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Early Posting

Accepted papers to appear in an upcoming issue

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

Ring-up-doped fiber for the generation of more than600W single-mode narrow-band output at 1018nm

Gonzalo Palma Vega, Till Walbaum, Matthias Heinzig, Stefan Kuhn, Christian Hupel, Sigrun Hein, Gerrit Feldkamp, Bettina Sattler, Johannes Nold, Nicoletta Haarlammert, Thomas Schreiber, Ramona Eberhardt, and Andreas Tünnermann

Doc ID: 359719 Received 07 Feb 2019; Accepted 17 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: We present the amplification of a narrow bandwidthsignal at a wavelength of 1018nm to a power exceeding600W with stable output polarization state. The beamshowed an excellent, nearly diffraction limited beamquality. The high power output could be realized usingan in-house designed and fabricated fiber with acore-cladding diameter ratio of 32/260, ultra-low NA of0.041 and ring-up-doping. A seed source with high ASEsuppression was also required, which was realized bya double-pass pre-amplifier with 13W output power.

Optical trapping below the diffraction limit with a tunable beam waist using super-oscillating beams

Yael Roichman, Harel Nagar, Tamir Admon, Doron Goldman, and Amir Eyal

Doc ID: 361740 Received 07 Mar 2019; Accepted 17 Apr 2019; Posted 18 Apr 2019  View: PDF

Abstract: Super-oscillating beams can be used to create light spots whose size is below the diffraction limit with a side ring of high intensity adjacent to them. Optical traps made of the super-oscillating part of such beams exhibit superior localization of submicron beads compared to regular optical traps. Here we focus on the effect of the ratio of particle size to trap size on the localization and stiffness of optical traps made of super-oscillating beams. We find a non-monotonic dependence of trapping stiffness on the ratio of particle size to beam size. Optimal trapping is achieved when the particle is larger than the beam waist of the super-oscillating feature but small enough not to overlap with the side ring.

Contactless online characterization of large-area conductive thin films by thermography and induction

Kari Remes, Antti Järvenpää, and Tapio Fabritius

Doc ID: 362176 Received 12 Mar 2019; Accepted 17 Apr 2019; Posted 18 Apr 2019  View: PDF

Abstract: Testing and characterization techniques intended for traditional electronics production are rarely compatible with modern large-area, thin film electronics manufacturing processes such as roll-to-roll fabrication. Online quality monitoring of conductive thin films is necessary for upscaling and maintaining high-yield production. Thermography has already shown its usefulness in this kind of applications but has suffered the lack of proper non-contact electrical heating. Now, a fully contactless quality inspection technique based on thermal imaging and induction heating is implemented and evaluated. This approach is capable to find out defected areas and to estimate conductivity degradation online with full coverage over conductive thin films.

Terahertz resonance switch induced by the polarization conversion of liquid crystal in compound metasurface

Shi-Tong Xu, Fei Fan, Yun-Yun Ji, Jie -Rong Cheng, and Shengjiang Chang

Doc ID: 364885 Received 11 Apr 2019; Accepted 17 Apr 2019; Posted 18 Apr 2019  View: PDF

Abstract: We experimentally demonstrate an active terahertz (THz) resonance switch induced by the polarization conversion in a compound metasurface, which is a LC layer sandwiched by a metallic wire grating and resonance metamaterial (LCGM). Here, the liquid crystal (LC) plays the role of polarization conversion, which can induce the TE resonance mode excited or disappeared. Moreover, there exists a localized resonance and multi-reflections between metallic grating and resonance metamaterial layers, and then the excited resonance will be greatly enhanced. The results show that the high extinction ratio of the resonance switch exceeds 30dB at 0.82THz. This work will bring new ideas for the research in developing THz phase, polarization and switch devices with LC and metasurface.

Measuring the nonlinear phase shift in a mode-locked laser

Carlos Perilla, Jérôme Genest, and Jean-Daniel Deschênes

Doc ID: 364347 Received 04 Apr 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: The spectrum of a mode-locked laser is downmixed to electrical frequencies using a tuneable continuous wave laser. By characterizing the amplified spontaneous emission relative to the laser mode positions, one can measure the nonlinear phase shift of the mode-locked laser while in operation.

Full characterization of 8 fs deep UV pulses via dispersion scan

Ayhan Tajalli, Thomas Kalousdian, Martin Kretschmar, Sven Kleinert, Uwe Morgner, and Tamas Nagy

Doc ID: 361557 Received 06 Mar 2019; Accepted 16 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: We report on the first characterization of deep UV pulses by the dispersion scan technique. Negatively chirped 8 fs deep UV pulses are generated via phase transfer of shaped few-cycle near-infrared pulses in a sum frequency generation process with narrow-band second harmonic. The pulses are characterized by dispersion scan technique incorporating cross-polarizedwave (XPW) generation nonlinearity. Being a single-beam degenerate four-wave mixing process, XPW does not acquire frequency conversion and thus is ideally suited for characterizing pulses in the UV, where material dispersion severely limits phase matching. The characterization method is benchmarked by measuring the dispersion effect of a known fused silica plate onthe pulses.

3.4-mJ 150-fs Fe:ZnSe hybrid mid-IR femtosecond system for driving extreme nonlinear optics

Ekaterina Migal, Andrey Pushkin, Boris Bravy, Viacheslav Gordienko, Nikita Minaev, Anatoly Sirotkin, and Fedor Potemkin

Doc ID: 361844 Received 20 Mar 2019; Accepted 16 Apr 2019; Posted 17 Apr 2019  View: PDF

Abstract: We report on entering new era of mid-IR femtosecond lasers based on amplification in relatively new gain chalcogenide medium Fe:ZnSe. Our hybrid all-solid-state laser system based on direct pulse amplification of femtosecond seed from three-stage AGS-OPA in Fe:ZnSe laser crystal optically pumped by Cr:Yb:Ho:YSGG Q-switched nanosecond laser (90 mJ, 45 ns, 2.85 µm) operating up to 10 Hz repetition rate regime provides 3.5-mJ 150-fs femtosecond pulses centered at 4.4 µm. Diode pumped Er:YAG/Er:YLF lasers makes it possible to increase the beam quality and repetition rate of proposed laser system up to 100 Hz. Focusing such a laser radiation into the ~3λ beam diameter allow to reach at focus laser intensity up to 10^16 W/cm^2 which is only an order of magnitude lower than a relativistic intensities 10^17 W/cm^2 and enough to drive strong nonlinear optics in mid-IR. We show as a proof-of-principle experiment the generation of four-octave spanning (from 350 nm up to 5.5 µm) supercontinuum in xenon.

Label-free cocaine aptasensor based on a long-period fiber grating

Anna Celebańska, yaser chiniforooshan, Monika Janik, Predrag Mikulic, BALASUBRAMANIAN SELLAMUTHU, RYAN WALSH, JONATHAN PERREAULT, and Wojtek Bock

Doc ID: 359826 Received 08 Feb 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: In this paper, we combined a promising bioreceptor, a cocaine aptamer MN6, with an ultrasensitive optical platform a long-period fiber grating (LPFG) to create a new cocaine biosensor. The cocaine induces a conformational rearrangement of the aptamer which changes the refractive index around the LPFG producing a measurable shift of the transmission spectrum. We were able to track subtle interaction between the receptor and cocaine molecules over a concentration range of 25 to 100 µM. The presented biosensor does not require labelling or signal enhancement, resulting in a simple user-friendly device.

Constant temperature operation of fiber-optic hot-wire anemometers

Nezam Uddin, Guigen Liu, Qiwen Sheng, and Ming Han

Doc ID: 360520 Received 20 Feb 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: We demonstrate the constant temperature (CT) operation of a fiber-optic anemometer based on a laser-heated silicon Fabry-Perot interferometer (FPI), where the temperature of the FPI is kept constant by adjusting the heating laser power through a feedback control loop and the output signal is the heating laser power. We show that the CT operation can dramatically improve the frequency response over the commonly-used constant power (CP) operation where the laser heating power is kept constant and the output signal is the temperature of the FPI. For demonstration, we use a 100-µm diameter, 200-µm thick silicon FPI attached to the tip of a single mode fiber as the anemometer. The FPI is heated by a 980 nm diode laser and the temperature is measured using a 1550 nm diode laser. The effect of flow changes is simulated by exposing the silicon FPI to the radiation from an external intensity-modulated laser beam. We show that the 10%-90% rise time of the step response in air was reduced from 625 ms for CP operation to 1.8 ms for CT operation and the 3-dB bandwidth was increased from 0.5 Hz for CP operation to 2 kHz for CT operation. The response of the anemometer also shows good linearity to the radiation power.

Excessively tilted fiber grating based vector magnetometer

Zhijun Yan, Tean Lu, Yuezhen Sun, Yarien Moreno, Qizhen Sun, Kaiming Zhou, Hushan Wang, Deming Liu, and Lin Zhang

Doc ID: 361640 Received 06 Mar 2019; Accepted 16 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: A compact optic-fiber vector magnetometer is proposed and experimentally demonstrated, which is based on an excessively tilted fiber grating (Ex-TFG) assistant with magnetic fluid (MF). Without any complicated processing, the cladding mode resonances of the bare Ex-TFG packaged by MF show high sensitivity to slight perturbations by the magnetic field. Due to the excellent magneto-optical properties of MF and the azimuth-dependent RI sensitivity of Ex-TFG, such magnetometer can achieve the magnetic field intensity sensitivity of 2.45nm/mT and the orientation sensitivity of 0.41nm/deg, respectively. And based on the spectral interrogation, the detection limit of the magnetic field intensity could reach around 8.1μT at the minimum wavelength measurement accuracy of 0.02nm.

Dual-color-pump multi-species CARS in hollow-core PCF with 20 ppm detection limit under ambient conditions

Rinat Tyumenev, Luisa Späth, Barbara Trabold, Goran Ahmed, Michael Frosz, and Philip Russell

Doc ID: 358743 Received 28 Jan 2019; Accepted 15 Apr 2019; Posted 18 Apr 2019  View: PDF

Abstract: We report coherent anti-Stokes Raman spectroscopy (CARS) in gas-filled single-ring hollow-core photonic crystal fiber (SR-PCF) using a dual-color pump. The long collinear path-length offered by SR-PCF strongly enhances the efficiency of the Raman interactions. Pressure-tuning the ZDW of the SR-PCF allows the Raman coherence prepared by seeded pumping at 515 nm to be used in the visible for phase-matched generation of an anti-Stokes signal from a second pump in the ultraviolet. This is because the unique dispersion profile in the vicinity of the zero dispersion wavelength (ZDW) enables simultaneous phase-matching of all known Raman transitions. By allowing wide spectral separation of the two pumps, this paves the way for suppression of the non-resonant background. We demonstrate that simultaneous multispecies CARS with a detection limit of 20 ppm is possible with only 20 kW of peak pump power delivered by a single laser source.

Surface plasmon resonance refractive index sensor based on fiber-interface waveguide inscribed by femtosecond laser

Changrui Liao, Yunfang Zhang, Chupao Lin, Yu Shao, Ying Wang, and Yiping Wang

Doc ID: 362554 Received 18 Mar 2019; Accepted 15 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: A novel surface plasmon resonance (SPR) configuration based on fiber-interface waveguide was proposed and realized by combing the technology of femtosecond laser writing waveguide with SPR effect for measuring refractive index (RI) of analyte. A U-shaped waveguide is inscribed in the coreless fiber and its bottom is very close to the fiber surface which can produce strong evanescent field being sensitive to ambient media. When the fiber surface is coated with a layer of gold film, the strong evanescent field can excite the SPR effect on the fiber surface. Most importantly, different from some types of fiber SPR sensors with a fragile physical structure, the fiber-interface waveguide SPR sensor exhibits an excellent mechanical strength. Such a SPR sensor exhibits a high sensitivity of ~3352nm/RIU at the RI value of ~1.395, which may have important practical applications in medicine, environmental monitoring, and food safety.

Dissipative dispersion-managed solitons in fiber-optic systems with lumped amplification

Vladislav Neskorniuk, Anton Lukashchuk, George Ovchinnikov, Franko Kueppers, and Arkadi Chipouline

Doc ID: 358595 Received 11 Feb 2019; Accepted 15 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: We numerically and experimentally studied the shape of the dissipative dispersion-managed solitons (DM-solitons) stably propagating over the lossy DM fiber-optic systems with lumped amplification. We found that, contrary to the lossless case, the chirp-free points of the dissipative DM-solitons are not located in the middle of the fiber spans in the dispersion map. This constitutes a qualitative difference between the dissipative DM-solitons of the lossy systems and the conservative ones of the lossless systems. The applied numerical method was verified both experimentally and by numerically solving nonlinear Schrödinger equation.

Large mode area optical fiber for photonic nanojet generation

Robin Pierron, Gregoire Chabrol, Stephane Roques, Pierre Pfeiffer, Yehouessi Jean-Paul, Geraud Bouwmans, and Sylvain Lecler

Doc ID: 352682 Received 26 Nov 2018; Accepted 13 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: The photonic nanojet (PNJ) generated by a shaped optical fiber tip is an attractive technology for laser micro-machining. The working distance has the same order of size as the fiber core diameter, therefore multimode fibers are generally preferred. However, the PNJ is due to the fundamental mode and therefore the energy coupled on the high-order modes does not contribute to the process. We demonstrate the benefit of a large mode area (LMA) optical fiber in the generation of the PNJ. A home-made 40 μm mode field diameter LMA fiber is compared with a 100/140 multimode shaped fiber tip. Similar micro-peaks are obtained and an energy gain is demonstrated. The coupled energy required was 8 times less intense with the LMA fiber, which may open new possibilities for laser micro and nano-processing.

Quartz tuning fork embedded off-beam quartz-enhanced photoacoustic spectroscopy

Lien Hu, Chuntao Zheng, Jie Zheng, Yiding Wang, and Frank Tittel

Doc ID: 362053 Received 11 Mar 2019; Accepted 13 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: In order to achieve a high acoustic coupling strength and detection sensitivity and to simplify the assembly and alignment process in quartz-enhanced photoacoustic spectroscopy (QEPAS) technique, a novel quartz tuning fork (QTF) embedded off-beam QEPAS (E-OB-QEPAS) spectrophone was proposed. The structural parameters of the acoustic micro-resonator of the E-OB-QEPAS spectrophone were optimized for enhancing the signal-to-noise ratio gain based on experimental investigation. Compared with the on-beam configuration using a bare QTF, a detection sensitivity enhancement by a factor of ~ 25 was achieved by embedding the QTF in one resonant tube. By using two resonant tubes simultaneously embedded with a QTF, dual-channel detection and a two-fold photoacoustic signal enhancement were realized and a detection sensitivity enhancement by a factor of ~20 and ~40 were achieved for the single-tube-enhanced and dual-tube-enhanced E-OB-QEPAS spectrophone, respectively.

Picosecond laser welding of glasses with large gap by rapid oscillating scan

Hang Chen, Leimin Deng, Jun Duan, and Xiaoyan Zeng

Doc ID: 361475 Received 04 Mar 2019; Accepted 12 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: The welding of glass using ultrafast laser has attracted much attention due to its potential applications in the fields of solar cells, implanted microelectronics, OLED, MEMS, microsensors and so on. However, the optical contact (gap < 100 nm) of two glasses is required for the welding process, which is a harsh condition in real engineering applications. A welding method that utilizes picosecond laser with small-scale rapid oscillating scan is presented in this paper to achieve the welding of glasses with natural stacking contact (gap ≈ 10 μm). The rapid oscillating scan of the laser facilitates the creation of sufficient molten material to fill the large gap and the release of internal thermal pressure during the welding process. The condensation of the welding area can further reduce the gap to less than 3 μm, which provides necessary conditions for realizing continuous welding. By using this method, a maximum joint strength up to 64 MPa can be achieved without any defects. The detail mechanism of laser welding with rapid oscillating scan was revealed in this paper. This research lays good foundation of large-gap glass welding technology to the engineering application.

Parallel optical random bit generator

Pu Li, Kunying Li, Xiaomin Guo, Yanqiang Guo, Yiming Liu, Bingjie Xu, Adonis Bogris, K. Alan Shore, and Yun-cai Wang

Doc ID: 359560 Received 04 Feb 2019; Accepted 12 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: We present an optical approach for high-speed parallel random bit generation based on stochastic pulse-to-pulse fluctuation in the supercontinuum (SC). Through spectrally demultiplexing the SC pulse sequence into different wavelength channels, we simultaneously extract multiple independent fast random bit streams from each SC pulse subsequences via associated comparators in parallel. Proof-of-concept experiments demonstrate that using our method, four 10 Gb/s random bit streams are obtained from a SC pulse source with verified randomness. Moreover, this method also provides a promising strategy to fabricate ultrafast random bit generators with Tb/s throughput capacity just by increasing additional wavelength channels.

High stability and multithreading phase coherent receiver for simultaneous transfer of stabilized optical and RF frequencies

Zitong Feng, xi zhang, rui wu, ding dan, Fei Yang, Yanguang Sun, Nan Cheng, You-Zhen Gui, and Haiwen Cai

Doc ID: 362442 Received 15 Mar 2019; Accepted 12 Apr 2019; Posted 15 Apr 2019  View: PDF

Abstract: We demonstrate a high stability and multithreading coherent receiver for simultaneous distribution of stabilized optical and RF frequencies. The technique is based on a monolithic electro-absorption modulator integrated with a distributed feedback laser, which can purify and amplify the optical carrier while recovering the RF signal as a high-speed photodetector. The large dynamic range and high bandwidth phase locking system preserves the stability of the receiver for optical and RF signals to 3.5 × 10-20 and 6.4 × 10-18 at 1000 s, respectively. Furthermore, a dual-stabilization system using this novel receiver is proposed for simultaneous transfer of ultrastable optical carriers and RF signals over a 263-km fiber link. The transferred frequency stabilities of the optical carrier and the 9.1 GHz signal are 6.5 × 10-20 and 1.6 × 10-17, respectively, for an averaging time of 10000 s.

Single-shot quantitative birefringence microscopy for imaging birefringence parameters

Zhen-Jia Cheng, Yang Yang, Hong-Yi Huang, Qing-Yang Yue, and Cheng-Shan Guo

Doc ID: 361052 Received 26 Feb 2019; Accepted 12 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: A method for realizing 2D single-shot measurements of birefringence parameters (both including the retardation and optic axis orientation) of anisotropic materials using a simple recording setup and an efficient processing algorithm. The recording setup can be built simply by inserting a circular polarizer and a polarization beam splitter, respectively, in the object path and the reference path of a conventional off-axis holographic imaging system, with no need of other adjustments. An algorithm for quantitatively retrieving the birefringence parameters from one single-shot hologram is proposed and demonstrated, in which a new quantity describing the birefringence, called complex birefringence parameter, is introduced and a set of formula used to extract the birefringence parameters is derived. Some experimental results are given for demonstrating the feasibility of the method, which reveals that the method may provide another effective approach for investigating the birefringence properties of dynamic anisotropic materials, especially the birefringence induced by ultrafast pulse lasers.

Noise suppression of mechanical oscillations in a microcavity for ultra-sensitive detection

Yanyan Zhi, Xiao-Chong Yu, Hao-Jing Chen, Bai-Ou Guan, and Yun-Feng Xiao

Doc ID: 362012 Received 11 Mar 2019; Accepted 12 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: Optical microcavities have been widely applied as sensitive detectors due to ultra-high quality factors and small mode volumes. Besides considering the optical mode as the sensing signal, the optomechanical oscillations induced by the optical spring effect also performs as an elegant sensing signal. However, the minimal size of a detectable analyte is limited by the relativelyweak light-matter interaction compared to the experimental noises. To improve the detection limit, many methods have been developed to either enhance device sensitivities or suppress experimental noises. In this work, we present a way to lower the detection limit by suppressing experimental noises of the mechanical frequency by three orders of magnitude. Utilizing a fiber tip as a benchmark analyte attaching onto the cavity, the mechanical frequency shift reflects the changes of the optical mode detuning of the cavity, predicting an effective tool for ultra-sensitive detection.

Spectral analysis for the generalized least-squares phase-shifting algorithms with harmonic robustness

Manuel Servin, Sotero Ordones, Moises Padilla, ANTONIO MUÑOZ, Jorge Flores, and Ivan Choque

Doc ID: 361455 Received 04 Mar 2019; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: We introduce the frequency transfer function (FTF) formalism for the generalized least-squares phase-shifting algorithms (GLS-PSAs), whose phase shifts are nonuniformly spaced. The GLS-PSA’s impulsive response is found by computing the Moore-Penrose pseudoinverse. FTF theory allows analyzing these GLS-PSAs spectrally, as well as easily find figures of merit such as signal-to-noise ratio (SNR) and harmonic rejection capabilities. We show simulations depicting that the SNR slightly decreases as the harmonic rejection robustness improves.

Classical entanglement underpins the propagation invariance of space-time wave packets

Ayman Abouraddy, Hasan Kondakci, and Miguel Alonso

Doc ID: 361691 Received 11 Mar 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: Propagation-invariant pulsed beams are generated by introducing appropriate tight correlations in their spatio-temporal spectrum. Such correlations between degrees of freedom constitute an example of what has been called `classical entanglement', which is a necessary but not sufficient requirement for propagation-invariance. We demonstrate theoretically and experimentally that a standard measure of entanglement, the Schmidt number, determines the propagation distance under which the wave packets retain their shape. Reduction in this degree of classical entanglement manifests itself in an increased spread in the measured spatio-temporal spectral correlations.

Resolution-enhanced light field displays by recombining subpixels across elemental images

Zong Qin, Ping-Yen Chou, Jui-Yi Wu, Cheng-Ting Huang, and Yi-Pai Huang

Doc ID: 361399 Received 05 Mar 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: Light field displays based on integral imaging feature ultra-compact volume and freedom of the vergence-accommodation conflict for advanced virtual reality and augmented reality devices; however, they currently suffer from low visual resolution. Considering subpixels have an intrinsically tripled resolution compared with triad pixels, this study develops a subpixel-level algorithm by recombing subpixels with relatively small raytracing errors from different elemental images. As a result, based on a highly accurate image formation model, the resolution of a typical system (pixel size: 7.8 μm, system thickness: 4.07 mm) is remarkably enhanced from 8.3 to 20.0 pixels per degree, for a gain of 2.41. In addition, the color breakup introduced by the chromatic subpixels is largely suppressed.

Four-photon absorption cross section measurements in UV fused silica at 473 nm

Yakov Grudtsin, Andrew Koribut, Leonid Mikheev, and Sergey Semjonov

Doc ID: 354612 Received 28 Dec 2018; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: With the use of I- and z-scan techniques, the four-photon absorption cross-section in a UV fused silica sample has been measured to be σ₄=(1.0±0.5)×10¯¹¹⁵ cm⁸s³ at 473 nm. This value is more than an order of magnitude lower than that known for other optical materials (KBr, KI, NaCl, TeO₂, and GeS₂).©

Stain-free subcellular-resolution astrocyte imaging using third-harmonic generation

Matvey Pochechuev, Alexandr Lanin, ilya kelmanson, Dmitry Bilan, Darya Kotova, artem chebotarev, Victor Tarabykin, Andrey Fedotov, Vsevolod Belousov, and Aleksei Zheltikov

Doc ID: 359904 Received 18 Feb 2019; Accepted 11 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: We demonstrate a stain-free, high-contrast, subcellular-resolution imaging of astroglial cells using epi-detected third-harmonic generation (THG). The astrocyte-imaging capability of THG is verified by colocalizing THG images with fluorescence images of astrocytes cytoplasmically stained with a genetically encodable fluorescent sensor. We show that, with a properly tailored focusing geometry, THG imaging can reliably detect significant subcellular features of astrocytes, including cell nuclei, as well as the soma shape and boundaries.

On-chip two-step microwave frequency measurement with high accuracy and ultra-wide bandwidth using add-drop micro-disk resonators

Yang Chen, Weifeng Zhang, jingxuan liu, and Jianping Yao

Doc ID: 362344 Received 14 Mar 2019; Accepted 11 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: An on-chip two-step microwave frequency measurement method with high accuracy and ultra-wide frequency measurement range is reported. A silicon photonic integrated micro-disk resonator (MDR) array is used to coarsely measure the signal frequency via an array of add-drop MDRs with smaller disk radii, and then an MDR with a larger radius is used to finely measure the signal frequency, which is done by monitoring the optical powers of the optical signals from the through port and drop port of the MDRs. The proposed system features very compact structure, ultra-wide frequency measurement range and high frequency measurement accuracy, which is verified by a proof-of-concept experiment using two MDRs with radii of 6 and 10 μm. Frequency measurement of microwave signals from 1.6 to 40 GHz is implemented with a measurement error of less than 60 MHz. The stability of the system is also evaluated.

A 1.2 kW quasi-steady-state diamond Raman laser pumped by an M2=15 beam

Sergei Antipov, Alexander Sabella, Robert Williams, Ondrej Kitzler, David Spence, and Richard Mildren

Doc ID: 359883 Received 19 Feb 2019; Accepted 10 Apr 2019; Posted 18 Apr 2019  View: PDF

Abstract: An external cavity diamond Raman laser with 1.2 kW output power is demonstrated for durations 7 times longer than the thermal lens time constant. An 83% slope efficiency and a 53% optical-to-optical efficiency were obtained for conversion from a 1.06 µm pump to the 1.24 µm first Stokes. The pump had an M² = 15 pump beam, demonstrating that efficiency can be maintained at the highest levels even when using exceptionally poor quality pumps. We show that an observed decrease in the output beam quality factor from M² = 2.95 to M² = 1.25 as power increased is evidence for thermal lens development in the diamond. The results foreshadow development of continuous-wave kW-class lasers or amplifiers based on single diamond elements and pumped efficiently by lasers having poor spatial coherence such as line-narrowed diode laser arrays.

Bound states of different pulses based on third order dispersion

Yazhou Wang, Jianfeng Li, Lunjun Hong, Fei Liu, Yiwen Shi, Xiaojun Zhou, and Yong Liu

Doc ID: 363900 Received 01 Apr 2019; Accepted 10 Apr 2019; Posted 18 Apr 2019  View: PDF

Abstract: Bound states of double pulses with different wavelengths are observed in a Tm-doped passively mode-locked fiber laser with near zero net cavity group-velocity dispersion (GVD) and strong third order dispersion (TOD). The double pulses in the bound states exhibit different pulse durations and peak powers. Simulations show that the two pulses experience different compressing and broadening processes during the intra-cavity evolution. This demonstration reveals new existence form of bound states, and enriches nonlinear dynamics of multi-pulse mode-locking.

Efficient femtosecond mid-infrared generation based on a Cr:ZnS oscillator and step-index fluoride fibers

Nathalie Nagl, Ka Fai Mak, Qing Wang, Vladimir Pervak, Ferenc Krausz, and Oleg Pronin

Doc ID: 359436 Received 15 Feb 2019; Accepted 10 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: Femtosecond light sources in the 3–5 µm region are highly sought after for numerous applications. While they can be generated using nonlinear effects in optical fibers, the efficiencies and effectiveness of frequency conversion can be significantly enhanced by using ultrashort driving pulses. Here we report on a few-cycle Cr:ZnS oscillator driving low-order soliton dynamics in soft-glass fibers. By selecting appropriate parameters, sub-two-cycle pulses or broad supercontinua spanning over 1.7 octaves from 1.6 µm to 5.1 µm can be generated at average power levels exceeding 300 mW. In the same setting, Raman-induced soliton self-frequency shifting (SSFS) has been exploited to generate sub-100 femtosecond pulses continuously tunable from 2.3 µm to 3.85 µm with a conversion efficiency of ~50%. These results demonstrate the vast potential of using Cr:ZnS or Cr:ZnSe lasers for powerful mid-infrared generation.

Ultra-efficient, 10-watt level mid-infrared supercontinuum generation in fluoroindate fiber

Tianyi Wu, Linyong Yang, Zhiyuan Dou, Ke Yin, Xuan He, Bin Zhang, and Jing Hou

Doc ID: 355204 Received 12 Dec 2018; Accepted 10 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: A 10-watt-level mid-infrared supercontinuum (MIR-SC) spanning 0.8-4.7 μm with ultra-high power conversion efficiency was generated in a piece of fluoroindate (InF3) fiber. The pump laser is a master oscillator power amplifier (MOPA) system seeded by a mode-locked fiber laser operating at 1956 nm with pulse repetition rate and pulse duration of 33 MHz and 60 ps, respectively. A piece of InF3 fiber is fusion spliced to the output end of the pump light source with a low fusion splicing loss of 0.12 dB. An endcap made of multimode aluminum fluoride (AlF3) fiber is used to protect the fiber tip from possible optical or thermal damage. Benefiting from the fiber endcap as well as the low-loss splicing joint between silica and InF3 fiber, high-power SC generation is achieved with a maximal output power of 11.3 W and a corresponding power conversion efficiency of 66.5%. Furthermore, the long wavelength edge of the obtained SC spectrum is extended to 4.7 μm. This paper, to the best of our knowledge, not only demonstrates the first 10-watt-level SC generation in InF3 fibers, but also achieves an enhancement of over 15% in power conversion efficiency compared with the literature on 10-watt-level fluoride-fiber-based SC laser sources.

Gain mechanism of femtosecond two-photon-excited lasing effect in atomic hydrogen

Pengji Ding, Maria Ruchkina, liu yi, Marcus L.E. Alden, and Joakim Bood

Doc ID: 358780 Received 28 Jan 2019; Accepted 10 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: By aiming to establish single-ended standoff combustion diagnostics, bidirectional lasing emissions of atomic hydrogen at 656 nm wavelength has been generated via two-photon resonant excitation by focusing 205 nm femtosecond laser pulses into a premixed CH₄/O₂ flame. The forward lasing strength is approximately one order of magnitude stronger than the backward one, due to the geometry of traveling wave excitation over a 2-mm-long pencil-shaped gain volume and the short gain lifetime of 3.5 ps. The gain coefficient of hydrogen lasing was determined to approximate 52/cm. As for the underlying physics of hydrogen lasing, amplified spontaneous emission (ASE) occurs simultaneously with four-wave mixing (FWM), and ASE dominates in the forward direction, whereas the backward lasing is virtually only ASE.

The Multi-function Double Rare Earh-doped Ball Sensor Based on Hollow-core Microstructure Fiber

Boyao Li, Meng Wu, Yaoyao liang, Ke Liu, Guiyao Zhou, Jiantao Liu, Zhiyun Hou, and ming xia

Doc ID: 361016 Received 26 Feb 2019; Accepted 10 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: In this paper, we demonstrated a multi-function sensor through splicing double rare eath-doped balls (REDB) with hollow-core microstructure fiber. Utilizing the different thermal expansion and thermo optic coefficient of silica and rare earth, the interference of REDB will more sensitive to temperature. On both ends of dual-ball, we spliced the anti-resonance fiber (ARF) for satisfying broad waveband transmission. In addition, the special anti-resonance loss peak of anti-resonance fiber can make the amplitude change of signal more obvious. Experiments show many signal, such as light, concentration, temperature and so on, can be acquired. And the temperature sensitive can reach to 1nm/⁰C, and the light response is obvious. Besides, we also analyze the concentration of P-Methylthiophenol, substances harmful to human beings in the environment. Its resolution can reach to 3.125E-5mol/L. These results indicate the sensor can be used in underground mine detection, environmental monitoring and so on.

Broadband mid-infrared coverage (2–17 μm) with few-cycle pulses via cascaded parametric processes

Qing Wang, Jinwei Zhang, Alexander Kessel, Nathalie Nagl, Vladimir Pervak, Oleg Pronin, and Ka Fai Mak

Doc ID: 360259 Received 15 Feb 2019; Accepted 10 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: A myriad of existing and emerging applications could benefit from coherent and broadband mid-infrared (MIR) light. Yet existing table-top sources are often complex or sensitive to interferometric optical misalignment. Here we demonstrate a significantly simplified scheme of broadband MIR generation by cascading the intra-pulse difference-frequency generation process in a specific nonlinear crystal. This allows pulses generated directly from mode-locked lasers to be used without further nonlinear temporal compression. The system, together with the driving beam, can provide an ultra-broadband coherent radiation coverage ranging from 2 μm to 17 μm with femtosecond pulse durations. This first demonstration of cascaded DFG in the mid-infrared range brings emerging time-domain spectroscopic techniques closer to real world applications.

9µm few-cycle optical parametric chirped-pulse amplifier based on LiGaS2

Shizhen Qu, Houkun Liang, Kun Liu, xiao zou, Wenkai Li, Qijie Wang, and Ying Zhang

Doc ID: 361405 Received 07 Mar 2019; Accepted 09 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: We report a long-wavelength mid-infrared, few-cycle optical parametric chirped-pulse amplifier (OPCPA), based on LiGaS2, pumped by a 1 μm Yb:YAG laser, at 10 kHz repetition rate. The mid-infrared OPCPA system generates pulses centered at 9 μm, with 14 μJ pulse energy, and 140 mW average power. 142 fs pule width which corresponds to less than 5 optical cycles at 9 μm is measured by an interferometric autocorrelator. It is, to the best of our knowledge, the first long-wavelength mid-infrared OPCPA, pumped at 1 μm wavelength. It paves the way for the energy and power scaling of the ultrafast long-wavelength mid-infrared lasers, by utilizing the advanced high-energy, high-power 1 μm pump lasers.

Grating assisted glass fiber coupler for mode selective co-directional coupling

Sebastian Schlangen, Kort Bremer, Sebastian Böhm, Felix Wellmann, Michael Steinke, Joerg Neumann, Bernhard Roth, and Ludger Overmeyer

Doc ID: 362074 Received 11 Mar 2019; Accepted 09 Apr 2019; Posted 10 Apr 2019  View: PDF

Abstract: To keep pace with the increasing demand of transmission capacity, space division multiplexing technologies are currently intensively investigated. In this context mode selective glass fiber couplers are of great interest due to their compatibility with existing glass fiber networks. In this work we present a novel type of mode selective glass fiber coupler for co-directional coupling based on fiber gratings and fused asymmetric fibers. The achieved mode selective coupling efficiency agrees well with numerical simulations performed for comparison. The benefits of the grating approach are a lower mode crosstalk and a simple adaption of the propagation constants through changing of the grating-period.

Non-Markovianity through quantum coherence in an all-optical setup

Marcello Henrique Passos, Paola Obando, Wagner Balthazar, Fagner Paula, Jose Augusto Huguenin, and Marcelo Sarandy

Doc ID: 362587 Received 15 Mar 2019; Accepted 09 Apr 2019; Posted 12 Apr 2019  View: PDF

Abstract: We propose an all-optical experiment to quantify non-Markovianity in an open quantum system through quantum coherence of a single quantum bit. We use an amplitude damping channel implemented by an optical setup with an intense laser beam simulating a single-photon polarization. The optimization over initial states required to quantify non-Markovianity is analytically evaluated.

Cascaded Rotational Doppler Effect

junhong deng, King Fai Li, Wei Liu, and Guixin Li

Doc ID: 362927 Received 20 Mar 2019; Accepted 09 Apr 2019; Posted 11 Apr 2019  View: PDF

Abstract: We propose and substantiate experimentally the cascaded rotational Doppler effect for interactions of spinning objects with light carrying spin angular momentum. Based on mirror symmetry for electromagnetic interactions, we reveal that the frequency shift can be doubled through cascading two rotational Doppler processes which are mirror-imaged to each other. This effect is further experimentally verified with a rotating half-wave plate, and the mirror-imaging process is achieved by reflecting the frequency-shifted circularly polarized wave upon a mirror with a quarter-wave plate in front of it. The mirror symmetry protected frequency shift enhancement could be applied for detection of rotating systems ranging from molecules to macroscopic bodies with high precision and sensitivity.

Symmetry breaking with opposite stability between bifurcated asymmetric solitons in parity-time-symmetric potentials

Jianke Yang

Doc ID: 362079 Received 11 Mar 2019; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: We report a new type of symmetry-breaking bifurcation of solitons in optical systems with parity-time-symmetric potentials. In this bifurcation, the two bifurcated branches of asymmetric solitons exhibit opposite stability, which contrasts all previous symmetry-breaking bifurcations in conservative and non-conservative systems. We show that this novel symmetry-breaking bifurcation can be exploited to achieve unidirectional propagation of high-intensity light beams in parity-time-symmetric potentials.

Large optical nonlinearity of ITO/Ag/ITO sandwiches based on Z-scan measurement

ke wu, Zhewei Wang, Jianhan Yang, and hui ye

Doc ID: 358887 Received 28 Jan 2019; Accepted 08 Apr 2019; Posted 16 Apr 2019  View: PDF

Abstract: Indium tin oxide (ITO) based sandwich structures with the insertion of silver (ITO/Ag/ITO) show large nonlinear optical enhancement of both nonlinear refraction and saturable absorption. Here, optical nonlinearity is measured using Z-scan experiment with a 1310 nm pulsed laser at normal incidence. The nonlinear refractive index (n_2=15.43×10^(-16) m^2/W) for ITO/Ag/ITO sandwich with a 14 nm silver interlayer and the nonlinear absorption coefficient (β=-648×10^(-11) m/W) for ITO/Ag/ITO sandwich with a 10 nm silver interlayer is about 18 and 16 times greater than that of single layer ITO, respectively. Meanwhile, Large FOM and modulation depth values hinted that ITO/Ag/ITO sandwiches are promising saturable absorber materials to switch continuous laser wave into laser pulses. These novel nonlinear optical properties make ITO/Ag/ITO sandwiches promising candidate for all-optical modulation devices at optical communication wavelength.

High extinction ratio on-chip pump-rejection filter based on cascaded grating-assisted contra-directional couplers in silicon nitride rib waveguides

Xiaomin Nie, Nina Turk, Yang Li, Zuyang Liu, and Roel G. Baets

Doc ID: 362763 Received 19 Mar 2019; Accepted 08 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: We present an on-chip filter that is based on the grating-assisted contra-directional coupler (GACDC) implemented on a silicon nitride rib waveguide platform. This filter enjoys the benefit of an unlimited free spectral range (FSR) on the red side of the stop/passband. Unlike a Bragg reflector, the GACDC filter has the advantage of coupling the rejected light contra-directionally into a bus waveguide, instead of reflecting it back to the input. This property makes it an add/drop filter suitable for pump rejection and allows effective cascading between multiple stages to provide an even higher extinction ratio compared to the single stage version. In this work, we experimentally demonstrate that a 16-stage cascaded GACDC filter can provide a stopband with a bandwidth smaller than 3 nm and an extinction ratio as high as 68.5 dB.

Tunable passively Q-switched Dy3+-doped fiber laser from 2.71 μm to 3.08 μm using PbS nanoparticles

Jianfeng Li, Hongyu Luo, Ying Gao, Xiaohui Li, Yong Liu, and Yao Xu

Doc ID: 363057 Received 21 Mar 2019; Accepted 06 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: We present a widely tunable passively Q-switched Dy3+ -doped ZBLAN fiber laser around 3 μm pumped at 1.1 μm using PbS nanoparticles (NPs) as the saturable absorber (SA) for the first time. At 2.87 μm, the modulation depth and saturation intensity of the SA were measured to be 12.5% and 1.10 MW/cm2, respectively. Stable Q-switching was achieved over a wavelength range of 2.71 ~3.08 μm (~370 nm), which is a record tuning range from a pulsed rare-earth-doped fiber laser, to our knowledge. A maximum output power of 252.7 mW was obtained, with a pulse energy of 1.51 μJ, a pulse width of 795 ns, and a repetition rate of 166.8 kHz. This demonstration implies that Dy3+ is a promising gain medium for tunable pulsed sources in the 3 μm band, and shows for the first time the potential of PbS as a mid-infrared SA.

An Yb fiber based laser source for tunable, narrow bandwidth picosecond pulses in the visible

Andreas Zumbusch and Lukas Ebner

Doc ID: 362610 Received 18 Mar 2019; Accepted 06 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: We present a simple Yb fiber pumped source for narrow bandwidth picosecond pulses which are tunable in the visible spectral region. This emission is obtained by frequency doubling of a soliton generated in a photonic crystal fiber. The system is attractive for different types of nonlinear optical microscopy and can easily be adapted to meet different experimental prerequisites. As an example, we demonstrate coherent anti-Stokes Raman scattering microscopy using the laser source described.

Flexible interferometric null testing for concave free-form surfaces using a hybrid refractive and diffractive variable null

SYONG CHEN, Shuai Xue, guipeng tie, ye tian, Hu hao, FENG Shi, xiaoqiang PENG, and XISHENG XIAO

Doc ID: 358906 Received 28 Jan 2019; Accepted 06 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: Free-form surfaces have been applied in a wide range of modern optical systems. As a supporting technique for fabricating free-form surfaces, interferometric null method for testing surface figure error has very limited flexibility. In this letter, we report a flexible interferometric null test method which can test free-form surfaces with a very broad departure varying range. In the presented flexible null method, a hybrid refractive and diffractive variable null (HRDVN) is utilized as the flexible null. The HRDVN has superb aberration types & amplitude adaptability and moderate phase generating accuracy. A flexible interferometric null testing setup was established using the HRDVN. Its superb adaptive capacity, simple configuration, and moderate test accuracy were successfully demonstrated by measuring a free-form surface with departure as large as about 180λ.

Sub-Hertz interferometry at the quantum noise limit

peng yang, Boya Xie, and Sheng Feng

Doc ID: 357044 Received 28 Jan 2019; Accepted 05 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: Quantum-noise limited interferometry for sub-Hertz phase measurement is of essence in precision metrology applications, such as gravitational wave detection. However, suppression of sub-Hertz classical noises below the shot noise level is very challenging in practice. Two-frequency interferometry has been previously proposed to avoid low frequency noises and may be useful for squeezing-enhanced high-precision phase measurement. Here we experimentally demonstrate a sub-Hertz interferometer at the standard quantum noise (shot noise) limit, by use of dual-frequency coherent probe light at the input and phase-sensitive heterodyne detection to measure the output interfered light. When the interferometer is locked at a dark fringe, the noise floor of the phase variance in the interferometer reaches the shot noise level down to Fourier frequencies below 1 Hz. This work should pave a way for a realization of sub-Hertz interferometry beyond the shot noise limit.

Low-loss fiber-to-chip interface for lithium niobate photonic integrated circuits

Mian Zhang, Lingyan He, Cheng Wang, Amirhassan Shams-Ansari, Rongrong Zhu, and Marko Loncar

Doc ID: 360986 Received 25 Feb 2019; Accepted 05 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: Integrated lithium niobate (LN) photonic circuits have recently emerged as a promising candidate for advanced photonic functions such as high-speed modulation, nonlinear frequency conversion and frequency comb generation. For practical applications, optical interfaces that feature low fiber-to-chip coupling losses are essential. So far, the fiber-to-chip loss (commonly > 10dB/facet) dominates the total insertion losses of typical LN photonic integrated circuits, where on-chip losses can be as low as 0.03 -0.1 dB/cm. Here we experimentally demonstrate a low-loss mode size converter for coupling between a standard lensed fiber and sub-micrometer LN rib waveguides. The coupler consists of two inverse tapers that convert the small optical mode of a rib waveguide into a symmetric guided mode of a LN nanowire,featuring a larger mode area matched to that of a tapered optical fiber. The measured fiber-to-chip coupling loss is lower than 1.7dB/facet with high fabrication tolerance and repeatability. Our results open door for practical integrated LN photonic circuits efficiently interfaced with optical fibers.

Characterization of 20-fs VUV pulses by plasma-mirror frequency-resolved optical gating

Ryuji Itakura, Hiroshi Akagi, and Tomohito Otobe

Doc ID: 361124 Received 26 Feb 2019; Accepted 05 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: We demonstrate that vacuum ultraviolet (VUV) pulses (λ ~ 160 nm) with 20-fs duration can be fully characterized by plasma-mirror frequency-resolved optical gating. Plasma is formed as an ultrafast optical switch on a fused silica surface by irradiation of an intense near-infrared femtosecond laser pulse. We measure time-resolved VUV reflection spectra of plasma, and retrieve it to simultaneously extract a nearly Fourier-transform limited VUV pulse shape and a time-dependent reflectivity of plasma using the least-square generalized projections algorithm. We show that there is almost no spatial dependence of the VUV pulse shape, whereas the plasma mirror reflectivity strongly depends on the spatial region.

Measuring the topological charge of optical vortices with twisting phase

Daomu Zhao and Donghui Shen

Doc ID: 363036 Received 25 Mar 2019; Accepted 05 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: We analyzed the propagation characteristics of the intensity of a vortex beam after passing through a twisting phase. It was found that the doughnut-like intensity pattern of a vortex beam would separate into several bright and dark fringes. The number of dark fringes between two bright spots is just equal to the topological charge (TC) of the vortex beam. Meanwhile, the intensity pattern varies with the sign of TC. Based on this property, we proposed a convenient method to measure the TC of a vortex beam by observing its intensity pattern after passing through a twisting phase. This detection technique is mainly based on the use of twisting phase, and the effect of parameters in twisting phase is also demonstrated and clearly studied. By choosing proper parameters in twisting phase, the separation speed of vortex beam’s intensity could be controlled in the experiment. The experimental results are in good agreement with the theoretical analyses.

Multiple foci modulation with controllable positions and intensity ratios through decomposed optimization

Tao Zhang, Mujun Li, Jinfeng Qiu, CUICUI SHI, and peng chen

Doc ID: 362633 Received 18 Mar 2019; Accepted 04 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: In this Letter, multiple foci modulation with controllable positions and intensity ratios is presented with a multi-belt binary phase mask in a tightly focusing system. Different from previous methods, the diffractive optical element (DOE) in our model is firstly virtually decomposed into two or more simple sub-DOEs. Then after optimization the sub-DOEs are combined to form the desired DOE through superposition. By such a decomposed optimization, the optimization complexities are greatly reduced and the calculation become simpler and more effective. Furthermore, since the quantities and structures of sub DOEs can be adjustable according to the original DOE, the method is very flexible and adaptable . As a demonstration, up to 9 foci on the optical axis are studied and simulation results show that multiple foci can be well modulated. The proposed method may provide a universal strategy for complex light field modulations in a simple way.

Formation of uniform two-dimensional subwavelength structures by delayed Triple femtosecond laser pulse irradiation

Sohail Jalil, Jianjun Yang, Mohamed ElKabbash, Yuhao Lei, Wanlin He, and Chunlei Guo

Doc ID: 360396 Received 18 Feb 2019; Accepted 04 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: Fabrication of subwavelength two-dimensional structures on metals is of paramount importance to modern nanophotonics. Here, we report a method to fabricate two dimensional conic structures on Nickel surfaces using a single beam with three, temporally delayed, pulses. The two-dimensional structures are fabricated over the entire irradiated region with relatively high uniformity. By controlling the delay between the three pulses, we control the effect of each pulse in creating laser induced periodic surface structures which enables the control of the two-dimensional structure features, namely, the period and structure dimensions. We explain the results based on the surface plasmon polariton-femtosecond laser interference model

All-fiber self-compensating polarization encoder for Quantum Key Distribution

Giuseppe Vallone, Costantino Agnesi, Marco Avesani, Paolo Villoresi, and Andrea Stanco

Doc ID: 361423 Received 04 Mar 2019; Accepted 04 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: Quantum Key Distribution (QKD) allows distant parties to exchange cryptographic keys with unconditional security by encoding information on the degrees of freedom of photons. Polarization encoding has been extensively used in QKD implementations along free-space, optical fiber and satellite-based links. However, the polarization encoders used in such implementations are unstable, expensive, complex and can even exhibit side-channels that undermine the security of the implemented protocol. Here we propose a self-compensating polarization encoder based on a Lithium Niobate phase modulator inside a Sagnac interferometer and implement it using only standard telecommunication commercial off-the-shelves components (COTS). Our polarization encoder combines a simple design and high stability reaching an intrinsic quantum bit error rate as low as 0.2%. Since realization is possible from the 800 nm to the 1550 nm band by using COTS, our polarization modulator is a promising solution for free-space, fiber and satellite-based QKD.

Iterative wavefront tailoring to simplify freeform optical design for prescribed irradiance

ZeXin Feng, Dewen Cheng, and Yongtian Wang

Doc ID: 361256 Received 11 Mar 2019; Accepted 04 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: The direct determination of a freeform optical surface for producing a prescribed irradiance from a point source is extremely complicated and tedious. Instead of directly formulating the freeform optical surfaces, we derive a general equation of a parametrized outgoing wavefront regardless of the structure of the optical element. A separate process is employed to construct the freeform optics following the solution of the wavefront equation. We iteratively revise the wavefront and accordingly update the freeform optics to improve the performance. The new method combines two features: (i) the formula derivation process is sufficiently simplified while the accuracy is still guaranteed, and (ii) it can flexibly construct a variety of freeform optical structures.

Gouy phase assisted topological transformation of vortex beams from fractional fork holograms

Maruthi Brundavanam, Satyajit Maji, and ARABINDA MANDAL

Doc ID: 359341 Received 01 Feb 2019; Accepted 04 Apr 2019; Posted 05 Apr 2019  View: PDF

Abstract: The topological transformation of optical vortex beams from fractional order fork holograms induced by controlled modulation of Gouy phase is demonstrated. The Gouy phase change is tuned by varying wavefront curvature of the input beam on the plane of fractional phase generating optic. The locus of the point of singularity traces a semi-circle about the beam axis with the maximum possible change of the associated Gouy phase. The morphology parameters describing the anisotropic vortex phases of generated optical vortices are tuned in the experiment with varying input wavefront curvature. Through the transformation of the transverse Poynting vector of the fractional vortex beams, control of the extrinsic orbital angular momentum is achieved. This could enable better manipulation control of an optically trapped micro-particle in a spatially structured beam.

Generation of 35 kW peak power 80 fs pulses at 3 µm from a fully fusion-spliced fiber laser

Hugo Delahaye, Geoffroy Granger, Jean-Thomas Gomes, Laure Lavoute, Dmitry Gaponov, Nicolas Ducros, and Sebastien Fevrier

Doc ID: 362073 Received 11 Mar 2019; Accepted 03 Apr 2019; Posted 03 Apr 2019  View: PDF

Abstract: Tunable femtosecond light sources in the short wave and middle wave infrared regions are of utmost importance for various applications ranging from multiphoton microscopy, mid-infrared supercontinuum generation to high-harmonic generation in solids. We report on an all-fusion-spliced fiber laser emitting 80 fs pulses up to 3 µm with 35 kW peak power. The laser is based on Raman self-frequency shift effect from 1560 nm up to 3000 nm in germanium-doped fibers fabricated by the widespread modified chemical vapor deposition process.

Inverted Hartmann mask for single-shot phase-contrast X-ray imaging of dynamic processes

Margarita Zakharova, Stefan Reich, Andrey Mikhaylov, Vitor Vlnieska, Tomy dos Santos Rolo, Anton Plech, and Danays Kunka

Doc ID: 362398 Received 14 Mar 2019; Accepted 02 Apr 2019; Posted 08 Apr 2019  View: PDF

Abstract: In this contribution, we present the application of the inverted Hartmann mask for time-resolved single-shot phase-contrast X-ray imaging. The inverted Hartmann mask is a periodic array of free-standing gold pillars. The array was manufactured by UV lithography and electroplating. Time-resolved measurements have been performed for imaging of pulsed laser ablation in liquids using white beam synchrotron radiation. Image processing was performed following the Fourier analysis approach. The inverted Hartmann mask in combination with single-shot imaging technique provides a sufficient differential phase contrast even at very short exposure times. It can be effectively used for phase-contrast X-ray imaging of fast dynamic processes with a temporal resolution on the millisecond scale.

Strong multiphoton absorption in chiral CdSe/CdS dot/rod nanocrystal-doped poly(vinyl alcohol) films

Xin Qiu, Junjie Hao, Junzi Li, Z. R. Gong, Shang LI, Jiaji Cheng, Xiaodong Lin, and Tingchao He

Doc ID: 362943 Received 20 Mar 2019; Accepted 01 Apr 2019; Posted 03 Apr 2019  View: PDF

Abstract: Cysteine-capped cadmium selenide/cadmium sulfide (CdSe/CdS) dot/rod nanocrystals (NCs) were synthesized and then doped in poly(vinyl alcohol) (PVA) films. Compared with an L-/D-cysteine-capped NC solution (10-4), the anisotropic factors of the circular dichroism and circular polarized luminescence in the doped PVA films increased by one order of magnitude, probably because of the enhanced anisotropy degree, crystal orientations, and ordered morphologies. The two- and three-photon absorption coefficients of the doped PVA films were determined as 0.58 cm/GW at 800 nm and 2.3×10-4 cm3/GW2 at 1300 nm, respectively. The chiral NC-doped PVA films are promising for applications in chirality-related nonlinear photonic devices.

Novel Numerical Algorithm with Fourth-Order Accuracy for the Direct Zakharov-Shabat Problem

Sergey Medvedev, Irina Vaseva, Igor Chekhovskoy, and Mikhail Fedoruk

Doc ID: 360847 Received 25 Feb 2019; Accepted 01 Apr 2019; Posted 03 Apr 2019  View: PDF

Abstract: We propose a new high-precision algorithm for solving the initial problem for the Zakharov-Shabat system. This method has the fourth order of accuracy and is a generalization of the second order Boffetta-Osborne scheme. It is allowed by our method to solve more effectively the Zakharov-Shabat spectral problem for continuous and discrete spectra.

Demonstration of Anti-Stokes Cooling in Yb-doped ZBLAN Fibers at Atmospheric Pressure

Jennifer Knall, Arushi Arora, Martin Bernier, Solenn Cozic, and Michel Digonnet

Doc ID: 357261 Received 18 Jan 2019; Accepted 01 Apr 2019; Posted 09 Apr 2019  View: PDF

Abstract: For the first time, optical cooling is demonstrated in a fiber at atmospheric pressure. Using a specialized slow-light fiber Bragg grating temperature sensor, -5.2 mK and -0.65 K were measured in a single-mode (1% YbF₃) and multimode (3% YbF₃) ZBLAN fiber with respective cooling efficiencies of 2.0% and 0.85%. Fitting a recently reported quantitative model of optical cooling in fibers to the measured temperature change dependence on the pump power per unit length validates the model and allowed us to infer the fibers’ absorptive loss and quenching lifetime, key parameters that are scarce in the literature. Knowledge of these values is necessary for accurate cooling predictions, and it will aid in the development of fibers for application in optical coolers and radiation-balanced lasers. The model predicts that the maximum negative temperature change for the multimode fiber (-0.95 K) is achieved with 1.7 W of 1030-nm pump power. These results confirm that a large doped area is essential to achieve significant cooling in a fiber device.

Multiscale, multispectral fluorescence lifetime imaging using a double clad fiber

Benjamin Sherlock, Cai Li, Xiangnan Zhou, Alba Alfonso Garcia, Julien Bec, Diego Yankelevich, and Laura Marcu

Doc ID: 359074 Received 31 Jan 2019; Accepted 01 Apr 2019; Posted 04 Apr 2019  View: PDF

Abstract: Fiber-based imaging of tissue autofluorescence using UV excitation is a highly flexible tool to probe structure and composition. In this letter, we report first results from a single-fiber imaging system employing a custom double-clad fiber to acquire multispectral fluorescence lifetime images at two spatial resolutions. We characterize the lateral point spread function and fluorescent background of the system and show how enhanced resolution can identify trabeculae in murine bone.

A 40dB Gain all Fiber Bismuth-doped Amplifier Operating in the O-band

Naresh Kumar Thipparapu, Yu Wang, Andrey Umnikov, Pranabesh Barua, David Richardson, and Jayanta Sahu

Doc ID: 354803 Received 11 Dec 2018; Accepted 01 Apr 2019; Posted 01 Apr 2019  View: PDF

Abstract: In this paper, we investigate and compare the gain and noise figure characteristics of bismuth (Bi)-doped fiber amplifiers configured in both single and double signal pass implementations. A maximum gain of 25dB and a noise figure of 4dB is measured at 1360nm in the single pass configuration for - dBm input signal power, whereas in the double pass configuration the gain of the amplifier is improved significantly by 14dB allowing us to achieve a gain of 39dB with a noise figure of 5dB. To the best of our knowledge, this is the highest gain reported to date using Bi-doped fiber as a gain medium. Furthermore, we also study the gain and noise figure dependency on pump power, signal power and pump wavelength for the double pass amplifier configuration. We observed similar gain and noise figure performance in the double pass configuration to that of the single pass configuration but with the benefit of less pump power and a shorter length of the Bi-doped fiber.

Coherent control of acoustic phonons by seeded stimulated Brillouin scattering

Yaming Feng, Fangxing Zhang, Yuanlin Zheng, Lei Chen, Dongyi Shen, Wenjie Wan, and Wei Liu

Doc ID: 347479 Received 11 Oct 2018; Accepted 01 Apr 2019; Posted 04 Apr 2019  View: PDF

Abstract: Coherent excitation of phonons by optical waves, one of the most important channels for light-matter interactions, provides a promising route for optical manipulation of microscopic acoustic phonons for quantum opto-mechanic and phononic devices. Prior researches like stimulated Brillouin scattering in fibers mainly emphasized on phonons’ amplitude modulation; however, coherent phase control of these phonons has not yet been well explored. Here we experimentally demonstrate a new mechanism to coherently control acoustic phonons’ phases by a seeded stimulated Brillouin scattering scheme in an optical fiber. Interference between acoustic phonons enables either nearly total transmission or enhanced reflection of optical waves, effectively controlled by phase modulation. This new technique addresses the crucial problem of phase-controlled phonon generation, paving the way for important applications in quantum opto-mechanic and phononic devices.

Seeing infrared optical vortex arrays with a nonlinear spiral phase filter

Fei Lin, Xiaodong Qiu, wuhong zhang, and Lixiang Chen

Doc ID: 360230 Received 18 Feb 2019; Accepted 31 Mar 2019; Posted 01 Apr 2019  View: PDF

Abstract: We demonstrate a new method to detect infrared optical vortex arrays efficiently, which is based on simultaneous upconversion imaging and spiral phase contrast via second harmonic generation (SHG) in the Fourier domain. In our experiment, we use a spatial light modulator to prepare a variety of 1064 nm structured vortex arrays and employ a vortex phase plate of different topological charges to serve as the nonlinear orbital angular momentum (OAM) filter. The SHG is done by mixing the Fourier spectra of input structured vortices with a single OAM beam in a type-II potassium titanyl phosphate (KTP) crystal. Then we can convert the input invisible vortex arrays into the visible SHG light fields, and the vortex cores are mapped and seen by bright Gaussian spots, revealing both their positions and topological charges. Our work has potential in the field of infrared imaging and monitoring.

Single-frequency self-sweeping Nd-doped fiber laser

Ivan Lobach, Sergey Kablukov, and Ekaterina Kashirina

Doc ID: 363661 Received 28 Mar 2019; Accepted 31 Mar 2019; Posted 02 Apr 2019  View: PDF

Abstract: We for the first time experimentally demonstrate a Nd-doped fiber laser with wavelength self-sweeping. The main feature of the laser is generation of periodic microsecond pulses where each of them contains practically only single longitudinal mode radiation with linewidth of about 1 MHz. The laser frequency changes from pulse to pulse with high linearity by one intermode beating frequency of the laser ~7.1 MHz. The laser generates linearly-polarized radiation near wavelength of 1.06 µm with self-sweeping range of up to 1.8 nm.

Focusing light in biological tissue through a multimode optical fiber: refractive index matching

Raphaël Turcotte, Carla Schmidt, Nigel Emptage, and Martin Booth

Doc ID: 361164 Received 13 Mar 2019; Accepted 30 Mar 2019; Posted 01 Apr 2019  View: PDF

Abstract: Controlling light propagation through a step-index multimode optical fiber (MMF) has several important applications, including for biological imaging. However, little consideration has been given to the coupling of fiber and tissue optics. Here, we characterized the effects of tissue-induced light distortions, in particular those arising from a mismatch in the refractive index of the pre-imaging calibration and biological media. By performing the calibration in a medium matching the refractive index of brain, optimal focusing ability was achieved, as well as a gain in focus uniformity within the field-of-view. These changes in illumination resulted in a 30% improvement in spatial resolution and intensity in fluorescence images of beads and live brain tissue. Beyond refractive index matching, our results demonstrate that sample-induced aberrations can severely deteriorate images from MMF-based systems.

Nano-antenna enhanced waveguide integrated light source based on MIS tunnel junction

Baohu Huang, Siping Gao, Yan Liu, Jian Wang, Zhenguo Liu, YONGXIN guo, and Lu Weibing

Doc ID: 361238 Received 07 Mar 2019; Accepted 30 Mar 2019; Posted 09 Apr 2019  View: PDF

Abstract: Ultrafast electro-optical conversion at nanoscale is of fundamental interest for information transfer and optical interconnects. Light emission from a quantum tunnel junction provides an opportunity owing to its unique capability of ultrafast response and small footprint. However, the main challenge to the wide adoption of the tunnel junction is its low emission efficiency caused by the low inelastic electron tunneling proportion and radiation efficiency. In this Letter, an electrically driven silicon light source with its efficiency enhanced by using a nano-antenna in a metal-insulator-semiconductor junction is proposed. Strong plasmon confinement in the nano-antenna provides large local density of optical states and bridges the wave vector mismatch between nanoscale volumes field confinement and far-field radiation. Two orders of magnitude of emission enhancement is achieved over typical planar MIS junctions.

Experimental realization of dark and antidark diffraction-free beams

Xinlei Zhu, Fei Wang, Chengliang Zhao, Yangjian Cai, and Sergey Ponomarenko

Doc ID: 362288 Received 13 Mar 2019; Accepted 29 Mar 2019; Posted 03 Apr 2019  View: PDF

Abstract: We report the first, to our knowledge, experimental realization of high-quality dark and antidark diffraction-free beams, first theoretically proposed by Ponomarenko et al. [Opt. Lett. 32, 2508 (2007)]. Our method employs a single spatial light modulator (SLM) and is based on superposing mutually uncorrelated but spatially coherent in the time domain Bessel modes with modal weights proportional to the SLM display times of the corresponding modes. We also experimentally verify diffraction-free properties of the generated beams upon their free space propagation.

Structured illumination in compact and field-portable3D-printed shearing digital holographic microscopy for resolution enhancement

Bahram Javidi, Ana Doblas, and Timothy O'Connor

Doc ID: 356786 Received 03 Jan 2019; Accepted 28 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: A compact and field-portable 3D-printed structured illumination (SI) digital holographic microscope based on shearing geometry is presented. By illuminating the sample using a SI pattern, the lateral resolution in both reconstructed phase and amplitude images can be improved up to twice the resolution provided by conventional illumination. The use of a 3D-printed system and shearing geometry reduces complexity of the system while providing high temporal stability. Experimental results for the USAF resolution target show a resolution improvement of a factor of two which corroborates the theoretical prediction. Resolution enhancement in phase imaging is also demonstrated by imaging a biological sample. To the best of our knowledge, this is the first report of a compact and field-portable structured illumination digital holographic system based on shearing geometry.

Compact dynamic optical isolator based on tandemphase modulators

Jiahui Wang, Shanhui Fan, and Qian Lin

Doc ID: 359487 Received 04 Feb 2019; Accepted 27 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: Non-magnetic dynamic optical isolators, constructedfrom modulators, provide a CMOS-compatible approachto optical isolation in integrated photonics. Thesize of these isolators is strongly constraint by boththe frequency and the strength of optical modulation.Recent developments in modulators have indicatedthat large modulation strength, with a magnitude refractiveindex modulation up to unity, may be possibleat GHz modulation frequency. In this paper, weshow that a previously proposed dynamic isolator design,based on tandem modulators, can be modified totake advantage of the possibility of such large modulationstrength. Compared with the previously proposed tandem-modulator design, our modification can lead tosignificant reduction of the device length without theneed to increase modulation frequency.

The Impact of Spatial Correlation in Fluctuations of the Refractive Index on Rogue Wave Generation Probability

Arash Mafi, Mostafa Peysokhan, and John Keeney

Doc ID: 359991 Received 12 Feb 2019; Accepted 27 Mar 2019; Posted 01 Apr 2019  View: PDF

Abstract: The presence of refractive index fluctuations in an optical medium can result in the generation of optical rogue waves. Using numerical simulations and statistical analysis, we have shown that the probability of optical rogue waves increases in the presence of spatial correlations in the fluctuations of the refractive index. We have analyzed the impact of the magnitude and the spatial correlation length of these fluctuations on the probability of optical rogue wave generation.

A high beam quality, Watt-level, widely tunable, mid-infrared OP-GaAs optical parametric oscillator

Qiang Fu, Lin Xu, Sijing Liang, Peter Shardlow, David Shepherd, Shaif-Ul Alam, and David Richardson

Doc ID: 360322 Received 19 Feb 2019; Accepted 26 Mar 2019; Posted 26 Mar 2019  View: PDF

Abstract: We demonstrate near-diffraction-limited performance from a mid-infrared (mid-IR), idler-resonant, fiber-laser-pumped, widely tunable, picosecond optical parametric oscillator (OPO) based on orientation-patterned GaAs (OP-GaAs). The OP-GaAs OPO is synchronously pumped by a picosecond Tm:fiber master–oscillator-power-amplifier (MOPA) system. An OPO tuning range of 4394-6102 nm (idler) and 2997-3661 nm (signal) is achieved, with maximum average powers of 1.18 W (idler, 5580nm) and 0.51 W (signal, 3136 nm). The idler beam has M2 values of 1.06 (x-direction) by 1.03 (y-direction).

Eigenvalue calibration method for 3×3 Mueller polarimeters

Ji Qi, Daniel Elson, and Danail Stoyanov

Doc ID: 359997 Received 12 Feb 2019; Accepted 25 Mar 2019; Posted 28 Mar 2019  View: PDF

Abstract: 3×3 Mueller polarimetry has shown promising potential for applications in tissue characterization. However, calibration of a 3×3 Mueller polarimeter has not been fully addressed to date. Here, we demonstrate an eigenvalue calibration method for 3×3 Mueller polarimeters, inspired by the eigenvalue calibration method for complete Mueller polarimeters. We also investigate the optimal combination of calibration measurements. Our method does not rely on modelling the PSG, PSA, or precise knowledge about the properties or orientations of the calibration samples. It is therefore easy to implement in practice, and experimental results are presented of a linear polarizer test sample as well as a biological specimen.

A compact, robust and high-efficiency generator of vector optical fields

Rui Liu, Ling-Jun Kong, Wen-Rong Qi, Shuang-Yin Huang, Zhou-Xiang Wang, Chenghou Tu, Yongnan Li, and Hui-Tian Wang

Doc ID: 349120 Received 24 Oct 2018; Accepted 21 Mar 2019; Posted 09 Apr 2019  View: PDF

Abstract: We design and realize a generator that can convert an orbital angular momentum (OAM) state into a vector polarization state. The generator is integrated by several commonly used optical elements and easy to make orglued. Compared with traditional interferometric ways for generating the vector optical fields, this integrated generator has compact and robust advantages and especially a high-efficiency of 87%.

Long-Term Stable Supercontinuum Generation and Watt-level Transmission in Liquid Core Optical Fibers

Kay Schaarschmidt, Hongwen Xuan, Jens Kobelke, Mario Chemnitz, Ingmar Hartl, and Markus Schmidt

Doc ID: 355507 Received 19 Dec 2018; Accepted 18 Jan 2019; Posted 27 Mar 2019  View: PDF

Abstract: Due to their unique properties such as transparency, tunability, nonlinearity and dispersion flexibility, liquid-core fibers represent an important approach for future coherent mid-infrared light sources. However, the damage thresholds of those fibers are largely unexplored. Here, we report on the generation of soliton-based supercontinuum in carbon disulfide (CS2) liquid-core fibers at average power levels as high as 0.5 W operating stable for a long term (>70 hours) without any kind of degradation or damage. Additionally, we also show stable high power pulse transmission through liquid-core fibers exceeding 1 W of output average power for both CS2 and tetrachloroethylene (C2Cl4) as core materials.

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