bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulse Amplification and Shaping using a Nonlinear Amplifying Loop Mirror
Authors: Greer E.J. , Smith K. , Doran N.J. , Bird D.M. , Cameron K.H.
Published: February 2023

In recent work [1], we have studied the the shaping of picosecond-duration optical pulses by the intensity-dependent transmission characteristics of a nonlinear fibre loop mirror. We demonstrated both experimentally and theoretically the advantages to be gained from this pulse shaping, in particular pulse compression and pedestal suppression. In this paper, we report on a Nonlinear Amplifying Loop Mirror (NALM) which performs both amplification and intensity filtering functions. We believe that this work will be of significance to all-optical transmission systems [2] and to some of the novel erbium fibre soliton laser configurations now being investigated [3].
Soliton formation and propagation in a high gain fibre laser.
Authors: Kelly S.M.J. , Smith K. , BIow K.J. , Doran N.
Published: February 2023

A source that exploits both soliton shaping and broadband high gain within a single fibre environment is particularly appealing. Recently, Smith et at [1], demonstrated this simple idea with a mode–locked erbium fibre laser. Short picosecond structures with temporal spectral and power characteristics consistent with fundamental soliton shaping were observed. An important feature of the experiment was that only a short length of high gain single mode erbium doped fibre was used. This limit contrasts with previous studies [2] and leads to soliton behaviour that is significantly different from that commonly associated with propagation in long fibres with low gain [3]. The results presented here form part of a theoretical study aimed at understanding the stable behaviour of solitons reported in this short length high gain limit.
Quantum Propagation in Optical Fibres
Authors: Blow K.J. , Loudon R. , Phoenix S.J.D.
Published: February 2023

Quantum theory, as normally formulated, describes systems enclosed in an artificial box through its time evolution. In some systems, such as a laser, the box may be a physical element such as a cavity. In optical fibre communications the situation is somewhat different. The optical field is continuously generated by a source such as a laser. Once generated the field propagates along an optical fibre and is detected in some form of receiver at the far end. Quantum theory, with its reliance on Hamiltonian systems necessarily conserves the total energy in the system whereas fibre communication is better described as a balance between sources and sinks. Under these circumstances it may be more appropriate to describe the spatial evolution of the field [1], [2], [3]. In this paper we describe an approach to the study of quantum propagation in optical fibres. The discussion will be based on the description of single mode weakly guiding fibres so that a one dimensional scalar wave equation can be used to describe the electric field.
Nonlinear optical polymers: Waveguide devices based on second order effects
Authors: Horsthuis Winfried H.G. , Möhlmann Gustaaf R. , Mertens Hans W.
Published: February 2023

In the past few years, organic materials have gained much interest for application in nonlinear optical devices. The initial scepsis towards these new materials has decreased, since interesting results have been obtained using these materials. The advantages of such materials, expected by early workers in the field, have partially been proven. High electro-optic coefficients have been reported, and reasonably well performing integrated optic devices have been realized [1]. Some other items, such as long term stability, mode matching and low cost production, still need further investigations and development. Nonlinear optic organic materials can be divided in several classes: organic (single) crystals, Langmuir-Blodgett films and several polymeric systems (solid-solutions, main-chain polymers, sidechain polymers). Until now, side-chain polymers appear to be the most promising class, mainly because of their attractive processing characteristics and the flexibility in molecular design.
Second harmonic generation from a polyurethane waveguide on a silver grating coupler
Authors: Kull M. , Coutaz J.-L. , Vitrant G. , Reinisch R. , Meyrueix R.
Published: February 2023

Organic waveguides are well suited for second harmonic (SH) generation [1]. We present here experimental results of SH generation from a polyurethane waveguide spin-coated on a silver grating coupler. As one of the waveguide boundaries is made from a metal it is possible to excite, in addition to guided modes, a surface plasmon (SP) at this boundary. We investigate the angular dependance of the SH generation from the polyurethane coated grating. The excitation of the electromagnetic resonances at the pump frequency lead to a large increase of the diffracted SH light intensity [2]. In order to study the wavelength dependence of the SH efficiency, we have employed two pump wavelengths - 1064 nm and 1318 nm. For the shorter wavelength pump, the SH falls within the absorption band of the polymer.
Finite Element Analysis of Two-Transverse-Dimensional Bistable Nonlinear Integrated Optical Waveguides
Authors: Rahman B.M.A. , Fernandez F.A. , Ettinger R.D. , Davies J.B.
Published: February 2023

There is considerable interest in the study of strong nonlinear effects in integrated optics for use in optical switching [1]. Nonlinear thin films have already been studied extensively by both analytical and numerical techniques. Only in more complex nonlinear waveguides, however, can one obtain very high power density for moderate input power through two-dimensional field confinement in a tiny cross-section.
Analysis of TM-polarized nonlinear guided waves based on a conservation law
Authors: Gniadek K. , Rusek M.
Published: February 2023

In recent years, the properties of the transverse magnetic TM polarized guided waves in nonlinear layered structures have been investigated theoretically in a number of papers [1 - 4]. The presence of two electric field components, one parallel (Ez) and one orthogonal (Ex) to the boundaries of a thin film guiding structure makes the analysis of TM waves more complicated than for the transverse electric TE polarized waves. For simplify the analysis in some works was assumed that TM-wave nonlinearity arises only through one component electric field. The more elaborate is approximation referred to as longitudinal uniaxial approximation in which the nonlinearity is expressed as dependent only on the electric field component parallel to the boundary [1]. The more realistic is transverse uniaxial approximation in which the nonlinearity arises from the dominant transverse Ex component of the electric field [5]. In the few papers [6 - 7] has been investigated TM polarized waves / surface polaritons / propagating along the interface separating of two media, one / or both / of which is nonlinear with the general intensity dependent dielectric function. The effective method analysis of TM nonlinear guided waves is separation of the two electric field components EX and EZ achieved by means of a conservation law. In this approach the properties of TM nonlinear guided waves can be study without the need to solve for the field profile [8]. Since the two field components Ex and Ez of TM wave are everywhere interrelated through the conservation law, then it is possible formally express one in terms of the other.
TE waves propagating in a nonlinear planar asymmetric converging waveguide Y junction
Authors: Chi Sien , Shi Tian-Tsorng
Published: February 2023

Recently nonlinear waveguide junctions have been investigated intensively for their interesting switching behaviors1,2. The waves propagating in a nonlinear converging waveguide Y junction in which the two branches and the stem are single mode waveguides are less reported. For a linear case, the field injected into the thinner branch at a distance from the junction will not evolve into the fundamental mode of the stem, and the field injected into the thicker branch will propagate without loss3. Here we simulate the waves propagating in the Y junction with a nonlinear cladding by using beam propagation method4, and we find that the field injected into the thinner branch is possible to transmit to the stem with a high efficiency.
Four-Wave Mixing Limitation In Multichannel Coherent Optical Communication
Authors: Nilsson Johan , Dado Milan , Jaskorzynska Bozena
Published: February 2023

Four-wave mixing (FWM) in a fiber is a nonlinear effect likely to impose severe restrictions on transmitted powers and channel spacing in optical frequency-division multiplexed (FDM) systems [1,2,3], hence limiting their information capacity. As a result of FWM waves at different frequencies can interact causing an inter-channel cross-talk. The efficiency of FWM is strongly dependent on the difference of phase velocities (phase-mismatch) between the interacting waves [4]. Therefore, it will mainly play a role in dispersion shifted (DS) fibres and for densely spaced channels as are possible in coherent systems.
Mixed states of optical solitons on different carrying frequencies
Authors: Kovachev LM.
Published: February 2023

Investigating the nonlinear interactions of the picosecond optical pulses with different frequencies in monomode optical fiber, one must take into consideration both linear effects. the dispersion and the group delay between waves. Besides, some additional nonlinear effects, as cross-phase modulation (CPM), four-photon parametric mixing (FPM), Raman amplifier (RA), appears. For optical pulses with soliton's powers as a rule, the group delay dominates among all other effects. Nevertheless there are some important cases, when it is possible to compensate group delay trough the nonlinear mechanisms.
Pulse Propagation in Nonlinear Optical Fibres with Spatial Inhomogeneities
Authors: Ryder E. , Parker D.F. , Mayer A.P.
Published: February 2023

The propagation of envelope pulses in nonlinear optical fibres with carrier wave frequency in the monomode regime is described by a pair of nonlinearly coupled nonlinear Schrodinger equations (NLS) [1].
Interactions between Solitons in a Monomode Fiber
Authors: Malomed Boris A.
Published: February 2023

In the present work, pairwise interactions between solitons are considered in two models of a nonlinear monomode fiber.
Ultrashort Pulse Amplification in Erbium-Doped Fibre Amplifiers
Authors: Korobkin D.V. , Khrushchev I.Yu. , Grudinin A.B. , Dianov E.M.
Published: February 2023

Erbium-doped optical fibres displaying broad gain bandwidth centred at the wavelength of minimum loss and negative group velocity dispersion make almost the ideal media for generation and amplification femtosecond range optical pulses. Several authors have studied both theoretically and experimentally the amplification of ultrashort pulses in such devices and have noted that not only resonant properties of fibre amplifier but also the Raman self-frequency shift are responsible for the net gain and pulse duration at the output of an amplifier[1-4].
Proposal of High Capacity All Optical TDMA Networks
Authors: Matera F. , Romagnoli M. , Settembre M. , Tamburrini M.
Published: February 2023

Two scheme of all optical TDMA networks are proposed with the demultiplexed processing obtained by means of an optical gate based on the second harmonic generation process. The maximum throughput is obtained when solitons are used and is equal to 125 Gb/s.
The Gain Saturation by The Random Pulse Train and Noise Characteristics of Long-Distance Soliton-Based System
Authors: Starodumov A.N.
Published: February 2023

In this work we investigate the degradation of the signal-to-noise power ratio (SNR) at the output of the communication line caused by the random fluctuations of a gain in lumped optical amplifiers. There are a few sources of gain fluctuation: effect of pump modulation, random deviiation of Erbium concentration from one amplifier to the next and others. In [1] Kubota et al. have considered by numerical simulation the soliton propagation over long distance taking into account the gain fluctiation (±1,5%). It was pointed out that the pulse width fluctuation over 9000 km was within ±10%, and the pulse shape was clearly distinguished from noises.
Influence of Self-Phase Modulation on Ultra Long-Span Optical Transmission At Zero Dispersion.
Authors: Carter S.F. , Bryant E.G. , Wright J.V.
Published: February 2023

There appear to be two distinct approaches to the design of future ultra long-span optically-amplified transmission systems. In the first, the signal wavelength is chosen to give operation in the region of anomalous dispersion. This is consistent with soliton operation, although other pulse shapes may propagate with little degradation. This paper is concerned with the second approach, where the operating wavelength is chosen to lie very close to the dispersion minimum. Self-phase modulation is now a source of potential impairment, and must be controlled.
Nonlinear Mixing of Optical Solitons with Different Frequences
Authors: Afanasjev V.V. , Vysloukh V.A.
Published: February 2023

The subject of this work is results of theoretical investigation and computer simulations of nonlinear dynamics of wave packets, forming under mixing of optical solitons. The interest to this problem is motivated by the important application of solitons to spectral multiplexing in soliton communication systems and by possibility to use soliton effects in femtosecond laser systems in order to control the parameters of short light pulses.
All-optical, all-fiber circulating shift register with inverter
Authors: Whitaker N. A. , Gabriel M. C. , Avramopoulos H. , Huang A.
Published: February 2023

An all-optical fiber-Sagnac interferometer switch and erbium amplifier have been combined to demonstrate a 254 bit circulating shift register with an inverter.
Nonlinear Directional Coupler in Al0.18Ga0.82As Near Half the Band Gap
Authors: Aitchison J. S. , Kean A. H. , Ironside C. N. , Villeneuve A. , Stegeman G. I.
Published: February 2023

We report the first experimental observation of an ultrafast all-optical switch in a semiconductor waveguide configuration where the transmission is not limited by absorption processes.
Field Dependent All-optical Switching in GaAs/AlGaAs Quantum Well Waveguide operating beyond the Two Photon Absorption Limit
Authors: Tsang H.K. , Penty R.V. , White I.H. , Grant R.S. , Sibbett W. , Soole J.B.D. , Colas E. , Andreadakis N.C. , LeBlanc H.P.
Published: February 2023

Recently, two photon absorption (TPA) in semiconductor materials has been found to impose a serious limitation on the amount of ultrafast optically induced phase modulation available for use in all-optical switching elements1. The limit arises because nonlinear absorption reduces the effective available nonlinear length of an element so that it is not possible to obtain large, ultrafast, all-optical phase modulation at a given switching power by merely increasing the device length. To date the magnitude of ultrafast all-optical phase modulation in semiconductor materials operating relatively close to the bandgap has proved insufficient for their use in all all-optical switching structures2,3, although it has been possible to obtain sufficient phase modulation by using the relatively slow (>50ps recovery time) refractive index change from photogenerated carriers4. In this paper we demonstrate that it is possible to work beyond the TPA limit by operating close to the half bandgap wavelength where TPA is minimal. We have observed over π radians ultrafast all-optical phase modulation in a GaAs/AlGaAs multi-quantum well (MQW) waveguide and have characterised the field and polarization dependences of the nonlinear absorption near half bandgap. These measurements show that GaAs/AIGaAs MQW waveguides can be successfully used for ultrafast all-optical switching in the 1.55μm optical fiber communications band.
Saturation of two-photon excited photoluminescence in Ge-doped fiber
Authors: LaRochelle Sophie , Blouin Alain , Ouellette François
Published: February 2023

The photosensitivity of Ge-doped fiber allows the fabrication of useful devices like Bragg gratings or intermodal couplers. Nevertheless, the physical mechanism leading to a permanent refractive index change is still not well understood. It has been suggested that the bleaching of an absorption band at 245 nm plays an important role in the process. One signature of this absorption band is the photoluminescence emitted around 400 nm [1]. This photoluminescence can be excited by direct absorption of UV light, and this method has been used previously to characterize the 245 absorption band [1,2]. We show here that the luminescence can also be excited by two-photon absorption of light around 500 nm. By measuring the photoluminescence signal as a function of the input intensity, we have observed significant deviation from the expected quadratic dependence, indicating a saturation of the two-photon absorption. From our measurements, the saturation intensity can be deduced, and the two-photon absorption cross-section can be estimated.
Passive, All-Fibre Source of Fundamental, Femtosecond Solitons
Authors: Richardson D.J. , Grudinin A.B. , Payne D.N.
Published: February 2023

Advances in erbium-doped fibre fabrication and the generation and amplification of ultra-short pulses [1-5] make the development of sub-100 fs pulse sources based on erbium-doped fibre a very attractive proposition.
Coherent Effects in Er-doped Fibers: Photon-Echo with Femtosecond Pulses
Authors: Silberberg Y. , da Silva V. L. , Heritage J.P. , Chase E.W. , Saifi M.A. , Andrejco M.J.
Published: February 2023

Optical fibers have proven to be one of the most important nonlinear media, even though in most cases the nonlinearity exploited is the notoriously weak Kerr effect of the silica-based fiber. By using doped fibers, new, stronger nonlinearities are possible. These stronger effects could allow for new phenomena and applications. Coherent effects, in particular, should be important when pulses shorter or comparable to the dephasing time of the impurity ions propagate in the fiber. Here we report, for the first time, the observation of accumulated photon-echo and free induction decay during the propagation of femtosecond pulses in Er doped fibers at 4.2°K.
Theory of Ultrashort Soliton Amplification in Erbium-Doped Fibers
Authors: Gabitov I.R. , Romagnoli M. , Wabnitz S.
Published: February 2023

The use of active fiber lasers and amplifiers for soliton generation and transmission seems to offer a breakthrough towards the application of nonlinear optics to all-optical information processing systems. As far as picosecond solitons are concerned, erbium-doped fibers simply behave as linear amplifiers. However, it is very important to understand what is the lower bound to the time width of a soliton that can be amplified in practice. Moreover, the amplification of ultrashort pulses is subject to both Raman and coherent effects which may add novel interesting physical effects to the soliton dynamics.
Ultrafast Optical Kerr Effect in Active Semiconductor Waveguides
Authors: Hultgren C.T. , Ippen E.P.
Published: February 2023

Active optical waveguides offer interesting possibilities for performing nonlinear functions in photonic circuits. By varying the injected carrier density one can change not only the linear components of gain and index of refraction but also the nonlinear ones. Some studies of ultrafast gain dynamics in AlGaAs(1) and InGaAsP(2) diode laser amplifiers have been performed previously. Four-wave mixing experiments with large frequency detunings in diode lasers (3,4) have provided frequency domain measurements of the magnitude of the nonlinear susceptibility of χ(3). The effect of dynamic index changes has also been revealed by the chirp and spectral changes experienced by ultrashort pulses traveling through amplifiers(5). In this paper we discuss direct measurements of optically induced changes in index of refraction in active AlGaAs waveguides. With femtosecond pump-probe measurements sensitive, separately, to induced phase and amplitude changes, we have studied the relative amplitudes of these dynamics as functions of wavelength and injection current. We observe nonlinearity due to changes in carrier number, carrier heating and, for the first-time, a large above-bandgap ultrafast optical Kerr effect. An interesting aspect of this latter, instantaneous nonlinearity is that it may be utilized without change in carrier number, by operating near the wavelength of nonlinear transparency (where stimulated emission equals absorption).
Nonlinear Directional Coupler Based on Rb:KTP-Waveguides
Authors: Buritskii K.S. , Dianov E.M. , Maslov V.A. , Chernykh V.A. , Shcherbakov E.A.
Published: February 2023

To create ultrahigh-speed long-distance optical fiber communication systems of new generation particularly soliton transmission lines and to implement information optical processing systems into practice it is necessary to develop different functional devices having less than 10 ps high-speed characteristics[1]. The best variant is the application with this aim of light-controlled integrated optical switches and gates, as the pulses of less than 10 fs duration are obtained precisely by the optical methods. Promising from this point of view is the switch based on nonlinear coupled optical waveguides previously used experimentally in the integrated-optical variant on lithium niobate [2] and gallium arsenide [3] base as well as in quartz fiber light guides [4,5].
Prospects for Nonlinear Organics in Guided Wave Optics
Authors: Stegeman George I.
Published: February 2023

Although it has been known for some time that organic materials can have large second and third order nonlinearities [1], it is only within the last five years that there has been a concentrated effort to try to make nonlinear devices out of them. This has been at least partly due to many misconceptions about organic materials which have been proven inaccurate. For example it was widely believed they have low damage thresholds, poor optical properties such as transmission, are not easily processible into device structures etc. In this paper we will review the linear and nonlinear properties of organic materials, how waveguides can and have been made out of them and some of the initial nonlinear devices which have reported.
Quasi-Phase-Matched Second-Harmonic Generation in Lithium Tantalate Waveguides : Experiments and Simulations
Authors: Åhlfeldt Henrik , Arvidsson Gunnar , Jaskorzynska Bozena
Published: February 2023

Several materials and methods are investigated in the search for devices for efficient frequency doubling of infra-red diode lasers to blue. Such compact light sources would find important applications in i.e. optical data storage, displays and spectroscopy.
Remote Nonlinear Switching and Large Nonlinear Effects in Resonant Optical Waveguides
Authors: Lederer Falk , Trutschel U. , Mann M. , Wächter Ch.
Published: February 2023

Waveguide configurations are promising candidates for all-optical switching and modulation due to the combination of diffractionless propagation of the fields (large interaction length) and the strong confinement of power. Both peculiarities enhance the effectivness of the nonlinear processes that produce the needed induced index change.
HE1m self-guided modes : vector solutions and stability
Authors: Archambault J.-L. , Lacroix S. , Snyder A.W.
Published: February 2023

Self-focusing in a medium of intensity-dependent refractive index has been extensively studied since the 60's. A particular case of self-focusing is the self-guided mode for which the natural tendency of a light beam to diffract is exactly compensated by the presence of a positive Kerr-law nonlinearity. A self-guided mode can also be seen as a mode of the waveguide it induces[1]. In this paper, we present a study of the HE1
m
self-guided modes of circular cross-section in an ideal (homogeneous, non-saturable and without absorption) Kerr-law nonlinear medium. Although scalar theory predicts, within its domain of validity, that these modes are unstable, our exact vectorial analysis shows that they are stable to cylindrical perturbations. This result. is in accordance with the recent work of Chen and Snyder who established the need of taking into account the polarization of self-guided cylindrical TE and TM modes[2].
Limitation for Transmission Capacity in Soliton - based Optical - fibre Communications due to Stimulated Brillouin Scattering
Authors: Montes Carlos , Rubenchik Alexander M.
Published: February 2023

For long-distance data communication based on coherent optical transmission in single-mode optical fibres, the use of soliton pulses as information carriers has raised a large interest since the NLS soliton concept (solution of the nonlinear Schrodinger equation) in dispersive optical fibres by Hasegawa and Tappert [1] and its first experimental verification by Mollenauer et al. [2]. High bit rate transmission capacity may be achieved by this technique if the minimum distance between solitons (5 to 10 times their width) avoids the interaction between them [3]. Recent experiments have demonstrated: (i) soliton transmission over more than 4000 km in a nonshifted-dispersion single-mode fibre (hereafter called n.d.-s.f.) in which losses are periodically compensated by Raman gain [4], and over 9000 km in a dispersion-shifted fibre [5] (hereafter called d.-s.f.); (ii) generation and transmission of high-bit rate optical solitons (up to a repetition rate fbit = 20 GHz) in dispersion-shifted fibres, losses being compensated by amplification in an Er3+ - doped fibre, using a color-center laser [6(a)], or a directly modulated distributed-feedback laser diode [6(b)].
Large Non-Resonant Nonlinearities in DANS Based Polymer Waveguides: Role of Microscopic Cascading
Authors: Assanto Gaetano , Stegeman George I. , Marques Manuel B. , Torruellas William E. , Horsthuis Winfried H.G. , Möhlmann Guus R. , Erdhuisen E.W.P.
Published: February 2023

Polymers can exhibit both large and fast nonresonant third-order nonlinearities which rely on π-electron delocalization and conjugation, as well as good physical and chemical properties suitable for the fabrication of nonlinear integrated optics devices. Soluble polymers with strong charge transfer states such asymmetrically substituted 4-dialkylamino-4′-nitro-stilbene (DANS) and 4-dialkylamino-4′-nitro-diphenylbu-tadiene (DAN2) side-groups were originally developed for electro-optic applications because of their large second order nonlinearities and low propagation losses in waveguide form.1 Using nonlinear grating coupling we found a large value for n2, the Kerr coefficient. Measurements and analysis of the spectral dispersion of third harmonic generation indicate that the dominant contribution to the nonlinearity is due to the local cascading of second order nonlinearities.2
Characteristics of Annealed Proton Exchanged Waveguides for Quasi-Phase-Matched Frequency Conversion in Periodically-Poled LiNbO3 Waveguides
Authors: Fejer M. M. , Bortz M. L. , Lim E. J.
Published: February 2023

Nonlinear frequency conversion in waveguides has been investigated since the first days of integrated optics, but practical applications were hampered by a lack of suitable pump lasers and the often inconvenient phase-matching characteristics of the available waveguides. Recent developments in high power (>100 mW) single-mode diode lasers and quasi-phase-matching techniques have led to renewed interest in waveguide frequency conversion. Periodic modulation of the optical properties of a nonlinear medium, quasi-phase-matching, is an attractive technique as it decouples phase-matching from birefringence and thus allows any interaction within the transparency range of the medium using any component of the nonlinear susceptibility tensor. The most efficient form of quasi-phase-matching involves periodic reversal of the sign of the nonlinear susceptibility (χ(2)) of the medium, with a period equal to an odd multiple of the coherence length of the interaction. In ferroelectrics, such a periodic sign reversal in χ(2) can be accomplished by periodic reversals in the orientation of the spontaneous polarization. Periodic incorporation of dopants has been found to induce domain reversal in several ferroelectrics, e.g. Ti or Li in LiNbO3, H in LiTaO3, and Rb and Ba in KTP, leading to rapid progress in device demonstrations in these material systems. [1–5] Several milliwatts of blue light generated by quasi-phase-matched (QPM) frequency doubling have been demonstrated in LiNbO3[3],[6], Ktp [4], and LiTaO3 waveguides [5], as has QPM difference frequency generation of 2.1 μm radiation in LiNbO3 waveguides. [7]
Flowing Afterglow Synthesis of Polythiophene Films
Authors: Haaland Peter , Targove James
Published: February 2023

Polymers of aromatic heterocycles such as thiophene and pyrrole have been actively investigated for their promising electrical and optical characteristics. However the use of these materials in waveguide structures has been constrained by morphological and synthetic barriers. Specifically, larger oligomers are less soluble causing multiphase chemical kinetics and irregular morphology in the metal-catalyzed coupling syntheses.fi] Electrochemical preparation methods also produce grainy or fibrillar material, most probably because the heterogeneous boundary conditions on film growth change as insulating or semi-conducting material is deposited on the electrodes. [2] We report here a synthetic approach to the polymeric heterocycle polythiophene using electronically excited argon metastables to activate organic precursors. This method is seen to produce dense, uniform films with desirable thiophene linkages and excellent optical properties.
Instabilities of a dispersive nonlinear all-fiber ring cavity
Authors: Vallée Réal , Piché Michel
Published: February 2023

Nonlinear optical cavities have been proposed for many applications such as bistability and optical switching. They have recently found an important application as the fast modulating element in coupled-cavity mode-locking. In this paper, we address the problem of the dynamical instabilities at the output of an all-fiber ring cavity synchronously pumped by a pulse train from a sync. pumped dye laser. Our analysis is based on a numerical simulation of the Nonlinear Schroedinger (NLS) equation and is primarily intended to explain recent experimental results1.
Doubly Nonlinear Fibre Loop Lasers
Authors: Langridge P. E. , Firth W. J.
Published: February 2023

Over the last decade, fibre-based devices incorporating single or multiple linear directional couplers have been the subject of theoretical and experimental investigation. These include fibre resonators [1-6] and linear [4] and nonlinear [7] loop mirrors. Except in [6] and [7], the devices involve linear propagation of a continuous wave (cw) or long pulse input. Only [7] studies operation with narrow pulses. Fibres have been incorporated in laser systems since the development of the soliton laser [8]. Recently, lasers with rare earth doped (neodymium [9] or erbium [10]) fibres as the active medium have been developed. All the above laser systems involve linear coupling to and from the fibre.
On The Mechanisms of Coherent Photovoltaic Effect for Second Harmonic Generation in Glass Fibers
Authors: Sokolov V.O. , Sulimov V.B.
Published: February 2023

Different models have been suggested for photoinduced second-harmnoic generation in silica fibers [1,2]. The model with charge carriers redistribution in the core of the fiber due to coherent photovoltaic effect was proposed in [3-15]. The coherent photovoltaic effect means that direct current appears in the glass under coherent pump and second-harmonic light waves. Theory of this effect was proposed in [16] but the expressions presented there are too complicated to get estimations of photocurrent and also the semiclassical method used there is not adequate to the phenomena. One of the possible mechanism of such effect was proposed in [4-8,11,13,15] but there is no consistent calculation of the photocurrent. So, the question on the microscopic mechanisms of coherent photovoltaic effect is still open.
Correlation of UV-radiation with the process of second harmonic generation in Ge-doped optical fibers
Authors: Baikabulov F.B. , Chernov P.V. , Isaev S.K. , Kornienko L.S. , Ribaltovsky A.O. , Yatsenko Yu.P.
Published: February 2023

To clarify the mechanism of second harmonic generation (SHG) in Ge-doped optical fibers, it is very important to know what leads to formation of permanent X(2) grating. Some of the reports [1-3] considered strong internal de fields to be the main reason for writing such gratings. In other papers [4-6] a lot of attention is paid to formation and orientation of color centers and permanent defects. In this great role can play UV-radiation due to simultaneous generation of the third or fourth harmonics.
Distributed out-coupling of second harmonic generation in a waveguide
Authors: Weissman Z. , Hardy A. , Marom E.
Published: February 2023

Frequency doubling of diode-laser light has been studied recently, to obtain compact short-wavelength coherent sources (e.g. green and blue) for various applications.1 In some materials, a strong optical nonlinearity is coupled with strong absorption and large dispersion, both of which prevent an efficient out-coupling of the SHG radiation. In many cases the harmonic absorption is strong, whereas the fundamental absorption is weak. This is typical to semiconductors in the vicinity of the band-gap, as well as to some organic materials, which strongly absorb in the green/blue region. In order to benefit from the large nonlinearity of these waveguide materials, it is essential to overcome absorption and dispersion. Whereas dispersion effects may be reduced by using various phase-matching techniques, absorption remains a problem. Here we propose a new way to reduce the effects of harmonic absorption in an SHG waveguide, as well as those of the dispersion.
Polarization induced switching and bistability in a nonlinear prism coupler
Authors: DANCKAERT Jan , VITRANT Guy , REINISCH. Raymond
Published: February 2023

Polarization may be an interesting parameter in optical computing devices1. Polarization induced irradiance switching was proposed as a new switching mechanism in nonlinear Fabry-Perot (NLFP) etalons under oblique incidence 2. In this context, the stationary response of Fabry-Perot etalons containing an anisotropic medium exhibiting a diffusive Kerr-type nonlinearity was investigated 3. Here, we will adress the question of the influence of polarization on the response of a nonlinear prism coupler (NLPC), where the waveguide shows a diffusive third order nonlinearity.
Directional Couplers with Varying Placement of Nonlinearity in Quaternary Semiconductors
Authors: Hussell C. P. , Srivastava R. , Ramaswamy R. V. , Bloemer M. , Ashley P.
Published: February 2023

The large optical nonlinearities exhibited by III-V multiple quantum well (MQW) materials1 have afforded some optimism in achieving large all-optical switching ratios with low threshold power and short device length. By using multiple quantum wells in the coupling as well as the guiding regions, Kam Wa et al. was the first to demonstrate partial switching between two parallel GaAs/AlGaAs MQW channel waveguides.2 This device, however, exhibited very high loss. Cada et al. argued that much better performance in terms of lower loss may be achieved by placing the MQW nonlinear medium in the coupling region only,3 but the experimental device still exhibited only partial switching.4 Several approaches to solve the problem of the nonlinear directional couplers in semiconductors have been proposed and since no general exact analytical treatment including absorption and nonlinear saturation is available, approximations or numerical simulation must be used. In this regard, Caglioti et al.5 presented a more complete analytical estimate for the characteristics of nonlinear directional couplers for operation above the resonance with large detuning.
Nonlinear switching characteristics of an ARROW-based Directional Coupler
Authors: Trutschel U. , Mann M. , Wächter C. , Lederer F. , Leine L.
Published: February 2023

ARROW'S (Antiresonant Reflecting Optical Waveguides) attracted a considerable interest within recent years [1]. Contrary to conventional waveguiding the underlying mechanism consists in phase - matched Fabry-Perot-action rather than total internal reflection. In this paper we show that the inclusion of the optical nonlinearity into an ARROW-based directional coupler scheme leads to novel all-optical switching characteristics.
All-Optical Switching in Optical Fibre Devices
Authors: Blow K.J.
Published: February 2023

A number of fibre based devices have been shown to be capable of performing all-optical switching. These include, polarisation discriminators [1], Mach-Zehnder interferometers [2], Sagnac interferometers [3] and coherent couplers [4]. The crucial feature common to these devices is the existence of two modes which can propagate independently in the linear regime. Polarisation based devices and couplers are described by a simple set of coupled equations which can either be in terms of the local modes (mode of a single core for the coupler, circular modes for polarisation) or the global (true) modes (symmetric and antisymmetric modes of the coupler, linear modes for polarisation). The latter choice exemplifies the connection with the interferometer based devices since the linear coupling operation is described in terms of the beating of the true modes in much the same way as the linear properties of the interferometer are described in terms of the beating between the fields in the two arms.
All Optical Gigabit Switching in a Nonlinear Loop Mirror using Semiconductor Lasers
Authors: Nelson B. P. , Blow K J , Constantine P D , Doran N J , Lucek J K , Marshall I W , Smith K
Published: February 2023

In a recent paper [1] we demonstrated an all-optical demultiplexer using a nonlinear optical loop mirror (NOLM) in which a signal at one wavelength is used to switch a signal at a different wavelength [2], [3]. The switching signal in that case was generated from a modelocked Nd-YAG laser at 1.32um operating at 76 MHz and the switched signal was a gain switched DFB laser operating at 1.56um at 1 GHz. The purpose of this present work is to extend the optical switching into the gigabit regime while, at the same time, avoiding high power laser systems.
Nonlinear Polarisation Effects in Self-Switching Nonlinear Fibre Loop Mirror Devices
Authors: Nayar B. K. , Finlayson N. , Doran N. J.
Published: February 2023

The nonlinear fibre loop mirror (NOLM) has been shown to be a versatile device for all-optical switching [1], ultrafast multiplexing/demultiplexing [2], logic applications [3], pulse shaping [4] and passive mode-locking for fibre lasers [5]. Initially, the NOLM devices were fabricated using polarisation-maintaining fibres due to concerns about polarisation stability. This can be particularly significant in self switching devices due to differential nonlinear polarisation rotation arising from the unequal powers in the counter-propagating signals. However, the use of polarisation-maintaining fibres is not attractive as coupler fabrication is difficult and a higher loss results when splicing to standard fibres. Recently, stable operation of a dual-wavelength NOLM ultrafast multiplexer/demultiplexer has been demonstrated using 6.4 km long standard telecommunication fibre [6]. In this paper we present experimental results on nonlinear polarisation effects in a self-switching NOLM fabricated from a standard telecommunication fibre.
Billiard Ball Soliton Interaction Gates
Authors: Islam M.N. , Soccolich C.E.
Published: February 2023

We demonstrate a temporal, conservative-logic interaction gate that can perform AND, inversion and routing functions. The billiard-ball like logic is based on elastic collisions between temporal solitons in optical fibers. Fredkin and Toffoli [1] introduced an interaction gate (Fig. 1a) as a universal, conservative-logic primitive and discussed a spatial implementation using the collision between billiard balls where the logic operation corresponds to the locus of the balls (Fig. 1b). The fundamental interest in the interaction gate results from the reversibility of the operation; i.e. the input values can be reconstructed from the output states. However, conservative, reversible gates may have limited practical value since generally they do not have logic level restoration (such as in digital gates) and they may not have gain or fan-out.
All-optical routing switch with tolerance to timing jitter at 2.5 Gb/s
Authors: French P. M. W. , Gabriel M. C. , Avramopoulos H. , Di Giovanni D. J. , LaMarche R. E. , Presby H. M. , Whitaker N. A.
Published: February 2023

All-optical demultiplexing and routing are necessary for the implementation of ultra-high bit rate time-division multiplexed communications systems. While existing electro-optic demultiplexers can be operated at extremely high speeds with sinusoidal drive signals [1], there is much interest in developing systems which can switch out arbitrary patterns of pulses from a data stream. If the pulses can be completely switched out, these systems could be used in signal routing applications. The wide bandwidth of all-optical devices based on the nonlinear Kerr effect in fibers should support this mode of switching at Gb/s rates and beyond. This experiment is a demonstration of such an arbitrary, all-optical demultiplexer/router which does not require a special pulse format (e.g. solitons), which is tolerant of environmental changes and which is insensitive to timing errors between the signal and control pulses. The approach used is not wavelength- dependent and can be made insensitive to the input polarization states.
Ultrafast, Dual-Path Optical Kerr Demultiplxer Utilizing a Polarization Rotating Mirror
Authors: Morioka T. , Takara H. , Saruwatari M.
Published: February 2023

All-optical signal processing attracts much attention to overcome the speed limitations imposed by the electrical circuits. An all-optical switching scheme using intensity-dependent refractive index in Kerr media, especially optical fibers, is one of the promising candidates for processing incoming densely time-multiplexed signals, namely optical demultiplexing, optical routing, and logic operations. To date, many excellent works on polarization switching[1], Mach-Zehnder[2] or Sagnac interferometer switching[3],[4],[5] have been presented for realizing the above functions.
Soliton Self-Trapping of Light Beams
Authors: BARTHELEMY A. , de la FUENTE R. , FROEHLY C. , GUY O. , SHALABY M. , REYNAUD F.
Published: February 2023

"Spatial Solitons" are monochromatic patterns exhibiting stable self-trapping above their self-focusing threshold. Self-trapping stability requires the two-dimensionality of the propagating fields. We describe the generation and properties of such beams in two and three dimensions.
Spatial dark solitons
Authors: Swartzlander G. A. , Andersen D. R. , Kaplan A. E.
Published: February 2023

Dark solitons [1] have provoked much interest [2-7] since they were first shown to be particular solutions of the two-dimensional (1+1)-D nonlinear Schrödinger equation (NSE) with a negative (self-defocusing type) nonlinear coefficient n2 (see Eq. (1) below). So far, only (1+1)-D temporal dark solitons (i.e. intensity minimums propagating along a nonlinear fiber on a quasi-cw bright background) have been observed experimentally [4-7]. Here we report the first observations [8] of stable spatial structures (e. g., stripes, crosses and grids) in the transverse cross-section of a cw optical beam propagating in a material with a self-defocusing nonlinearity, with these structures having a strongly pronounced soliton nature — namely that of spatial dark solitons (SDS's). Although no (2+1)-D analytical solution for dark solitons in the NSE is known to date, our experimental and numerical data with various 2-D amplitude and phase masks provide strong evidence that the phenomenon observed by us is indeed due to spatial dark solitons. Furthermore, our results here on quasi-(1+1)-D propagation (see also [8,9]) have shown excellent agreement with the well known analytical results for (1+1)-D dark solitons [1]. In comparison to temporal dark solitons SDS's are easy to create and observe experimentally, requiring as little as a HeNe laser and some slightly absorbing fluid. Most recently, one of the authors (D.R.A.) with his coworkers have observed SDS's in pulse radiation in ZnSe crystals [10]. Various applications of SDS's can be envisioned, such as optical encoding, limiting, switching and computing, and nonlinear filtering.
Spatial Solitons: Mutual Interactions and Magneto-Optic Surfaces
Authors: Boardman A.D. , Xie K.
Published: February 2023

There has been a lot of recent activity on spatial solitons1-10, including some very interesting work on soliton interactions™. The latter work relies entirely upon the linear theory of rays in a graded index medium. This is a valuable viewpoint but since spatial solitons are solutions of the nonlinear Schrödinger equation (NLSE) they appear to lend themselves particularly well to a particle-like description. Indeed, quite a number of authors2-7 have adopted this fairly useful analogy with classical mechanics. It is an approach, however, that embodies a strong simplification arising from the use of the parabolic form of the Schrödinger equation. Namely, a paraxial approximation. The implication for the particle/ray approach is that, for a given direction, only a narrow cone of rays around it lie within the approximation zone. This is exactly what is required to consider the strong interaction case. If the chosen direction axis is along a real interface, for example, then only angles close to grazing instance can be permitted. This feature of the theory was anticipated a long time ago in a now famous paper by Kaplan11.
Transverse Solitary Waves: Observation and Computation
Authors: Khitrova G. , Grantham J.W. , Jiajin Xu , Gibbs H.M. , Valley J.F.
Published: February 2023

We present here a spatial instability, free from longitudinal feedback, in which a beam propagating in one direction in a self-focusing medium breaks up into more and more filaments as the input power is increased.1 These cell-exit patterns (solitary waves) are stable and highly reproducible, showing that they are seeded by fixed phase variations across the input profile and not by random fluctuations. The physics of the formation of the solitary waves is the competition between self-focusing and diffraction leading to the eigenmodes of propagation, i.e., to the solitary-wave solutions of nonlinear Schrödinger-type equations. Our cell-exit spatial patterns are stable, even though they may jitter a little, and are highly reproducible as the input power is scanned up and down. By including the small inherent fixed-phase variations, we reproduced the experimental patterns and bifurcation routes. Consequently, even larger aberrations were intentionally introduced. The instability nature of this phenomenon is emphasized by the slowness (on the order of one second) with which the reproducible pattern is regained after the beam is momentarily interrupted.
Spatial Solitons in Planar Waveguides
Authors: Sammut R.A. , Pask C. , Li Q.Y.
Published: February 2023

Recent papers2. We explore the nature and accuracy of this assumption beginning with the stable, isolated soliton and returning at the end to the general propagation problem.
Spatial Solitons in Planar Waveguides
Authors: Aitchison J. S.
Published: February 2023

The use of self-trapped optical beams to perform signal processing and logic functions has been the subject of an increasing amount of research over the course of the last few years. Spatial solitons, which arise from the competition between diffraction and self-focusing, have the ability to interact with each other, with nonlinear interfaces and to guide light of a different wavelength. There are two general classes of spatial soliton, namely: bright and dark, in the following discussion both types will be considered.