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Accepted papers to appear in an upcoming issue

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Measurement of UV-induced absorption and scattering losses in photosensitive fibers

Xavier Roselló-Mechó, Martina Delgado-Pinar, Jose Cruz, Antonio Diez, and Miguel Andrés

Doc ID: 322974 Received 19 Feb 2018; Accepted 20 May 2018; Posted 21 May 2018  View: PDF

Abstract: UV-assisted fabrication of gratings using photosensitive fibers is a well-established technique, based on the UV-induced permanent modification of the refractive index of the fiber material. As a result, the absorption coefficient is also changed. Here, we exploit the thermal sensitivity of whispering gallery modes resonances of the fiber itself to measure the profile of the heating along an irradiated fiber versus the input power and for different UV radiation intensities. Our technique allows discriminating between the absorption and scattering contributions to the overall losses, by comparing the results obtained with our technique with direct transmission measurements. Different photosensitive fibers are characterized by means of this technique. Non uniform UV irradiation of photosensitive fibers can be characterized with this technique.

Chalcogenide glass waveguides with paper-based fluidics for mid-infrared absorption spectroscopy

Vinita Mittal, Milos Nedeljkovic, David Rowe, Ganapathy Senthil Murugan, and James Wilkinson

Doc ID: 328711 Received 18 Apr 2018; Accepted 20 May 2018; Posted 21 May 2018  View: PDF

Abstract: We demonstrate the integration of paper fluidics with mid-IR chalcogenide waveguides to introduce liquid samples to the waveguide evanescent field for analysis. Spectroscopy of model analytes (water and IPA) having well-defined mid-IR absorptions, on a ZnSe rib waveguide fabricated on silicon, is demonstrated in the wavelength range 2.6 – 3.7 µm, showing their O-H and C-H stretching absorptions. The results are compared with a theoretical waveguide model, achieving good agreement. It is concluded that the presence of paper in the evanescent field does not interfere with the waveguide measurements, opening up opportunities to combine low-cost paper-based fluidics and integrated photonic technologies.

Broadband light absorption of an Al semishell-MIM nanostrucure in the UV to near-infrared regions

Kishin Matsumori and Ryushi Fujimura

Doc ID: 328642 Received 20 Apr 2018; Accepted 19 May 2018; Posted 21 May 2018  View: PDF

Abstract: A plasmonic broadband light absorber, whose absorption is insensitive to incident angles and polarizations, in the UV to near-infrared regions is demonstrated. In experimental observations, the maximum average absorption of 83% over the wavelength range from 300 to 1000 nm was confirmed. Our proposed plasmonic absorber is based on a three-layer stack of metal-insulator-metal, and the top metal layer is nanostructured by colloidal lithography. This structure comprises of Al, which is excellent and cost-effective plasmonic material. These fabrication simplicity and economical material allow us to produce large scale device of solar absorbers.

Efficient estimation of subdiffusive optical parameters in real time from spatially resolved reflectance by artificial neural networks

Matic Ivancic, Peter Naglic, Franjo Pernus, Bostjan Likar, and Miran Bürmen

Doc ID: 323459 Received 22 Feb 2018; Accepted 18 May 2018; Posted 21 May 2018  View: PDF

Abstract: Subdiffusive reflectance captured at short source-detector separations provides increased sensitivity to the scattering phase function and hence allows superficial probing of the tissue ultrastructure. Consequently, estimation of subdiffusive optical parameters has been the subject of many recent studies focusing on lookup table-based (LUT) inverse models. Since adequate description of the subdiffusive reflectance requires additional scattering phase function related optical parameters, the LUT inverse models, that grow exponentially with number of estimated parameters, become excessively large and computationally inefficient. Herein, we propose the first artificial neural network-based inverse Monte Carlo model that overcomes the limitations of the LUT inverse models and thus allows efficient real-time estimation of optical parameters from subdiffusive spatially resolved reflectance. The proposed inverse model retains the accuracy, is about four orders of magnitude faster than the LUT inverse models, grows only linearly with the number of estimated optical parameters and can be easily extended to estimate additional optical parameters.

Electronically delay-tuned upconversion cross-correlator for characterization of mid-infrared pulses

Laurent Huot, Peter Moselund, Peter Tidemand-Lichtenberg, and Christian Pedersen

Doc ID: 327377 Received 02 Apr 2018; Accepted 18 May 2018; Posted 21 May 2018  View: PDF

Abstract: In this paper, a novel method for the characterization of mid-infrared pulses is presented. A cross-correlator system with no moving parts combining ultra-broadband pulsed upconversion detection with fast active electronic delay tuning was built to perform time-resolved spectral characterization of 1.6 ns mid-infrared supercontinuum pulses. Full wavelength/time spectrograms were acquired in steps of 20 ps over a range that can in theory extend to microseconds, in a matter of seconds, with 48 ps temporal resolution and 22 cm-¹ spectral resolution in the 2700 nm to 4300 nm range. This work proves the potential of the use of electronic delay tuning instead of mechanical delay for applications like cross-correlators and laser spectroscopy where their fast precise tunability and long delay ranges are a strong asset.

Modulating complex beams in amplitude and phase using fast tilt-micromirror arrays and phase masks

Matthias Roth, Joerg Heber, and Klaus Janschek

Doc ID: 324983 Received 20 Mar 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: The article proposes a system for the spatial modulation of light in amplitude and phase at kHz frame rates and high spatial resolution. The focus are fast spatial light modulators (SLMs) consisting of continuously tiltable micromirrors. We investigate the utilization of such SLMs in combination with a static phase mask (PM) in a 4f setup. The PM enables the complex beam modulation in a linear optical arrangement. Furthermore, adding so-called phase steps to the PM increases both the number of image pixels at constant SLM resolution and the optical efficiency. We illustrate our concept based on numerical simulations.

Simplified read schemes for krypton tagging velocimetry in N₂ and air

Muhammad Mustafa and Nicholaus Parziale

Doc ID: 329018 Received 25 Apr 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: The background and results for two simplified read schemes for krypton tagging velocimetry (KTV) are presented. The first scheme utilizes the excitation/re-excitation approach found in the literature, but replaces the pulsed dye-laser used for the re-excitation step with a continuous-wave, narrow-band, laser diode. The second scheme is a single-laser setup with no read laser where the fluorescence of the tagged Kr is imaged at successive times. Results are presented and compared to historical data for experiments performed in 99% N₂/1% Kr and 95% air/5% Kr underexpanded jets. The approach with the laser diode has higher signal, while the single-laser approach yields more consistent results. Both schemes maintain an SNR comparable to that in the literature, but with a simpler setup that enables future high-repetition rate KTV experiments.

Linear response theory for periodically driven systems with non-Markovian effects

Hong-Zhi Shen, X X Yi, Shuang Xu, Hong Li, and Song lin Wu

Doc ID: 330661 Received 30 Apr 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: In linear response theory, all the works devoted to studies on this topic formulated in the Schr\"odinger picture, in which the key quantity ${{\hat \varphi }_n}(t) = U(t)[{{\hat Y}_n},{\rho _{eq}}]{U^\dag }(t)$ with $U(t) = \mathcal {T}{e^{ - \frac{i}{\hbar }\int_0^t {\hat H(t')dt'} }}$ is not a density matrix. Second, the Kubo formula for Floquet periodic driving systems in non-Markovian regimes have not been clear so far. In this Letter, we propose a new method to address those issues by introducing Heisenberg operators to derive an exact susceptibility for the non-Markovian Floquet periodic-driving system. The susceptibility includes all the influences of the environment on the Floquet system. We will show that the susceptibility connects closely to the structure of Floquet energy spectrum of the whole system (system plus environment). Moreover, we can read out Floquet bound-states in the first Brillouin zone of the whole system from the susceptibility. The presented results may find applications in quantum engineering with open systems following modulated periodic evolution in quantum optics.

Self calibration of lensless holographic endoscope using programmable guide stars

Robert Kuschmierz, Elias Scharf, Juergen Czarske, and Nektarios Koukourakis

Doc ID: 320588 Received 24 Jan 2018; Accepted 18 May 2018; Posted 21 May 2018  View: PDF

Abstract: Endoscopes enable optical keyhole access in differentapplications such as biophotonics. Commonly, coherentfiber bundles (CFB) in conjunction with lens systemsare employed, resulting in a fixed image plane.Since CFBs feature strong phase distortions only pixelatedintensity patterns can be transmitted. These limitationscan be overcome by digital optical phase conjugation.This enables lensless holographic endoscopesfor the generation of pixelation free arbitrary light patternswithout distal optics for applications such as scanningmicroscopy, optical tweezers or optogenetics. Itrequires a non-invasive in-situ calibration of the complexoptical transfer function of the CFB without distalaccess, however. We present a novel in-situ calibrationprocedure, which does not require invasive access andis based on a programmable guide star.

Fresnel diffraction due to phase gradient singularity

Ahad Saber, Ehsan Ahadi Akhlaghi, and zahra abbasi

Doc ID: 326143 Received 19 Mar 2018; Accepted 18 May 2018; Posted 18 May 2018  View: PDF

Abstract: In this letter, a singularity in the phase gradient is introduced as a new origin of the diffraction from phase objects. The continuity in the amplitude and phase of the wave, and singularity in the phase gradient are assumed to describe this phenomenon. Fresnel diffraction of Fresnel double mirror and biprism are studied as practical examples, and the diffracted intensity distribution is calculated. We show that the intensity of the diffracted field varies with an almost constant period along the average propagation direction. Using this value and the fringe spacing of the interference pattern on a plane normal to the average propagation direction, the angle between two interfering beams and wavelength of the incident light could be simultaneously derived. The diffraction pattern of the Fresnel double mirror and Fresnel biprism were obtained experimentally, which were in good agreement with the theoretical results.

Energy scalable, offset-free ultrafast mid-infrared source harnessing self-phase modulation enabled spectral selection

Guoqing Chang, Gengji Zhou, Franz Kaertner, and Qian Cao

Doc ID: 326477 Received 21 Mar 2018; Accepted 17 May 2018; Posted 18 May 2018  View: PDF

Abstract: We demonstrate a high-power offset-free ultrafast mid-IR laser source based on difference frequency generation (DFG). Powerful signal pulses are obtained by filtering the rightmost spectral lobe of optical spectra broadened by fiber-optic nonlinearities dominated by self-phase modulation. The resulting mid-IR pulses are tunable from 7 μm to 18 μm with up to 5.4-mW average power. We experimentally and numerically investigate power scaling of this DFG source and demonstrate that increasing the signal power is an efficient approach for generating high power mid-IR pulses. Our approach has the potential to implement close to Watt level mid-IR frequency combs

High-speed image-reconstruction algorithm for a spatially multiplexed image and application to digital holography

Tatsuki Tahara, Takuya Gotohda, Takanori Akamatsu, Yasuhiko Arai, Tomoyoshi Shimobaba, Tomoyoshi Ito, and Takashi Kakue

Doc ID: 325533 Received 07 Mar 2018; Accepted 17 May 2018; Posted 21 May 2018  View: PDF

Abstract: We propose a high-speed image-reconstruction algorithm for a spatially multiplexed image that is obtained by spatial frequency-division multiplexing. The algorithm utilizes smoothing, and does not require any Fourier transform and iterative procedure to extract the desired information selectively from a single image. Numerical and experimental results show its validity and color holographic imaging ability. More than ten times acceleration is achievable in comparison to the Fourier transform method when using a CPU and an image sensor with 4 Mega pixels. Furthermore, three times speeding up can be achieved in the case of using a graphics processing unit (GPU).

Surface-enhanced circular dichroism by multipolar radiative coupling

Junsuk Rho and Jungho Mun

Doc ID: 326112 Received 15 Mar 2018; Accepted 17 May 2018; Posted 18 May 2018  View: PDF

Abstract: We present numerical investigation on mechanism of surface-enhanced circular dichroism of chiral medium near nano-antennas. Strong circular dichroism was observed from chiral medium surrounding nano antennas with multipolar resonant modes, and the strong circular dichroism was more correlated to the multipolar resonances than to nearfield enhancement or optical helicity enhancement. According to this observation, we suggest multipolar radiative coupling between the nano antennas and chiral medium as a possible mechanism of the strong chiral response. This work clarifies a mechanism of surface-enhanced chiral responses and would be useful for designing enantiomeric-sensing platform and realizing devices relying on strong chirality, such as topological metamaterials for scattering-immune propagation of light and negative index metamaterials.

Long-range surface plasmon polariton detection with graphene photodetector

Ho-Seok Ee, You-Shin No, Jinhyung Kim, Hong-Gyu Park, and Min-Kyo Seo

Doc ID: 328112 Received 13 Apr 2018; Accepted 17 May 2018; Posted 21 May 2018  View: PDF

Abstract: We present an integration of a single Ag nanowire with a graphene photodetector and demonstrate an efficient and compact detection of long-range surface plasmon polaritons (SPPs). Atomically thin graphene provides an ideal platform to detect the evanescent electric field of SPPs extremely bound at the interface of the Ag nanowire and glass substrate. Scanning photocurrent microscopy directly visualizes the polarization-dependent excitation and detection of the SPPs. The SPP detection responsivity is readily controlled up to ~17 mA/W by the drain-source voltage. We believe that the graphene SPP detector will be a promising building block for highly integrated photonic and optoelectronic circuits.

Experimental observation of the emergence of Peregrine-like events in focusing dam break flows

Christophe Finot, Julien Fatome, Bertrand Kibler, and Frederic Audo

Doc ID: 326532 Received 21 Mar 2018; Accepted 16 May 2018; Posted 18 May 2018  View: PDF

Abstract: Simple photonic fiber-based workbenches have been able to emulate well-known nonlinear wave dynamics occurring in deep- or shallow- water conditions. Here, by investigating the nonlinear reshaping of a flattop pulse upon propagation in an anomalous dispersive optical fiber, we observe that typical signatures of focusing dam break flows and Peregrine-like breather events, can locally coexist into spontaneous pattern formations. Experimental measurements are in good agreement with our numerical predictions. © 2018 Optical Society of America

Broadband and low-loss mode scramblers using CO₂-laser inscribed long-period gratings

Yunhe Zhao, Haoshuo Chen, Nicolas Fontaine, Jiaxiong Li, Roland Ryf, and Yunqi Liu

Doc ID: 327557 Received 03 Apr 2018; Accepted 16 May 2018; Posted 18 May 2018  View: PDF

Abstract: We demonstrate broad-band and low-loss 3-mode and 6-mode mode scramblers employing CO₂-laser inscribed long-period gratings (LPGs) for space-division multiplexing. Step-index (SI) few-mode fibers are used to avoid mode coupling to the cladding modes. We characterize the mode scramblers using a swept-wavelength interferometer. Mode-dependent loss (MDL) and modal transfer matrices over C+L band are present. Demonstrated mode scramblers are with negligible MDL and insertion loss (IL) contributed to high performance CO₂-laser inscription.

Simultaneous measurement of gas absorption spectra and optical pathlengths in a multipass cell by FMCW interferometry

Xiutao Lou, CHEN CHEN, Yabo Feng, and Yong Kang Dong

Doc ID: 327996 Received 09 Apr 2018; Accepted 16 May 2018; Posted 17 May 2018  View: PDF

Abstract: We present a novel method based on optical frequency-modulated continuous-wave (FMCW) interferometry that can realize simultaneous measurement of gas absorption spectra and optical pathlengths (OPLs) in the widely-used multipass cells (MPCs). This method involves twice Fourier transforms (FTs), by which the gas absorption spectrum and the OPL are retrieved in frequency and time domains, respectively. Various OPLs are achieved by retrieving gas absorption spectra associated with different reflection positions in the MPC. As a demonstration, absorption spectra of acetylene around 1520 nm are measured using a commercial White type MPC. Our proposed method shows advantages for MPC-based gas sensing applications in significant relaxation of OPL calibration demands and flexible extension of measurement dynamic range.

Enhanced differential detection technique for resonator integrated optic gyro

Qiwei Wang, Li Shuang Feng, Hui Li, Xiao Wang, Yongze Jia, and Danni Liu

Doc ID: 327708 Received 09 Apr 2018; Accepted 15 May 2018; Posted 15 May 2018  View: PDF

Abstract: An enhanced differential detection technique (EDDT) is proposed to suppress common-mode signal and improve detection accuracy of the resonator integrated optic gyro (RIOG). Reciprocity of the RIOG based on transmissive resonator is effectively promoted by proposing a novel structure, which is benefit for suppressing the reciprocal error. Theoretical analysis shows the differential-mode output of the EDDT, which is in proportion to gyro angular rotation, can be amplified without the limitation of the RIOG’s common-mode signal. The appropriate gain of the EDDT is also calculated by considering intrinsic noises of the RIOG. With the EDDT technique, a long-term bias stability of 0.0029 deg/s is successfully observed over a 2-hour timeframe which, to the best of our knowledge, is the best result reported in the open literature for the open-loop RIOG based on waveguide ring resonator.

Pulse train interaction and control in a microcavity laser with delayed optical feedback

Soizic Terrien, Bernd Krauskopf, Neil Broderick, Rémy Braive, Grégoire Beaudoin, ISABELLE SAGNES, and Sylvain barbay

Doc ID: 325270 Received 02 Mar 2018; Accepted 15 May 2018; Posted 18 May 2018  View: PDF

Abstract: We report experimental and theoretical results on the pulse train dynamics in an excitable semiconductor microcavity laser with integrated saturable absorber and delayed optical feedback. We show how short optical control pulses can trigger, erase or retime regenerative pulse trains in the external cavity. Both repulsive and attractive interactions between pulses are observed, and are explained in terms of the internal dynamics of the carriers. A bifurcation analysis of a model consisting of a system of nonlinear delay differential equations shows that arbitrary sequences of coexisting pulse trains are very long transients towards weakly stable periodic solutions with equidistant pulses in the external cavity.

A highly standardized multicolor femtosecond fiber system for orthogonal micro-photomanipulation of DNA and chromatin

Michael Schmalz, Ines Wieser, Felix Schindler, Christina Czada, Alfred Leitenstorfer, and Elisa Ferrando-May

Doc ID: 325316 Received 13 Mar 2018; Accepted 14 May 2018; Posted 18 May 2018  View: PDF

Abstract: We present a three-color femtosecond Er/Yb:fiber laser enabling highly specific and standardized nonlinear optical manipulation of live cells. The system simultaneously provides bandwidth-limited 80-fs pulses with identical intensity envelope centered at wavelengths of 515 nm, 775 nm and 1035 nm, respectively, in the focus of a confocal microscope. We achieve this goal by combining high-order dispersion control via e.g. chirped fiber Bragg gratings with proper bandwidth management in each nonlinear conversion step. Wavelength-selective and non-interfering induction of DNA photoproducts and DNA strand breaks, as well as fluorescence photo-activation of a PAGFP-histone fusion protein are demonstrated. The capability to introduce different types of DNA lesions and perform photoswitching experiments in an orthogonal manner is essential for quantitative studies on DNA repair and chromatin dynamics.

Single-polarization large-mode-area fiber laser mode-locked with a nonlinear amplifying loop mirror

Wu Liu, Haosen Shi, Jiahua Cui, Chen Xie, Youjian Song, Chingyue Wang, and Ming-lie Hu

Doc ID: 328238 Received 13 Apr 2018; Accepted 14 May 2018; Posted 15 May 2018  View: PDF

Abstract: The generation of high-power ultra-short pulses from a passively mode-locked fiber laser is reported based on the combination of a single-polarization large-mode-area photonic crystal fiber with a nonlinear amplifying loop mirror design. The introduction of a non-reciprocal phase shift in the loop mirror enables self-starting of the mode-locked laser, while the polarizing large-mode-area fiber supports environmentally stable high-power operation. Mode-locking in the soliton-like, stretched-pulse and all-normal-dispersion regime is characterized respectively. The laser generates stable pulses with up to 2 W average power at 72 MHz repetition rate, corresponding to a single pulse energy of 28 nJ. The output pulses are dechirped to a near transform-limited duration of 152 fs. The proposed fiber oscillator presents an alternative approach to high power ultrafast laser sources along with the environmental stability.

Broadened region for robust optical bistability in a nonlocal core-Kerr shell nanoparticle

Yang Huang and Lei Gao

Doc ID: 330439 Received 27 Apr 2018; Accepted 13 May 2018; Posted 15 May 2018  View: PDF

Abstract: With the self-consistent mean field approximation in the framework of full-wave nonlocal scattering theory, we carry out a theoretical study on the optical bistability in a nonlocal nanoparticle coated with a Kerr-type nonlinear shell. A Nonlocality enhanced Fano profile is found in its scattering spectrum. We demonstrate the nonlocality-broadened bistable region in the geometrical parameter space. we perform the investigation of the nonlinear dependences of the near field intensity and far field scattering on the incident wavelength, and found the input-wavelength-controllable as well as the input-field-intensity-controllable scattering. We check the stability of the nonlinear steady states and perform its temporal dynamical evolutions.

Particle Tracking by Repetitive Phase-Shift Interferometric Super Resolution Microscopy

Itay Gdor, Xiaolei Wang, Matthew Daddysman, Yuval Yifat, Rosemarie Wilton, Mark Hereld, Marie-Françoise Noirot-Gros, and Norbert Scherer

Doc ID: 326382 Received 28 Mar 2018; Accepted 13 May 2018; Posted 15 May 2018  View: PDF

Abstract: Accurate and rapid particle tracking is essential for addressing many research problems in single molecule and cellular biophysics, and colloidal soft condensed matter physics. We developed a novel three-dimensional (3D) interferometric fluorescent particle tracking approach that does not require any sample scanning. By periodically shifting the interferometer phase, the information stored in the interference pattern of the emitted light allows localizing particles positions with nanometer resolution. This tracking protocol was demonstrated by measuring a known trajectory of a fluorescent bead with sub-5 nm axial localization error at 5 Hz. Finally, the interferometric microscopy was used to track RecA protein in Bacillus subtilis bacteria to demonstrate its compatibility with biological systems.

High-Q chaotic lithium niobate microdisk cavity

Li Wang, Cheng Wang, Jie Wang, Fang Bo, Mian Zhang, Qihuang Gong, Marko Loncar, and Yun-Feng Xiao

Doc ID: 322691 Received 27 Feb 2018; Accepted 12 May 2018; Posted 18 May 2018  View: PDF

Abstract: Lithium niobate (LN) is the workhorse for modern optoelectronics industry and nonlinear optics. High quality (Q) factor LN microresonators are a promising candidate for applications in optical communications, quantum photonics and sensing. However, the phase-matching requirement of traditional evanescent coupling methods poses significant challenges to achieve high coupling efficiencies of the pump and signal light simultaneously, ultimately limiting the practical usefulness of these high Q factor LN resonators. Here, for the first time, we demonstrate deformed chaotic LN microcavities that feature directional emission patterns and high Q factors simultaneously. The chaotic LN microdisks are created using conventional semiconductor fabrication processes, with measured Q factors exceeding 106 in the telecommunication band. We show that our devices can be free-space coupled with high efficiency by leveraging directional emission from the asymmetric cavity. Using this broadband approach, we demonstrate orders of magnitude enhancement of free-space collection efficiency of second harmonic generation signal compared with a circular microdisk.

Tailorable dual-wavelength-band multiplexing in a TE-mode focusing subwavelength grating coupler

Wen Zhou, Zhenzhou Cheng, Xiankai Sun, and Hon Tsang

Doc ID: 328754 Received 18 Apr 2018; Accepted 12 May 2018; Posted 21 May 2018  View: PDF

Abstract: A transverse-electric-mode focusing subwavelength grating coupler (FSWGC) is proposed and demonstrated for dual-wavelength-band multiplexing (DWBM) and light coupling from a single-mode fiber into a suspended-membrane waveguide for the first time. Location and separation of the two coupling peaks can be flexibly tailored based on a proposed design methodology. As a proof of concept, two DWBM FSWGCs working at (1486.0, 1594.5) nm and (1481.5, 1661.5) nm are experimentally demonstrated with coupling efficiencies of (18.3%, 20.1%) and (14.5%, 17.5%), 3-dB bandwidths of (55.0, 30.5) nm and (44.0, >39.5) nm, respectively. A DWBM FSWGC working at (1480, 1830) nm with a wavelength separation of 350 nm and coupling efficiencies of (38.0%, 33.2%) is also numerically predicted.

Scattering and absorption in dense discrete random media of irregular particles

Johannes Markkanen, Timo Väisänen, Antti Penttilä, and Karri Muinonen

Doc ID: 327882 Received 10 Apr 2018; Accepted 11 May 2018; Posted 21 May 2018  View: PDF

Abstract: We present an approximate numerical solution for the multiple scattering problem involving densely packed arbitrarily shaped small particles. We define incoherent volume elements that describe the statistics of the random medium and formulate an order-of-scattering solution for the entire random medium. We apply the T-matrix formalism to compute the incoherent interactions of irregular particles in the sequence of scattering events in the Monte Carlo radiative transfer (RT) algorithm. The T-matrices for the volume elements of arbitrarily shaped particles are computed by the volume integral equation (VIE). We show that the approximate solution is in agreement with the numerically exact VIE solution for a small spherical random medium. Finally, we demonstrate the importance of applying irregular particle shape models in the analysis of multiple scattering by a large random medium of non-spherical particles.

Raman-Kerr frequency combs in Zr-doped silica hybrid microresonators

Hyungwoo Choi and Andrea Armani

Doc ID: 325371 Received 05 Mar 2018; Accepted 11 May 2018; Posted 17 May 2018  View: PDF

Abstract: Resonant cavity-enhanced Kerr frequency combs have been demonstrated using a range of cavity materials. Regardless of cavity type, one fundamental challenge is achieving low or flat dispersion while maintaining high efficiency four wave mixing. Here, we demonstrate a Raman-Kerr frequency comb using a Zr-doped silica hybrid toroidal microcavity. The Zr-doped layer both flattens the dispersion and increases the stimulated Raman scattering (SRS) efficiency. This enhancement enables the generation of four-wave-mixing around both the Stokes’s and anti-Stoke’s Raman scattering emissions. As a result, the Raman-Kerr frequency comb spans more than 300 nm in the near-IR region with less than 5.2mW of input power.

Fibonacci terahertz imaging by silicon diffractive optics

Domas Jokubauskis, Linas Minkevicius, Mindaugas Karaliūnas, Simonas Indrišiūnas, Irmantas Kašalynas, Gediminas Račiukaitis, and Gintaras Valušis

Doc ID: 328405 Received 17 Apr 2018; Accepted 11 May 2018; Posted 15 May 2018  View: PDF

Abstract: Fibonacci or bifocal terahertz (THz) imaging is demonstrated experimentally employing silicon diffractive zone plate (SDZP) in a continuous wave mode. Images simultaneously recorded in two different planes are exhibited at 0.6 THz frequency with the spatial resolution of wavelength. Multi-focus imaging operation of the Fibonacci lens is compared with a performance of the conventional silicon phase zone plate. Spatial profiles and focal depth features are discussed varying the frequency from 0.3 THz to 0.6 THz. Good agreement between experimental results and simulation data is revealed.

Elastography with low-frame-rate laser speckle contrast imaging using the aliasing effect

Xiao Chen, Jinling Lu, and Pengcheng Li

Doc ID: 325668 Received 08 Mar 2018; Accepted 11 May 2018; Posted 15 May 2018  View: PDF

Abstract: Elastography is an attractive technique for quantifying the mechanical properties of biological tissue. Here, we report an elastography method with low-frame-rate laser speckle contrast imaging (LSCI) using the aliasing effect. This method needs only one excitation source, a low-frame-rate camera, and no synchronization between excitation and acquisition. The accuracy of the elasticity measurement was validated on tissue-mimicking phantoms by comparing the value with the elasticity measured by a high-frame-rate LSCI and by the rheometer. Elastography was also performed on chicken breast in vitro.

Density characterization of discharged gas-filled capillaries based on two-color group velocity delay

Jeroen Van Tilborg, Anthony Gonsalves, Eric Esarey, Carl Schroeder, and Wim Leemans

Doc ID: 326244 Received 21 Mar 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: Electrically-discharged plasma structures, typically of several cm in length and sub-mm in diameter, have been applied to guide laser pulses in laser plasma accelerators (LPAs) and to focus ion and relativistic electron beams in compact, radially-symmetric transport configurations.Knowledge of the on-axis plasma density is critical, dominating LPA physics such as injection, acceleration, and dephasing, as well as mitigating beam-driven wakefield effects in particle beam transport.Traditional density interferometry has been ineffective for these laser-machined structures, while group velocity delay (GVD) techniques involve combining two laser lines with corresponding alignment complexities and sensitivities.Here the GVD technique is advanced by using only one incoming probe laser pulse. Through insertion of a frequency-doubling crystal, the relative density-dependent GVD between the co-propagating fundamental and harmonic pulses is recorded through spectral interferometry. This in-situ technique was validated on 1.5-cm long plasma structures, measuring electron densities of 1e17-1e18 cm-3 for various fill pressures.

Time domain diffuse correlation spectroscopy: Modeling the effects of laser coherence length and instrument response function

Xiaojun Cheng, Davide Tamborini, Stefan Carp, Oleg Shatrovoy, Bernhard Zimmerman, Danil Tyulmankov, Andy Siegel, Megan Blackwell, Maria Angela Franceschini, and David Boas

Doc ID: 327050 Received 29 Mar 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: Diffuse correlation spectroscopy (DCS) is an optical technique that non-invasively quantifies an index of blood flow ($BF_i$) by measuring the temporal auto-correlation function of the intensity fluctuations of light diffusely remitted from the tissue. Traditional DCS measurements use continuous wave (CW) lasers with coherence lengths longer than the photon path lengths in the sample to ensure that the diffusely remitted light is coherent and generates a speckle pattern. Recently, we proposed time domain DCS (TD-DCS) to allow measurements of the speckle fluctuations for specific path lengths of light through the tissue, which has the distinct advantage of permitting analysis of selected long path lengths of light to improve the depth sensitivity of the measurement. However, compared to CW-DCS, factors including the instrument response function (IRF), the detection gate width, and the finite coherence length need to be considered in the model analysis of the experimental data. Here, we present a TD-DCS model describing how the intensity autocorrelation functions measured for different path lengths of light depend on the coherence length, pulse width of the laser, the detection gate-width, the IRF, the $BF_i$, and the optical properties of the scattering sample. Predictions of the model are compared with experimental results using a homogeneous liquid phantom sample which mimics human tissue optical properties. The $BF_i$s obtained from the TD-DCS model for different path lengths of light agree with the $BF_i$ obtained from CW-DCS measurements, while the standard simplified model underestimates the $BF_i$ by a factor of $\sim 2$. This work establishes the theoretical foundation of the TD-DCS technique and provides guidance for future $BF_i$ measurements in tissue.

Continuous-wave, singly-resonant, intracavity optical parametric oscillator based on a single-mode-laser-diode-pumped Yb: KYW laser

Zhaowei Zhang, Zhenwen Ding, Pei Liu, and Ye Li

Doc ID: 328258 Received 12 Apr 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: We report a continuous-wave (cw), intra-cavity, singly-resonant OPO (ICSRO) based on an Yb: KYW laser pumped by a single-mode laser diode (LD). Pumping the ICSRO by a low-noise single-mode LD, combined with the reduced heat generation due to the lower quantum defect of the Yb: KYW laser system, effectively eliminated the onset of relaxation oscillations, which has been a long-standing problem in previous multi-mode-LD-pumped ICSROs, and resulted in a cw ICSRO being operated free of relaxation oscillations. At an LD power of 515mW, the generated idler power was 21mW at ~ 3500 nm. To the best of our knowledge, this is the first demonstration of a single-mode-LD-pumped ICSRO.

Energy density and energy flux in the focus of an optical vortex: reverse flux of light energy

Alexey Kovalev, Victor Kotlyar, and Anton Nalimov

Doc ID: 326689 Received 22 Mar 2018; Accepted 11 May 2018; Posted 14 May 2018  View: PDF

Abstract: Using the Richards-Wolf formulae for an arbitrary circularly polarized optical vortex with an integer topological charge m, we obtain explicit expressions for all components of the electric and magnetic field strength vectors near the focus, as well as expressions for the intensity (energy density) and for the energy flux (components of the Poynting vector) in the focal plane of an aplanatic optical system. For m = 2, from the obtained expressions follows that the energy flux near the optical axis propagates in the reversed direction, rotating along a spiral around the optical axis. On the optic axis itself, the reversed flux is maximal and decays rapidly with the distance from the axis. For m = 3, on the contrary, the reversed energy flux in the focal plane is minimal (zero) on the optical axis and increases (until the first ring of the light intensity) as a squared distance from the axis. This effect of the reversed flux can be used to demonstrate another known effect –"optical tractor".

Phased-Locked Two-Color Single Soliton Microcombs in Dispersion-Engineered Si3N4 Resonators

Gregory Moille, Qing Li, Sangsik Kim, Daron Westly, and Kartik Srinivasan

Doc ID: 326840 Received 28 Mar 2018; Accepted 11 May 2018; Posted 14 May 2018  View: PDF

Abstract: We propose and theoretically investigate a dispersion-engineered Si₃N₄ microring resonator, based on a cross-section containing a partially-etched trench, that supports phase-locked, two-color soliton microcomb states. These soliton states consist of a single circulating intracavity pulse with a modulated envelope that sits on a continuous wave background. Such temporal waveforms produce a frequency comb whose spectrum is spread over two widely-spaced spectral windows, each exhibiting a squared hyperbolic secant envelope, with the two windows phase-locked to each other via Cherenkov radiation. The first spectral window is centered around the 1550 nm pump, while the second spectral window is tailored based on straightforward geometric control, and can be centered as short as 750 nm and as long as 3000 nm. We numerically analyze the robustness of the design to parameter variation, and consider its implications to self-referencing and visible wavelength comb generation

Actively Q-switched dual-wavelength pumped Er3+:ZBLAN fiber laser at 3.47 μm

Nathaniel Bawden, Hiraku Matsukuma, Ori Henderson-Sapir, Elizaveta Klantsataya, Shigeki Tokita, and David Ottaway

Doc ID: 327957 Received 10 Apr 2018; Accepted 11 May 2018; Posted 11 May 2018  View: PDF

Abstract: We demonstrate the first actively Q-switched fiber laser operating in the 3.5 μm regime. The dual-wavelength pumped system makes use of an Er3+ doped ZBLAN fiber and a germanium acousto-optic modulator. Robust Q-switching saw a pulse energy of 7.8 μJ achieved at a repetition rate of 15 kHz, corresponding to a peak power of 14.5 W.

Large Negative and Positive Optical Goos-Hänchen Shift in Photonic Crystals

Yu-Po Wong, Yu Miao, Jinhie Skarda, and Olav Solgaard

Doc ID: 328077 Received 13 Apr 2018; Accepted 11 May 2018; Posted 14 May 2018  View: PDF

Abstract: Low-loss photonic crystal mirrors exhibit positive andnegative Goos-Hänchen shift (GHS) due to the strongangular and wavelength dependencies of their reflectedphase. This letter demonstrates, theoretically, numerically,and experimentally, the existence of large positiveand negative Goos-Hänchen shift in Photonic Crystal(PC) mirrors. Simple algebraic relation shows thatpositive effective thickness yields positive (negative)GHS for resonances that blue (red) shift with angle,while the opposite is true for interfaces with negativeeffective thickness. Spatiotemporal coupled mode theorydemonstrates the above relation for simple systemswith one or two resonance modes, and it also showsthe existence of both positive and negative GHS. Theseeffects are numerically and experimentally verified incomplex PCs with several resonance modes.

High-sensitivity measurement of angular velocity based on an optoelectronic oscillator with an intra-loop Sagnac interferometer

Muguang Wang, jing zhang, yu tang, Qi Ding, Beilei Wu, Yuguang Yang, Hongqian Mu, Bin Yin, and Shuisheng Jian

Doc ID: 327564 Received 04 Apr 2018; Accepted 10 May 2018; Posted 14 May 2018  View: PDF

Abstract: A novel scheme for angular velocity measurement has been proposed and demonstrated by using an optoelectronic oscillator (OEO) incorporating a Sagnac interferometer. In the OEO resonant cavity, the optical carrier (OC) and the 1st-order sidebands propagate in opposite directions in a Sagnac loop. Thus the rotation-induced Sagnac phase difference between the OC and 1st-order sidebands will produce an oscillating frequency shift of the OEO which is proportional to the rotation angular velocity. Then a high-sensitivity angular velocity measurement is realized by monitoring the oscillating microwave frequency. The system is free from the lock-in problem and the sensitivity scale is measured to be 51.8 kHz/(rad/s).

Cherenkov radiation from 1550 nm pumping in tapered photonic crystal fibers

Jesper Laegsgaard

Doc ID: 328316 Received 16 Apr 2018; Accepted 10 May 2018; Posted 11 May 2018  View: PDF

Abstract: The generation of Cherenkov radiation from soliton compression of 1550 nm pulses in tapered photonic crystal fibers is analyzed numerically, with a view to generating short wavelength-tunable output pulses in the visible range. It is shown that low-noise femtosecond light sources with spectral power densities approaching those of existing supercontinuum sources are feasible with existing fiber laser and tapering technology.

Shear-enhanced diffraction from thin permanent gratings in dye-doped nematic liquid crystal cells

ANIS ALAYET, MOHAMED GHARBIA, Umberto Bortolozzo, Aurelie Jullien, Stefania Residori, and Jean-Pierre Huignard

Doc ID: 324756 Received 27 Feb 2018; Accepted 10 May 2018; Posted 14 May 2018  View: PDF

Abstract: Permanent gratings are recorded in planar aligned dye-doped nematic liquid crystal cells under visible light illumination. By increasing the irradiation intensity and the exposure time several diffraction orders of the recorded gratings are obtained in the Raman-Nath regime of diffraction. Moreover, by laterally applying a transverse shear on one of the confining plates of the cell, an enhancement of the diffraction efficiency is achieved which follows the period of the grating. By microscope inspection, surface gratings formed by the dye adsorption are revealed both on the front and rear window of the cell, indicating that the diffraction amplification originates from the coherent superposition of the orders diffracted by these gratings when displaced of half a period one from another. The effect provides self-matched amplification of diffraction with a simple cell, a single photo-inscription stage and elementary displacement steps.

3-D dark traps for low refractive index bio-cells using single optical fiber Bessel beam

Yu Zhang, Tang Xiaoyun, Yaxun Zhang, WENJIE SU, Zhihai Liu, Xinghua Yang, Jianzhong Zhang, Jun Yang, Kyunghwan Oh, and Libo Yuan

Doc ID: 325772 Received 09 Mar 2018; Accepted 10 May 2018; Posted 14 May 2018  View: PDF

Abstract: We proposed and experimentally demonstrated a 3-dimension dark traps for low refractive index bio-cells using a single optical fiber Bessel beam. The Bessel beam was produced by concatenating single mode fiber and a step index multimode fiber, which was then focused by a high refractive index glass microsphere integrated on the fiber end facet. The focused Bessel beam provided multiple dark fields along the axial direction, where stable trapping of low refractive index bio-cell was realized in a high refractive index liquid bath. All-fiber and seamlessly integrated structure of the proposed scheme can find ample potentials as micro-optical probe in in-situ characterization and manipulation of multiple bio-cells with refractive indices lower than that of liquid bath.

Channeled spatio-temporal Stokes polarimeters

Israel Vaughn, Andrey Alenin, and J. Scott Tyo

Doc ID: 323365 Received 22 Feb 2018; Accepted 10 May 2018; Posted 11 May 2018  View: PDF

Abstract: We present the analysis and design of spatio-temporal channeled Stokes polarimeters. We extend our recent work on optimal pixelated polarizer arrays by utilizing temporal carrier generation, resulting in polarimeters which achieve super-resolution via the tradeoff between spatial bandwidth and temporal bandwidth. Utilizing the channel space description, we present a linear Stokes and two full-Stokes imaging polarimeter designs which have the potential to operate at the full frame rate of the imaging sensor of the system by using a hybrid spatio-temporal carrier design. If the objects are not spatially bandlimited, then the achievable temporal bandwidth is more difficult to analyze, however a spatio-temporal tradeoff still exists.

Maximizing Young fringe visibility with a universal SU2 polarization gadget

Massimo Alonzo, Massimo Santarsiero, and Franco Gori

Doc ID: 327898 Received 09 Apr 2018; Accepted 10 May 2018; Posted 15 May 2018  View: PDF

Abstract: When a Young interferometer is fed by a general electromagnetic field, the fringe visibility may change upon insertion of an anisotropic optical element over one of the interferometer pinholes. The maximum visibility that the fringes may exhibit in this way is theoretically known, but no direct experimental check seems to be available. Here, we discuss the scheme of an experimental test. In particular, maximum fringe visibility is obtained with a three-component universal SU2 polarization gadget for arbitrary coherence features of the illuminating field. Confirming results obtained with a suitable experimental setup are presented.

Codoped Dy3+-Pr3+ GaGeSbS fibers for mid-IR broad emission

Julien Ari, Florent Starecki, boussard-pledel catherine, Yannick Ledemi, Younes Messaddeq, Jean-Louis DOUALAN, Alain BRAUD, Bruno BUREAU, and Virginie Nazabal

Doc ID: 320721 Received 16 Mar 2018; Accepted 10 May 2018; Posted 18 May 2018  View: PDF

Abstract: Rare earth doped materials are means to obtain cost effective infrared light sources, with enough brilliance for applications such as gas sensing. Within a sulfide matrix, the simultaneous luminescence of both Pr3+ and Dy3+ in the Ga5Ge20Sb10S65 glass is reported. The use of these two rare earths is giving rise to a broad continuous luminescence in the 2.2-5.5 µm wavelength range, what could be used as a mid-IR light source for gas sensing applications. The demonstration of carbon dioxide and methane detection using a fiber drawn from this material is reported.

Lyman-α source for laser cooling antihydrogen

Gerald Gabrielse, Bartosz Głowacz, Dieter Grzonka, Chris Hamley, Eric Hessels, Nathan Jones, Gunn Khatri, Siu-Au Lee, Cole Meisenhelder, Tharon Morrison, Edouard Nottet, Cory` Rasor, Sam Ronald, Taylor Skinner, Cody Storry, Eric Tardiff, Dylan Yost, Daniel Martinez Zambrano, and Marcin Zielinski

Doc ID: 328396 Received 01 May 2018; Accepted 09 May 2018; Posted 21 May 2018  View: PDF

Abstract: We present a Lyman-α laser developed for cooling trapped antihydrogen. The system is based on a pulsed Ti:sapphire laser operating at 729 nm that is frequency doubled using an LBO crystal and then frequency tripled in a Kr/Ar gas cell. After frequency conversion, this system produces up to 5.7 μW of average power at the Lyman-α wavelength. This laser is part of the ATRAP experiment at the antiproton decelerator in CERN.

Development of a three-legged, high-speed, burst-mode laser system for simultaneous measurements of velocity and scalars in reacting flows

Sukesh Roy, Naibo Jiang, Paul Hsu, Tongxun Yi, Mikhail Slipchenko, Josef Felver, Jordi Estevadeordal, and James Gord

Doc ID: 328106 Received 10 Apr 2018; Accepted 09 May 2018; Posted 09 May 2018  View: PDF

Abstract: We report the development of a three-legged, high-speed, high-energy, burst-mode laser system for the simultaneous measurement of velocity, temperature, and key combustion species in turbulent reacting flows. The laser system is designed to simultaneously amplify a four-pulse sequence (including a doublet pulse for particle image velocimetry (PIV) measurements) with variable pulse separations at a repetition rate up to 500 kHz and a burst duration of 1–10 ms. With the three-legged, burst-mode laser system, we demonstrate simultaneous measurements of velocity using PIV and planar laser-induced fluorescence imaging of hydroxyl and formaldehyde in a turbulent jet flame.

Multi-mode four-wave mixing with a spatially-structured pump

Ryan Glasser, Jon Swaim, Erin Knutson, and Onur Danaci

Doc ID: 322981 Received 15 Feb 2018; Accepted 09 May 2018; Posted 09 May 2018  View: PDF

Abstract: We demonstrate a new four-wave mixing (4WM) geometry based on structured light. By utilizing near-field diffraction through a narrow slit, the pump beam is asymmetrically structured to modify the phase matching condition, generating multi-mode output in both the spatial and frequency domains. We show that the frequency parameter enables selection of various spatial-mode outputs, including a twin-beam geometry which preserves relative intensity squeezing shared between the two beams. The results suggest that the engineering of atomic states via structured light may provide a pathway to a diverse set of quantum resources based on multi-mode squeezed light.

Frequency-domain Hong-Ou-Mandel interference with linear optics

Poolad Imany, Ogaga Odele, Mohammed Al Alshaykh, Hsuan-Hao Lu, Daniel Leaird, and Andrew Weiner

Doc ID: 327034 Received 29 Mar 2018; Accepted 09 May 2018; Posted 11 May 2018  View: PDF

Abstract: The Hong-Ou-Mandel interference is one of the most fundamental quantum-mechanical effects that reveals a non-classical behavior of single photons. Two identical photons that are incident on the input ports of an unbiased beam splitter always exit the beam splitter together from the same output port, an effect referred to as photon bunching. In this Letter, we utilize a single electro-optic phase modulator as a probabilistic frequency beam splitter, which we exploit to observe Hong-Ou-Mandel interference between two photons that are in different spectral modes yet identical in other characteristics. Our approach enables linear optical quantum information processing protocols using the frequency degree of freedom in photons, such as quantum computing techniques with linear optics.

A dual-color distributed Bragg reflector fiber laser with simultaneous emission at 1.06 μm and 1.55 μm wavebands

Yang Ran, Zhiyuan Xu, Feng Furong, Peng Xiao, Yizhi Liang, Long Jin, and Bai-Ou Guan

Doc ID: 327950 Received 09 Apr 2018; Accepted 09 May 2018; Posted 11 May 2018  View: PDF

Abstract: A dual-wavelength fiber laser is realized by use of Er/Yb co-doped active fiber and a pair of novel Bragg-grating reflectors. The Bragg grating presents strong reflections of both third and second harmonics in the gain wavelength range of ytterbium and erbium ion respectively, enabling the laser emitted at 1.06 μm and 1.55 μm wavebands simultaneously with a short linear cavity structure. Adjusting reflectivity of the harmonics in the grating can influence the intensity contrast of the two lasing signals. Optimization on the compactness and brightness of the laser is achieved by adapting the harmonic wavelengths with the optimal gain windows of the ytterbium and erbium ions.


Vladislav Shcheslavskiy, Marina Shirmanova, Varvara Dudenkova, Konstantin Lukyanov, Alena Gavrina, Anastasia Shumilova, Elena Zagaynova, and Wolfgang Becker

Doc ID: 327900 Received 13 Apr 2018; Accepted 08 May 2018; Posted 14 May 2018  View: PDF

Abstract: While laser scanning fluorescence lifetime imaging (FLIM) is a powerful approach for cell biology, its small field of view (typically less than 1 mm) makes it impractical for imaging of large biological samples that is often required for biomedical applications. Here we present a system that allows to perform FLIM on macroscopic samples as large as 18mm with a lateral resolution of 15μm. The performance of the system is verified with FLIM of endogenous metabolic cofactor reduced nicotinamide adenine dinucleotide (phosphate), NAD(P)H, and genetically encoded fluorescent protein mKate2 in a mouse tumor in vivo.

The influence of attenuation on a self-organized second harmonic generation in a germanium doped microstructured silica fiber

Sylwia Majchrowska, Jakub Pabisiak, Tadeusz Martynkien, Pawel Mergo, and Karol Tarnowski

Doc ID: 328410 Received 18 Apr 2018; Accepted 08 May 2018; Posted 14 May 2018  View: PDF

Abstract: Observation of the efficient second harmonic generation in the silica fibers drew a lot of interest as the second-order processes in centrosymmetric materials should not occur. In this study we extended a theoretical model of the self-organized second harmonic generation to include an attenuation and investigated the influence of fiber loss on the self-organized SHG process. We performed calculations of energy conversion efficiency for the second harmonic generation in microstructured optical fibers. Finally, we referred the simulation results to the measured SHG efficiency in a microstructured side-hole germanium doped silica fiber. The extended model should be applied for the fibers with loss beyond 0.01 dB/m. Even in such fibers the efficient second harmonic generation without an external second harmonic beam is possible.

Flexible Thin Broadband Microwave Absorber Based on Pyramidal Periodic Structure of Lossy Composite

Yixing Huang, Xujin Yuan, Changxian Wang, Mingji Chen, Liqun Tang, and Daining Fang

Doc ID: 328766 Received 19 Apr 2018; Accepted 08 May 2018; Posted 14 May 2018  View: PDF

Abstract: Microwave absorber with broadband absorption and thin thickness is one of main research interests in this field. A flexible ultrathin and broadband microwave absorber comprised by multiwall carbon nanotubes (MWCNT), spherical carbonyl iron (SCI) and silicone rubber is fabricated in a newly proposed pyramidal spatial periodic structure (SPS). The SPS with equivalent thickness of 3.73mm covers the -10dB and -15dB absorption bandwidth in the frequency range 2-40GHz and 10-40GHz respectively. The excellent absorption performance is achieved by concentration and dissipation of the electromagnetic field inside different parts of the magnetic-dielectric lossy protrusions in different frequency ranges.

Interlocking Kerr-microresonator frequency combs for microwave to optical synthesis

Travis Briles, Jordan Stone, Tara Drake, Daryl Spencer, Connor Fredrick, Qing Li, Daron Westly, Robert Ilic, Kartik Srinivasan, Scott Diddams, and Scott Papp

Doc ID: 324666 Received 23 Feb 2018; Accepted 08 May 2018; Posted 09 May 2018  View: PDF

Abstract: We report accurate phase stabilization of an interlocking pair of Kerr-microresonator frequency combs. The two combs, one based on silicon nitride and one on silica, feature nearly harmonic repetition frequencies and can be generated with one laser. The silicon-nitride comb supports an ultrafast-laser regime with three-optical-cycle, 1-picosecond-period soliton pulses and a total dispersive-wave-enhanced bandwidth of 170 THz, while providing a stable phase-link between optical and microwave frequencies. We demonstrate nanofabrication control of the silicon-nitride comb's carrier-envelope offset frequency and spectral profile. The phase-locked combs coherently reproduce their clock with a fractional precision of <6×10^{-13}/τ, a behavior we verified through two hours of measurement to reach <3× 10^{-16}. Our work establishes Kerr combs as a viable technology for applications like optical-atomic timekeeping and optical synchronization.

Control of Second Harmonic Generation in Doubly Resonant Aluminum Nitride Microrings to Address Rubidium Two-Photon Clock Transition

Joshua Surya, Xiang Guo, Changling Zou, and Hong Tang

Doc ID: 325565 Received 07 Mar 2018; Accepted 08 May 2018; Posted 09 May 2018  View: PDF

Abstract: Nonlinear optical effects have been studied extensively in microresonators as more photonics applications transition to integrated on-chip platforms. Particular to precision timekeeping, integrated second harmonic generation (SHG) is a critical component in the extension and stabilization of frequency combs, allowing the realization of high efficiency chip-scale optical clocks. However, there remains a challenge in precision tuning of these on-chip devices to match a specific comb line or a narrow optical clock transition, as both require picometer precision in wavelength control. In this work, we analyzed the phase-matching window and resonance wavelength with respect to varying ring width, ring radius and temperature. A chip with precise design parameters was fabricated with phase-matching realized at the exact wavelength of two-photon transition of 85-Rubidium. This procedure can be generalized to any target pump wavelength in the telecom-band with picometer precision.

High-energy picosecond pulses from a 2850 nm fiberamplifier

Yigit Aydin, Vincent Fortin, Darren Kraemer, Alex Fraser, Real Vallee, and Martin Bernier

Doc ID: 325818 Received 12 Mar 2018; Accepted 08 May 2018; Posted 09 May 2018  View: PDF

Abstract: We report the demonstration of a 2850 nm diodepumpedHo3+, Pr3+ co-doped fluoride fiber amplifierthat delivers average power of 2.45 W, pulses with 122μJ energy and 500 ps duration at a repetition rate of 20kHz. To the best of our knowledge, the average powerand pulse energy are the highest obtained from a subnanosecondfiber source operating in the 3 μm spectralregion. The amplifier is seeded by an optical parametricgeneration (OPG) source and is pumped around 915nm using widely available InGaAs laser diodes.

Transmission matrix approaches for non-linear fluorescence excitation through multiple scattering media

Mickael Mounaix, Duc Minh Ta, and Sylvain Gigan

Doc ID: 326094 Received 15 Mar 2018; Accepted 08 May 2018; Posted 15 May 2018  View: PDF

Abstract: Several matrix approaches were developed to control light propagation through multiple scattering media under illumination of ultrashort pulses of light. These matrices can be recorded either with spectral or temporal resolution. Thanks to wavefront shaping, temporal and spatial refocusing have been demonstrated. In this work, we study how these different methods can be exploited to enhance a two-photon excitation fluorescence process. We first compare the different techniques on micrometer-size isolated fluorescent beads. We then demonstrate point-scanning imaging of such fluorescent microbeads located after a thick scattering medium, at a depth where conventional imaging would be impossible because of scattering effects.

Conversion from non-orthogonally to orthogonally polarized optical single-sideband modulation using optically injected semiconductor lasers

Yu-Han Hung, Chin-Hao Tseng, and Sheng-Kwang Hwang

Doc ID: 326544 Received 29 Mar 2018; Accepted 07 May 2018; Posted 08 May 2018  View: PDF

Abstract: This study investigates an optically injected semiconductor laser for conversion from non-orthogonally to orthogonally polarized optical single-sideband modulation. The underlying mechanism relies solely on nonlinear laser characteristics, and only a typical semiconductor laser is thus required as the key conversion unit. Such conversion can be achieved for a broadly tunable frequency range up to at least 65 GHz. After conversion, the microwave phase quality, including linewidth and phase noise, is mostly preserved and simultaneous microwave amplification of up to dB is feasible.

Novel Equalization Technique for Optical Sources with Direct Modulation

hyunchae chun, Ariel Gomez, Grahame Faulkner, and Dominic O'Brien

Doc ID: 326786 Received 23 Mar 2018; Accepted 07 May 2018; Posted 09 May 2018  View: PDF

Abstract: In this letter, a novel equalization method for directly modulated optical sources is introduced. Conventional source equalization methods balance the low and high-frequency responses of the source by cutting down the low-frequency components in any drive signal. Typically, this ensures a flat frequency and linear signal response up to some predetermined upper-frequency limit. It is conventionally done under a fixed linear dynamic range, but it is found that source’s dynamic range varies by frequency. In this paper, we describe a novel method that determines the limit of signal linearity at each frequency and uses this to create the enhanced equalizer response. This leads to an improved source bandwidth and in practice allows greater transmitted signal energy. Experimental results for a resonant cavity LED transmitter show data rate improvement of ~40% and to the best of our knowledge, a record data rate of 8.76 Gb/s, with bit-error-rate less than 3.8x10^3.

High-controlled Bloch wave propagation in surfaces with broken symmetry

döne yılmaz, Aydan Yeltik, and Hamza Kurt

Doc ID: 327612 Received 04 Apr 2018; Accepted 06 May 2018; Posted 07 May 2018  View: PDF

Abstract: We propose and demonstrate reduced symmetry photonic surfaces providing high-controlled Bloch wave propagation. The backward and dual directional propagations have been observed in the proposed low-symmetric periodic structures without variation in the unit-cell filling factor. Frequency-domain analyses present group indices up to negative/positive - 7/+96 as the strong indicators of the observed directional controlled surface waves driven by the orientation angle in the range of 20º-90º. Further verification of the index-based propagation direction has been achieved through detailed time-domain analyses and microwave experiments. Smart management of the propagation direction in low-symmetric surfaces has great potential for the next-generation photonic applications.

End-to-end deep neural network for quantitative photoacoustic imaging

Chuangjian Cai, Kexin Deng, Cheng Ma, and Jianwen Luo

Doc ID: 326784 Received 23 Mar 2018; Accepted 05 May 2018; Posted 09 May 2018  View: PDF

Abstract: An end-to-end deep neural network, ResU-net, is developed for quantitative photoacoustic imaging. A residual learning framework is used to facilitate optimization and to gain better accuracy from considerably increased network depth. The contracting and expanding paths enable ResU-net to extract comprehensive context information from multispectral initial pressure images and to subsequently infer a quantitative image of chromophore concentration or oxygen saturation (sO2). According to our numerical experiments, the estimations of sO2 and indocyanine green concentration are accurate and robust against variations in both optical property and object geometry. An extremely short reconstruction time of 22 ms is achieved.

Experimental limits for Eigenvalue Calibration in Liquid-Crystal Mueller-Matrix Polarimeters

Neil Bruce, Oscar Rodriguez Herrera, Juan Lopez-Tellez, and Omar Rodriguez-Nuñez

Doc ID: 326929 Received 26 Mar 2018; Accepted 05 May 2018; Posted 11 May 2018  View: PDF

Abstract: A numerical study is carried out to find the experimental conditions necessary for the eigen-value calibration procedure to work correctly in a liquid-crystal variable retarder based Mueller-matrix polarimeter. Using the error between the simulated experimental Mueller matrix in a polarimeter with errors and the expected ideal Mueller matrices for 4 calibration samples, the maximum experimental errors are estimated for a succesful eigen-value calibration. It is found that the retarder axes orientations have smaller permitted errors than the retardation values.

Stationary and oscillatory bound states of dissipative solitons created by the third-order dispersion

Boris Malomed, Hidetsugu Sakaguchi, and Dmitry Skryabin

Doc ID: 326518 Received 21 Mar 2018; Accepted 04 May 2018; Posted 09 May 2018  View: PDF

Abstract: We consider the model of fiber-laser cavities near the zero-dispersion point, based on the complex Ginzburg-Landau equation with the cubic-quintic nonlinearity and including third-order dispersion (TOD) term. It is well known that this model supports stable dissipative solitons. We demonstrate that the same model gives rise to several families of robust bound states of the solitons, which exists only in the presence of the TOD. There are both stationary and dynamical bound states, with oscillating separation between the bound solitons. Stationary states are multistable, corresponding todifferent values of the separation. With the increase of the TOD coefficient, the bound state with the smallest separation gives rise the oscillatorystate through the Hopf bifurcation. Further growth of TOD leads to a bifurcation transforming the oscillatory limit cycle into a strange attractor, which represents the chaotically oscillating dynamical bound state. Families of multistable three- and four-soliton complexes are found too, the ones with the smallest separation between the solitons again ending by the transition to oscillatory states through the Hopf bifurcation.

Generation of sub-two-cycle CEP-stable optical pulses at 3.5 µm from a KTA-based optical parametric amplifier with multiple-plate compression

Faming Lu, Peiyu Xia, Yoshiyuki Matsumoto, Teruto Kanai, Nobuhisa Ishii, and Jiro Itatani

Doc ID: 324952 Received 02 Mar 2018; Accepted 04 May 2018; Posted 09 May 2018  View: PDF

Abstract: We demonstrate the generation of 21-fs (1.8-optical-cycle), 45-µJ, carrier-envelope-phase (CEP)-stable optical pulses with an octave-spanning spectrum from 2.2 to 4.9 µm. Multi-cycle output pulses (120 fs, 149 µJ, 3.5 µm, 300 Hz) from a KTA-based optical parametric amplifier are compressed down to the sub-two-cycle regime using YAG and Si plates. The single-shot CEP stability of the compressed pulses is measured to be 283 mrad for 500 seconds. This robust and compact scheme realizes a field strength of 282 MV/cm with loose focusing, opening a new regime of attosecond strong-field physics in solids.

Isotropic single-photon sources

Iñigo Liberal, Iñigo Ederra, and Yue Li

Doc ID: 324628 Received 21 Feb 2018; Accepted 04 May 2018; Posted 09 May 2018  View: PDF

Abstract: Classical antenna theory establishes that there are no coherent isotropic radiators. Thermal radiators can be isotropic, but they lack temporal coherence. Here, we demonstrate that quantum interference processes enable the design of isotropic and unpolarized single-photon sources that preserve temporal coherence properties. We illustrate how this effect can be realized with relatively simple multi-level emitters with degenerate ground states, and we discuss potential implementations based on atomic and solid-state single-photon sources.

Mode-locking in a tapered two-section quantum dot laser: design and experiment

Paolo Bardella, Lukas Drzewietzki, Michel Krakowski, Igor Krestnikov, and Stefan Breuer

Doc ID: 328148 Received 11 Apr 2018; Accepted 04 May 2018; Posted 11 May 2018  View: PDF

Abstract: In this work, the pulse generation and pulse train stability of a tapered two-section InAs/InGaAs quantum dot laser emitting at 1250 nm is numerically predicted and experimentally verified. Simulations based on a multi-section delayed differential equation model are used to properly design a laser source able to generate stable mode-locked pulses at a 15 GHz repetition rate with picosecond width and output power larger than 1 W, and to identify the device stability regions depending on the bias conditions. Possible instabilities are associated with the existence of a leading or trailing edge net gain window outside of the optical pulse. Experimentally, we confirm the existence of different stability regions where instabilities manifest in broadband or multi-periodic pulse train amplitude modulations. Our results confirm the correctness to the design and may be helpful in achieving high-power pulses while avoiding detrimental pulse train instabilities both being important for time-critical applications.

Graphene-based tunable Imbert-Fedorov shifts and orbital angular momentum sidebands for reflected vortex beams in terahertz region

Linqing Zhuo, wenjin long, Mengjiang Jiang, Wenguo Zhu, Heyuan Guan, Jieyuan Tang, JianHui Yu, Huihui Lu, Jun Zhang, and Zhe Chen

Doc ID: 327463 Received 02 Apr 2018; Accepted 04 May 2018; Posted 11 May 2018  View: PDF

Abstract: Upon reflection, a light beam embedded with m-order orbital angular momentum (OAM) will undergo Imbert-Fedorov (IF) shift, which induces OAM sidebands. The energies of the neighboring {-m-1} and {-m+1} sideband modes of the reflected beam are always equal. Controllable OAM sidebands are theoretically achieved by introducing a monolayer graphene in a three-layer structure composed of air, hexagonal boron nitride, and metal. By modulating the Fermi energy of graphene, the OAM dependent IF shift can be tuned from positive to negative values, and the OAM sideband modes can be suppressed or enhanced, since the reflectivity for perpendicular and parallel polarizations vary with the Fermi energy. These findings provide alternative method for the control of optical OAM in the terahertz region.

Flexible single-mode delivery of high power 2 µm pulsed laser using antiresonant hollow-core fiber

Elizabeth Mei Yin Lee, JIAQI LUO, Biao Sun, VINCENT RAMALINGAM, Ying Zhang, Qijie Wang, Fei Yu, and Xia Yu

Doc ID: 327061 Received 28 Mar 2018; Accepted 04 May 2018; Posted 07 May 2018  View: PDF

Abstract: We demonstrate flexible high average power 2 µm nanosecond pulse transmission using antiresonant hollow core fibers (AR-HCF). 39.1 W average power is delivered using a coiled 1.7 m AR-HCF, which is designed for single-mode guidance and good higher-order mode suppression. This is the highest average power delivered by a flexible long HCF in this wavelength without the need for protective gases or vacuum conditions, to the best of our knowledge. The effect of bending on the fiber output power and beam profile is also investigated. The Gaussian-like output beam profile is maintained up to 7.5 cm bending radius.

Optimized microfiber-based third harmonic generation with adaptive control of phase mismatch

Xiujuan Jiang, Dandan Zhang, Timothy Lee, and Gilberto Brambilla

Doc ID: 327357 Received 02 Apr 2018; Accepted 04 May 2018; Posted 07 May 2018  View: PDF

Abstract: It is demonstrated that structure-independent incident pump power could be utilized, via its effect on nonlinear phase modulations, to adaptively compensate for the random phase mismatch caused by surface roughness in microfiber-based intermodal third harmonic generation. The output harmonic of a fabricated microfiber can be improved and optimized, thus efficient third harmonic generation with efficiency reaching several percent could realistically be achieved. This effective approach could be applied to other waveguide-based frequency conversion processes.

Light-extraction enhancement of GaN-based 395 nm flip-chip light-emitting diodes by Al-doped ITO transparent conductive electrode

Jin Xu, Wei Zhang, Meng Peng, Jiangnan Dai, and Changqing Chen

Doc ID: 319601 Received 15 Jan 2018; Accepted 04 May 2018; Posted 07 May 2018  View: PDF

Abstract: The distinct ultraviolet (UV) light absorption of indium tin oxide (ITO) limits the performance of GaN-based near-UV light-emitting diodes (LEDs). Herein, we report Al-doped ITO with enhanced UV transmittance and low sheet resistance as the transparent conductive electrode for GaN-based 395 nm flip-chip near-UV LEDs. The thickness dependence of optical and electrical properties of Al-doped ITO films is investigated. The optimal Al-doped ITO film exhibited a transmittance of 93.2% at 395 nm and an average sheet resistance of 30.1Ω/sq. Meanwhile, at an injection current of 300 mA, the forward voltage decreased from 3.14 to 3.11 V and the light output power increased by 13% for the 395 nm near-UV flip-chip LEDs with the optimal Al-doped ITO over those with pure ITO. Our work provides a simple and repeatable approach to further improve the light extraction efficiency of GaN-based near-UV LEDs

Screening and fluctuation of topological charge in random wave fields

Lorenzo De Angelis and Laurens Kuipers

Doc ID: 327031 Received 29 Mar 2018; Accepted 03 May 2018; Posted 09 May 2018  View: PDF

Abstract: Vortices, phase singularities and topological defects of any kind often reflect information that is crucial to understand physical systems in which such entities arise. With near-field experiments supported by numerical calculations, we determine the fluctuations of the topological charge for phase singularities in isotropic random waves, as a function of the size R of the observation window. We demonstrate that for 2D fields such fluctuations increase with a super-linear scaling law, consistent with a R log R behavior. Additionally, we show that such scaling remains valid in presence of anisotropy.

Hartmann wavefront sensor characterization of a high charge vortex beam in the XUV spectral range

Fabrice SANSON, Alok Pandey, Fabrice Harms, Guillaume Dovillaire, Baynard Elsa, Julien Demailly, Olivier Guilbaud, Bruno Lucas, Olivier Neveu, Moana Pittman, David Ros, Martin Richardson, Eric Johnson, Philippe Balcou, Sophie Kazamias, and Wenzhe Li

Doc ID: 326068 Received 14 Mar 2018; Accepted 02 May 2018; Posted 14 May 2018  View: PDF

Abstract: We demonstrate for the first time the ability of XUV Hartmann wavefront sensors to characterize high charge vortex beams produced by high order harmonic generation up to the order of 25. We also show that phase matched absorption limited high harmonic generation is able to maintain the high charge vortex structure of the XUV beam even in rather long (1 cm) generationmedium.

Nanosecond laser damage initiation at 0.35 µm in fused silica

Pierre Grua, Laurent Lamaignère, Maxime Chambonneau, Roger Courchinoux, and Jerome Neauport

Doc ID: 325471 Received 06 Mar 2018; Accepted 02 May 2018; Posted 03 May 2018  View: PDF

Abstract: In nanosecond regime, the laser-induced damage density at the exit surface of fused silica optics at the wavelength of 0.35~µm shows a characteristic behavior: in a specific fluence range, the surface damage density begins to grow exponentially as a function of fluence and then tends to saturate at high fluences. Up to now no satisfactory explanation of these peculiarities could be provided. We herein detail a statistical model based on laser-matter interaction, where two types of absorbing precursors are involved in the energy deposit: subsurface micro-cracks and surface impurities. We evidence that this model predicts this characteristic damage density for a large range of fluences and different polishing processes.

Spatial beam cleanup by pure Kerr processes in multimode fibers

Jesper Laegsgaard

Doc ID: 325964 Received 13 Mar 2018; Accepted 02 May 2018; Posted 03 May 2018  View: PDF

Abstract: Recent experiments with pulse propagation in multimode graded-index fibers have shown a nonlinear improvement in beam quality, even in situations where dissipative processes such as Raman scattering play no significant role. In this paper, numerical simulations of beam cleanup by third-order Kerr nonlinearities in a multimode fiber are used to demonstrate that in the absence of dissipative processes, beam cleanup is crucially dependent on spectral/temporal disorder, and does not occur in a continuous-wave model. This finding is in accordance with fundamental considerations on entropy.

Optical trapping with planar silicon metalenses

Georgiy Tkachenko, Daan Stellinga, Andrei Ruskuc, Mingzhou Chen, Kishan Dholakia, and Thomas Krauss

Doc ID: 326126 Received 15 Mar 2018; Accepted 02 May 2018; Posted 03 May 2018  View: PDF

Abstract: Contactless manipulation of micron-scale objects in a microfluidic environment is a key ingredient for a range of applications in the biosciences, including sorting, guiding and analysis of cells and bacteria. Optical forces are powerful for this purpose but typically require bulky focusing elements to achieve the appropriate optical field gradients. To this end, realizing the focusing optics in a planar format would be very attractive and conducive to integration of such microscale devices either individually or as arrays. Here, we report on the first experimental demonstration of optical trapping in water using planar silicon metalenses illuminated with a collimated laser beam. The structuresconsist of high-contrast gratings with a locally varying period and duty-cycle. They are designed to mimic parabolic reflectors with a numerical aperture of 0.56 at a vacuum wavelength of 1064 nm. We achieve both twoand three-dimensional trapping, with the latter realised by omitting the central Fresnel zones. The study highlights the versatility of such lithographically defined metastructures for exerting optical forces without the need for traditional optical elements.

Two-level and two-period modulation for closed-loop interferometric fiber optic gyroscopes

Rodrigo Bacurau, Alex Dante, MARLLON SCHLISCHTING, Anderson Spengler, and Elnatan Ferreira

Doc ID: 326855 Received 30 Mar 2018; Accepted 02 May 2018; Posted 03 May 2018  View: PDF

Abstract: We propose and experimentally demonstrate a modulation technique for closed-loop interferometric fiber optic gyroscopes that improves its scale factor control and allows for the construction of gyroscopes with optimized angle random walk. The proposed two-level and two-period modulation is composed by two intercalated periods of the square-wave modulation, one with amplitude of ϕ rad and the other with amplitude of 2π-ϕ rad. As in the two-level modulation, the angular velocity is obtained from the difference of consecutive output levels. Modulation depth error is obtained from the difference of the mean levels of the output from two consecutive periods. The proposed technique eliminates the limitation of square-wave modulation: inefficient scale factor control at low angular velocities. Additionally, it requires slower analog-to-digital converter than four-level modulation.

Fast and accurate wavefront reconstruction in two-frame phase-shifting interferometry with unknown phase step

Zhongtao Cheng and Dong Liu

Doc ID: 324515 Received 19 Feb 2018; Accepted 01 May 2018; Posted 03 May 2018  View: PDF

Abstract: A fast and accurate wavefront reconstruction method for two-frame phase-shifting interferometry is proposed. The unknown phase step between the two interferograms is estimated directly by solving a quartic polynomial equation, and then the phase map is readily reconstructed after obtaining the phase step. The whole phase reconstruction process is nearly analytical, thus very fast and easy to realize. Good performance of the proposed method is demonstrated by reconstructing the phase maps from simulated and real fringes along with comparisons to several existed well-established algorithms.

Work on a quantum dipole by a single photon pulse

Daniel Valente, Frederico Brito, Robson Ferreira, and Thiago Werlang

Doc ID: 324971 Received 27 Feb 2018; Accepted 01 May 2018; Posted 03 May 2018  View: PDF

Abstract: Energy transfer from a quantized field to a quantized dipole is investigated.We find that a single photon can transfer energy to a two-level dipole by inducing a dynamic Stark shift, going beyond the well-known absorption and emission processes.A quantum thermodynamical perspective allows us to unravel these two energy transfer mechanisms and to identify the former as a generalized work and the latter as a generalized heat.We show two necessary conditions for the generalized work transfer by a single photon to occur, namely, off-resonance and finite linewidth of the pulse.We also show that the generalized work performed by a single-photon pulse equals the reactive (dispersive) contribution of the work performed by a semiclassical pulse in the low-excitation regime.

Phase-Dependent Ionization of Hydrogen by Intense Sub-Cycle Pulses

Josh Karpel and Deniz Yavuz

Doc ID: 330498 Received 26 Mar 2018; Accepted 01 May 2018; Posted 03 May 2018  View: PDF

Abstract: We have performed simulations and analytic calculations that show strong carrier-envelope phase dependence in the ionization of hydrogen atoms using intense sub-cycle sub-femtosecond laser pulses.When the pulse width is comparable to the classical orbit time of the initial bound state, sine-like pulses can ionize more than cosine-like pulses that have the same fluence.This result is the opposite of what is expected from a tunneling-like model, where the ionization probability primarily depends on the peak amplitude of the electric field during the pulse.

Measurement of phase refractive index of photonic crystal fiber mode

Julius Vengelis, Vygandas Jarutis, and Valdas Sirutkaitis

Doc ID: 327796 Received 06 Apr 2018; Accepted 01 May 2018; Posted 01 May 2018  View: PDF

Abstract: We present a new experimental technique for measurement of the refractive index of photonic crystal fiber fundamental mode. We demonstrate that phase refractive index of photonic crystal fiber mode can be estimated by analyzing phase shift of interfering adjacent longitudinal laser modes of continuous wave laser corresponding to shift from constructive to destructive interference. Experiment results are in very good agreement with numerically simulated phase refractive index values.

Multi-megawatt, self-seeded Mamyshev oscillator

Pavel Sidorenko, Walter Fu, Logan Wright, Frank Wise, and Michel Olivier

Doc ID: 325013 Received 28 Feb 2018; Accepted 01 May 2018; Posted 08 May 2018  View: PDF

Abstract: We demonstrate a fiber oscillator that achieves 3 MW peak power, is easily started, and is environmentally stable. The Mamyshev oscillator delivers 190-nJ pulses that can be compressed externally to 35 fs duration. Accurate numerical modeling of the gain medium provides insight into the behavior and performance of the device.

Investigation of propagation dynamics of truncated vector vortex beams

Balaji Srinivasan, Pachava Srinivas, Chithrabhanu Perumangatt, NIJIL LAL, and Ravindra Singh

Doc ID: 323133 Received 15 Nov 2017; Accepted 30 Apr 2018; Posted 01 May 2018  View: PDF

Abstract: In this paper, we experimentally investigate the propagation dynamics of truncated vector vortex beams generated using a Sagnac interferometer. Upon focusing, the truncated vector vortex beam is found to regain its original intensity structure within the Rayleigh range. In order to explain such behavior, the propagation dynamics of truncated vector vortex beam is simulated by decomposing it into a sum of integral charge beams with associated complex weights. We also show that the polarization of the truncated composite vector vortex beam is preserved all along the propagation axis. Experimental observations are consistent with theoretical predictions based on previous literature and are also in good agreement with our simulation results. The results hold importance as vector vortex modes are eigenmodes of the optical fiber.

Focused anti-scatter grid for background reduction in x-ray fluorescence tomography

Jakob Larsson, Kian Shaker, and Hans Hertz

Doc ID: 325960 Received 13 Mar 2018; Accepted 30 Apr 2018; Posted 01 May 2018  View: PDF

Abstract: X-ray fluorescence tomography is an emerging imaging technology with potential for high-spatial resolution molecular imaging. One of the key limitations is the background noise due to Compton scattering since it degrades the signal and limits the sensitivity. In the present Letter we present a linear focused anti-scatter grid that reduces the Compton scattering background. An anti-scatter grid was manufactured and evaluated both experimentally and theoretically, with Monte-Carlo simulations. The measurements showed a 31% increase in signal-to-background ratio and simulations of an improved grid showed that this can easily be extended up to >75%. Simulated tomographies using the improved grid shows a large improvement in reconstruction quality. The anti-scatter grid will be important for in vivo x-ray fluorescence tomography since the background reduction allows for faster scan times, lower dose and lower nanoparticle concentration.

Single-mode light guiding in diamond waveguides directly written by focused proton beam

Huining Jin, Shuvan Prashant Turaga, Sudheer Kumar Vanga, and Andrew Bettiol

Doc ID: 326947 Received 27 Mar 2018; Accepted 30 Apr 2018; Posted 03 May 2018  View: PDF

Abstract: Ion-implanted waveguides were directly written in bulk single-crystal diamond by scanning a focused 2 MeV proton beam. By controlling the fluence and the lateral size of the proton beam, a bright and near-circular single mode profile was observed. Propagation loss and effective refractive index of the guided mode was measured by the Fabry-Perot technique, confirming single-mode guiding. Micro-Raman maps of the waveguides were used to visualize damage profiles and defect distributions induced by the proton beam. The demonstration of single-mode light guiding in our waveguides shows that direct proton beam writing is a promising tool in the rapid manufacture of integrated optical circuits in bulk diamond.

All-fiber, single-frequency and single-mode Er3+:Yb3+ fiber amplifier at 1556nm core-pumped at 1018nm

Omar de Varona Ortega, Michael Steinke, Joerg Neumann, and Dietmar Kracht

Doc ID: 328727 Received 18 Apr 2018; Accepted 29 Apr 2018; Posted 02 May 2018  View: PDF

Abstract: Emerging applications, such as gravitational wave astronomy, demand single-frequency lasers with diffraction limited emission at 1.5 μm. Fiber amplifiers have greatly evolved to fulfill these requirements. Hundreds of watts are feasible using large mode area and specialty fibers. However, their application in few-watts to tens-watts in monolithic systems is unnecessarily complex due to the poor commercial availability of fiber components and standard integration procedures. In this work we propose and experimentally demonstrate a novel and simple method to amplify single-frequency signals at 1.5 μm up to tens of watts by core-pumping single-mode Er3+:Yb3+ fiber amplifiers at 1018 nm. The proof-of-principle system is tested with different active fibers, lengths and seed power levels. Over 11W with an efficiency of more than 48% versus launched power is achieved. Additionally, performance degradation during operation was observed for which photodarkening due to P1 defects might be an explanation.

FBG Wavelength demodulation based on radio frequency optical true time delay method

jin wang, Wan Zhu, Ma Chenyuan, and Xu Tong

Doc ID: 327861 Received 09 Apr 2018; Accepted 29 Apr 2018; Posted 07 May 2018  View: PDF

Abstract: A new fiber Bragg grating (FBG) wavelength shift demodulation method based on optical true time delay microwave phase detection (OTTD-MPD) is proposed. We used a microwave photonics link (MPL) to transport a radio frequency (RF) signal over a dispersion compensation fiber (DCF). The wavelength shift of the FBG will cause the time delay change of the optical carrier that propagates in an optical fiber with chromatic dispersion, which will result in the variation of the RF signal phase. A long DCF was adopted to enlarge the RF signal phase variation. An IQ mixer was used to measure the RF phase variation of the RF signal propagating in the MPL, and the wavelength shift of the FBG can be obtained by the measured RF signal phase variation. The experiment results showed that the wavelength shift measurement resolution is 2pm when the group velocity dispersion of the DCF is 79.5ps/nm and the frequency of the RF signal is 18GHz, respectively. The demodulation time is as low as 0.1ms. The measurement resolution can be improved simply by using higher frequency of the RF signal and longer DCF or larger chromatic dispersion value of the DCF.

Turbulence correction with artificial neural networks

Sanjaya Lohani and Ryan Glasser

Doc ID: 324720 Received 27 Feb 2018; Accepted 28 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: We design an optical feedback network making use of machine learning techniques and demonstrate via simulations its ability to correct for the effects of turbulent propagation on optical modes. This artificial neural network scheme only relies on measuring the intensity profile of the distorted modes, making the approach simple and robust. The network results in the generation of various mode profiles at the transmitter that, after propagation through turbulence, more closely resemble the target mode. The corrected optical mode profiles at the receiver are found to be nearly identical to the desired profiles, with near-zero mean square error indices. We are hopeful that the present results combining the fields of machine learning and optical communications will greatly enhance the robustness of free-space optical links.

Auto-phase-locked measurement of time-gated luminescence spectra with microseconds delay

zece zhu and Xuewen Shu

Doc ID: 322876 Received 09 Feb 2018; Accepted 28 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: Time-resolved techniques are widely used in measuring the spectra and lifetimes of the excited states of molecules. However, the relative apparatus always require gated detector and phase matching circuitry, which are expensive to implement and maintain. Herein, a novel auto-phase-locked method for time-gated luminescence spectra measurement was developed by adjusting the exciting and detecting optical paths to pass through the same chopper wheel, which simultaneously acted as pulse generator and detecting shutter. This low-cost system needs no phase matching circuitry or control system. It can detect time-gated luminescence spectra with a delay time of only microseconds, demonstrating a high temporal resolution for thermally activated delayed fluorescence detection.

Unique Loss Characteristics in TE₀₁ Modes of Conventional Photonic Bandgap Fibers

Hirokazu Kubota, NOBUAKI KOSAKE1, Yuji Miyoshi, and Masaharu Ohashi

Doc ID: 323149 Received 13 Mar 2018; Accepted 27 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: We report modeling that demonstrates reduction of transmission loss and broadening of the bandwidth of a conventional hollow-core photonic bandgap fiber. Numerical investigation reveals that transmission loss of the high order TE₀₁ mode is lower than that of the fundamental HE₁₁ mode in fibers with thick cladding walls. By comparing dispersion curves of photonic bandgap fibers with different core-wall thicknesses, we show that the TE₀₁ mode has weaker coupling strength to a surface mode than the HE₁₁ mode does. This re- sult opens way for wider transmission band and lower transmission loss in photonic bandgap fibers that are subject to the detrimental effects of surface modes.

Optical approach to concurrence and polarization

Francisco De Zela

Doc ID: 326085 Received 15 Mar 2018; Accepted 27 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: We address a recently established relationship: $\mathcal{C}^2+\mathcal{P}^2 = 1$, which engages concurrence ($\mathcal{C}$) and polarization ($\mathcal{P}$). Said relationship has revealed a striking connection between two seemingly unrelated measures. Indeed, while $\mathcal{C}$ quantifies entanglement -- which is widely seen as a quantum-information resource -- $\mathcal{P}$ quantifies the amount of coherence between optical field components. We discuss the conditions under which $\mathcal{C}$ and $\mathcal{P}$ may be related to one another and show how the optical approach discloses entanglement as a resource that may be found in both the quantum and the classical domain. This is confirmed by a proposed Bell violation that can be exhibited using either quantum or classical light.

Self-assembly Three-dimensional Optical devices: from Microsphere to Micro-lens array

Hui Ding, Ying Yue, Han Chunyang, and Sihao Chen

Doc ID: 327958 Received 10 Apr 2018; Accepted 27 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: We report rapid formation of three-dimensional micro optical devices by silica nanoparticles self-assembly at face-centered cubic (fcc) structure. By controlling the hydrophobic interactions, the self-assembled products are fabricated into different morphologies, which include micro sphere and hemisphere. These structures have specific applications of microsphere resonant cavity and microlens array. The whisper gallery mode (WGM) of the formed microsphere is excited by the tapered fiber to demonstrate the optical characters of the microsphere. Moreover, the properties of the fabricated microlens and microlens array are tested through inserted in an imaging system. Ultimately, the optical devices with advanced functions are demonstrated by the secondary phase infiltrating into interstitial space of silica nanoparticles. This report will open a new direction in manufacturing multifunctional and miniature optical devices by an ultrasimple self-assembly approach.

Measurement of isocontours for dissipative Kerr solitons

Xinbai Li, Boqiang Shen, Heming Wang, Kiyoul Yang, Xu Yi, Qifan Yang, Zhiping Zhou, and Kerry Vahala

Doc ID: 323414 Received 19 Feb 2018; Accepted 26 Apr 2018; Posted 26 Apr 2018  View: PDF

Abstract: Dissipative Kerr solitons can be generated within an existence region of pumping power versus cavity-pump detuning frequency. By comparing modeling with measurement, the contours of constant soliton power and constant pulse width in this region are studied. These contours impart structure to the existence region that is helpful in understanding soliton locking and stabilization methods.

Two-dimensional nonlinear modes and frequency combs in bottle microresonators

Yaroslav Kartashov, Michael Gorodetsky, Alexandre Kudlinski, and Dmitry Skryabin

Doc ID: 326985 Received 27 Mar 2018; Accepted 26 Apr 2018; Posted 07 May 2018  View: PDF

Abstract: We report frequency comb generation in a bottle micro-resonator accounting for the azimuthal and axial degrees of freedom. We first identify a discrete set of the axial nonlinear modes of a bottle microresonator that appear as tilted resonances bifurcating from the spectrum of linear axial modes. We then study azimuthal modulational in-stability of these modes and show that families of 2D soliton states localized both azimuthally and axially bifurcate from them at critical pump frequencies. Depending on detuning, 2D solitons can be either stable, or form persistent breathers, chaotic spatio-temporal patterns, also exhibit collapse-like evolution.

Measuring high-order optical orbital angular momentum with a hyperbolic gradually-changing-period pure-phase grating

Zhibing Liu, She Gao, Wenda Xiao, Jishun Yang, xincheng huang, Yuanhua Feng, Jianping Li, Weiping Liu, and Zhaohui Li

Doc ID: 327299 Received 03 Apr 2018; Accepted 26 Apr 2018; Posted 09 May 2018  View: PDF

Abstract: We present a method to measure the high-order orbital angular momentum (OAM) state of a light beam with a static hyperbolic gradually-changing-period pure-phase grating (HGCP-PPG). From the number and orientation of the fringes of the Hermite-Gaussian like diffraction intensity pattern, the OAM state of the incident Laguerre-Gaussian beam can be measured. Experimental detection of the OAM state up to ±100-order has been achieved. This method is high efficient and robust because the HGCP-PPG is adaptive to high-order OAM beam and tolerant of the misalignment of the incident OAM beam.

Babinet-bilayered geometric phase optical elements

Etienne Brasselet

Doc ID: 327412 Received 30 Mar 2018; Accepted 25 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: Inspired by the complementary diffractive elements associated with Babinet's principle, we propose a bilayered subwavelength grating design in order to cancel out the spatial modulation of the dynamical phase usually associated with space-variant birefringent phase retardation. This concept is illustrated in the framework of single-mode Laguerre-Gauss beam shaping in the visible domain.

Bubbles, drops and solid particles recognition from real or virtual photonic jets reconstructed by digital in-line holography

Matthias Sentis, Fabrice Onofri, and Fabrice Lamadie

Doc ID: 328152 Received 12 Apr 2018; Accepted 25 Apr 2018; Posted 02 May 2018  View: PDF

Abstract: The image of the photonic jet (also called caustic) formed by a large, transparent and spherical particle, reconstructed by digital in-line holography (DIH), is shown to be similar to the Airy pattern observed atthe focus of a diffraction-limited lens. The analysis of this image, real or virtual depending on whether the particle relative refractive index is above or below one, allows characterizing the particle composition via its refractive index. Experiments clearly demonstrate the value of this method for the simultaneous 3D characterization and differentiation of the dynamics, size and composition of gas, liquid and solid particles in multiphase flows.

Directional Emission of Rhodamine 6G on Top of a Silver Grating

Ekembu Tanyi, Soheila Mashhadi, Sahana BHATTACHARYYA, Tal Galfsky, Vinod Menon, Evan Simmons, Viktor Podolskiy, Natalia Noginova, and Mikhail Noginov

Doc ID: 321044 Received 01 Feb 2018; Accepted 23 Apr 2018; Posted 02 May 2018  View: PDF

Abstract: We have observed directional spontaneous emission of Rhodamine 6G dye deposited on top of a silver grating and found that its angular distribution patterns were strongly different in TE and TM polarizations. The latter were related to the dispersion curves determined based on the polarized reflection spectra measured at multiple incidence angles. The most intriguing finding of this study was a resonance, which was coupled with TE polarized light and determined the characteristic double crescent patterns in the TE polarized spontaneous emission. This observation, as well as nearly similar resonance observed in TM polarization, were tentatively explained in terms of leaky waveguide modes supported by a film of dye-doped polymer.

Graphene-metal hybrid metamaterials for strong and tunable circular dichroism generation

Zhong Huang, Kan Yao, Guangxu Su, Wei Ma, Lin Li, Yongmin Liu, Peng Zhan, and Zhenlin Wang

Doc ID: 325105 Received 02 Mar 2018; Accepted 23 Apr 2018; Posted 02 May 2018  View: PDF

Abstract: Strong and dynamically controlled circular dichroism (CD) effect has aroused great attention due to its desirable applications in modern chemistry and life sciences. In this Letter, we propose a graphene-metal hybrid chiral metamaterial to generate mid-infrared CD with intensity more than 10%, which can be actively controlled over a wide wavelength range. In addition to the strong tunability, the CD signal intensity of our nanostructure is drastically larger than that of the purely graphene-based chiroptical nanostructures. Our design offers a new strategy for developing tunable chiral metadevices, which could be used in various applications such as biochemical detection and information processing.

Dense Relativistic Electron Mirrors from a Laguerre-Gaussian Laser-Irradiated Micro-Droplet

Li-Xiang Hu, Tong-Pu Yu, Hanzhen Li, Yan Yin, Paul McKenna, and F Q Shao

Doc ID: 325415 Received 06 Mar 2018; Accepted 23 Apr 2018; Posted 24 Apr 2018  View: PDF

Abstract: We investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly-polarized Laguerre-Gaussian lasers. The surface electrons are expelled from the droplet by the laser radial electric field and evolve into dense sheets after leaving the droplet. These electrons are trapped in the potential well of the laser transverse ponderomotive force and are steadily accelerated to about 100 MeV by the inherent longitudinal electric field. Particle-in-cell simulations indicate that the relativistic electron mirrors are characterized by high beam charge, narrow energy spread and large angular-momentum, which can be utilized for bright compact X/γ-ray pulse generation and photon vortex formation.

Simultaneous off-axis multiplexed holography and regular fluorescence microscopy of biological cells

Yoav Nygate, Gyanendra Singh, Itay Barnea, and Natan Shaked

Doc ID: 326843 Received 28 Mar 2018; Accepted 20 Apr 2018; Posted 26 Apr 2018  View: PDF

Abstract: We present a new technique for obtaining simultaneous multimodal quantitative phase and fluorescence microscopy of biological cells, providing both quantitative phase imaging and molecular specificity using a single camera. Our system is based on an interferometric multiplexing module, externally positioned at the exit of an optical microscope. In contrast to previous approaches, the presented technique allows conventional fluorescence imaging, rather than interferometric off-axis fluorescence imaging. We demonstrate the presented technique for imaging fluorescent beads and live biological cells.

High contrast high intensity repetitive petawatt laser

Hiromitsu Kiriyama, Alexander Pirozhkov, Mamiko Nishiuchi, Yuji Fukuda, Koichi Ogura, Akito Sagisaka, Yasuhiro Miyasaka, Michiaki Mori, Hironao Sakaki, Nicholas Dover, Kotaro Kondo, James Koga, Timur Esirkepov, masaki kando, and Kiminori Kondo

Doc ID: 325774 Received 09 Mar 2018; Accepted 20 Apr 2018; Posted 01 May 2018  View: PDF

Abstract: We report the generation of 63 J of broadband pulse energies at 0.1 Hz from the J-KAREN-P laser, which is based on an OPCPA/Ti:sapphire hybrid architecture. Pulse compression down to 30 fs indicates a peak power of over 1 PW. High temporal contrast of 10¹² prior to the main pulse has been demonstrated with 10 J output energy. High intensities of 10²² W/cm² on target by focusing a 0.3 PW laser with an f/1.3 off-axis parabolic mirror have been achieved. Fundamental processes of laser-matter interaction at over 10²² W/cm² intensities belong to an absolutely new branch of science that will be the principal research task of our infrastructure.

Stability of Ince-Gaussian beams in elliptical core few-mode fiber

Sahil Sakpal, Giovanni Milione, Ming-Jun Li, Mehdi Nouri, Hiva Shahoei, Tim LaFave, Solyman Ashrafi, and Duncan MacFarlane

Doc ID: 324722 Received 27 Feb 2018; Accepted 20 Apr 2018; Posted 07 May 2018  View: PDF

Abstract: A comparative stability analysis of Ince-Gaussian and Hermite-Gaussian modes in elliptical core few-mode fiber is provided to inform the design of spatial division multiplexing systems. The correlation method is used to construct crosstalk matrices that characterize the spatial modes of the fiber. Up to six low-order modes are shown to exhibit about -20 dB crosstalk. The crosstalk performance of each mode set is found to be similar. However, a direct comparison between modes of equal Gouy phase shift, a parameter that ensures identical beam quality and phase at the detector, demonstrates better relative power transmission for Ince-Gaussian beams. This result is consistent with natural modes supported by a 100 m elliptical core fiber for which a mode ellipticity of ε"=" 2 was found to be optimal. The relative power difference is expected to be magnified over longer fiber lengths in favor of Ince Gaussian modes.

656 W Er-doped Yb-free large-core fiber laser

Huaiqin Lin, Yujun Feng, Yutong Feng, Pranabesh Barua, Jayanta Sahu, and Johan Nilsson

Doc ID: 324633 Received 21 Feb 2018; Accepted 16 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: A continuous-wave erbium-doped ytterbium-free fiber laser generates a record-breaking pump-power-limited output power of 656 W at ~1601 nm when cladding pumped by 0.98-μm diode lasers. The slope efficiency was 35.6% with respect to launched pump power and the beam quality factor (M²) was ~10.5. This M²–value excludes a fraction ~25% of the power which emerged from the cladding, which we attribute in part to mode-coupling between the 146-μm core and 700-μm inner cladding. Whereas these parameters are adequate for in-band tandem-pumping of Tm-doped fiber lasers, we predict that an output power of over 1 kW is possible by pumping with state-of-the-art 0.98-μm diode lasers, even with a smaller core that allows for improved beam quality.

Sources for random arrays with structured complexdegree of coherence

Zhangrong Mei and Olga Korotkova

Doc ID: 326064 Received 14 Mar 2018; Accepted 15 Apr 2018; Posted 03 May 2018  View: PDF

Abstract: Simultaneous control of the far-field spectral density distribution together with the modulus and the phase of the complex degree of coherence of a beam radiated by a stationary source is hard to achieve in view of the intrinsic constraints on the source cross-spectral density. We tackle this problem by employing the Laguerre-Gaussian modes instead of the commonly used Gaussian mode for the source field realizations, in combination with the degree of source coherence radiating to spectral density arrays. We show that the produced spectral density arrays with Cartesian and polar symmetries have special features in both the modulus and the phase of the complex degree of coherence.

Near ground measure and numerical simulation of plane wave covariance of intensity in anisotropic turbulence

Melissa Beason, Christopher Smith, JOSEPH COFFARO, Sara Belichki, Jonathan Spychalsky, Franklin Titus, ROBERT CRABBS, Larry Andrews, and Ronald Phillips

Doc ID: 326381 Received 20 Mar 2018; Accepted 14 Apr 2018; Posted 30 Apr 2018  View: PDF

Abstract: Experimental measurements were recently made which displayed characteristics of plane wave propagation through anisotropic optical turbulence. A near-plane wave beam was propagated a distance of one and two kilometers at a height of two meters above the concrete runway at the Shuttle Landing Facility, Kennedy Space Center, Florida during January and February of 2017. The spatial-temporal fluctuations of the beam were recorded and covariance of intensity calculated. These data sets were compared to a theoretical simulation of covariance of intensity for a plane wave.

Inverse prism based on temporal discontinuity andspatial dispersion

Alireza Akbarzadeh, Nima Chamanara, and Christophe Caloz

Doc ID: 321063 Received 31 Jan 2018; Accepted 13 Apr 2018; Posted 19 Apr 2018  View: PDF

Abstract: We introduce the concept of the inverse prism asthe dual of the conventional prism and deducefrom this duality an implementation of it based ontemporal discontinuity and spatial dispersion providedby anisotropy. Moreover, we show that thisinverse prism exhibits the following three uniqueproperties: chromatic refraction birefringence,ordinary-monochromatic and extraordinary polychromatictemporal refraction, and linear to-Lissajous polarization transformation.

Optical-resonance-enhanced nonlinearities in aMoS₂-coated single-mode fiber

Haojie Zhang, Noel Healy, Antoine Runge, Chung Che Huang, Daniel William Hewak, and Anna Peacock

Doc ID: 321040 Received 01 Feb 2018; Accepted 27 Mar 2018; Posted 30 Mar 2018  View: PDF

Abstract: Few-layer molybdenum disulfide (MoS₂) has an electronicband structure that is dependent on the numberof layers and is, therefore, a very promising material foran array of optoelectronic, photonic and lasing applications.In this work, we make use of a side-polished opticalfiber platform to gain access to the nonlinear opticalproperties of the MoS₂ material. We show that the nonlinearresponse can be significantly enhanced via resonantcoupling to the thin film material, allowing for theobservation of optical modulation and spectral broadeningin the telecoms band. This route to access thenonlinear properties of 2D materials promises to yieldnew insights into their photonic properties.

Experimental Demontration of 20-Gb/s Dual-band Nyquist PAM-4 transmission over Short-Reach IMDD system using super-Nyquist sampling technique

Deng Rui, Jing He, Jianjun Yu, Xin Xiao, Kai Lyu, and Xin Xiangjun

Doc ID: 318674 Received 29 Dec 2017; Accepted 23 Mar 2018; Posted 08 May 2018  View: PDF

Abstract: In this letter, we experimentally demonstrate a dual-band Nyquist PAM-4 intensity modulation direct detection (IMDD) system using real-time field programmable gate array (FPGA)-based receiver. Although the sampling rate of the analog-to-digital converter (ADC) used in the receiver is only 5-GSa/s and there is no mixer at the receiver side, the system can successfully realize 22-km SSMF transmission with 20-Gb/s data rate by using super-Nyquist sampling technique. To our knowledge, this is the first experimental demonstration of non-single-band signal transmission over IMDD system based on super-Nyquist sampling technique. In addition, power weighting technique is also applied in the system. The experimental results show that with the help of power weighting technique, the BER of the system can be reduced from 6.1×10-3 to 2.6×10-3.

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