bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamical Transverse Laser Patterns
Authors: Brambilla M. , Cattaneo M. , Lugiato L. A. , Pirovano R. , Prati F. , Kent A. J. , Oppo G.-L. , Coates A. B. , Weiss C. O. , Green C. , D’Angelo E. J. , Tredicce J. R.
Published: February 2023

The spatial and spatio-temporal phenomena that emerge in the transverse structure of the electromagnetic field have attracted a lot of attention in recent years1,2. We consider a cylindrically symmetrical laser with spherical mirrors, and describe the dynamics in terms of the competition among different Gauss-Laguerre modes of the cavity. In this presentation we focus on the case in which the mode competition leads the laser to approach a dynamical state which, according to the values of the control parameters, can be periodic or quasiperiodic.
Pattern formation in a multimode CO2 laser
Authors: Hennequin D. , Lepers C. , Louvergneaux E. , Dangoisse D. , Glorieux P.
Published: February 2023

The spatio-temporal dynamics of a Perot-Fabry CO2 laser is experimentally studied. The cavity is composed of two mirrors with a lens inserted between them. This system permits to reach very large Fresnel numbers by adjusting the location of the lens, and so to vary the frequency spacing between transverse modes on a wide range [1], typically from almost 0 to 20 MHz in our case, while the free spectral range is 80 MHz. Two other control parameters are available: the pump parameter and the cavity length.
Defect dynamics in the evolution of the transverse pattern of a laser
Authors: Abraham N. B. , Balle S. , Chen Z. , DAngelo E. J. , Tredicce J. R.
Published: February 2023

Recently we reported1 numerical solutions of the full set of Maxwell-Bloch equations for a laser with transverse profile variations, finding examples of multimode pulsations without defects and examples of defect-mediated pulsations that could be periodic or turbulent. The onset of turbulence was illustrated by the loss of spatial correlation -- the decorrelation of intensity fluctuations at separated points - as the number of defects increased. In that work, we also reported the first results of parallel studies using more physical limitations on the transverse profile of the excitation mechanism and using spatially distributed spontaneous emission noise. The transverse profile limitations effectively suppressed the higher order radial modes, thereby enlarging the spatial extent of the coherent structure surrounding each defect. The enlarging of the size of coherent structures around each defect, reaching a significant fraction of the size of the overall patterns, was sufficient to increase their interaction to a global one, causing entrainment of the motion of the defects after long transients, with the final states being periodic motion. We elaborate on these results in the present work.
Turbulent Patterns in Wide Gain Section Two-Level and Raman Lasers
Authors: Jakobsen P.K. , Wenden S.G. , Moloney J.V. , Newell A.C.
Published: February 2023

The close synergism between experiment and theory for Rayleigh-Benard fluid convection has led to the development of sophisticated theoretical models which accurately predict the onset of widely diverse pattern forming turbulent convection. Close to threshold a multiple scales weakly nonlinear analysis yields a universal class of amplitude equations which accurately predict the formation of roll, hexagon, defect patterns and various instabilities of the underlying roll solutions. An elegant study by Busse of the nonlinear regime established that turbulent patterns and stable rolls could coexist beyond the first instability threshold.
Interference and Dislocation Patterns in Linear Waves
Authors: Berry Michael
Published: February 2023

Phase singularities (dislocations and disclinations) are generic in waves, linear or not, and occur in light, sound, microwaves, quantum waves and the tides. They are complementary to the caustic singularities of geometrical optics.
Pattern Formation, Pattern Recognition, and Associative Memory
Authors: Haken H.
Published: February 2023

Spatial and temporal patterns can be spontaneously formed in a variety of systems treated in physics, chemistry, biology and other disciplines. Such patterns may be coherent oscillations in the laser and their interactions with each other, spatio-temporal patterns in fluids, chemical reactions and a great variety of morphogenetic processes in biology.
Integrated Optics: Beyond the Filed of Dreams
Authors: Alferness R.C.
Published: February 2023

After years of research, much anticipation, and some frustration, integrated photonic components are now key enablers for a new generation of commercial optical systems. In applications, including digital modulators and polarization scramblers in undersea systems, passive components for loop and wavelength-division-multiplexed systems, multi-functional circuits for fiber gyros, and linear modulators for CATV distribution, system designers are increasingly relying upon integrated components. As we go forward in an environment potentially rich with applications, the challenge for integrated photonics will be to react quickly to market needs, reduce costs, and broaden application areas by providing increased functionality through a higher level of integration.
Integrated Photonics in the RACE Program
Authors: Lagasse Paul
Published: February 2023

The most significant research results obtained in the European RACE II program in the field of integrated photonic circuits and their system applications will be reviewed.
New Technical Career Strategy
Authors: Chang Milton
Published: February 2023

Tremendous opportunities await people with a technical education who are willing to take a broader view of their skills. A low-risk model to start a business will also be presented.
Electromagnetic Resonance Mediated Second Harmonic Generation: Peaks or Dips?
Authors: Popov E. , Reinisch R. , Neviere M.
Published: February 2023

One of the attractive features of grating couplers for second harmonic generation is that these couplers enable electromagnetic resonances at the pump and/or the second harmonic frequency. It is usually believed that the resonant excitation of guided waves (waveguide modes or surface plasmons) leads to an increase of the second harmonic efficiency. This may not be always the case, as reported by M. Kull et al. [1]. This effect has received no explanation till now. We show here that the dips observed in ref. [1] are due to the existence of nonlinear zeros. In the following the undepleted pump approximation is assumed. It simplifies the problem of second harmonic generation at grating couplers so that there exists a scattering matrix [2] at the second harmonic frequency 2ω which linearly links the vector B2ω of scattered amplitudes (at 2ω) to a source vector A2ω, which comes from the square of the field amplitudes at ω: Thus A2ω has a double complex pole, denoted by β1p when the scattered amplitudes at w have a single pole β1p. Given another resonance at 2ω, the scattering matrix S will present another single pole, denoted by β2p.
A New Method to Treat Second-order Nonlinear Optical Interactions in Nonlinear Medium With Periodical Structure
Authors: Xu C. Q. , Okayama H. , Kawahara M.
Published: February 2023

Difference frequency generation (DFG) and second harmonic generation (SHG) in nonlinear medium with a periodical structure have attracted much attention, because of their potential applications in optical communication systems [1] and optical information processes [2]. Since all the three wavelengths involved in DFG can be in transparence region of semiconductors, semiconductor DFG devices such as AlGaAs, usually have large nonlinearity and small band-gap, are peculiar interesting. In the periodical structure, linear and nonlinear optical parameter modulations as well as propagation loss are usually very important to conversion efficiency. Although theoretical analyses that involve linear and nonlinear optical parameter modulations have been carried out extensively for SHG[3]~[6], little work has been reported for DFG [7].
Application of NLO susceptibility-corrugated scheme to Cerenkov-radiative SHG in a new organic copolymer
Authors: Azumai Yuji , Seo Iwao , Sato Heihachi
Published: February 2023

Although organic polymers have been extensively used for second harmonic generation (SHG), the phase-matching between the fundamental and SH waves cannot essentially be satisfied to their bulk scheme as commonly done in inorganic crystals. Among various approaches to take the phase-matching the Cerenkov-radiative scheme is one of the promisings, in particular, suitable to organic polymers, of which the nonlinear optical(NLO) susceptibility χ(2) is uniformly distributed over the guiding layer of a slab-guide. Then, the authors et al have firstly proposed to adopt a periodic or chirped periodic χ(2) structure into the guiding layer even to the Cerenkovian scheme and have successfully demonstrated enhanced SHG power with an organic copolymer, i.e., VDCN/VAc film.1,2 For enhancing conversion efficiency it is quite required not only to pursue an optimum geometrical structure onto the waveguide, but also to find an appropriate polymer having large NLO χ(2) value including optical properties preferable to both fundamental and SH waves. In the present paper we shall experimentally apply the Cerenkov-radiative scheme with the periodic χ(2) to a newly developed organic copolymer,3 i.e., vinylidene cyanide/P-hydroxy vinyl benzoate copolymer having 4-nitro-4’-oxo biphenyl chro­mophore (VDCN/VBZ-BPN) at a pulsed Nd:YAG 1.06 μm laser line as the fundamental wave.
Waveguide SHG Device Using an Organic Crystal Isopropyl-4-acetylphenylurea
Authors: Yamamoto Hironobu , Sugiyama Tsunetoshi , Jung Jaeho , Kinoshita Takeshi , Sasaki Keisuke
Published: February 2023

Efficient blue and green SHG devices are important for high-density optical recording, laser printing and optical measurement systems as a high energy photon source. In particular, waveguide device is advantageous because of its high conversion efficiency, compactness, and variety of phase-matching technique. Organic SHG materials have been potentially attractive due to their large χ(2)[1]. However, practical disadvantages of organic materials remain such as efficiency/transparency trade-off and undeveloped device-processing technology.
Ultimate Capacity of WDM Soliton Transmissions with Sliding Filters
Authors: Matera F. , Romagnoli M. , Settembre M. , Wabnitz S. , Kodama Y.
Published: February 2023

A major limitation to the transmission capacity of soliton-based periodically amplified fiber links [1] is provided by the fluctuations of the pulse arrival time due to the accumulation of small frequency deviations from the amplifier noise [2]. The output time jitter (and the resulting bit-error-rate) may be reduced by means of bandwidth limited amplification [3] and sliding frequency filters [4-5]. In wavelength division multiplexed (WDM) soliton systems, the periodic power variation of the solitons between amplifiers leads to asymmetric soliton collisions [6]. Whenever a soliton in, say, the first channel experiences collisions with solitons of an adjacent channel, two distinct sources of randomness arise. First, the information-bearing sequence of solitons in the second channel is random. Since each collision leads to a small time displacement of the soliton center, multiple collisions lead to a random net time shift at the system output, which however is nearly the same for adjacent solitons in the first channel, and no significant bit error rate results. The second source of randomness is much more harmful and is due to the collision asymmetry whenever the collision distance is close to the amplifier spacing (resonance condition). In fact, the center of the collision is located at random in between amplifiers and originates a small residual positive or negative soliton frequency shift. The accumulation of these random shifts along the link produces a jitter of the soliton output time position as in the case of ref. [2]. We analyse here the effects of strong filtering on the resonant dynamics of multiple soliton collisions between solitons of different wavelengths. We show by perturbation theory and full numerical simulations that the ultimate capacity of WDM transoceanic soliton systems may be much increased by means of in-line filters, and in particular with sliding filters, irrespectively of initial time overlaps between the channels.
Cherenkov radiation by solitons in optical fibers
Authors: Akhmediev Nail , Karlsson Magnus
Published: February 2023

Classical Cherenkov radiation appears when a small object moves in a medium with a velocity exceeding the phase velocity of the waves in the given medium[1]. It is assumed that the source has dimensions much smaller that the wavelength. The source of radiation does not necessarily have to be a real particle, but can be, for example, waves of polarisation induced in a nonlinear medium by external fields. If the size of the source is finite and comparable with the wavelength at least in one direction, then the radiation is defined in this direction by the 'Cherenkov conditions' rather than full phase-matching conditions. In nonlinear optics, the concept of Cherenkov radiation was introduced by Tien et al. in 1970 [2]. Their experiment shows that a thin-film pump beam can generate a second-harmonic (SH) beam in the substrate below the film. The phase velocity of the induced nonlinear polarization is higher than the phase velocity of the waves in the substrate, or the effective wavenumber of the polarization in the film must be shorter than the wavenumber of the waves in the substrate at the SH frequency. The emerging SH-beam is therefore tilted with respect to the longitudinal direction of the pump, due to the longitudinal phase-matching of the wave vectors. This is an example of Cherenkov radiation with longitudinal phase-matching, but without transverse phase-matching.
All-Optical 100 Gbit/s TDM Transmission Technologies
Authors: Kawanishi Satoki
Published: February 2023

All-optical time-division-multiplexed (TDM) transmission technologies will be essential for future ultrahigh-speed all-optical networks. They include ultrashort transform-limited (TL) pulse generation, all-optical modulation/ time-division multiplexing, high-speed timing extraction and all-optical time-division demultiplexing. In this paper, the TDM transmission technologies that use ultrahigh-speed optical nonlinear phenomena are reviewed. A recent 100 Gbit/s, 200 km optical transmission experiment [1] is shown and problems that must be overcome to achieve > 100 Gbit/s transmission are also discussed.
Steering of Multidimensional Solitons in Nonlinear Fiber Arrays
Authors: Aceves A. B. , De Angelis C. , Luther G. G. , Rubenchik Alexander M. , Turitsyn Sergei K.
Published: February 2023

Passive or active waveguides coupled to form an array have many applications [1, 2]. Because the output characteristics can be changed by tuning the input power, a waveguide array based on optical fibers called the Nonlinear Fiber Array (NFA) may permit ultrafast, all-optical switching. Such a device was first proposed in Ref. [3]. Recently it was shown that when group velocity dispersion becomes important in NFA’s, nonlinearity, dispersion, and the discrete effect of linear coupling along the array balance permitting the stable propagation of multidimensional light bullets [4]. In this paper we show that these beams can be exploited in NFA’s for all-optical-information-processing. To steer a signal on the dispersive NFA, phase shifts can be introduced to initiate translation along the array of fibers. As the light energy propagates, a quasi-collapse phenomenon begins to localize it. Once the energy is localized over a few fibers, its translation along the array is stopped. The output fiber is selected by the combination of launch speed, which is a function of the gradient of the phase shift along the array, and localization rate, which is a function of the initial power.
Bistability and Switching in a Rib Waveguide Resonator
Authors: Peschel U. , Michaelis D. , Peschel T. , Lederer F.
Published: February 2023

Photonic data transmission and processing require highly efficient all-optical elements for signal amplification, switching and data storage. It could be shown experimentally that semiconductor planar resonators can be envisaged as promising candidates [1]. In particular, optical bistability, that has been shown to exist in these configurations, opens a wide field of applications. Because the operating frequencies are near the band gap of the direct semiconductors used the nonlinearities are giant. Hence the critical power for nonlinear effects to occur is fairly moderate. In view of these advantages it might be worthwhile to study such resonators in a waveguide scheme because it can be included into integrated optics configurations. In planar resonators one has not to worry about the absorption, being extremely large near the gap, because the overall thickness is only a few micrometers and they are usually operated in reflection. The situation appears more involved in waveguides. Usually one prefers to exploit the transmitted signal in order to separate input and output channels. Moreover the efficiency of the distributed Bragg reflectors, surrounding the cavity, is usually some orders of magnitude less than that of conventional planar mirrors requiring rather long reflectors. Because the cavity length exceeds that of planar resonators considerably too one has to guarantee that the overwhelming part of the resonator is essentially transparent for the guided mode. This has of course the consequence that it does not contribute to any resonant nonlinear effect. Hence we propose a resonator that is only loaded by a thin layer of nonlinear but absorbing material (GaAs) in the cavity region (see Fig.1).
Control Strategies for Temporal Dark Solitons
Authors: Allen K.M. , Doran N.J. , Smith N.J. , Williams J.A.R.
Published: February 2023

Recently, interest has been shown in understanding the behaviour of dark solitons in optical fibres [1], and assessing their usefulness for optical communications. The motivation is twofold; firstly in order to upgrade installed fibres operating in the normal dispersion regime, and secondly to take advantage of the apparently superior immunity of dark solitons to certain perturbations such as amplifier spontaneous emission noise [2]. However, a final assessment of the usefulness of dark solitons cannot be made until it is known what methods, if any, are available to control effects such as timing jitter and pulse to pulse interactions.
Cancellation of Third-Order Nonlinear Effects in Amplified Fiber Links by Dispersion Compensation, Phase Conjugation, and Alternating Dispersion
Authors: Marhic M. E. , Kagi N. , Chiang T.-K. , Kazovsky L. G.
Published: February 2023

The third-order nonlinearity in optical fibers is the cause of the related phenomena of self-phase modulation (SPM), four-wave mixing (FWM), and cross-phase modulation (XPM). The FWM generation efficiency in a single fiber segment depends on the propagation constant mismatch Δβ between the participating waves.1 A common technique to reduce FWM in WDM networks is to use high-dispersion fibers, but a drawback is that high dispersion in turn leads to pulse shape distortion. Hence the need arises to compensate for this high dispersion. Means have been introduced to do so, including: localized dispersion compensation (DC) by placing a dispersion compensator after each segment;2 alternating dispersion (AD), i.e. reversing the sign of the dispersion coefficient in consecutive fiber segments;3 phase conjugation (PC) between two consecutive segments.4,5 Here we show that by broadening the approach to FWM reduction, to encompass all the tools listed above, one can find a combination which can in principle completely cancel all third-order nonlinear effects in a two-segment link. We first present the proof for FWM, and then discuss its extension to XPM and SPM.
A Numerical Study of Soliton Bit-Streams in a WDM Communication System
Authors: Boardman A.D. , Mehta H. , Putman R.C.J. , Sangarpaul A.K. , Wilkins M. , Xie K.
Published: February 2023

To date, relatively few papers have been published on the subject of WDM (Wavelength Division Multiplexing) as applied to a soliton communication system[1-8]. However, with the advent of TDM, (Time Division Multiplexing) and considering the effects of Gordon-Haus jitter, the bit repetition rate limit can be reached even for short pulse widths and it is now natural to look for methods of increasing the information throughput with different frequency bit-streams.
Light Depolarization Induced by Kerr Nonlinearity in Long Fiber Links
Authors: Matera F. , Mecozzi A. , Settembre M.
Published: February 2023

In long-haul links, the simultaneous presence of Group Velocity Dispersion (GVD), Polarization Mode Dispersion (PMD) [1], Kerr effect and Amplifier Spontaneous Emission (ASE) noise of the in-line optical amplifiers can induce severe light distortion. In particular, the light depolarization can be affected. This is an important issue for systems based upon Polarization Modulation (PM) [2]. The evolution of polarization in long-haul soliton-based systems has been already investigated [2]. A single soliton changes its polarization state during propagation, but it always preserves a definite state of polarization along its pulse shape. In this work, we investigate the properties of the polarization evolution of Non Return to Zero (NRZ) pulses in the presence of PMD, Kerr effect and ASE noise of the in-line amplifiers, in the propagation regime of low GVD.
All-Optical demultiplexing without pulse breakup using different signal and control wavelengths
Authors: Villeneuve A. , Mamyshev P. , Kang J. U. , Stegeman G. I. , Aitchison J. S. , Ironside C. N.
Published: February 2023

We have previously reported the observation of all-optical demultiplexing, where the signal and control pulse trains had different polarizations [1]. We used a nonlinear directional coupler, fabricated in AlGaAs and operated at half the band-gap. However, the use of different polarizations resulted in a far from optimum demonstration of demultiplexing; pulse break-up was present and the different polarizations had different coupling lengths. Below we report on more recent results where different wavelengths and different pulse duration are used to improve the demultiplexing operation.
Analysis of a second-order nonlinear Bragg reflector
Authors: Leo Giuseppe , Assanto Gaetano
Published: February 2023

Cascading of χ(2) nonlinearities, due to the large phase shifts obtainable at the fundamental frequency through up- and down-conversion in phase-mismatched second harmonic generation, is a novel and promising approach to all-optical switching. [1] Since nonlinear phase shifts drive most all-optical devices, some typical guided-wave configurations have been in vestigated in the presence of a cascaded second-order interaction. [2,3] In this communication we analyze numerically the operation of a distributed feedback grating (DFBG) realized in a χ(2) material, focussing on the simple case of a periodic corrugation coupling forward and backward waves at the fundamental frequency (FF, ω). As shown below, due to the nonlin-early generated phase-shift in the FF waves, an initially reflecting structure is able to switch to a transmitting state when the input power is increased.
Optical Power Limiting By SHG In The Čerenkov Regime
Authors: Krijnen Gijs J.M. , Stegeman George I. , Hoekstra Hugo J.W.M.
Published: February 2023

The interest in χ(2)-materials and related nonlinear wave-propagation effects has been driven for a long time by potential applications in efficient blue-light generation by Second Harmonic Generation (SHG) and electro-optical switching [1]. From a practical point of view the interest in SHG has been dominated by guided mode - guided mode (here referred to as type A) interactions rather than by guided mode - radiation mode (type B) interactions (also called Čerenkov radiation) since in the latter case analytical relations are difficult to obtain (due to the problems associated with normalisation of radiation modes) and because the geometrical shape of the emerging SH light is not favourable. Numerical studies on type B interactions [2] have merely focused on the SHG efficiency of structures in which the index of the the core at

2
ω

(

n
c

2
ω

)

is larger than the index of the cladding at

2
ω

(

n

cl

2
ω

)

and in which both are larger than the effective index of the guided modes at

ω

(

N

eff

ω

)

. In this paper we report on numerical investigations on type B SHG of structures with

n

cl

2
ω

>

n
c

2
ω

>

N

eff

ω

. We find that in the Čerenkov regime the depletion of the fundamental can be almost complete when there is phase-matching to a leaky mode at 2ω due to the high propagation losses (10-1000 dB/cm) of these modes [3], The increasingly more complete conversion with increasing input power makes this type of interaction very interesting for optical power limiting of the input beam at co. Benefits of this scheme are a large dynamic range, the potential absence of heating (because it does not require intrinsic absorption), adjustable limiting levels and a wide wavelength bandwidth.
Increased Amplifier Spacing in a Soliton System with Partial Dispersion Compensation
Authors: Grudinin A.B. , Goncharenko I.A.
Published: February 2023

Recently very impressive results of soliton transmission at bit rate as high as 20 Gb/s over 9000 km were demonstrated in a system where the dispersion was periodically compensated [1,2]. The use of a dispersion compensating element in a soliton transmission system was in fact a milestone which demonstrates that the application of techniques thought to be compatible only with linear (NRZ) systems can improve the performance of nonlinear systems as well.
Power dependence effects on the modulational instability spectra for highly birefringent fibers
Authors: Dinda P. Tchofo , Millot G. , Haelterman M. , Seve E.
Published: February 2023

Modulational instability commonly refers to a non-degenerate stimulated four-wave mixing (FWM) interaction where phase matching is achieved through compensation of chromatic dispersion by self-phase modulation (SPM)[1]. In highly birefringent libers, phase matching of the FWM process responsible for MI does not require nonlinear dependence of the wavevectors contrary to single-mode or scalar MI. Apart from the analysis of Ref.[2] where a slight nonlinear dependence of the sideband frequencies was observed, in most previous experimental works on FWM processes in highly birefringent fibers, power dependent phase-matching effects were not evidenced[3,4]. The main reason for this is that the critical power level is well beyond any practical power levels, for operating conditions where the two pump waves copropagate with the same frequency. Quite to the contrary, when the two pump waves propagate with different frequencies, one can approach the critical power by just changing the frequency separation between the two pump waves, and thus observe power dependence effects.
Quasi-phasematched parametric interactions in waveguides
Authors: Fejer M. M.
Published: February 2023

Quasi-phasematched (QPM) frequency conversion in waveguides has been been widely studied in recent years as a means for efficient generation of coherent radiation. Second harmonic, sum, and difference frequency generation, as well as optical parametric amplification and oscillation have been demonstrated at a number of laboratories. In the best developed materials systems, periodically-poled ferroelectrics with ion-exchanged waveguides, wavelengths from the ultraviolet (<370 nm) to the mid-infrared (4 μm) have been generated with near-infrared pump lasers. Efficiencies exceeding 1000%/W-cm2, and CW output power in the blue exceeding 20 mW have been generated.
Nonlinear absorption and refraction in poly 3-BCMU polydiacetylene optical waveguides in the low loss fibre communications windows
Authors: Boyle A. J. , Pender W. A. , Blau W. J. , Baek Y. , Kang J. , Fuerst R. , Jaeger M. , Stegeman G.I.
Published: February 2023

The nonlinear susceptibility of the first soluble polydiacetylenes was measured by Chance1 in 1980, and poly(3BCMU) and poly(4BCMU) were among these. Most of the work done on χ(3) in poly(3BCMU) and poly(4BCMU) since have been measurements taken in solutions of the polymers, or in gels of the polymers in nonsolvents. These materials can be processed into thin films by spin-coating from concentrated solutions. This forms an amorphous film where the chains are aligned randomly in the plane of the film. It is not surprising therefore to see the published values of n2 for these amorphous films are an order of magnitude lower than for the crystalline poly(PTS), as the polarized electric field is not interacting with the maximum number of delocalised electrons. The work of Hsu2 shows that if the poly(BCMU) films are deposited with the chains aligned the nonlinearity increases by a factor of 5 on the spin coated films and approaches the value of n2 for poly(PTS). The work of Rochford3 and Townsend4 have been the only channel waveguide experiments in poly(4-BCMU). No channel waveguide experiments to measure n2 have been reported in poly(3-BCMU).
Light Trapping in Quasi-Phase-Matched Second-Harmonic Generation
Authors: Torner Lluis , Torres Juan P. , Petrov Dmitrii , Stegeman George I.
Published: February 2023

Quasi-phase-matching (QPM) offers a very attractive approach to produce highly-efficient parametric wave-mixing interactions in quadratic nonlinear optical media.1 Conventional phase-matching techniques used to compensate for the phase-velocity mismatch between the waves of difference frequencies that interact in the nonlinear medium are based on the birefringence and thermal properties of the materials involved. Hence, the overall efficiency of the interaction is limited by a variety of effects, mainly Poynting vector spatial beam walk-off due to the different propagation directions of energy and phase fronts in anisotropic media, non-convenient operation temperatures and crystalline optical axes orientations, and the value of the second-order nonlinear coefficients accessible through the polarization of the waves involved in the parametric interaction.
Soliton switching in type II second-harmonic generation
Authors: Mollame R. , Assanto G. , Trillo S.
Published: February 2023

Soliton propagation in transparent media was believed to be a feature of materials with cubic nonlinearity. However, solitary wave propagation in the form of mutually trapped spatial envelopes (i.e., spatial simultons) have been recently demonstrated also in quadratic media [1]. Although such trapping was originally predicted nearly two decades ago [2], it attracted a lot of theoretical and experimental efforts only recently, due to the growing activity on cascading, and the impact that solitons might have for potential applications. As far as the latter aspect is concerned, one of the key issues is the possibility of all-optical switching and routing of optical signals. Before the advent of solitons, several schemes employing quadratic materials have already been proposed, and some of them have also been succesfully demonstrated [3-4]. However, the major drawback, common to all the proposed devices is the fact that their operation was proposed and/or investigated within the cw regime. As a consequence, in the pulsed regime, the performances of these devices are essentially limited by the fact that the pulses could not be switched as units or particles, as it would be desirable in a pure digital processing scheme. Viceversa, we show in this communication, that solitary waves of quadratic media have the capability to perform nearly ideal digital operation. In particular we focus our attention on type II SHG in the 1+1 dimensional case, which applies to either temporal solitons, or spatial solitons in waveguides [1]. We investigated the most appealing case for which the second-harmonic (SH) is not launched at the input. Switching is implemented at fundamental frequency (FF) by acting over the two FF input components only. Two different regimes are considered (see Fig. 1): a) for nearly symmetric excitation of the FF soliton components, the output polarization state is uniform and very sensitive to small input imbalances, (i.e., to the input polarization angle), b) the polarization rotation of an intense soliton component may be controlled in a phase-insensitive way by a weaker control pulse. In both cases, the nonlinear crystal in conjunction with a polarization analyzer behaves as a switch. Note that similar results are valid also for the nondegenerate three-wave which is governed by formally equivalent However in this case, the soliton input is constituted by two envelopes at different frequency. Therefore, since switching relies on the nonlinear phase-shifts experienced by the components, soliton switching requires the nonlinear crystal to be placed in an interferometric device.
Acoustic Effect in Optical Fibers
Authors: Pilipetskii A. N.
Published: February 2023

The first experiments on long-distance soliton transmission1 revealed a strange long-range interaction between pulses. Shortly thereafter it was shown theoretically that this long-range interaction is due to the electrostrictive excitation of acoustic waves by light pulses and the subsequent interaction of light pulses with excited acoustic waves.2 Further theoretical and experimental investigations showed that the acoustic effect significantly increases the soliton timing jitter in communication lines and limits both the bit rates and information transmission distances.3 This acoustically-induced pulse interaction does not only manifest itself in the long-distance soliton propagation; experiments on passively modelocked fiber ring lasers indicate the presence of a long-range interaction that can lead to regular pulse spacing inside the laser cavity.4 Theoretical calculations show that the acoustic interaction between passively modelocked pulses in fiber ring lasers are complicated and can cause pulse bunching or can stabilize periodic sequences of pulses.5
Bright and Dark Solitons in Non-Kerr Materials
Authors: Kivshar Yuri S.
Published: February 2023

It is known that optical beams can propagate unchanged in the form of self-guided waves or spatial optical solitons due to compensation of the beam diffraction by nonlinearity-induced change in the material refractive index [1]. Many of the properties of spatial optical solitons, including the stability analysis [2] and the inverse scattering technique [3], are unique for the Kerr materials when the nonlinear part of the refractive index nnl(I) depends linearly on the light intensity I, nnl(I) = n2I, where n2 is the so-called Kerr coefficient. However, since the first efforts to observe self-guidence and spatial solitons experimentally, in applications one deals with non-Kerr materials where the dependence nnl(I) is not linear, e.g. it saturation. Recently it has been also shown, theoretically and experimentally, that self-guided beams can be observed in crystals with a strong photorefractive effect [4] and also due to phase-matched parametric interactions in a χ(2) nonlinear medium [5,6]. In many cases, propagation of nonlinear waves in such non-Kerr materials are described by the nonlinear Schrödinger with a more general dependence of the refractive index on the beam intensity. The main purpose of this talk is to present a panoramic overview of different properties of solitary waves in nonKerr materials including the detailed discussion of the stability of (scalar and vector) bright and dark solitons and the soliton coupled states.
Polarised dark solitons and their interactions
Authors: Sheppard Adrian P. , Kivshar Yuri S.
Published: February 2023

Since their prediction and discovery more than twenty years ago, optical solitons have received ever increasing attention from the research community. Temporally confined solitons propagating as pulses in optical fibres have been used in experimental transmission systems and are touted for the next generation of transoceanic cables [1]. More futuristically, nonlinear switches that rely on the interaction between spatially confined solitons are being investigated in a variety of media [2]. Topological solitons, also known as kink or dark solitons, typically appear as a localised intensity dip on a finite background [3], and like their bright counterparts, have been observed in fibres [4] and bulk materials [5]. They are generally more robust than bright solitons and have been the object of recent research considering the influence of polarisation [6,7].
Compression and Amplification of Weak Signal Pulses by Solitons in the Anomalous Dispersion Regime of Optical Fibers
Authors: de Souza R. F. , Hickmann J. Miguel
Published: February 2023

Optical pulse compression is by now a well established technique for the generation of subpicoseconds and/or femtosecond pulses which can find applications in optical fiber communications systems and photonic switching. However, the technique requires light sources with appreciable peak powers, which are not generally available from compact sources. The reason for that is, either in a fiber-grating compressor or in a high-order soliton compressor, a nonlinear phase shift (chirp) must be induced on the signal pulse in order to be compensated by a dispersive delay line. To overcome this problem, a linear chirp can be produced across the signal pulse through cross-phase modulation induced by a copropagating intense pump pulse in an optical fiber.
Characterising the inclusion of a fibre Bragg grating in a nonlinear optical loop mirror
Authors: Hemingway J.-P. , Steele A.L.
Published: February 2023

The self-switching capabilities of the nonlinear optical loop mirror (NOLM)1 fibre configuration have become an integral part of many all-optical signal processing applications2. In its operation as a single-wavelength device the switching is achieved by inducing unequal nonlinear phases in the two counterpropagating pulses in the fibre loop. The phase difference seen with recombination at the coupler results in reflection or transmission from the device, dependant upon the input intensity. A number of approaches have been suggested to achieve the required break in loop symmetry1,3-5, one of which reported experimentally 5, uses a fibre Bragg grating (FBG) spliced into the loop. The single-wavelength operation of this device was shown to provide wavelength discrimination in its switching characteristics.
Broadband Uniform-Gain Fiber Optical Parametric Amplifiers: Influence of Nonlinearity Coefficient Dispersion
Authors: Marhic M. E. , Park Y. , Yang F. S. , Kazovsky L. G.
Published: February 2023

We have recently shown theoretically that a two-pump fiber optical parametric amplifier (OPA), operated near the fiber zero-dispersion wavelength, λ0, can exhibit very uniform gain over a wide wavelength range [1]. For example, a standard dispersion-shifted fiber operated near λ0 = 1550 nm can exhibit 20 dB of gain over a 45 nm bandwidth, with a gain ripple not exceeding 0.1 dB. The fact that the predicted ripple is so small raises the question of whether it might not be substantially increased by incorporating into the model some features left out of the original model as a first approximation. Of particular concern are the facts that we assumed: (i) a single nonlinearity coefficient γ to describe interactions between different waves; (ii) that this γ did not change with frequency. Even if (i) were correct, (ii) clearly is questionable because: 1) we are interested in large frequency ranges (say up to 50 nm bandwidth); 2) γ has both explicit and implicit wavelength dependences. Specifically, γ is given by γ = 2πn2/λA
eff
, where n2 is the nonlinear-index coefficient, λ is the vacuum wavelength, and A
eff
is the effective core area. Ae
ff
generally increases with λ, and thus the denominator of γ can exhibit a fairly strong λ-dependence. In addition n2, which is determined by the materials making up the core and cladding, may also be wavelength dependent. In this paper we study the influence of the dispersion of λAe
ff
on the OPA gain characteristics. We also assume a priori that the various interactions are governed by different γ’s, and we keep these throughout the entire calculation. We will show that, because of symmetries governing the interacting frequencies, the gain spectrum uniformity of the fiber OPA will not be greatly affected by the inclusion of these additional effects.
Compensation splitting scheme for dealing with dispersion and self-phase modulation in communication systems
Authors: Paré C. , Villeneuve A. , Bélanger P.-A.
Published: February 2023

In optical communication systems, the use of alternating dispersion is a common way to deal with bit-rate limitations caused by dispersive pulse broadening. An alternative to this technique was proposed by Yariv et al[1] some time ago. It was suggested that a phase-conjugate conversion of the signal at the middle of the propagation length would cancel, at the line output, the accumulated dispersive effects over the first half propagation. Although more complicated than the first technique, this approach has the advantage of also being able to compensate for the self-phase modulation effects incurred through the Kerr nonlinearity of silica fibers, as first demonstrated experimentally by Watanabe et al[2].
An Improved Perturbation Theory for Optical Solitons Near the Zero-Dispersion Point
Authors: Malomed B. A. , Uzunov I. M. , Lederer F.
Published: February 2023

In communication lines operated near the zero-dispersion point, the
third-order dispersion (TOD) can strongly affect the pulse dynamics.
Hence, it is necessary to develop proper theoretical tools for this
case. Besides the numerical methods, a perturbation theory that can
take into account the bandwidth-limited amplification (BLA) and
nonlinear gain (NLG) or losses is required. The latter perturbations
can considerably reduce soliton interactions. With regard to a
combined effect of TOD and BLA, it was shown [1] that, e.g., a decay
of a two-soliton bound state caused by TOD can be prevented by BLA. A
new idea put forward in [2, 3] was that BLA which compensates for the
linear and nonlinear losses can, simultaneously, absorb the resonance
radiation emitted under the action of TOD, thus lending the soliton a
much better stability. This effect has been experimentally observed in
[4]. For large values of TOD, however, the soliton was obtained
numerically [3] in a state with a conspicuous velocity, which differed
from that predicted by the usual perturbation approach [5] by a factor
of 2.
All Fibre Tunable Source of Picosecond Pulses at 1545 nm
Authors: Traynor N.J , Sysoliatin A.A , Grudinin A.B
Published: February 2023

In this paper we present a simple method of production of tunable soliton pulses of picosecond duration around 1545 nm. Our system uses solely passive techniques to produce and modify, both temporally and spectrally, a stable stream of soliton pulses, which represents simplifications over previous techniques to produce such pulses1, which have required implementation of active techniques. This source has potential as a general laboratory tool with a tuning range of >50nm, making it a viable alternative to other sources such as colour centre lasers. The availability of high peak pulse powers also makes it an attractive source for second and third order non-linear effects such as second harmonic generation, cascaded optical non-linearities and optical switching.
Dark Spatial Soliton Stripe Instability
Authors: Tikhonenko Vladimir , Christou Jason , Luther-Davies Barry , Kivshar Yuri S.
Published: February 2023

The dynamics of spatial solitons in two transverse dimensions has recently become a topic of considerable interest[1]. The “extra” transverse dimensionality permits a greater degree of freedom in soliton behaviour, as seen in experiments demonstrating nonlinear rotation of optical vortex solitons in a self-defocusing medium[2]. In self-focusing media, the conservation of transverse angular momentum was shown to influence the dynamics of bright spatial solitons interaction[3]. The increased dimensionality also changes the stability properties of solitons from their counterpart solitons of a single transverse dimension. We report here on the first experimental investigation of instability associated with dark soliton stripe propagation through a saturable self-defocusing medium. These instabilities were shown to be an effective mechanism for the generation of optical vortex soliton pairs of opposite topological charge.
The seeding and all-optical patterning of polymer materials
Authors: Nunzi J.-M. , Fiorini C. , Etilé A.-C.
Published: February 2023

A key issue in the field of nonlinear optical polymers for second-order process is the achievement of a non-centrosymetric order. One challenging prospect is to achieve it by optical means in order to take full advantage of its rich processing capabilities. Indeed, the all-optical poling of polymers offers an interesting alternative to the realization of non-centrosymmetric structures. Of particular interest is the possibility to control extensively the spatial and tensorial properties of polymers using optical beams.1
Collision, fusion, and spiralling of interacting solitons in a bulk quadratic medium
Authors: Steblina V.V. , Buryak A.V. , Kivshar Yu.S.
Published: February 2023

Self-guided optical beams (or spatial solitons) have attracted substantial research interest because they hold a promise of ultra-fast all-optical switching and controlling light by light. Soliton interactions have been analyzed theoretically and experimentally mostly for planar geometries [1], and only recent experimental discoveries of stable (2+1)-dimensional solitons in different nonlinear media [2] initiated the experimental study of fully three-dimensional interactions between solitary beams. Recently, experimental results demonstrating non-planar interaction and spiralling of two incoherent beams in a photorefractive medium have been reported [3]. However, since earlier papers on the soliton interactions [4], no systematic analysis of non-planar soliton interactions in a bulk medium has been developed so far.
Enhancement of cascaded phase shift and all-optical intensity modulation in quadratic media with local distortion of phase mismatch
Authors: Lee Wangkeun , Kim Hongki , Cha Myoungsik
Published: February 2023

Second order cascaded phase shift and all- optical intensity modulation
are theoretically investigated by introducing an additional local
phase mismatch along the wave propagation. The optimal position and
strength of the local phase mismatch were found to maximize the
cascaded phase shift at various input fundamental intensities. A
maximum enhancement of 85% in the cascaded phase shift has been
obtained relative to the uniformly phase mismatched case at a moderate
input intensity. All-optical intensity modulation is also proposed
with a similar structure. About 9 times intensity amplification was
observed from a small input optical signal biased with a uniform
fundamental intensity at another optimum set of the local phase
mismatch parameters (position and strength).
Theory of modulational instability in periodic media with a Kerr nonlinearity
Authors: de Sterke C. Martijn
Published: February 2023

Modulational instability in periodic media with a Kerr nonlinearity is investigated using coupled mode theory. In the presence of anomalous dispersion, the standard nonlinear Schroedinger results are obtained at low powers, though at higher powers deviations from this well-known behavior occur. For normal dispersion an instability with a finite threshold is found. This instability has no equivalent in the nonlinear Schroedinger equation.
Domination of ‘neck’ instability over ‘snake’ one in type II second harmonic generation
Authors: Skryabin Dmitry V. , Firth William J.
Published: February 2023

We investigate modulational instability (MI) of 1-dimensional
three-wave parametric solitons in presence of normal group velocity
dispersion. In particular, we show that the ‘snake’ instability is
strongly suppressed by the ‘neck’ one. This result is in a sharp
contrast with previously studied MI in Kerr and type I quadratic
media.