bluuebunny/crossref_metadata_2025 huggingface dataset:
Quasi-Phasematched Optical Parametric Oscillators in Lithium Niobate Waveguides as Sources of Widely Tunable Infrared Coherent Radiation
Authors: Arbore M.A. , Bortz M.L. , Fejer M.M.
Published: February 2023

Efficient, low power, compact sources of tunable coherent near and mid-infrared wavelength radiation are necessary for many applications, including communications, spectroscopy, and process monitoring. Nonlinear optical frequency conversion that shifts laser diode outputs to the desired wavelength has attracted significant attention as a means to meet these requirements. Optical parametric oscillators (OPOs) offer near or mid-infrared wavelengths with extremely wide tunability while requiring only a single pump laser. An OPO is a resonant device which divides short-wavelength pump radiation into a pair of longer-wavelength signal and idler waves. Because of the large circulating signal (and sometimes idler) fields, overall energy conversion efficiency is much larger than that of single-pass interactions such as difference frequency generation (DFG). Because parametric gain increases with pump power while cavity losses generally remain fixed, a minimum pump power is required so that round-trip gain exceeds round-trip loss. One current challenge for OPOs is reducing the oscillation threshold to levels attainable with diode lasers.
Nonlinear Propagation In An Optical Fractal Structure
Authors: Bertolotti M. , Moretti F. , Sibilia C. , Masciulli P.
Published: February 2023

In this paper we study the input-output characteristic of a fractal nonlinear optical Fabry-Perot resonator. The 1D dielectric integrated resonator is obtained alternating two nondispersive planar dielectric layers of unperturbed refractive index n
2
and n
1
(n2 > n1) of thickness such that their optical path is the same. The initiator is the layer of refractive index n2. If L is the optical path of the initiator, the generator is obtained substituting the central part of the initiator having an optical path of L/3 with the layer of refractive index n1 and thickness such that the optical path is L/3 again. The resonator is obtained iterating the operation on the left and right third optical path, and stopping the iteration at the N-th step.
Nonlinear Polarization Switching in an InGaAs/GaAs Quantum Well Amplifier
Authors: Lin Ming-San , Yang C. C. , Hong Minghwei , Chen Young-Kai
Published: February 2023

Nonlinear self-switching is an important step toward all-optical signal processing and passive mode-locking of lasers. In nonlinear self-switching, the power-dependent coupling of energy between two channels is caused by the imbalance of nonlinear gain/absorption and/or refractive-index between the two channels. In this paper, we report the experimental results of nonlinear polarization switching in an InGaAs/GaAs single quantum well(QW) GRINSCH optical amplifier. The amplifier consists of a 10 nm InGaAs well. On either side of the well, it includes a 40 nm GaAs barrier, an about 200 nm graded-index separate confinement layer with AlxGa1-xAs (x drops from 0.4 to 0), and an Al0.4Ga0.6As p/n type cladding. It lased at the threshold current 120 mA with 20 % duty cycle at 974 nm. The amplifier had a length about 300 μm and a ridge 50 μm wide for lateral guiding. The electro-luminescence in the TE (TM) mode was centered near 975 (940) nm, indicating the relative energy state of the heavy and light hole subbands. In the experiment, we used a Ti:Sapphire laser (Mirra 900) for femtosecond and cw optical signals. After the signals passed through the amplifier, their polarization status and power distributions between the TE and TM directions were recorded, as shown in Fig. 1.
Statistics of Four-Wave Mixing Crosstalk
Authors: Forghieri Fabrizio , Tkach R. W. , Chraplyvy A. R.
Published: February 2023

Four-wave mixing (FWM) is the dominant nonlinear effect in intensity-modulated wavelength-division multiplexed (WDM) optical communication systems using dispersion-shifted fiber (DSF). In WDM systems with equally spaced channels all the product terms generated by FWM in the bandwidth of the system fall at the channel frequencies. The mixing products generated at the channel frequencies coherently interfere with the signals, giving rise to crosstalk. Due to the coherent nature of FWM interference in equally spaced WDM systems, a single mixing product generated on one of the channels with a power 20 dB lower than the signal power is enough to cause a ±1 dB fluctuation in the received power [1].
Dark soliton generation and propagation using a normally dispersive, dispersion decreasing fiber
Authors: Richardson D.J. , Chamberlin R.P. , Dong L. , Payne D.N.
Published: February 2023

The generation and propagation of bright and dark soliton pulses is an area of great scientific interest with relevance to many futuristic telecommunication and optical-processing applications. Bright solitons have been the subject of intense experimental investigation; however, the experimental study of dark soliton behaviour has been limited. This situation is in no small part due to the difficulty of generating and measuring such pulse forms [1,2,3] (for review see Ref.[4] and references within).
Periodic Spatial Solitons
Authors: Snyder Allan W , Hewlett Simon , Mitchell D John
Published: February 2023

Periodic (second order) solitons exist in an idealized saturating medium. We give a physical explanation for why they result from scaling up a fundamental soliton.
First Experimental Observation of Solitary Pulse Propagation in Semiconductors below Half-the-Band-Gap
Authors: Aitchison J. S. , Hamilton C. F. , Kennedy G. T. , Sibbett W. , Biehlig W. , Peschel U. , Peschel T. , Lederer F.
Published: February 2023

We show that ultrashort pulses may propagate without broadening in a properly tailored rib-loaded Anti-Resonant-Reflecting-Optical Waveguide (ARROW) made in the AlGaAs system.
Experimental Demonstration of Soliton Transmission Over 28,000 km Using Dispersion Management
Authors: Jacob J. M. , Carter G. M. , Menyuk C. R. , Golovchenko E.A. , Pilipetskii A N.
Published: February 2023

Dispersion management is a well-established means for improving the performance of nonreturn-to-zero (NRZ) data transmission for optical fiber communications [1]. In these systems, dispersion management is used to avoid four-photon mixing. Recent work has demonstrated that dispersion management in soliton transmission systems is also a promising technique for improving system performance [2] – [4]. By keeping the local dispersion high and the average dispersion low, it is possible to reduce timing jitter while having sufficient pulse energy to avoid amplitude errors. We report here for the first time that it is possible to stably transmit solitons using a dispersion map in which almost all of the fiber is in the normal regime but in which the average dispersion is anomalous. Stable transmission over 28,000 km at 8 Gbit/s was experimentally observed.
Low-power all-optical switching using chalcogenide glass fibers
Authors: Asobe Masaki , O’hara Takahiko , Yokohama Itaru , Kaino Toshikuni
Published: February 2023

It has been revealed that As2S3-based
chalcogenide glass fiber has large nonlinearity and long interaction
length. We previously demonstrated optical Kerr shutter operation
using As2S3-based glass fiber with a gate power
of 3 W.1) In this paper, we present two experimental
approaches to reducing switching power.
Bloch Wave Theory of Modulational Polarization Instabilities in a Birefringent Fiber
Authors: Wabnitz Stefan , Trillo Stefano
Published: February 2023

The nonlinear polarization changes of an intense pump wave in optical birefringent fibers [1, 2] may substantially affect the parametric gain spectra of a frequency detuned signal. Although this effect is important for several applications involving birefringent fibers in fiber lasers and switches, earlier analyses of parametric gain have been restricted to cases where no pump polarization rotation occurs [3]-[7]. In fact, only the cases where the input polarisation of the pump beam is coupled on either one of the birefringence axes, or equally split between the axes of a high-birefringence fiber, were considered. We present here the full pump-power dependence of the modulational gain spectra for an arbitrary input polarization state of the pump with respect to the birefringence axes. We believe that the present analysis is crucial for a proper description of the experimental results [8]-[10] and for assessing the practical applicability of the modulational instability gain for all-optical processing devices.
Efficient wavelength conversion in QPM devices
Authors: Webjörn J. , Nam D. , Siala S. , Sanders S. , Waarts R. , Welch D.
Published: February 2023

By now, the many potential applications of a rugged blue laser source are well established, for instance printing, displays, and optical storage. In a longer time perspective, the direct-emitting blue and green semiconductor lasers are of course the most promising candidates. For the near-term supply of solid-state blue lasers, however, various hybrid approaches are being pursued. Examples include intracavity doubling in ring cavity lasers or in microchip lasers, and the approach that has been studied at SDL: single-pass frequency doubling of diode lasers in quasi-phase- matching (QPM) waveguides.
Oscillations of Solitary Waves in Nonlinear Quadratic Media
Authors: Peschel U. , Etrich C. , Lederer F. , Malomed B. A. , Kivshar Y. S.
Published: February 2023

Recently, solitary waves characterized by a mutual locking of the fundamental and second harmonics in quadratically nonlinear media attracted a lot of attention [1]. The excitation of solitary waves, the evolution of unstable ones or numerical collision experiments with them reveal a prominent feature of the solutions under consideration. It turns out that persistent oscillations appear in many cases. They are practically undamped and may exhibit fairly large amplitudes. The extreme stability of the excited oscillations is astonishing for a nonintgrable system. This also is of great importance for future applications. Given a realistic experimental situation the second harmonic is excited via the fundamental wave only and strong oscillations cannot be avoided. Thus a stationary solitary wave with no oscillations seems to be more or less an exception.
Mode Interplay via Quadratic Cascading in a Lithium Niobate Channel Waveguide
Authors: Conti Claudio , De Rossi Alfredo , Assanto Gaetano
Published: February 2023

Several guided-wave devices based on quadratic cascading [1-2] have been proposed,[3-8] and a few of them recently demonstrated in Lithium Niobate (LN).[9-10] In this Communication, we numerically investigate the nonlinear (NL) response of a waveguide, where the two dominant modes at 1.55μm spatially interfere at the output due to the cascading process via SHG.
The effect of pulse walk-off on the amplitude and phase modulation in a quadratically nonlinear medium
Authors: Kobyakov A. , Schmidt E. , Lederer F.
Published: February 2023

During the past several years it has been shown that cascading of quadratic nonlinearities, i.e. the consecutive up-and down-conversion of an optical field, may have a realistic potential in all-optical signal processing as a supplement or an alternative to cubic nonlinear effects [1,2]. Potentially reduced power requirements and interesting peculiarities have led to various device concepts [2-5] where some of them have been already implemented. Major differences to the cubic scenario consist in the unavoidable coexistence of amplitude and phase modulation where the latter one can be almost homogeneous across a short pulse [2,3]. This is advantageous in comparison to self-phase modulation in cubic materials which generates a strong chirp. The primary disadvantage of cascading is the pulse walk-off due to the different group velocities of the participating waves. In particular, this effect is intruding in fairly long waveguide configurations in which all-optical devices are most likely supposed to be realized. Until now, most experiments were carried out in thin bulk samples where the walk-off can be neglected. Thus, the continuos wave (CW) approximation with the time being a mere parameter could be applied in modelling these experiments.
Effect of natural optical activity on the propagation of photorefractive solitons
Authors: Królikowski Wieslaw , Akhmediev Nail , Andersen David R. , Luther-Davies Barry
Published: February 2023

Spatial solitons in photorefractive media have been the subject of intense theoretical and experimental investigations [1]. One of the first experimental demonstrations of self-focusing and self-defocusing effects has been done in cubic barium titanium oxide (BTO) crystal [2], where the so called screening solitons [3] have been observed. The cubic crystals are attractive because for some crystallographic orientation, the optical beam either experiences self-focusing or self-defocusing, depending on polarization. Thus, for fixed direction of the biasing electric field, bright, dark or coupled bright and dark solitary beams are possible. However, some cubic crystals exhibit strong natural optical activity (OA) which is 6.3°/mm for BTO. Since the photorefractive nonlinearity strongly depends on polarization, polarization rotation may destroy the soliton propagation. In the present work, we examine the influence of optical activity on propagation of screening solitons in cubic PR crystal.
Power Transfer in Multiport Waveguide Devices Made from Solitons
Authors: Miller P. D. , Akhmediev N. N.
Published: February 2023

Light-guiding-light phenomena [1] suggest a number of applications in all-optical information processing. One of the most interesting effects is the ability of the spatial soliton, created by a strong beam inducing a sech-type refractive index profile, to behave as a waveguide, carrying a weak probe beam [2]. These waveguides can be made either with bright [2] or dark [3] spatial solitons. Such facts suggest further that colliding solitons might serve as X-junctions [5,6] and more generally as multiport devices. Several such devices have been analyzed to date [6,7]. The use of a probe beam with the same frequency as the pump is preferable because these devices then have no losses in the impact area of two solitons [6]. Moreover, a probe beam injected into one of the channels has no reflected component in this case. It passes through the impact area of the soliton collision and is distributed totally among the output channels. This is one of the essential properties of any ideal NxN switch. On the other hand, the use of a probe beam of the same frequency introduces the problem of its separation from the pump. Thus, from the experimental point of view it is more convenient to use a weak probe beam at different frequency [7], in which case the probe can be separated from the pump simply by spectral filtering. However, in this case “solitonic” devices like X-junctions or NxN switches lose their beauty because of losses in the soliton collision area [7] and the fact that an input beam can potentially be reflected into any of the input channels.
Phase-matched second-harmonic generation in KNbO3 channel waveguides
Authors: Fluck D. , Pliska T. , Günter P. , Beckers L. , Buchal Ch.
Published: February 2023

Frequency doubling of near-infrared lasers in channel waveguides offers the potential of building robust, compact and reliable blue lasers. KNbO3 is one of the candidate materials for high efficiency frequency doubling of AIGaAs and InGaAs laser diodes and of diode-pumped solid-state lasers, e.g. Nd:YAG and Nd:YVO4 lasers, into the blue spectral range thanks to its large nonlinear optical coefficients and its favourable phase-matching (PM) conditions1.
Second-harmonic generation from tetragonal chalcopyrite-structure semiconductor thin films
Authors: Bottomley D. J. , Fons P. J. , Niki S. , Yamada A. , Mito A. , Bi W. , Tu C. W.
Published: February 2023

Tetragonal chalcopyrite-structure semiconductor crystals have acquired a niche within the realm of nonlinear optics (NLO) as second order NLO materials in the 2 μm to 20 μm wavelength infra-red region [1]. Examples include AgGaS2, AgGaSe2, ZnGeP2, CdGeAs2 and HgGa2S4. Compared with other NLO crystals, chalcopyrite-structure crystals are characterized by high nonlinearities and low damage thresholds. The latter quality makes them ill-suited to frequency-converting powerful laser beams, which is why they tend to be applied only in the infra-red region, where the few alternative crystals suffer from similar problems.
Beam Pointing Stabilization with Spatial Solitary Waves in Quadratic Media
Authors: Leo Giuseppe , Assanto Gaetano , Torruellas William E.
Published: February 2023

Spatial solitary waves of the quadratic nonlinearity were discovered in the early 70's [1] and have been the subject of numerous investigations [2-5] due to the renewed emphasis placed on cascading for all-optical processing. [6-7] Such waves were recently demonstrated in bulk KTP crystals and Lithium Niobate planar waveguides, underlining the potential interest of such self-guiding fields for signal processing applications.[8-9] Among them, angular steering versus seed input phase [10] and versus power imbalance between input polarizations [11] have been reported in KTP. In this Communication, we elucidate some specific features of Type I and Type II second harmonic generation (SHG) interactions leading to the formation of 2+1 spatial solitonlike waves. Specifically, we demonstrate how a small angular tilt in the input fundamental frequency (FF) beam can provide pointing stabilization against peak power fluctuations when Type I (scalar) or Type II (vectorial) interactions are employed, while Type II processes can compensate random input angle perturbations in the weaker FF polarization component.
An approximation procedure for the Zakharov-Shabat eigenvalue problem for real single-humped potentials
Authors: Desaix M. , Anderson D. , Lisak M. , Quiroga-Teixeiro M. L.
Published: February 2023

The nonlinear Schrödinger equation, describing the dynamical evolution of an optical pulse under the influence of linear (anomalous) dispersion or diffraction and nonlinear self-phase modulation can be taken in the form: where q(t) represents the form of the initially launched pulse. A key role in the inverse scattering scheme for solving the nonlinear Schrödinger is played by the concomitant Zakharov-Shabat scattering problem, [1]: where v1 and v2 are the Jost functions, which satisfy the asymptotic relations: v1 → exp(–iζt) and v2 → 0 as t → –∞.
Vectorial Solitary Waves in Media with a Second-Order Nonlinearity
Authors: Etrich C. , Peschel U. , Lederer F. , Malomed B. A.
Published: February 2023

During the last years the interest in solitary-wave effects in quadratically nonlinear media has increased rapidly. Bright, dark and grey solitary waves were found in the case of scalar second harmonic generation (SHG) where two photons of the fundamental wave create one photon of the second harmonic [1, 2]. In contrast, all investigations of the vectorial or so-called type II SHG (two photons of two different fundamental waves create one photon of the second harmonic) concentrated on cw-operation only. Interesting effects like phase insensitive transistor-like action, polarization switching or high nonlinearly induced phase changes were demonstrated [3, 4]. Thus it should be worthwhile to look for solitary waves in vectorial SHG too. In this system the energy imbalance between the two fundamental waves is a new conserved quantity during propagation. Thus, comparing with scalar SHG we expect to find a two-parameter family of solitary wave solutions.
Interaction of Bragg solitons in fiber gratings: Numerical results
Authors: Litchinitser N.M. , Eggleton B.J. , de Sterke C.M. , Agrawal G.P.
Published: February 2023

The interaction between two Bragg solitons in a fiber grating is investigated numerically in both infinite and finite geometries. In certain limits, Bragg solitons interactions exhibit features reminiscent of fiber solitons. More generally, the interaction features are found to depend on the initial soliton separation.
Grating enhanced all-optical switching in a Mach-Zehnder interferometer
Authors: Keller H.-M. , Sipe J. E.
Published: February 2023

We consider a Mach-Zehnder interferometer with a Bragg grating in one
arm, and model the resulting nonlinear switch in time-dependent
simulations. Compared with a pure Mach-Zehnder device the switching
threshold is significantly reduced; compared with a gap soliton switch
a reasonable operating bandwidth and low pulse distortion is
achieved.
Coupled-mode equations for deep quadratically nonlinear gratings
Authors: Arraf Awdah , de Sterke C. Martijn
Published: February 2023

The coupled-mode equations for light propagating through deep quadratically nonlinear gratings are derived by expanding in the Bloch functions of the linear structure. Our results show that these equations differ from those for shallow gratings in that the coefficients have different values, and that additional nonlinear terms appear.
Modulational instabilities in a nonlinear all-fiber cavity
Authors: Coen S. , Haelterman M. , Emplit Ph.
Published: February 2023

Over the last decade modulational instability (MI) in optical fibers has attracted much attention for both its fundamental and applied interests [1]. MI in fibers can be interpreted as a stimulated four-wave-mixing process that is naturally phase-matched by the balance between chromatic dispersion and Kerr nonlinearity. In self-focusing Kerr media, such as silica optical fibers, anomalous dispersion is required in order for this phase matching process to occur. In the presence of normal dispersion, phase matching can be achieved with the help of an extra degree of freedom that is provided by the coupling with an additional intense carrier wave of different polarization [2] or wavelength [3]. In 1992 Haelterman et al. suggested in a theoretical work that this extra coupling mechanism is not necessary to obtain an extension of MI to the normal dispersion regime [4]. It was shown that when nonlinear dispersive waves are subject to cavity boundary conditions, the underlying four-wave mixing processes are altered so as to make possible MI with normal dispersion.
Self-Trapped Optical Beams in Semiconductors
Authors: Chauvet M. , Hawkins S.A. , Salamo G.J. , Segev M. , Bliss D.F. , Bryant G.
Published: February 2023

Spatial solitons in photorefractive materials have been the subject of recent interest.1-6 Compared with Kerr spatial7 solitons, the most distinctive features of spatial solitons are that they are observed at low light intensities and that trapping occurs in both transverse dimensions. Until now, photorefractive spatial solitons have been observed in the tungsten bronze ferroelectric oxides and in the nonferroelectric sillenite oxides. Several reasons have led us to carry out similar experiments in the photorefractive semiconductor crystal InP:Fe.8,9 First, this material is sensitive in the range of the near-infrared wavelengths used in optical telecommunications. Second, the photorefractive effect in semiconductors has the advantage of a faster response time than that observed in either the tungsten bronze or the sillenite crystal materials. Third, the possibility of monolithic integration with other optoelectronic components (lasers, detectors) is also attractive.
Incoherent dark quasi-solitons in biased photorefractive media
Authors: Coskun Tamer H. , Christodoulides Demetrios N. , Mitchell Matthew , Chen Zhigang , Segev Mordechai
Published: February 2023

Self trapping of coherent light beams in nonlinear media has been extensively studied in last three decades or so. Recently however, it has been experimentally [1,2] and theoretically [3] demonstrated that self trapped partially incoherent bright beams are also possible in biased photorefractive crystals. Incoherent bright photorefractive spatial solitons were also lately identified using a self-consistent multimode approach [4]. At this point, it is by no means clear whether incoherent dark solitons are also possible in biased photorefractive media. Moreover, if this is the case, it will be of interest to understand their coherence properties or fluctuation statistics during propagation.
Self-trapping of dark incoherent light beams
Authors: Chen Zhigang , Mitchell Matthew , Segev Mordechai , Coskun Tamer H. , Christodoulides Demetrios N.
Published: February 2023

Thus far, dark solitons have been studied using spatially-coherent light beams only. However, nature is full of incoherent light as well as coherent light. In fact, many sources of electromagnetic radiation emit spatially incoherent light. Recently, our group has demonstrated that bright beams from a spatially incoherent light source can form incoherent solitons in non-instantaneous nonlinear media [1,2]. Can such incoherent beams support dark solitons? Here we report the first experimental observation of self-trapping of spatially-incoherent dark beams in the form of one-dimensional dark stripes and of two-dimensional dark vortices. Self-trapping of dark incoherent beams, or, in a broader sense, self-trapping of dark incoherent wave-packets, is a fundamentally new concept. Even though we have shown previously that bright incoherent beams can self-trap in a nonlinear medium [3-5], the extension to dark beams (or voids borne on the background of incoherent beams that are otherwise uniform in space) is far from being obvious. From the applications view-point, since in general self-trapped beams (bright and dark, coherent and incoherent) induce waveguides in the volume of a bulk nonlinear medium, our experiments offer a unique possibility of controlling incoherent light with incoherent light, or, even more surprising, controlling coherent light with incoherent light. This means that light which originates from Light Emitting Diodes (LEDs), which is spatially-incoherent, can be used to guide, steer and control laser beams.
Collision-induced timing jitter in dispersion-managed soliton systems
Authors: Ablowitz Mark J. , Biondini Gino , Chakravarty Sarbarish , Horne Rudy L.
Published: February 2023

Wavelength-division multiplexing (WDM) offers the potential for considerable increase in data transmission rates. However, it also raises a number of issues of theoretical and practical importance. One of these issues is the timing displacement effects due to nonuniform soliton collisions in the presence of amplifiers, which induce permanent frequency and velocity shifts of the solitons [1]. In a previous letter [2] we developed a stochastic analysis of collision-induced timing jitter when amplifiers are present. In this paper we include the effects of filters and dispersion management in the analysis. Given typical values of the system parameters, we are able to calculate explicitly the total root mean square timing jitter, the expected bit error rate and the maximum length of error-free transmission.
Conditions for stationary pulse propagation in the strong dispersion management regime
Authors: Lakoba T.I. , Yang J. , Kaup D.J. , Malomed B.A.
Published: February 2023

Recently there has been intensive research on pulse propagation in dispersion-managed fibers, where pieces of fiber with opposite signs of dispersion are concatenated periodically (see, e.g., [1] and references therein). When the local dispersion lengths are much smaller than the nonlinear and the average dispersion lengths, it is termed strong dispersion management (DM) regime.
Propagation of Light Beam in Sillenite Crystal with a Square-Wave Applied Field
Authors: Shandarov Stanislav M. , Nazhestkina Nadezhda I. , Kobozev Oleg V. , Litvinov Rudol’f V. , Kargin Yuri F. , Volkov Vladimir V.
Published: February 2023

Enhancements in a gradient-type photorefractive response can be achieved in cubic crystals through the use of ac-field techiques1-3. However, the standard linear models of the photorefractive effects in the presence of an applied ac-field1,2,4,5 are valid for low modulation depth of light intensity6.
Continuous-wave measurement of the fiber nonlinear index
Authors: Monzon D. , Starodumov A.N. , Barmenkov Yu. O. , Torres I.
Published: February 2023

Optical nonlinearities have become a serious limitation in long-distance communication systems. A simple and accurate method for measuring the nonlinear Kerr has become necessary in order to predict system performance. Since the original technique proposed by Stolen et al [1] in 1978 several methods, that exploit different nonlinear effects, such as self-and cross-phase modulation [2-5], modulation instability [6] and four-wave mixing [7] have been developed for measuring n2 in optical fibers. Many of these methods, based on phase shift detection, require picosecond pulsed lasers or specially designed optical sources and suffer from a large uncertainty in the nonlinear phase shift measurements.
Bright and Dark Pulses in Fibre Lasers and Optical Transmission Lines
Authors: Ankiewicz Adrian , Akhmediev Nail , Soto-Crespo J. M.
Published: February 2023

In recent years, narrow pulses of light called solitons have allowed for very high bit-rate transmission in optical fibre systems [1,2]. The basic idea is that the (small) nonlinearity of the glass (viz. a small increase in refractive index with intensity of light) is used to cancel the dispersion suffered by a pulse, thus forming an unchanging soliton which can propagate a great distance [3]. Short pulses can be generated in a passively mode-locked fiber lasers. These devices can be described to a high accuracy using cubic-quintic Ginzburg-Landau equation [4-6].
Optical fiber strain sensor with high precision and extended dynamic range based on a coupled optoelectronic oscillator
Authors: Feng Danqi , Tang Yangxu , Gao Ya , Deng Ming
Published: February 2023

We have proposed and experimentally demonstrated an optical fiber strain sensor with high precision and extended dynamic range based on a coupled optoelectronic oscillator (COEO). The COEO is a combination of an OEO and a mode-locked laser, sharing one optoelectronic modulator. The feedback between the two active loops makes the oscillation frequency equal to the mode spacing of the laser. It is equivalent to a multiple of the natural mode spacing of the laser, which is affected by the applied axial strain to the cavity. Therefore, we can evaluate the strain by measuring the oscillation frequency shift. Higher sensitivity can be obtained by adopting higher frequency order harmonics owing to the accumulative effect. We carry out a proof-to-concept experiment. The dynamic range can reach 10000 με. Sensitivities of 6.5 Hz/με for 960 MHz and 13.8 Hz/με for 2700 MHz are obtained. The maximum frequency drifts of the COEO in 90 mins are within ±148.03 Hz for 960 MHz and ±303.907 Hz for 2700 MHz, which correspond to measurement errors of ±22 με and ±20 με. The proposed scheme has the advantages of high precision and high speed. The COEO can generate an optical pulse whose pulse period is influenced by the strain. Therefore, the proposed scheme has potential applications in dynamic strain measurement.
Low threshold current density and high power InGaN-based blue-violet laser diode with an asymmetric waveguide structure
Authors: Zhang Zhenzhuo , Yang Jing , Liang Feng , Chen Ping , Liu Zongshun , Zhao Degang
Published: February 2023

Performance of InGaN-based blue-violet laser diodes (LD) with different waveguide structure were investigated by simulation and experimental methods. Theoretical calculation demonstrated that threshold current (Ith) can be reduced and slope efficiency (SE) can be improved by using an asymmetric waveguide structure. Based on the simulation results, a LD with 80-nm-thick In0.03Ga0.97N lower waveguide (LWG) and 80-nm-thick GaN upper waveguide (UWG) is fabricated with flip chip package. Under continuous wave (CW) current injection at room temperature, its optical output power (OOP) reaches 4.5 W at an operating current of 3 A and the lasing wavelength of 403 nm. The threshold current density (Jth) is 0.97 kA/cm2 and the SE is about 1.9 W/A.
100-GHz ultra-short high-peak-power colliding-pulse mode-locked laser with asymmetric coating
Authors: Sun Defan , Lu Dan , Zhang Ruikang , Wang Huan , Yang Qiulu , Zhao Lingjuan
Published: February 2023

By using colliding-pulse mode-locking (CPM) configuration with asymmetric cladding layer and coating, 1.5-µm AlGaInAs/InP multiple quantum well (MQW) CPM lasers with high-power and ultra-short pulse generation capability at a repetition rate of 100 GHz are reported. The laser adopts a high-power epitaxial design, with four pairs of MQWs and an asymmetrical dilute waveguide cladding layer to reduce the internal loss, maintaining good thermal conductivity while increasing the saturation energy of the gain region. The asymmetric coating is introduced, as compared to conventional CPM laser with symmetric reflectivity, to further increase the output power and shorten the pulse width. With a high reflection (HR) coating of 95% on one facet and another facet as cleaved, 100-GHz sub-picosecond optical pulses with peak power on a Watt level are demonstrated. Two mode-locking states, the pure CPM state and the partial CPM state, are investigated. Pedestal-free optical pulses are obtained for both states. For the pure CPM state, a pulse width of 564 fs, an average power of 59 mW, a peak power of 1.02 W, and an intermediate mode suppression ratio over 40 dB are demonstrated. For the partial CPM state, a pulse width of 298 fs is demonstrated.
Longitudinal evolution from scalar to vector beams assembled from all-dielectric metasurfaces
Authors: Xu Wenhui , Li Jie , Yao Jianquan
Published: February 2023

Vector vortex beams (VVBs) with non-uniform polarization states have a wide range of applications, from particle capture to quantum information. Here, we theoretically demonstrate a generic design for all-dielectric metasurfaces operating in the terahertz (THz) band, characterized as a longitudinal evolution from scalar vortices carrying homogeneous polarization states to inhomogeneous vector vortices with polarization singularities. The order of the converted VVBs can be arbitrarily tailored by manipulating the topological charge embedded in two orthogonal circular polarization channels. The introduction of the extended focal length and the initial phase difference effectively guarantees the smoothness of the longitudinal switchable behavior. A generic design approach based on vector-generated metasurfaces can assist in the exploration of new singular properties of THz optical fields.
Deflection of a reflected intense spatiotemporal optical vortex beam
Authors: Guo Xinju , Zhang Lingang , Zhang Xiaomei , Shen Baifei
Published: February 2023

In this Letter, we reveal a new deflection effect in the reflection of an intense spatiotemporal optical vortex (STOV) beam. When a STOV beam with relativistic intensities (>1018 W cm−2) impacts on an overdense plasma target, the reflected beam deviates from the specular reflection direction in the incident plane. Using two-dimensional (2D) particle-in-cell simulations, we demonstrated that the typical deflection angle is of a few milliradians and can be enhanced by using a stronger STOV beam with tightly focused size and higher topological charge. Though similar to the angular Goos–Hänchen effect, however, it is worth emphasizing that the deviation induced by a STOV beam exists, even in normal incidence, revealing an essentially nonlinear effect. This novel effect is explained from the viewpoint of angular momentum conservation, as well as the Maxwell stress tensor. It is shown that an asymmetrical light pressure of the STOV beam breaks the rotational symmetry of the target surface and leads to nonspecular reflection. Unlike the shear press of an Laguerre-Gaussian beam, which only acts in oblique incidence, the deflection caused by the STOV beam exists more widely, including in normal incidence.
A novel role for trithorax in the gene regulatory network for a rapidly evolving fruit fly pigmentation trait
Authors: Weinstein Michael L. , Jaenke Chad M. , Asma Hasiba , Spangler Matthew , Kohnen Katherine A. , Konys Claire C. , Williams Melissa E. , Williams Ashley V. , Rebeiz Mark , Halfon Marc S. , Williams Thomas M.
Published: February 2023

Animal traits develop through the expression and action of numerous regulatory and realizator genes that comprise a gene regulatory network (GRN). For each GRN, its underlying patterns of gene expression are controlled bycis-regulatory elements (CREs) that bind activating and repressing transcription factors. These interactions drive cell-type and developmental stage-specific transcriptional activation or repression. Most GRNs remain incompletely mapped, and a major barrier to this daunting task is CRE identification. Here, we used anin silicomethod to identify predicted CREs (pCREs) that comprise the GRN which governs sex-specific pigmentation ofDrosophila melanogaster. Throughin vivoassays, we demonstrate that many pCREs activate expression in the correct cell-type and developmental stage. We employed genome editing to demonstrate that two CREs control the pupal abdomen expression oftrithorax, whose function is required for the dimorphic phenotype. Surprisingly,trithoraxhad no detectable effect on this GRN’s keytrans-regulators, but shapes the sex-specific expression of two realizator genes. Comparison of sequences orthologous to these CREs supports an evolutionary scenario where thesetrithoraxCREs predated the origin of the dimorphic trait. Collectively, this study demonstrates howin silicoapproaches can shed novel insights on the GRN basis for a trait’s development and evolution.
Differentiating between Bayesian parameter learning and structure learning based on behavioural and pupil measures
Authors: Rutar Danaja , Colizoli Olympia , Selen Luc , Spieß Lukas , Kwisthout Johan , Hunnius Sabine
Published: February 2023

Within predictive processing two kinds of learning can be distinguished: parameter learning and structure learning. In Bayesian parameter learning, parameters under a specific generative model are continuously being updated in light of new evidence. However, this learning mechanism cannot explain how new parameters are added to a model. Structure learning, unlike parameter learning, makes structural changes to a generative model by altering its causal connections or adding or removing parameters. Whilst these two types of learning have recently been formally differentiated, they have not been empirically distinguished. The aim of this research was to empirically differentiate between parameter learning and structure learning on the basis of how they affect pupil dilation. Participants took part in a within-subject computer-based learning experiment with two phases. In the first phase, participants had to learn the relationship between cues and target stimuli. In the second phase, they had to learn a conditional change in this relationship. Our results show that the learning dynamics were indeed qualitatively different between the two experimental phases, but in the opposite direction as we originally expected. Participants were learning more gradually in the second phase compared to the first phase. This might imply that participants built multiple models from scratch in the first phase (structure learning) before settling on one of these models. In the second phase, participants possibly just needed to update the probability distribution over the model parameters (parameter learning).
‘The wife should do as her husband advises’: Understanding factors influencing contraceptive use decision making among married Pakistani couples—Qualitative study
Authors: Sarfraz Mariyam , Hamid Saima , Kulane Asli , Jayasuriya Rohan
Published: February 2023

This paper explores the perceptions and attitudes of married couples which prevent them from using modern contraceptive for purpose of family planning, based on semi-structured interviews with 16 married couples from rural Pakistan. This study, with married couples, not using any modern contraceptives, discussed issues of spousal communication and religious norms using qualitative methods. Despite near universal knowledge of modern contraceptives among married Pakistani women, the use continues to be low, with high unmet need. Understanding the couple context about reproductive decision making, pregnancy and family planning intentions is imperative to helping individuals fulfil their reproductive desires. Married couples may have varying intentions and desires about family size; a lack of alignment between partners may lead to unintended pregnancies and affect uptake and use of contraception. This study specifically explored the factors which prevent married couples from using LARCs for family planning, despite their availability, at affordable prices in the study area of rural Islamabad, Pakistan. Findings show differences between concordant and discordant couples regarding desired family size, contraceptive communication and influence of religious beliefs. Understanding the role that male partners play in family planning and use of contraceptives is important in preventing unintended pregnancies and improving service delivery programmes. This study also helped identify the challenges married couples, particularly men have in understanding family planning and contraceptive use. The results also show that while men’s participation in family planning decision making is limited, there is also a lack of programs and interventions for Pakistani men. The study findings can support development of appropriate strategies and implementation plans.
Knowledge, attitude, and readiness towards disaster management: A nationwide survey among healthcare practitioners in United Arab Emirates
Authors: Shanableh Sawsan , Alomar Muaed Jamal , Palaian Subish , Al-Ahmad Mohammad Majed , Ibrahim Mohamed Izham Mohamed
Published: February 2023

Health professionals are expected to be knowledgeable on disaster medicine and prepared to deal with medicine disasters. This study aimed to assess the level of knowledge, attitude, and readiness to practice disaster medicine among health care workers in the United Arab Emirates (UAE) and determine the influence of sociodemographic factors on the practice of disaster medicine. A cross-sectional survey conducted among various healthcare professionals in different healthcare facilities in the UAE. An electronic questionnaire was used and randomly distributed throughout the country. Data were collected from March to July 2021. The questionnaire consisted of 53 questions distributed among four sections: demographic information, knowledge, attitude and readiness to practice. The questionnaire distribution involved a 5-item of demographic information, a 21-item of knowledge, a 16-item of attitude and an 11-item of practice. A total of 307 (participation rate ~80.0%, n = 383) health professionals practicing in the UAE responded. Of these, 191 (62.2%) were pharmacists, 52 (15.9%) were physicians, 17 (5.5%) were dentists, 32 (10.4%) were nurses, and 15 (4.9%) were others. The mean experience was 10.9 years [SD ±7.6] (median 10, IQR 4–15). The median (IQR) overall knowledge level was 12 (8–16) and the maximum knowledge level was 21. The overall knowledge level differed significantly between the age groups of the participants (p = 0.002). The median (IQR) of overall attitude was (57, 50–64) for pharmacists, (55, 48–64) for physicians, (64, 44–68) for dentists, (64, 58–67) for nurses, and (60, 48–69) for others. The total attitude score differed significantly between the different professional groups (p = 0.034), gender (p = 0.008) and workplace (p = 0.011). In terms of readiness to practice, respondents’ scores were high and not significantly related to age (p = 0.14), gender (p = 0.064), professional groups (p = 0.0.762), and workplace (p = 0.149). This study showed that health professionals in the UAE have moderate levels of knowledge, positive attitudes, and high readiness to engage in disaster management. Gender and place of work can be considered as influencing factors. Professional training courses and educational curriculums related to disaster medicine can be beneficial to further reduce the knowledge-attitude gap.
Does decision confidence reflect effort?
Authors: Hagura Nobuhiro , Esmaily Jamal , Bahrami Bahador
Published: February 2023

Goal directed behaviour requires transformation of sensory input to decision, and then to output action. How the sensory input is accumulated to form the decision has been extensively studied, however, the influence of output action on decision making has been largely dismissed. Although the recent emerging view postulates the reciprocal interaction between action and decision, still little is known about how the parameters of an action modulates the decision. In this study, we focused on the physical effort which necessarily entails with action. We tested if the physical effort during the deliberation period of the perceptual decision, not the effort required after deciding a particular option, can impact on the process of forming the decision. Here, we set up an experimental situation where investing effort is necessary for the initiation of the task, but importantly, is orthogonal to success in task performance. The study was pre-registered to test the hypothesis that the increased effort will decrease the metacognitive accuracy of decision, without affecting the decision accuracy. Participants judged the direction of a random-dot motion stimuli, while holding and maintaining the position of a robotic manipulandum with their right hand. In the key experimental condition, the manipulandum produced force to move away from its position, requiring the participants to resist the force while accumulating the sensory evidence for the decision. The decision was reported by a key-press using the left-hand. We found no evidence that such incidental (i.e., non-instrumental) effort may influence the subsequent decision process and most importantly decision confidence. The possible reason for this result and the future direction of the research are discussed.
EmoKbGAN: Emotion controlled response generation using Generative Adversarial Network for knowledge grounded conversation
Authors: Varshney Deeksha , Ekbal Asif , Tiwari Mrigank , Nagaraja Ganesh Prasad
Published: February 2023

Neural open-domain dialogue systems often fail to engage humans in long-term interactions on popular topics such as sports, politics, fashion, and entertainment. However, to have more socially engaging conversations, we need to formulate strategies that consider emotion, relevant-facts, and user behaviour in multi-turn conversations. Establishing such engaging conversations using maximum likelihood estimation (MLE) based approaches often suffer from the problem of exposure bias. Since MLE loss evaluates the sentences at the word level, we focus on sentence-level judgment for our training purposes. In this paper, we present a method namedEmoKbGANfor automatic response generation that makes use of the Generative Adversarial Network (GAN) in multiple-discriminator settings involving joint minimization of the losses provided by each attribute specific discriminator model (knowledge and emotion discriminator). Experimental results on two bechmark datasets i.e the Topical Chat and Document Grounded Conversation dataset yield that our proposed method significantly improves the overall performance over the baseline models in terms of both automated and human evaluation metrics, asserting that the model can generate fluent sentences with better control over emotion and content quality.