bluuebunny/crossref_metadata_2025 huggingface dataset:
Proper Dispersion Tailoring in Semiconductors as Prerequisite for Soliton Formation
Authors: Peschel U. , Peschel T. , Lederer F.
Published: February 2023

Bright solitons to exist in materials with a focusing nonlinearity require an anomalous dispersion (GVD < 0). This condition can be met in fused silica fibers beyond the zero-dispersion wavelength. Unfortunately, semiconductors that are fairly attractive for all-optical elements because of their large off-resonant nonlinearities (below half the band gap) exhibit a huge normal GVD (D≈1000ps2/km) thus prohibiting the formation of bright solitons. Hence, there is a great deal of interest to identify smart device concepts that allow for the overcompensation of the wrong material dispersion. Such concepts could be used to avoid the experimentally observed pulse break up in nonlinear AlGaAs directional couplers by using temporal solitons [1]. Moreover, spatio-temporal objects (light bullets) [2] could be studied because the required interplay of diffraction, anomalous dispersion and focusing nonlinearity would occur in properly designed planar waveguide structures. Because the device length of semiconductor waveguides is limited to about 2" the anomalous dispersion should exceed some thousands of ps2/km for pulse lengths of some hundred fs.
KTP Blue Laser For Optical Storage
Authors: Tohma Teruo , Bierlein John D.
Published: February 2023

In order to achieve the substantial increases in capacity needed for future optical storage applications, a compact blue light source is essential. One of the most promising candidates for such a source is the frequency doubled infrared laser diode which utilizes a segmented KTP waveguide.1) As we have reported previously, this waveguide consists of an initial section designed for quasi phase matched SHG of the laser diode followed by a Bragg reflection section which is used to lock the laser diode to the wavelength needed for SHG.2) Such a waveguide was lens coupled to an AR coated laser diode to produce 1.6 mW at 425 nm. However, in order to use such a laser for high density optical disc storage systems, higher power and smaller size are strongly desired.
Fabrication of GaAs Orientation Template Substrates for Quasi-Phasematched Guided-Wave Nonlinear Optics
Authors: Eyres L.A. , Ebert C.B. , Harris J.S. , Fejer M.M. , Chui H. C.
Published: February 2023

Quasi-phasematched nonlinear optical frequency conversion in waveguides is a flexible and efficient technique for generating visible and infrared radiation from low-power near infrared diode lasers. While demonstrated conversion efficiencies have been high1-3, a formidable difficulty remains in the path of widespread implementation of waveguide frequency conversion techniques. The separately fabricated diode lasers and nonlinear waveguides must be aligned together to sub-micron tolerances with high yield and excellent long-term reliability. Monolithic integration of diode lasers and nonlinear devices onto the same substrate is an attractive solution to this problem, particularly if the nonlinear devices are fabricated in semiconductor materials.
Ultra-low jitter, multi-wavelength GHz pulse source with high optical frequency stability based on 200 nm supercontinuum filtering
Authors: Morioka T. , Uchiyama K. , Kawanishi S. , Suzuki S. , Saruwatari M.
Published: February 2023

To realize large-capacity time-division-multiplexed (TDM: >100 Gbit/s), wavelength-division multiplexed (WDM: >10 channels) all-optical networks, multi-wavelength optical pulse sources with low timing jitter and high optical frequency stability are required. Multi­wavelength pulse generation by filtering supercontinuum (SC) is a promising technique because of its wide continuous spectrum range selectivity (~200 nm), and high optical frequency stability, which is merely determined by that of the passive WDM demultiplexing filter employed. Recently, we generated 200 nm SC for picosecond to femtosecond WDM pulse generation [1]-[2] and frequency conversion [3], and demonstrated the feasibility of SC pulses as optical sources by transmitting <2 ps SC pulses over 40 km [4]. In this paper, we present an ultra-low jitter (<0.3 ps), multi-wavelength channel (>200 channels altogether, 0.8 nm spacing) 6.3 Gbit/s pulse source with the high optical frequency stability of 1.3 GHz/°C by filtering low jitter 200 nm SC with a 16 x 16 arrayed-waveguide grating wavelength demultiplexer.
Efficient method for simulation of chirped pulse compression in an optical fiber
Authors: Jaskorzynska B. , Nilsson J. , Sergeev A. , Vanin E.
Published: February 2023

Compression of a chirped (frequency modulated) optical pulse is an attractive method to reach very short pulse duration [1]. Theoretical analysis of a compression stage in a typical linear dispersive system, as a pair of gratings or a prism, is straightforward. In the recently demonstrated [2] compact device for generation of high energy femtosecond pulses, however, broad-band linearly chirped pulses obtained from a fast-tuned diode laser are compressed in an optical fiber. Fiber nonlinearity may significantly influence the pulse shape and has, therefore, to be taken into account while modelling the compression stage. Inclusion of a nonlinear term into the propagation equations implies that no analytical solution can be obtained and numerical marching-on schemes have to be applied in order to simulate pulse shape evolution along the fiber. The problem with applying the standard numerical schemes for a compression of a strongly chirped pulse is that the pulse duration may decrease by several order of magnitudes and hence a large computational window and a very dense computational grid is required to resolve the pulse shape both and the beginning and the end of the fiber. For methods involving Fourier transformation a very dense sampling is needed even at the beginning of the compression stage because of broad spectral width of the chirped pulse. This makes standard numerical methods very inefficient. To circumvent the problem we propose to simulate the pulse evolution using the time frame that is compressed along the fiber.
Polarisation dependence of ultrafast nonlinear refraction in semiconductor waveguides
Authors: Hutchings D. C. , Aitchison J. S. , Wherrett B. S. , Kennedy G. T. , Sibbett W.
Published: February 2023

There is considerable interest in the optical Kerr effect, described by the nonlinear refractive index n2, as it can be employed to perform high-speed, all-optical switching. Semiconductor waveguides offer an attractive media for compact, integrated all-optical switching.1,2 The dispersion of n2 in direct-gap, zinc- blende semiconductors was recently accurately calculated using a four-band Kane model.3 In this paper the polarisation dependence of nonlinear refraction in zinc-blende semiconductors will be addressed. This dependence has two aspects to it: (1) an optical polarisation dependence which provides a variation in n2 for linear and circular polarisations.4 This variation can occur even for isotropic media. The same dependence also gives a different value for the cross-phase-modulation using parallel and perpendicular polarisations (orthogonal cross-phase-modulation was employed in a demonstration of all-optical demultiplexing5). (2) a material polarisation dependence which provides a variation in n2 depending on how the optical polarisation is orientated with respect to the crystalline axes.
High Nonresonant Third Order Nonlinearity in Low Loss DMOP-PPV Polymer Waveguides
Authors: Gabler Th. , Bartuch U. , Michelotti F. , Bräuer A. , Waldhäusl R. , Hörhold H.-H.
Published: February 2023

The figure of merit for a nonlinear waveguide device is defined by the nonlinear refractiveindex change and the propagation losses. The device must be operated at a wavelength where on the one hand the nonlinear effect is as high as possible and on the other hand the propagation losses are low in order to take advantage of the accumulating nonlinear phase change along the waveguide. The task is to find the best operation wavelength for the device made of a certain material. For that reason we have now started to make investigations in the wavelength range from 0.7 -1.0 μm with respect to both, the nonlinear χ(3) values and the absorption a (one and two photon absorption). In this paper we report on the results at λ > 900 nm for poly (1,4-phenylene-1,2- di(4-methoxy- pheny) vinylene), DMOP-PPV, a new conjugated polymer of the widely studied PPV-series (see figure 1).
Optical Properties of PPV for All-optical Switching
Authors: Luther-Davies Barry , Woodruff Maneerat , Samoc Anna , Samoc Marek
Published: February 2023

Poly(p-phenylenevinylene) (PPV) is a conjugated polymer known for its interesting optical and electrical properties. In particular, its large third-order optical nonlinearity measured by degenerate four-wave mixing (DFWM) has been reported by several workers1,2,3,4. Of special interest is the processability of PPV in the form of its soluble precursor, which allows fabrication of this otherwise insoluble conjugated polymer into films of pure PPV or composites of PPV using an inorganic (sol-gel)5,6 polymer host.
Nonlinear Waveguiding in a Photorefractive Slab with Nonlocal (Diffusion Type) Nonlinearity
Authors: Aguilar P.A. Marquez , Mondragon J.J. Sanchez , Stepanov S.
Published: February 2023

Nonlinear waveguiding in media with spatially local Kerr-like nonlinearity attracted intensive attention recently [1]. Similar type of nonlinearity can also be realized in photorefractive crystals (PRCs) with drift mechanism of recording [2] where it needs remarkably lower light intensities - up to 100 μW/cm2 in some cases. This type of nonlinearity was utilized in recent experiments on bright [3,4] and dark [5] spatial soliton propagation in ferroelectric SrxBal-x NbO6 (SBN) and cubic Bi12 TiO20 (BTO) crystals.
All Optical Storage in Nonlinear Periodic Slab Waveguides
Authors: Costantini B. , Aceves A.B. , De Angelis C.
Published: February 2023

Periodical optical waveguides have been the subject of many theoretical and experimental studies, both in the linear regime (since they can be used to realize optical wavelength filters [1, 2]) and in the nonlinear regime ( in which the counter-balancing of group velocity dispersion, due to the periodic variation of the linear refractive index, and the effect of nonlinearity, leads to the so called “gap-solitons” [3, 4]). In the study of periodic optical waveguides it is generally assumed that the functions describing the two counterpropagating modes can be separated into the product of two independent components. One (say F(x,y)) for the dimensions where the guiding effect provided by linear variation of the refactive index is supposed to be unaffected by nonlinearity and determined as a solution of a linear problem; the other (say q1,2(z, t)) describes the time evolution of the envelope in the direction where the guiding effect is given only by the nonlinearity. In doing so all the influence of the nonlinearity on the mode shape F(x,y) is lost and the approach may thus hide some important features of the governing equation. We study here counterpropagating waves in a periodic slab waveguide, without applying the separation of variables described above: this leads to discover important features of two dimensional gap solitons, which could be exploited for all optical storage of information. In pursuing this goal we make use of a variational method [5] and we then confirm the validity of our analytical results through numerical integration of the governing equations.
Symmetry-breaking bifurcation in synchronously driven fiber cavities
Authors: Haelterman M. , Vitrant G. , Mateos J. Garcia
Published: February 2023

Synchronously driven fiber cavities constitute a class of devices of growing interest. They can be found in practice as the basic elements of a large number of fiber-based devices such as the APM laser, the Raman laser or the modulation instability laser.1 Their use have also been proposed for the development of passive soliton generator2 and soliton memory.3 Although passive fiber cavities are conceptually simple devices, they exhibit a rich spectrum of complex behaviors. Several types of complex dynamical features have been described among which one finds: optical bistability, period doubling cascades, chaos, and polarization multistability and instabilities. The role of fiber dispersion in the cavity dynamics has recently attracted much attention and has been identified as being one of the crucial ingredients for the understanding of the fiber cavity dynamics.4,5
Limits of the Perturbative Scalar Calculation of Self-Phase Modulation Effects
Authors: Fontaine Marie , Tzolov Velko P. , Godbout Nicolas , Lacroix Suzanne
Published: February 2023

Kerr-type nonlinear optical devices working in a self-phase modulation (SPM) regime, such as tapered nonlinear fibers, appear to be very promising for the design of all-fiber optical switches [1]. Crucially important for devices based on nonlinear tapered fibers is the waist diameter to maximize the magnitude of the nonlinear Kerr effect. To determine the optimal diameter, we computed the nonlinear propagation constant β
NL
as a function of the guided power P. In the range of diameters of interest for nonlinear applications, the field is guided by the air-cladding interface. Due to the strongly guiding conditions, the scalar theory is expected not to provide the exact modal characteristics. In this paper, four different numerical methods are used to investigate the nonlinear modal properties of tapered fibers: (1) a first-order scalar perturbation method; (2) a first-order vectorial perturbation method; (3) an exact numerical solution of the scalar (Helmholtz) equation; (4) an exact numerical solution of the Maxwell's equations. A comparison of the results obtained by the scalar approaches and by their vectorial counterparts is presented.
Nondegenerate Four-Wave Mixing in Tensile Strained MQW Semiconductor Optical Amplifier
Authors: Yamada Atsushi , Yamaguchi Yuko , Otsubo Toshinobu , Miyagi Koichiro , Taniguchi Akira
Published: February 2023

To realize an ultrahigh speed optical transmission system, applications of nonlinear phenomena have recently been investigated for optical DEMUX with four-wave mixing(1), (2) or dispersion compensation(3). If an optical fiber is employed as a nonlinear device, the fiber need to be very long for high efficiency because of the very small nonlinear effect ion of the fiber. This causes the system to become unstable. The use of a semiconductor optical amplifier (SOA) as the nonlinear device, however, have an advantage in this point. With such function as a switching device, the SOA is expected to play a major role as the nonlinear device. We investigated the characteristics of the Nondegenerate four-wave mixing (NDFWM)(4) with the input signal power and the device length on these SOAs. The devices which are used in this measurement are polarization independent SOAs using tensile strained quantum wells.
Focusing Properties of Photoinduced Photorefractive Lenses
Authors: Aguilar P.A. Marquez , Mondragon J.J. Sanchez , Stepanov S.
Published: February 2023

Original experimental results on spatial soliton propagation of bright [1-3] and dark [4] types were reported for different photorefractive crystals (PRCs) recently. These were basically experiments with drift (of local type) photorefractive nonlinearity which can be observed usually under application of external DC electric field or due to the photogalvanic mechanism of charge transfer in LiNbO3 [5].
All-optical multiplexing of femtosecond signals using an AlGaAs nonlinear directional coupler
Authors: Kang J. U. , Krijnen G. , Stegeman G. I. , Villeneuve A. , Aitchison J. S. , Ironside C. N.
Published: February 2023

One of the most powerful applications of integrated all optical switching devices is the multi/demultiplexing of high repetition rate signals. All-optical demultiplexing using nonlinear directional couplers (NLDC) has been successfully demonstrated in recent years[1]. All-optical multiplexing has also been demonstrated using fibers[2]. However, because of the weak nonlinearity in the fiber, fiber lengths on the order of kilometers are required. Thus, such devices suffer from long transit times which can be unacceptable. The passive means of multiplexing, using 3 dB couplers, Y-junctions and such, suffer from a 3 dB loss. Using strong pump pulses to control a signal pulse train through cross-phase modulation, we demonstrate an efficient and compact method of multiplexing femtosecond signals using a NLDC.
Optical solitons in media with quadratic and cubic nonlinearities
Authors: Trillo Stefano , Buryak Alexander V. , Kivshar Yuri S.
Published: February 2023

Self-trapping and soliton-like propagation due to interplay of dispersion and nonlinearity-induced phase shift due to cascaded nonlinearities [1] has attracted a great deal of interest [2-6]. Soliton propagation may occur either in the form of strongly coupled symbiotic pairs for the fundamental-frequency (FF) and the second-harmonic (SII) fields [2-6], or in the limit of nonzero mismatch, for which the propagation is governed by an equivalent nonlinear Schrödinger (NLS) equation for the FF field, obtained by means of asymptotic techniques [7]. However, in χ(2) materials there always exist cubic nonlinearities which might become also important and even compete with quadratic nonlinearities. Here we analyze the effect of such competing nonlinearities on properties of solitary waves. As we will show, self-phase (SPM) and cross-phase (CPM) modulation induced by a cubic nonlinearity can strongly perturb solitary waves of a purely quadratic medium, and they may eventually destroy them. Nevertheless, we show that, even for such competing nonlinearities, stable solitary waves do exist.
Coherent Modulation Instability in Fibres with Varying Birefringence
Authors: Murdoch S. G. , Harvey J. D.
Published: February 2023

In the normal dispersion regime, two forms of modulation instability have been observed when birefringent single mode fibres are subjected to intense pump pulses. These instabilities are the cross phase or XPMI process [1,2] and the coherent or PMI process[3,4]. In both of these processes, the generated sidebands develop at the peak of the gain, which occurs corresponds to the phase matching condition between the pump and the sidebands corrected for the optical Ken- effect. In this work we report on the development of modulation instability in birefringent fibres, using fibre winding geometries in which phase mismatches are deliberately induced.
Investigation of black-gray soliton interaction.
Authors: Foursa Dmitri , Emplit Philippe
Published: February 2023

Dark soliton properties have been investigated extensively over the
last few years due to their potential application as carrier bits in
telecommunication systems [1-5]. The particular case of the dark
soliton and the most studied one is the pulse, which is an
antisymmetric function of time with an abrupt π phase shift and zero
intensity at its centre and will be refered to as “black” soliton in
the following.
Efficient Second Harmonic Generation at 1.5 μm in Composite Polymeric Channel Waveguides
Authors: Jäger Matthias , Stegeman George I. , Horsthuis Winfried H.G. , Möhlmann Guus R. , Flipse Marinus C.
Published: February 2023

Efficient Second Harmonic Generation (SHG) has been a continuing goal for not only frequency conversion but also for cascading effects such as all-optical switching, spatial solitary waves, etc1. To date high efficiencies have been demonstrated only in ferroelectric crystals.2 However, some poled polymers have even higher nonlinear coefficients and offer ease of processing and low cost fabrication. Several phase-matching techniques have been demonstrated in poled polymers, such as quasi-phase-matching (QPM)3-6, modal dispersion phase matching7-9, Cerenkov phase-matching10-12, and anomalous dispersion phase matching13. However, very few experiments have progressed from the slab to the channel waveguide stage. We demonstrate phase-matched SHG in a channel waveguide made of 4-dimethylamino-4’-nitrostilbene (DANS) side-chain polymer. Our SHG figure of merit η=P2
ω
/(PωL)2=14 %/W-cm2 is the highest non-resonant value reported for poled polymers and is competitive with those of the best inorganic crystals14.
Blue Light Generation In A Periodically-Poled RbTiOAsO4 Waveguide
Authors: Risk W. P. , Loiacono G. M.
Published: February 2023

There is currently great interest in the use of quasi-phasematched waveguide devices for a variety of frequency conversion applications. A number of ferroelectric materials have been studied that permit periodic poling and waveguide fabrication, such as lithium niobate (LN), lithium tantalate (LT), and potassium titanyl phospate (KTP). In KTP, periodic domain inversion can be produced using an applied electric field,1 and waveguides can be fabricated using a Rb↔K ion-exchange process.2 Compared to LT and LN, KTP has the advantage that the coercive field is much lower (~ 2kV/mm).
Soliton Emission from an AlGaAs Waveguide
Authors: Dumais Patrick , Veillette Martin , Villeneuve Alain , Aitchison J. Stewart , Hamilton Craig J.
Published: February 2023

Since the early days of nonlinear integrated optics, a lot of interest has been put towards studying the propagation of light in media with non uniform nonlinearities. In these early papers, the cladding, substrate, and the waveguide layers were either linear or nonlinear. Contrarily to most all-optical switches, these highly nonlinear waveguides work because of the change in the shape of the field caused by the nonlinearity, whereas in most switches the field shape does not vary much. The recent work on the disordering of multiple quantum wells (MQW) has revealed that the nonlinearity of a MQW layer can be locally reduced in the MQW plane by as much as 60% [1]. This result makes the observation of highly nonlinear waveguide phenomena possible in AlGaAs at half the band gap.
Bistable Solitary Waves and Switching Waves with a Hexagonal Pattern in Semiconductor Planar Resonators
Authors: Michaelis Dirk , Peschel Ulf , Lederer Falk
Published: February 2023

Since many years it is well-known that planar resonators filled with a nonlinear material may exhibit bistability and various kinds of instabilities [1]. Two-dimensional patterns and stationary localized structures (SLS) could be observed provided that transverse effects were taken into account. SLS attract a great deal of interest because it is believed that their particle-like behavior can be potentially exploited in future data processing and storage systems. SLS were found in media with saturable dispersive focusing as well as saturable absorptive nonlinearities [2,3]. Hitherto, it is common believe that in dispersive defocusing media only switching waves rather than SLS may exist. Unfortunately, highly nonlinear materials, as e.g. semiconductors operated near the band gap exhibit a defocusing nonlinearity. The aim of this paper is to show that even in these materials SLS are allowed to exist due to an interplay of transverse effects (diffraction, diffusion), saturation and nonlinearity.
Temporal Solitary Waves with Walk-Off in Nonlinear Quadratic Media and their Stability
Authors: Etrich C. , Peschel U. , Lederer F. , Malomed B. A.
Published: February 2023

Recently solitary waves based on a quadratically nonlinear interaction attracted a lot of attention in nonlinear optics. They were found to exist as selfguided beams in planar waveguides [1]. Both spatial and temporal solitary waves are described by the same evolution Until now only a one-parameter family of such solutions is known. In the spatial case this corresponds to the fundamental and second harmonics propagating in the same direction. No spatial walk-off is induced, e.g. by birefringence. The spatial walk-off can be avoided in a planar waveguide, whereas in the temporal case the situation is much more complicated. The known one-parameter family of solitary wave solutions corresponds to a certain carrier frequency where the group velocities of the two pulses (fundamental and second harmonics) are equal. In most materials such a frequency does not exist. Here we concentrate on the more common situation where the two pulses may move away from each other due to a group velocity difference. The family of solitary wave solutions obtained is two-parametric and applies to the case of spatial walk-off as well.
Ultrafast all-optical signal processing using semiconductor laser amplifiers
Authors: Manning R.J. , Poustie A.J. , Blow K.J.
Published: February 2023

Over the past few years, there has been unprecedented progress in the use of nonlinear effects in semiconductor laser amplifiers (SLAs) for high speed all-optical signal processing. Amongst the many exciting results reported are all-optical demultiplexing experiments at data rates of 40 Gbit/s upwards to 160 Gbit/s [1,2], and wavelength conversion experiments at 20 Gbit/s [3], With the development of integrated devices, truly small-scale all-optical switches now seem possible for all-optical add-drop multiplexing applications, and for all-optical regeneration [4]. The small length (100s of μms.) of these devices mean that, for the first time, all-optical bit serial processing is a realistic possibility. In this paper we shall discuss some of the functional elements it is possible to build, and the crucial role that carrier dynamics play in SLAs. These dynamics allow switching rates approaching ~ 100 GHz [5], and also lead to a rich variety of effects in feedback experiments we have recently conducted in our laboratories.
Nonlinear Multi-Core Directional Couplers in AlGaAs
Authors: Millar P. , Aitchison J. S. , Kang J. U. , Stegeman G. I. , Villeneuve A.
Published: February 2023

Nonlinear, multicore, directional couplers exhibit power dependent transmission characteristics which have a wide range of potential applications in future all optical systems. These include modulators , power splitters , wavelength filters and all optical interconnections.[1] Recent theoretical studies [2] have shown that three guide couplers have sharper switching characteristics than the standard dual core coupler and should therefore, be of interest in all-optical switching , pulse narrowing and pulse shaping applications. In addition, multiguide structures with varying coupling coefficients have also been studied with a view to observing discrete spatial solitons [3] and have potential utilization in beam steering and switching applications.
Analytical Theory of NRZ Signal Transmission
Authors: Kodama Y.
Published: February 2023

Several recent experiments demonstrated the feasibility of high-bit-rate, long-haul optical telecommunications using IMDD nonreturn-to-zero (NRZ) signals in periodically amplified fiber links operating close to the zero group-velocity-dispersion (GVD) wavelength [1,2]. Both experiments [1, 2] and numerical simulations [3] show that distortion of the NRZ signal results from spectral broadening due to amplifier noise induced-four-wave mixing (FWM), and from fiber self-phase modulation (SPM) in combination with the small residual GVD. While noise-seeded FWM may be suppressed by means of dispersion management [4], the signal distortion due to SPM and GVD sets a stringent upper limit to the transmitted signal power.
Stable Soliton Transmission with Increased Energy using Dispersion Management and Periodic Saturable Absorption
Authors: Govan D. S. , Smith N. J. , Knox F. M. , Doran N. J.
Published: February 2023

We present results of numerical simulations which show that, by using a combination of dispersion management and a weak saturable absorber, it is possible to transmit a pulse with energy substantially greater than that possible in a system that does not use these techniques. Using input pulses of 6.0ps we have found that stable pulses for this system exist for a wide range of input powers.
Gap Solitons in Quadratically Nonlinear Waveguides
Authors: Peschel Thomas , Peschel Ulf , Lederer Falk , Malomed Boris
Published: February 2023

Gap solitons are known to exist in configurations where the dispersion is created by the coupling of two waves with strongly different group velocities and the material exhibits a cubic nonlinearity [1,2]. Usually, this coupling emerges in periodically corrugated waveguides (Bragg gratings) where the forward and backward waves are coupled. Recently, it has been shown that spatial solitons may also exist due to quadratic nonlinearities [3]. In this environment temporal solitons suffer from the pulse walk-off and could not be experimentally observed until now. Hence, the question arises whether gap solitons may be supported by quadratic nonlinearities and how they are affected by the pulse walk-off. These are the subjects we are addressing in this paper.
Electric Field Poling Of Quasi-Phase-Matched Optical Fibres
Authors: Kazansky P.G. , Pruneri V.
Published: February 2023

Ten years have passed since the discovery of photoinduced quasi-phase-matched second harmonic generation in optical fibres [1-3]. However, until fairly recently, second harmonic generation in optical fibres has been more of scientific than practical interest, owing to the low levels of induced nonlinearity (~10-3 pm/V, which is four orders of magnitude less than in inorganic crystals, e.g. lithium niobate). The mystery of photoinduced χ(2) gratings was finally solved on the basis of the coherent photogalvanic effect [4]: a high (104-5 V/cm) spatially oscillating electrostatic field appears in glass as a result of charge separation induced by coherent photocurrent, oscillating with a period determined by the coherence length; this electric field produces a quasi-phase-matching χ(2) grating in proportion to χ(3). The conversion efficiency reported in the first experiments on photoinduced SHG-~ 5 % from a peak pump power of ~ 20 kW-is still among the highest conversion efficiencies achieved so far in optical fibres. The reasons for these relatively high conversion efficiencies has to be searched in the long length (tens of centimetres) and good uniformity of the photoinduced gratings.
Squeezing in χ(2) nonlinear waveguides
Authors: Anderson Matthew E. , Raymer M. G.
Published: February 2023

Years after its first observation, squeezed light is still the premiere vehicle for demonstrating the importance of quantum mechanics in optics; it is an inherently "non-classical" signal field which eludes explanation by classical physics. Current progress in squeezing is being fueled by advances in nonlinear devices and measurement theory. Here we will briefly review the history of squeezed light and discuss the advantages of generating squeezed light in waveguides.
Photorefractive Spatial Solitons
Authors: Segev Mordechai , Shih Ming-feng , Chen Zhigang , Mitchell Matthew , Salamo Greg , Chauvet M. , Crosignani Bruno , DiPorto Paolo , Valley George C.
Published: February 2023

We present an overview of the experimental and theoretical understanding of spatial solitons in photorefractive materials. There are three generic types at present: quasi-steady-state, screening and photovoltaic solitons. The
quasi-steady-state solitons
(predicted and discovered first) exist during the slow screening process of an externally applied field in bright and dark realizations and in one and two transverse dimensions.(1,2) The
screening solitons
were predicted and recently observed(3-7) in a photorefractive material (SBN) with an externally applied field which is nonuniformly screened at steady-state. The
photovoltaic solitons
were predicted and observed(8,9) in photorefractive materials with a strong photovoltaic current (e.g. LiNbO3) and use the refractive index perturbation associated with the photovoltaic field to guide and confine the planar soliton. By and large, none of these solitons have properties similar to those of conventional Kerr solitons. Perhaps the most important distinctions between Photorefractive and Kerr solitons is the existence of photorefractive solitons at microwatts and lower power levels and in two transverse dimensions. Photorefractive solitons also induce waveguides that can guide other beams. When a guided beam is at a non-photosensitive wavelength it be much more intense than the soliton that induced the waveguide. Thus, a 1-microwatt soliton can guide a 1-watt beam.(10) All these unique features suggest the practicality of using photorefractive solitons for beam steering, optical wiring, interconnects, and other nonlinear optical devices.
Cascading of second-order processes in a type II phase-matched SHG crystal applied to mode-locking of a CW Nd:YAG laser
Authors: Couderc V. , Guy O. , Lefort L. , Barthélémy A.
Published: February 2023

It has been shown recently that a quadratic non-linear crystal may be used for all-optical signal processing. It was demonstrated that amplitude modulation, phase modulation, transistor action, phase conjugaison was feasible thanks to parametric interactions occurring in crystals cut for second harmonic generation (SHG). The main part of these applications was considered under phase mismatched condition1,2,3,4 and relied on the cascading of sum and difference frequency generation (SFG+DFG). With the use of type II crystal a cascading effect still happens in the case of perfect phase-matching provided the two orthogonally polarized inputs at the fundamental frequency carry different intensity5,6,7. This is even one of the most efficient configuration to achieve all-optical processing with the lowest control powers. The interaction between the two waves at the fundamental frequency and the second harmonic wave may be used in specific arrangement to achieve ultrafast switching, pulse compression8, and saturable absorption or transparency9,10. In particular, we have already demonstrated that a type II SHG crystal excited by unbalanced fundamental intensities on its neutral axis gives rise at the output to an electromagnetic field whose state of polarization is intensity dependent (figure 1). In the case of high imbalance between the two fundamental inputs, the weakest fundamental input may completely vanish during propagation because of the SHG process and be further regenerated by difference frequency generation with an opposite phase. The nonlinear evolution of the polarization was previously exploited in a polarization gate geometry to realize a device with self induced transparency9. It was suggested that the same set-up could be used intracavity to achieve mode-locking of a laser. This forms the subject of the present communication since we report the mode locking operation of a diode pumped CW Nd:YAG laser by means of intensity dependent polarization evolution in a KTP crystal.
450kW, all fibre, picosecond Chirped Pulse Amplification system based on a large mode area fibre Bragg grating compressor
Authors: Broderick N. G. R. , Taverner D. , Richardson D. J. , Dong L. , Caplen J. E. , Ibsen M.
Published: February 2023

Chirped pulse amplification (CPA) is a well known technique for producing high power short optical pulses1,2 suitable for nonlinear optical experiments. Using such techniques with bulk amplifier systems it is possible to produce femtosecond optical pulses with terawatts of peak power3.
One-dimensional quadratic walking solitons in lithium niobate planar waveguides
Authors: Baek Y. , Schiek R. , Stegeman G. I.
Published: February 2023

Quadratic solitons were observed a few years ago during second harmonic generation in both bulk crystals (2D) and planar waveguides (1D)[1,2]. They consist of strongly coupled fundamental and harmonic fields which propagate locked together in space without diffraction due to a combination of the cascaded nonlinearity and the strong inter-beam coupling inherent in SHG.
Transverse Instabilities of Higher-Order Spatial Solitons in Quadratic Nonlinear Media
Authors: Skryabin Dmitry V. , Firth William J.
Published: February 2023

Stationary ring structures exist in χ(2) media. Most fragment: we calculate the daughter solitons’ escape speed analytically. Surprisingly, some implode, preserving cylindrical symmetry.
Self-induced transparency in Bragg reflectors: gap solitons near absorption resonances
Authors: Kozhekin A. , Kurizki G.
Published: February 2023

Pulse propagation in a non-uniform resonant medium, e.g., a periodic array of resonant films, can destroy self-induced transparency (SIT), because the pulse area is then split between the forward and backward (reflected) coupled waves, and is no longer conserved. Should we then anticipate severely hampered transmission through a medium whose resonance lies in a reflective spectral domain (photonic band gap) of a periodically- layered structure (a Bragg reflector)? We have shown both analytically and numerically that it is possible for the pulse to overcome the band-gap reflection and produce SIT in a near-resonant medium embedded in a Bragg reflector.1 The predicted SIT propagation is a principally new type of a gap soliton.
Effect of Two-Photon Absorption Nonlinearity on Short Pulse Propagation in Semiconductor Optical Amplifiers at Transparency
Authors: Tang J.M. , Shore K.A.
Published: February 2023

The amplification of ultrashort optical pulses in Semiconductor Optical Amplifiers (SOAs) has been the subject of considerable research interest, because the ultrafast carrier dynamics in SOAs is important for tailoring devices with applications in optical frequency conversion [1], high speed optical signal manipulation in optoelectronic integrated circuits and for understanding the high-speed modulation response of semiconductor lasers. With a view to such applications, numerical investigations have been undertaken of the picosecond pulse saturation behaviour of SOAs [2]. The effect of nonlinearity on the chirp characteristics of piosecond pulse amplification have also been reported [3].
Soliton-like pulses generated by mode-locked lasers with either slow or fast saturable absorber response
Authors: Akhmediev N. N. , Ankiewicz A. , Lederer M. J. , Luther-Davies B.
Published: February 2023

The passively mode-locked laser [1, 2, 3, 4, 5] is a much-studied device in recent years. Ultra-short pulse generation in laser systems makes use of a variety of schemes including figure-of-eight fiber laser design [1], fast saturable absorbers [4], additive pulse mode-locking [5] and nonlinear polarization rotation [6, 7]. The use of a semiconductor saturable absorber mirror with relatively slow response time and even slower recovery time has been suggested for a passively mode-locked soliton laser [8]. Experimental verification of this possibility has been reported in [9]. In the present work, we present an exact soliton-like solution for pulses generated by a solid-state laser with a semiconductor saturable absorber with slow recovery time.
The role of birefringence in modulation instability fiber ring resonators
Authors: Tonello Alessandro
Published: February 2023

Modulation instability (MI) in normal dispersion regime has been investigated, during the last decade, because of possible applications ranging from pulse train formation to tunable generation of coherent light beams. Recently, particular attention has been devoted to folded setups such as fiber rings [1], and experimental results have been already obtained [2].
Influence of High Probe-Power on Multi-Wave Mixing Characteristics of Semiconductor Lasers
Authors: Tang J.M. , Shore K.A.
Published: February 2023

Multiwave mixing in semiconductor lasers is of interest for frequency translation and spectral inversion in long-haul optical communication systems and also for the generation of phase conjugate signals which may be used in turn to influence the noise and linewidth properties of other semiconductor lasers. In earlier work [1] attention has been given to the opportunities for achieving enhanced nearly degenerate multiwave mixing through careful cavity design of Fabry-Perot laser structures. In particular the use of asymmetric two-section laser diodes was shown to offer the prospect of broadband laser diode phase conjugate reflection [2] and enhanced tuning [3]. Recently attention has been given also to highly degenerate four-wave mixing in DFB lasers [4].
All-optical soliton switching in a periodically poled lithium niobate
Authors: Ibragimov E.
Published: February 2023

Recent experiments have demonstrated that nonlinear materials with the second-order (χ(2)) non-linearities can be used not only for harmonic and parametric generation but also in applications to all-optical switching for which nonlinear phase distortions are required: spatial soliton-like waves on cascaded χ(2) × χ(2) nonlinearity permit the implementation of second-order processes to the all-optical switching [1, 2]. However in the temporal domain soliton-like waves on χ(2) × χ(2) nonlinearity are difficult to achieve because of low second-order dispersion in most nonlinear materials.
Stability of Quasi-Periodic Solitary Pulse Trains In Nonintegrable Hamiltonian Wave Systems
Authors: Arnold J. M.
Published: February 2023

Considerable interest centres at the present time on the problem of approximating the dynamical motion of solitons by an underlying discrete dynamical system. It has recently been demonstrated that the dynamics of N-solitons of the Nonlinear Schrodinger Equation (NSE) is quite well approximated by Complex Toda Lattice Equations (CTLE) in the limit of large separation of almost identical solitons with arbitrary phases [1-4]. The Lagrangian method proposed in [1, 2] is a direct reduction procedure which does not depend on the integrability of the original equations, and is applicable in principle to any Hamiltonian system having sufficiently well behaved solitary waves. Here it is shown that a Lagrangian theory similar to that of Gorshkov-Ostrowski [5] reduces a large class of nonintegrable Hamiltonian wave systems to a double Toda lattice in the limit of large separations of identical solitary pulses, generalising the results of [1-4] quite considerably.
Beam control and switching in nonlinear meso-optical structures
Authors: Citrin David S. , Tomsovic Steven , Torruellas William E.
Published: February 2023

Optical structures which confine light in mesoscale dimensions are of increasing interest for applications requiring an active control of the optical light properties. Recent advances in the fundamental understanding of such structures has lead to the prediction and demonstration of unusual and intriguing emission patterns in highly chaotic mesoscopic cavities containing Laser emitting dyes.[1,2] Here, we investigate the influence of a controlling nonlinearity of second and third order in the spatio-temporal dynamics of single and multiple cavity arrangements. In the single cavity case the presence of a nonlinear interaction results in the disappearance of the chaotic evolution while in the multiple cavity case a new geometry resulting in a 2D optical switching network is investigated.
Self-organization, motion and decay of vectorial dichromatic cavity solitons
Authors: Peschel U. , Michaelis D. , Etrich C. , Lederer F.
Published: February 2023

Spatial solitons represent a balance between diffraction in continuous or linear coupling in discrete systems and a nonlinearly induced phase modulation which can be evoked e.g. by cubic (SPM, XPM) or quadratic nonlinearities (phase modulation due to frequency mixing). These peculiar nonlinear objects behave in many situations, e.g. in the presence of perturbations and in collisions, like robust particles. Until now primary emphasis was paid to the behavior of spatial solitons in conservative systems where energy, momentum and angular momentum are conserved [1]. They can be viewed as self-guiding beams which can be potentially used for ultrafast all-optical routing and steering.
Ultrafast All-Optical Waveguide Devices Based On Bandgap Resonant Nonlinearities
Authors: LiKamWa Patrick
Published: February 2023

Carrier induced nonlinearities in semiconductor multiple quantum wells have been utilized to achieve ultrafast optical gating in waveguide devices. A temporal switching window of 9ps has been demonstrated.
All-optical switching using modal interference due to the cascaded nonlinearity
Authors: Baek Y. , Assanto G. , Schiek R. , Stegeman G. I.
Published: February 2023

It has been verified that second-order nonlinear process can cause the energy transfer between interacting waves which results in the modification of phase fronts of interacting waves[1]. Many all-optical switching devices have been demonstrated recently implementing such principle[2,3]. One of the most characteristic features of cascading is that the magnitude of the nonlinear phase distortion itself is a function of wavevector mismatch condition. Also in waveguide geometry, the propagation constant of each existing mode is different. Therefore if two modes are launched together in a second-order nonlinear material, for a specific wavevector mismatch condition, one can introduce larger nonlinear phase shift in one mode than the other. Reported here is all-optical switching using modal interference in a LiNbO3 channel waveguide.
Self-writing channel waveguides in As2S3 thin films by two-photon absorption
Authors: Meneghini Chiara , Villeneuve Alain
Published: February 2023

Due to their structural flexibility, amorphous chalcogenide glasses, for example as2s3, show a variety of photoinduced effects, such as refractive index change and photodarkening. Bragg gratings1 and photoinduced integrated optical devices2 have already been fabricated by near bandgap light exposure (~500 nm).
Wavelength Conversion by Difference-Frequency-Generation for Telecommunications Applications
Authors: Yoo S. J. B.
Published: February 2023

Wavelength Division Multiplexing (WDM) networks make very effective utilization of the fiber bandwidth and offer flexible interconnections based on wavelength routing. In high capacity, dynamic WDM networks, blocking due to wavelength contention can be reduced by wavelength conversion. Wavelength conversion also allows distributed management of the network and facilitates scalability and modularity of the network. Numerous wavelength conversion techniques have been proposed and demonstrated to date. Wavelength conversion by Difference-Frequency-Generation (DFG) offers a number of unique characteristics not available in other techniques. DFG offers full transparency to signal formats and protocols; DFG accommodates analog and digital signals, ASK and FSK modulation schemes. DFG is also free from classical noise such as Amplitude-Spontaneous-Emission (ASE) and allows simultaneous multi-channel conversion with no significant crosstalk.
Efficient generation of infrared light in LiNbO3 waveguides with integrated coupling structures
Authors: Chou M. H. , Arbore M. A. , Fejer M. M. , Galvanauskas A. , Harter D.
Published: February 2023

Difference-frequency mixing (DFM), in which a pump at frequency ω
p
is mixed with a signal at frequency ω
s
to generate an idler at frequency ω
i
= ω
p
- ω
s
, is useful for generating infrared radiation. By mixing the outputs of two infrared lasers, one can generate coherent infrared radiation1,2 for spectroscopic applications such as molecular sensing3; one can also apply DFM to wavelength conversion in wavelength-division-multiplexed (WDM) communication systems.4,5 Optical parametric generation (OPG) and optical parametric oscillation (OPO)6, in which a strong pump is mixed with vacuum noise input, are useful for generating widely tunable infrared radiation from a single pump laser. DFM in bulk nonlinear crystals has been demonstrated with AgGaS2 and AgGaSe27 and with periodically-poled LiNbO3 (PPLN)3, but with low conversion efficiencies. Waveguide confinement has been shown to increase single-pass conversion efficiencies for second harmonic generation by factors up to 1000, as compared with bulk. However guided-wave DFM has, to date, failed to demonstrate comparable improvements to the bulk, primarily because of difficulties in coupling of the pump radiation. In this paper, we address the mode launching problem using integrated mode coupling structures, including mode filters, adiabatic tapers and directional couplers. Using these coupling components, we have demonstrated efficient guided-wave DFM in periodically-poled LiNbO3 and guided-wave OPG.