numerical solutions. Fundamental solitons and 1D multipoles with $k=1$ and $2$ nodes, as well as vortices with winding number $m=1$, are completely stable. For multipoles with $k\geq 3$ and vortices with $m\geq 2$, alternating stripes of stability and instability are identified in their parameter space.

Non-Hermitian topological phase transition in PT-symmetric mode-locked lasers

Stefano Longhi

Doc ID: 352526 Received 20 Nov 2018; Accepted 28 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: The delocalization transition found in the Anderson model in the presence of an imaginary gauge field is a landmark example of non-Hermitian topological phase transition. Originally proposed by Hatano and Nelson, its topological nature has been disclosed only very recently. Here it shown that a non-Hermitian topological phase transition can be observed in the frequency spectrum of an actively mode-locked laser in a parity-time (PT) symmetric configuration with incommensurate disorder of cavity axial mode frequencies.

Fiber optic temperature sensors with polymer-based fluorescent materials

Sandra Escobar and Juan Hernandez-Cordero

Doc ID: 351397 Received 23 Nov 2018; Accepted 27 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: We demonstrate an optical fiber sensor based on the fluorescence emission of rare-earth active ions hosted by a polymer matrix. The temperature sensitive composite material is fabricated by simple mixing of the rare-earth ions in powder form (NaY₀.₇₇Yb₀.₂₀Er₀.₀₃F₄) with the polymer (polydimethylsiloxane, PDMS). This fluorescent material is then incorporated on the tip of silica-glass optical fibers to obtain a point temperature sensor probe. Temperature measurements are obtained through the fluorescent intensity ratio technique (FIR), yielding a linear response and minimizing spurious effects on the fluorescence signal. The fiber sensors fabricated with this material provide good performance within a temperature range of 20-100ºC, excellent linearity (r² = 0.999) and good thermal and fluorescent stability.

Comparison of single-side and double-side pumping of membrane external-cavity surface-emitting lasers

Hermann Kahle, Jussi-Pekka Penttinen, Hoy-My Phung, Patrik Rajala, Antti Tukiainen, Sanna Ranta, and Mircea Guina

Doc ID: 356544 Received 02 Jan 2019; Accepted 27 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: We studied and compared single-side pumping (SSP) and double-side pumping (DSP) of a semiconductor membrane external-cavity surface-emitting laser (MECSEL). The MECSEL active region was based on an AlGaAs quantum well structure embedded between two silicon carbide (SiC) wafer pieces that were used as transparent intra-cavity (IC) heat spreaders creating a symmetrical cooling environment. The gain structure targeted emission at 780 nm, a wavelength region that is important for many applications and where development of high-brightness high-power laser sourcesis gaining more momentum. By DSP at 20°C heat sink temperature we could reduce the laser threshold from 0.79 W to 0.69 W of absorbed pump power while the maximum output power was increased from 3.13 W to 3.22 W. The differential efficiency was improved from 31.9 % to 34.4 %, which represents a record value for SiC-cooled vertically emitting semiconductor lasers. The improvements are enabled by a reduced thermal resistance of the gain element by 9 % compared to SSP. The beam quality was measured to be M² < 1.09. Finally, we demonstrate a maximum tuning range from 767 to 811 nm. This wavelength range was not addressed by any MECSEL or vertical-external-cavity surface-emitting laser (VECSEL) device before and extends the available wavelengths for semiconductor based high-quality beam and high-power laser sources to a wavelength window relevant for quantum-technology, spectroscopy, or medicine.

Simple yet universal fabrication strategy for focused photoacoustic transmitter

Qi Li, Haobo Zhu, Chuhuan Feng, Zhiwei He, Wei Dong, and Hongbin Yu

Doc ID: 355298 Received 13 Dec 2018; Accepted 27 Jan 2019; Posted 04 Feb 2019  View: PDF

Abstract: Aiming to address existing technical challenge and explore a simple yet effective and universal solution for making polydimethylsiloxane (PDMS) based focused photoacoustic transmitter, a novel fabrication strategy is proposed. Different from traditional technical route based on direct photoacoustic layer coating on rigid concave substrate, it works by utilizing an elastomeric molding process, through which the originally flat photoacoustic conversion layer, consisting of PDMS-candle soot nanoparticles (CSNPs)/PDMS-PDMS composite, will be transformed into concave contour with controllable radius of curvature and finally merged into a soft PDMS substrate. For proof of concept demonstration, two types of focused photoacoustic transmitters (6.3mm and 8mm focal lengths) operating at 5.3MHz with -6dB bandwidth of 134% have been successfully fabricated, both showing distinct acoustic focusing capability and high energy conversion efficiency. Moreover, different from conventional focused counterparts, acoustic signals with nearly symmetric bi-polar waveform can be obtained at the focuses, facilitating ultrasound cavitation based applications.

Direct detection of the idler THz radiation generated by spontaneous parametric down-conversion

Galiya Kitaeva, Vladimir Kornienko, Kirill Kuznetsov, Ivan Pentin, Konstantin Smirnov, and Yury VAKHTOMIN

Doc ID: 356592 Received 02 Jan 2019; Accepted 26 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: We study parametric down-conversion of optical laser radiation in the strongly frequency-non-degenerate regime which is promising for the generation of quantum-correlated pairs of extremely different spectral ranges, the optical and the terahertz ones. The possibility to detect tenuous terahertz-frequency photon fluxes generated under low-gain spontaneous parametric down-conversion is demonstrated using a hot electron bolometer. Experimental dependences of the terahertz radiation power on the detection angle and on the pump intensity are analyzed.

Coherent two-octave-spanning supercontinuum generation in lithium-niobate waveguides

Mengjie Yu, Boris Desiatov, Yoshitomo Okawachi, Alexander Gaeta, and Marko Loncar

Doc ID: 356474 Received 02 Jan 2019; Accepted 24 Jan 2019; Posted 31 Jan 2019  View: PDF

Abstract: We demonstrate coherent supercontinuum generation (SCG) in a monolithically integrated lithium-niobate waveguide, under the presence of second- and third-order nonlinear effects. We achieve more than two octaves of optical bandwidth in a 0.5-cm-long waveguide with 100-picojoule-level pulses. Dispersion engineering of the waveguide allows for spectral overlap between the SCG and the second harmonic which enables direct detection of the carrier-envelope offset frequency fCEO using a single waveguide. We measure the fCEO of our femtosecond pump source with a 30-dB signal-to-noise ratio.

Super resolution photolithography using dielectric photonic crystal

Gaofeng Liang, Xi Chen, Zhongquan Wen, Gang Chen, and L. Jay Guo

Doc ID: 352013 Received 15 Nov 2018; Accepted 24 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: Although the plasmonic photolithography can break through the diffraction limit and produce super resolution patterns, the performance of high loss from metal severely obstructs its application in practice. Here, we proposed a novel photolithography method based on a photonic crystal (PC) structure, where the dielectric multilayer are analyzed systematically. It is shown that the PC can efficiently transmit the desired high-k waves, which is advantageous in generating deep subwavelength patterns and realizing super resolution lithography. In our design, PC composed of alternating stacked 9 layers of dielectric multilayer is demonstrated. The periodic patterns with a half-pitch of 30 nm (~λ/6) is formed in the photoresist layer. Furthermore, this PC-based lithography system is tolerant to the surface roughness in multilayer. The analyses indicate that the dielectric PC-based design is applicable for super resolution lithography to produce nanopatterns with strong field intensity, high aspect ratio, and great uniformity.

Octave-spanning supercontinuum generation in nanoscale lithium niobate waveguides

Juanjuan Lu, Joshua Surya, Xianwen Liu, Yuntao Xu, and Hong Tang

Doc ID: 355389 Received 14 Dec 2018; Accepted 24 Jan 2019; Posted 14 Feb 2019  View: PDF

Abstract: We demonstrate octave-spanning supercontinuum generation in unpoled lithium niobate waveguides, which are engineered to possess the anomalous dispersion and pumped by a turn-key femtosecond laser centered at 1560 nm. Tunable dispersive waves and strong phase-matched second harmonic generation are both observed by controlling the widths of waveguides. The major features of the experimental spectra are reproduced by numerical modeling of the generalized nonlinear Schrödinger equation, which can be used to guide waveguide designs for tailoring the supercontinuum spectrum. Our results identify a path to a simple and integrable supercontinuum source in lithium niobate nanophotonic platform and will enable new capabilities in precision frequency metrology.

Localized Surface Plasmon Resonance Biosensor: An Improved Technique for SERS Response Intensification

Saiful Islam, Jakeya Sultana, Rifat Ahmmed Aoni, Md Selim Habib, Alex Dinovitser, BRIAN W.-H. NG, and Derek Abbott

Doc ID: 352132 Received 15 Nov 2018; Accepted 23 Jan 2019; Posted 24 Jan 2019  View: PDF

Abstract: As technology continues to advance, the development of novel sensing systems opens up new possibilities for low cost, practical biosensing applications. In this paper, we demonstrate a localized surface plasmon resonance (LSPR) system that combines both wave-guiding and plasmonic resonance sensing with a single microstructured polymeric structure. Characterizing the sensor using Finite Element Method (FEM) simulation results show a record wavelength sensitivity (WS) of $111000$~nm$/$RIU, high amplitude sensitivity (AS) of $2050$~RIU$^{-1}$, high sensor resolution and limit of detection (LOD) of $9\times10^{-7}$~RIU and $8.12\times10^{-12}$ RIU$^{2}/$nm respectively. Furthermore, these sensors have the capability to detect an analyte within the refractive index (RI) range of $1.33$ to $1.43$ in the visible to mid-IR therefore being potentially suitable for applications in biomolecular and chemical analyte detection.

Broadband photoacoustic spectroscopy of ¹⁴CH₄ with a high-power mid-infrared optical frequency comb

Juho Karhu, Teemu Tomberg, Francisco Senna Vieira, Guillaume Genoud, Vesa Hänninen, Markku Vainio, Markus Metsälä, Tuomas Hieta, Steven Bell, and Lauri Halonen

Doc ID: 356527 Received 08 Jan 2019; Accepted 22 Jan 2019; Posted 25 Jan 2019  View: PDF

Abstract: We report a photoacoustic spectroscopy setup with a high-power mid-infrared frequency comb as the light source. The setup is used in broadband spectroscopy of radiocarbon methane. Due to the high sensitivity of a cantilever-enhanced photoacoustic cell and the high power light source, we can reach a detection limit below 100 ppb in a broadband measurement with a sample volume of only a few milliliters. The first infrared spectrum of ¹⁴CH₄ is reported and given a preliminary assignment. The results lay a foundation for the development of optical detection systems for radiocarbon methane.

Local wavefront mapping in tissue using computational adaptive optics OCT

Fredrick South, Yuan-Zhi Liu, Pin Huang, Tabea Kohlfarber, and Stephen Boppart

Doc ID: 351676 Received 12 Nov 2018; Accepted 22 Jan 2019; Posted 24 Jan 2019  View: PDF

Abstract: Identification and correction of wavefront aberrations is often necessary to achieve high-resolution optical images of biological tissues, as imperfections in the optical system and the tissue itself distort the imaging beam. Measuring the localized wavefront aberration provides information on where the beam is distorted and how severely. We have recently developed a method to estimate the single-pass wavefront aberrations from complex optical coherence tomography (OCT) data. Using this method, localized wavefront measurement and correction using computational OCT was performed in ex vivo tissues. The computationally-measured wavefront varied throughout the imaged OCT volumes, and therefore a local wavefront correction outperformed a global wavefront correction. The local wavefront measurement was also used to generate tissue aberration maps. Such aberration maps could potentially be used as a new form of tissue contrast.

Second Harmonic Generation in AlGaAs-On-Insulator Waveguides

Stuart May, Marc Sorel, Matteo Clerici, and Michael Kues

Doc ID: 357160 Received 08 Jan 2019; Accepted 22 Jan 2019; Posted 30 Jan 2019  View: PDF

Abstract: Second harmonic generation is demonstrated for the first time in AlGaAs-on-insulator waveguides at telecom wavelengths. Using this material platform a maximum internal normalised efficiency of 1202±55%W-1cm-2 is achieved for a 100fs pulsed excitation wavelength at 1560nm. This finding is important towards enabling new chip-scale devices for sensing, metrology and quantum optics

High average power 88 W OPCPA system for high repetition rate experiments at the LCLS X-ray free-electron laser

Katalin Mecseki, Matthew Windeler, Alan Miahnahri, Joseph Robinson, James Fraser, Alan Fry, and Franz Tavella

Doc ID: 357260 Received 10 Jan 2019; Accepted 22 Jan 2019; Posted 01 Feb 2019  View: PDF

Abstract: We present a 100 kHz, sub-20 fs optical parametric chirped pulse amplifier (OPCPA) system delivering 88.6 W average power at a center wavelength of 800 nm. The seed pulses are derived from the pump laser via white-light continuum generation and are amplified in three non-collinear OPCPA stages. The final two high power stages are pumped with a 661 W Yb:YAG InnoSlab amplifier. A simple and robust design is used for the OPCPA system to avoid thermal effects and enhance long term stability, resulting in excellent beam quality and high conversion efficiency. This is the highest average power OPCPA system reported to date.

Observation of non-linear interference on a silicon photonic chip

Takafumi Ono, Gary Sinclair, Damien Bonneau, Mark Thompson, Jonathan Matthews, and John Rarity

Doc ID: 354496 Received 05 Dec 2018; Accepted 20 Jan 2019; Posted 22 Jan 2019  View: PDF

Abstract: Photonic integrated circuits represent a promising platform for applying quantum information science to areas such as quantum computation, quantum communication and quantum metrology. While the linear optical approach has greatly contributed to this field, it is often possible to improve the functionality and scalability by making use of non-linear processes. One interesting process is the interference between two non-linear optical processes, where the interference occurs by removing the information as to which of two processes have occurred. In this Letter, we demonstrate a non-linear interferometer in the pair-photon generation regime by using spontaneous four-wave mixing in an integrated silicon photonic chip. We observe a non-linear interference in the production rate of photon pairs generated from two different four-wave mixing waveguides. We obtain an interference visibility of 96.8\%. This work shows the possibility of integrating and controlling nonlinear-optical interference components for silicon quantum photonics.

Negative refraction of plane electromagnetic waves in non-uniform double-negative media

Hanna Sliusarenko, Vadym Pazynin, and Leonid Pazynin

Doc ID: 356017 Received 26 Dec 2018; Accepted 20 Jan 2019; Posted 22 Jan 2019  View: PDF

Abstract: We propose a new model of a plane-layered medium with a fixed positive refractive index but variable non-vanishing dielectric permittivity and magnetic permeability. An analytical solution of the problem of a plane electromagnetic wave propagation through the medium has been found. It is shown that the negative-refraction effect occurs in this type of medium, in particular, an explicit expression for the field has been first obtained in the region of its formation. This result suggests that the necessary condition for the occurrence of this effect in quite complex media is not the negativity of their refractive index, but only the requirement of simultaneous negativity of the real parts of dielectric permittivity and magnetic permeability. We also demonstrate that the medium is passive (absorbing) if a plane E-polarized wave propagates in it, and the active (amplifying) one in the case of H-polarized wave propagation.

SiNx-Si interlayer coupler using gradient index metamaterial

Pengfei Xu, Yanfeng Zhang, Shuailong Zhang, Yujie Chen, and Siyuan Yu

Doc ID: 356679 Received 02 Jan 2019; Accepted 20 Jan 2019; Posted 25 Jan 2019  View: PDF

Abstract: In this work, we demonstrate a metamaterial (MM)-based SiNx-Si interlayer coupler. Gradient index (GRIN) metamaterial was employed to achieve refractive index matching, balancing the large difference in refractive index between Si (~3.42) and SiNx (~2). In addition to this, a two layer SiNx interlayer coupler was proposed to further minimize the coupling loss and interlayer crosstalk. Finally, we demonstrated a three-dimensional (3D) SiNx -Si interlayer coupler with -0.6 dB insertion loss per layer propagation, with 40 nm 1-dB-bandwidth (1530-1570 nm) and < -45 dB interlayer crosstalk. These promising results demonstrate the great potential of using GRIN MM-based SiNx -Si interlayer coupler in 3D photonic integration.

Rotating polarization using Berry’s phase in asymmetric silicon strip waveguides

Ryan Patton and Ronald Reano

Doc ID: 355297 Received 13 Dec 2018; Accepted 20 Jan 2019; Posted 29 Jan 2019  View: PDF

Abstract: Light propagating in an out-of-plane curvilinear waveguide acquires a Berry’s phase, which rotates optical polarization. The effect is promising for realizing waveguide polarization controllers. In high index contrast platforms, such as silicon on insulator, however, small waveguide cross-section asymmetries reduce the amount of polarization rotation. To overcome this, we present a method based on periodic spatial modulation of Berry's phase. Ninety degree polarization rotation is achieved even in the presence of waveguide asymmetry. Using a numerical model based on Jones calculus, we demonstrate the approach with 303 × 300 nm² asymmetric silicon waveguides. We convert polarization from TE to TM with greater than 20 dB polarization extinction ratio over a 100 nm bandwidth in a 110 × 240 μm² footprint.

High performance tunable, self-similar fiber laser

Chunyang Ma, Ankita Khanolkar, and Andy Chong

Doc ID: 355301 Received 14 Dec 2018; Accepted 18 Jan 2019; Posted 31 Jan 2019  View: PDF

Abstract: We report a tunability study of a mode-locked Yb-doped self-similar fiber laser. The center wavelength is tunable from 1030 nm to 1100 nm without losing mode-locking by adjusting a narrow intracavity spectral filter. Undesirable amplified spontaneous emission is suppressed by heating up the gain fiber. As a tunable mode-locked fiber laser, the performance (~100 fs and ~4 nJ) is exceptional owing to a unique self-similar pulse evolution.

Infrared Laser Locking to Rubidium Saturated Absorption Spectrum via a Photonic Chip Frequency Doubler

Jia-Cheng Xie, Jia-Qi Wang, Zhu-Bo Wang, Xin-Xin Hu, Xiang Guo, Rui Niu, Joshua Surya, Ji-Ze Zhang, Chunhua Dong, Guang-can Guo, Hong Tang, and Chang-Ling Zou

Doc ID: 356515 Received 04 Jan 2019; Accepted 16 Jan 2019; Posted 28 Jan 2019  View: PDF

Abstract: Photonic integrated resonators stand out as reliable frequency converters due to their compactness and stability, with second-harmonic generation (SHG) efficiencies of up to 17000$\bm{/W}$ reported recently in aluminum nitride microrings. In this work, a sufficiently strong second-harmonic (SH) signal up to microwatts was generated by a photonic integrated frequency doubler using a milliwatt infrared (IR) laser source. Furthermore, increased SHG bandwidth covering $\bm{^{85}}$Rb and $\bm{^{87}}$Rb D$\bm{_2}$ transition lines as well as saturated absorption spectroscopy (SAS) were demonstrated by tuning the pump power and chip temperature. Here, we present, to the best of our knowledge, the first successful locking of an IR laser to Rb saturated absorption lines via a photonic chip frequency doubler.

Unipolar subcycle pulse-driven nonresonant excitation of quantum systems

Anton Pakhomov, Rostislav Arkhipov, Ihar Babushkin, Mikhail Arkhipov, Nikolay Rosanov, Ayhan Demircan, and Uwe Morgner

Doc ID: 353270 Received 30 Nov 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: The interaction of subcycle pulses with quantum systems is considered when the pulse duration becomes much smaller than the timescales of electron oscillations. We show analytically that the interaction process in this case is governed by the so called electric pulse area. The efficient nonresonant excitation of quantum system by subcycle pulses with high degree of unipolarity is demonstrated. Obtained results are confirmed by direct numerical solution of multi-level Bloch equations.

Cost-efficient half-duplex 10-Gbit/s all-optical indoor optical wireless communication enabled by a low-cost Fabry-Perot laser/photodetector

Chao Li, Xuebing Zhang, Eduward Tangdiongga, Xiaoyu Dai, Cheng-Ting Tsai, Huai-Yung Wang, Yuanjiang Xiang, Gong-Ru Lin, Zizheng Cao, and Ton Koonen

Doc ID: 354706 Received 06 Dec 2018; Accepted 16 Jan 2019; Posted 17 Jan 2019  View: PDF

Abstract: To develop an indoor optical wireless communication (OWC) system, both the system complexity/cost and data rate need to be taken into consideration. In this letter, a cost-efficient half-duplex OWC system for photonic home area network applications is proposed and experimentally demonstrated. A low-cost Fabry-Perot laser diode (FP-LD) is proposed to be employed as both the downlink receiver (Rx) and uplink transmitter (Tx) at the user side. Enabled by the Fabry-Perot transceiver (FP-TRx), the indoor transmission of 10-Gbit/s 4-level pulse-amplitude-modulation (PAM-4) signal for both down- and uplink is experimentally achieved over 1.7-km SMF and 1.1-m free space. Moreover, the proposed scheme also enables to operate orthogonal frequency division multiplexing (OFDM) signal. The BER levels of multi-gigabit OFDM data for both down- and uplink over 10-hour measurement are all under 7% forward error correction (FEC) limit of 3.8×10-3, which indicates the proposed system is robust, thus can provide a promising solution for high-speed low-cost home area OWC networks.

Symmetry-wise nanopatterning and plasmonic excitation of ring-like gold nanoholes by structured femtosecond laser pulses with different polarizations

Sergey Kudryashov, Pavel Danilov, Alexey Porfirev, Irina Saraeva, Andrey Rudenko, Sergey Kudryashov, Sofia UMANSKAYA, Alexander Kuchmizhak, Dmitry Zayarny, Andrey Ionin, Svetlana Khonina, and Nikolay Busleev

Doc ID: 349232 Received 25 Oct 2018; Accepted 02 Jan 2019; Posted 24 Jan 2019  View: PDF

Abstract: Low- and ultralow-energy tightly focused 200-fs, 515-nm donut-shaped laser pulses at 0.25- and 0.65-NA focusing were used for single-shot ablative pulse-energy scalable nanopatterning of 50-nm thick gold film and the following plasmonic excitation of dye monolayer photoluminescence in the fabricated nanostructures, respectively. The same pulses at much lower, non-ablative nJ-energies, the same focusing and linear, azimuthal or radial polarizations provided efficient spectrally- and symmetry-matched excitation of both localized and delocalized surface electromagnetic modes in the separate, ring-like through holes and their arrays in the film envisioned by our modeling, resulting in polarization-sensitive yield of rhodamine 6G dye photoluminescence. The demonstrated consistency between the symmetries of the donut-shaped low-energy photo-exciting laser beam, its polarization state and the donut-shaped gold nanostructures, produced by the same beam at high, ablative pulse energies, paves the way to smart, self-consistent nanofabrication and plasmonic sensing, when the structured light interacts with the consistently structured matter.

Optical AC coupling power stabilization at frequencies close to the gravitational wave detection band

Steffen Kaufer and Benno Willke

Doc ID: 349735 Received 23 Nov 2018; Accepted 23 Dec 2018; Posted 24 Jan 2019  View: PDF

Abstract: Optical AC Coupling has been established as a highlysensitive alternative to multi-photodiode arrays in thedetection of laser power noise. Previous experimentswere limited by the linewidth of the resonators usedin these experiments. This letter describes a dedicatedsetup, which uses an optical resonator with a linewidthof 4 kHz which is one magnitude smaller than in earlierexperiments. To optimize the Optical AC couplinggain the novel approach of using a tunable impedancematching is described. An Optical AC coupling basedpower stabilization feedback control loop is setup andcharacterized at frequencies overlapping with the terrestrialgravitational wave detection band. The performanceof the new experiment is mainly limited byexpected noise sources down to frequencies of about1 kHz and about 7 dB better than its classical equivalentat frequencies between 8 kHz and 60 kHz.

Combined multiphoton and photoacoustic imaging for stratigraphic analysis of paintings

George Tserevelakis, Vassilis Tsafas, Kristalia Melessanaki, Giannis Zacharakis, and George Filippidis

Doc ID: 351349 Received 07 Nov 2018; Accepted 17 Dec 2018; Posted 11 Jan 2019  View: PDF

Abstract: Herewith, we demonstrate the effective combination of non-linear (multiphoton) and photoacoustic imaging for the high resolution stratigraphic analysis of multilayered art objects with emphasis on paintings. A novel convolution based algorithm is additionally applied for the precise discrimination of non-linear signals, providing valuable information as regards to the thickness and composition of successive varnish and paint layers in mock-up samples. On the other hand, photoacoustic contrast complements the extracted data by revealing well-hidden graphite underdrawings below the paint, at high sensitivity levels. The final composite images are directly compared with cross-sectional brightfield observations, validating the capabilities of the bimodal diagnosis in terms of measurement accuracy and contrast specificity. The presented hybrid diagnostic approach has the potential to optimize delicate interventions in works of art such as the selective removal of aged materials, promoting thus a significantly improved restoration outcome.

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