bluuebunny/crossref_metadata_2025 huggingface dataset:
Interconversion of Optical Solitons
Authors: Vanin E. V. , Sergeev A. M. , Lisak M. , Quiroga-Teixeiro M. , Anderson D.
Published: February 2023

One of the fundamental areas of laser physics, which for a long time has attracted a strong interest, is the interaction of ultra-short laser pulses with nonlinear active media. Recently, this interest has been stimulated by the fast progress in the development of techniques for generation of femtosecond laser pulses [1]. An important theoretical question in connection with this application is the discovery of solitary wave pulse structures and the concomitant analysis of their stability. A number of physical parameters, possibly obtaining in the experiment, caused a different points of view on this problem. In ref.[2] the Ginzburg-Landau equation was considered to describe additive pulse mode-locking structures and the stability of stationary pulses was investigated. This equation is the generalization of the nonlinear Shrödinger (NLS) and describes laser pulse propagation in an active medium with group velocity (GVD), gain dispersion, Kerr nonlinearity of the refractive index, and intensity dependent losses. Another extended version of the NLS equation was considered in ref.[3,4]. This equation describes a medium with broad band gain, GVD, Kerr nonlinearity, and nonlinear saturable amplification. A new dissipative optical soliton was discovered in ref.[4]. The dissipative optical solitons have a stationary intensity profile and a permanently shifting frequency, because their existence is made possible by a balance between GVD and nonlinear saturable gain. Moreover, these solitons can become trapped at the zero-dispersion point due to the self-frequency shift, if this point where the maximum of the group velocity is reached is located inside the gain band [5]. Obviously, both effects can be considered together and new solitary wave structures having the features of both additive pulse mode-locking structures and dissipative optical solitons can be obtained. However before doing this it is useful to investigate the influence of another factors on the dissipative optical solitons.
High Bit-rate Soliton Transmission through Distributed Amplifiers
Authors: Rottwitt K. , Varming P. , Lester C. , Povlsen J. H. , Elgin J.
Published: February 2023

The behaviour of a periodically amplified soliton is well described as a stable soliton multiplied on a fast varying function (typically the decay and amplification of the signal), provided that the period ZA of the fast varying function is much shorter than the soliton period Z0 [1,2]. The stability criterion ZA/Z0<<1 is difficult to sustain in high bit-rate systems, where Z0 becomes very small (few km). Both numerically and experimentally, violation of this criterion is reported to result in instability [1,3].
Soliton Logic Gate Using Low-Birefringent Fiber in a Nonlinear Optical Loop Mirror (Low-Bi-NOLM)
Authors: Vaziri M. , Williams G. R. , Islam M.N. , Hill K. O. , Malo B.
Published: February 2023

Using computer simulations, we design a new all-optical logic gate that is a hybrid between soliton dragging logic gates (SDLG) and nonlinear optical loop mirrors (NOLM). We find that the advantages of blending SDLG’s and NOLM's are lower switching energy (as low as 5.3 pj) and a timing window whose width is the sum from the two mechanisms (3.3 pulse width wide). The novel element of our design is a polarization maintaining (PM), low-birefringent (low-bi) fiber that is made by carefully wrapping a low-bi fiber on a cylindrical mandrel. The use of low-bi fibers increases the interaction length between the input pulses by two orders of magnitude compared to the case of standard PM fibers.
Second Order Nonlinearity in Corona-Poled Corning 7059 Glass Film Waveguides
Authors: Horinouchi S. , Imai H. , Zhang G.J. , Fukao K. , Kinoshita T. , Mito K. , Sasaki K.
Published: February 2023

To date much study has been carried out to investigate the origin of the second order nonlinearity in silica-based glass fibers, bulk glasses, and glass films. Glass materials have a lot of advantages such as transparency, low loss, ready availability, and low cost. If the mechanism of the origin is made clear, the glass film waveguide will prepare potential devices for frequency doubling, or electro-optic modulation and switching. In this paper an experiment of the phase matched blue second harmonic generation was done and a phenomenological model responsible for the induced second order nonlinearity in the glass films is proposed.
Enhanced Nonlinearity in Rb-exchanged KTiOPO4 Waveguides
Authors: Laurell F , Åhlfeldt H.
Published: February 2023

Blue sources based on quasi-phasematched (QPM) second harmonic generation (SHG) of diode laser radiation in waveguides are presently developed. The segmented KTiOPO4 (KTP) waveguide [1] is an attractive waveguide choice for which very high conversion efficiency numbers have been reported for SHG to blue light around 425 nm. Eger et al. have obtained normalized efficiencies of ηnorm= 800%W-1cm-2 [2] and Bierlein et al. [3] have occasionally seen SHG signals corresponding to normalized efficiencies higher than 1000%W-1cm-2.
290-Femtosecond Optical Pulse Generation using Gain-Switched Laser Diode with Nonlinear Optical Loop Mirror
Authors: Ohta Hiroshi , Oki Tokukoh
Published: February 2023

Recently, subpicosecond optical pulses from laser diodes (LDs) have been necessary for ultrahigh-speed transmission, optical and electrooptical sampling systems, spectroscopy, etc. The most studied method to generate such pulses is the erbium-doped fiber laser.[1] However, with this method it is difficult for some applications to change the repetition rate of the pulses. Another common method under study is the gain switching scheme which has the advantage of controllability of repetition rate, but the disadvantage of a pulse width of several ten-picoseconds or more. While compression schemes for gain switching pulses using linear compression fibers and soliton compression fibers have been successfully proposed, the generated pulse is not always transform limited, and has pedestals.[2]
Amplification and Compression of a Weak Pulse through Stimulated Raman Scattering and Cross-Phase Modulation in Optical Fibers
Authors: de Souza R. F. , Fonseca E. J. S. , Gouveia-Neto A. S. , Hickmann J. Miguel
Published: February 2023

It has been proposed the use of Raman gain and cross-phase modulation in order to amplify and simultaneously compress an weak signal pulse by copropagating it in the anomalous dispersion region of an optical fiber with an intense pump pulse in the normal dispersion region [1]. In this work we show for the first time experimental results of this technique, supported by numerical simulations.
Asymmetric Twin-section Semiconductor Laser Structures for Broad-band Phase Conjugation
Authors: Yee W.M. , Shore K.A.
Published: February 2023

Multiwave mixing in above-threshold semiconductor laser structures can be utilised to generate phase conjugate signals in both reflection and transmission modes. The present paper demonstrates that asymmetric twin-section laser diodes can be configured to yield enhanced broad band phase conjugation. The phase conjugate reflectivities of the structures may be used to narrow the linewidth of laser diodes. Their phase conjugate transmission properties may be exploited for four-wave mixing cancellation in multichannel optical fibre systems.
Simulation of 10000 km Transmission with 20 Gb/s Signals Using Cancellation of Dispersion-Induced Kerr Effect
Authors: Shirasaki M.
Published: February 2023

Since optical fiber amplifiers were developed, the fiber loss does not limit the transmission distance. But there are two effects, the chromatic dispersion and Kerr nonlinearity of the fiber, which limit the distance and the bit-rate of the transmission. In order to avoid these effects and transmit a lightwave over a longer distance, one may use optical solitons in a fiber1 or convert the lightwave into the phase conjugate wave in the transmission line2. These methods, however, require precise adjustments of the transmission parameters.
Solitons with oscillating tails - can they be used as information carriers in optical communication lines?
Authors: Akhmediev N. N. , Buryak A. V. , Karlsson M.
Published: February 2023

Picosecond pulse propagation in optical fibers is well-known to be governed by the nonlinear Schrödinger equation (NLSE)[1,2]. This equation models the effects of group-velocity dispersion (GVD) and nonlinearity. As a result of the balance between them, a special class of pulses (solitons) can propagate in optical fibers without changing their form[3]. Optical solitons are therefore expected to be suitable information carriers in optical communication systems.
An Integrated Saturable Absorber Employing Spatial Solitons.
Authors: Aitchison J.S. , Villeneuve A. , Kang J.U. , Wigley P.G. , Stegeman G.I.
Published: February 2023

Semiconductors and in particular AlGaAs, have proved to be optimum nonlinear materials when operated below the half band gap. Large phase shifts have been observed, with a minimal nonlinear absorption. The large nonlinear refractive index found in AlGaAs can also be used to observe spatial solitons, at lower power levels that have previously been employed in CS2 and glass waveguides[1,2]. AlGaAs is thus an ideal candidate for the study and implementation of devices which utilise spatial solitons[3]. Here we report on a device which employs spatial solitons for all-optical switching[4].
Ultrafast all-optical switching in semiconductor waveguides
Authors: Ironside C. N. , Aitchison J. S , Stegeman G. I. , Villeneuve A. , Sibbett W.
Published: February 2023

This paper reviews recent progress in ultrafast all-optical switching in semiconductor waveguides. Nonresonant third order optical nonlinearity is employed at photon energies just below half the band-gap energy of the semiconductor to effect ultrafast all-optical switching. Pulses as short as 150 fs have been switched without significant multiphoton absorption or pulse break up. A new resonant optical nonlinearity is reported which depends on optically induced switching of a resonant tunneling diode; the timescale of the effect is currently being investigated.
Localization and beam steering with spatial solitons in inhomogeneous arrays of nonlinear waveguides
Authors: Peschel T. , Muschall R. , Lederer F.
Published: February 2023

In the present paper we describe the evolution of spatial solitary waves in an inhomogeneous array of nonlinear waveguides. Such a configuration can be implemented, e.g., by an appropriate arrangement of strip waveguides on a GaxAl1-xAs wafer. This material exhibits a positive Kerr nonlinearity if we choose the frequency of operation below half its bandgap. We have depicted a scheme of the system considered in fig. 1: By means of a variational approach we obtain a set of equations for the evolution of the characteristic parameters of the spatial solitary wave under consideration. Since we avoid any continuum-approximation our results represent the best possible fit to the real solution that is achievable with the trial function used.
Two Dimensional Spatial Solitons with Second-Order Nonlinearities
Authors: Torner Lluis , Menyuk Curtis R. , Torruellas William E. , Stegeman George I.
Published: February 2023

In addition to harmonic generation and frequency-mixing, intense light beams propagating in χ(2) nonlinear media exhibit a variety of self- and cross-phase modulation effects which until recently were commonly thought to occur only in χ(3) interactions. One important example is the propagation of soliton-like waves, in which the fundamental and second-harmonic waves mutually focus and trap each other. The (1+1) trapping (i.e. one transverse dimension and one propagation dimension) yields both spatial and temporal solitons that can in principle occur in planar waveguides and fibers, respectively [1]-[2] Although spatial solitons appear to be easier to obtain experimentally than temporal solitons, their excitation still requires nearly phase-matched propagation in high quality planar waveguides. In this paper we report our investigations on the propagation of Gaussian beams in bulk χ(2) media [3]. Contrarily to the conventional self focusing case in bulk Kerr like media, we show that stable 2D-soliton like propagation is possible, in the paraxial, in phase matchable materials with a quadratic nonlinear response. Under a variety of currently available experimental conditions, in the presence of finite mismatch and linear walk-off between the fundamental and second harmonic waves, we predict the experimental observation of such new physical processes.
Parametric Amplification and Squeezing in Quasi-Phase-Matched Waveguides
Authors: Anderson Matthew E. , Beck M. , Raymer M.G. , Bierlein J.D.
Published: February 2023

Nonlinear optical waveguides hold promise as parametric amplifiers and as sources of quadrature-squeezed light. The confinement of the pump field drastically increases the efficiency of the nonlinear conversion. In addition, the control of the spatial mode profiles by the waveguide geometry should diminish the effect of gain-induced diffraction, which has been seen to limit the amount of attainable squeezing in bulk parametric crystals.1 Using subpicosecond laser pulses, we have observed parametric gain as well as quadrature squeezing in a quasi-phase matched KTP waveguide.
Chemical Patterning Technique for Periodic Poling of KTP Waveguides
Authors: Risk W. P. , Lau S. D.
Published: February 2023

Periodically-poled waveguides have become important for nonlinear frequency conversion because of the advantages inherent in quasi-phasematching and in the guided-wave nature of the interaction.1 A variety of techniques have been used to produce periodically-poled waveguides; one that has received particular attention is electric field poling, in which an electric field large enough to invert ferroelectric domains is applied to a periodic electrode.2,3 This approach to domain inversion suffers from difficulties inherent in controlling the width of the inverted domain, which is necessary in order to optimize the second harmonic output power.
Mixed-Mode Spatial Solitons in Semiconductor Waveguides with Cubic Anisotropy
Authors: Ostrovskaya E. A. , Akhmediev N. N. , Stegeman G. I. , Kang J. U. , Aitchison J. S.
Published: February 2023

In birefringent optical fibers, linearly-polarized solitons associated with the fast mode become unstable at a certain power level [1,2]. A similar instability exists in planar waveguides made from isotropic materials [3]. It has been shown for the first time in [4,5], that the physical reason for this instability in isotropic materials is the appearance of new elliptically-polarized solitons above a certain critical power. In this work we prove that new solitons also exist in media with cubic anisotropy. Moreover, we have found that in planar waveguides made from cubic crystals, the symmetry allows the existence of two pairs of families of mixed-mode spatial solitons above the instability thresholds for TE and TM-modes. These replace the single pair of the isotropic media case. In these mixed-mode solitons, both TE and TM components are nonzero, with the phase difference between them being 0, π (the pair of linearly-polarized solitons) or ±π/2 (the pair of elliptically-polarized solitons). They propagate without change in the state of polarization and exhibit no polarization rotation. One pair of new soliton states bifurcates from the TM-mode while the other pair bifurcates from the TE mode at a different value of the initial beam power. It is important to note that our present investigation reveals the stability of one pair of families of the mixed-mode solitons at any value of power above the critical one, in contrast to elliptically-polarized solitons in isotropic media, which are always unstable.
Modelling of Parametric Amplification in the Cerenkov-Idler Configuration in Planar Waveguides
Authors: Thyagarajan K. , Rastogi Vipul , Shenoy M. R. , Ostrowsky D. B. , De Micheli M. , Baldi P.
Published: February 2023

The need for tunable optical sources operating over a wide wavelength range has attracted considerable attention to the study of optical parametric amplifiers and oscillators. In contrast to bulk, integrated optical waveguides can provide parametric amplification with moderate powers due to confinement of the optical energy in a small cross-section, over long interaction lengths [1]. Parametric fluorescence and oscillation in LiNbO3 waveguides with crystal temperature above 200°C and pump wavelengths in the visible region was demonstrated many years ago [2,3]. Recently, using first order quasi-phase-matching (QPM) scheme, parametric fluorescence at ambient temperature using the largest nonlinear coefficient d33 in LiNbO3 channel waveguides has been observed, with a cw Ti:Sapphire laser as the pump [4]. Parametric amplification and oscillation have also been observed in such waveguides using a Q-switched Ti:Sapphire laser pump [5].
Improved performance of polarisation switching (SAND) devices
Authors: Gontijo I. , Walker A. C. , Kennedy G. T. , Sibbett A. W.
Published: February 2023

Dichroism - polarisation dependent absorption - can form the basis of a single-wavelength photonic switch in anisotropic materials such as CdS crystal platelets[1] or InGaAs quantum wells.[2] Whereas fibre-based switching devices rely on non-resonant nonlinearities in glasses and, consequently, require high irradiance-length products, Semiconductor All-optical Nonlinear Dichroic (SAND) devices need only be a few hundred micrometres long and can be operated with picosecond pulses of about 1 pJ.[2] To distinguish the control pulse from the signal pulse, the control is polarised so as to maximise its absorption and hence cause the maximum excitation of the semiconductor. The change in refractive index induced by the photogenerated free electron-hole pairs is sensed by the signal, which is polarised so as to minimise absorption losses. A switched signal can become a control pulse simply by rotating its polarisation and consequently the SAND devices are directly cascadable. When operating such a device the control acts as a pump pulse and the signal being switched is a probe pulse. These are the terms used in the remainder of this paper.
Stabilization of Soliton Wavelength-Division-Multiplexed Transmissions
Authors: Kodama Yuji , Matera Francesco , Wabnitz Stefan
Published: February 2023

In this work, we consider the bandwidth limitations in soliton wavelength-division-multiplexed (WDM) transmission systems [1, 2]. The present analysis suggests different methods to overcome two of the main sources of instability that limit the available optical bandwidth, namely third-order dispersion (TOD) and resonant soliton-soliton collisions [6, 4, 5]. In refs.([2, 4, 5]), this last limitation was removed by tapering the group-velocity-dispersion (GVD) of the fiber according to the periodic energy loss in-between amplifiers.
Bright and Dark Solitary Waves near Linear Material Resonances
Authors: Peschel U. , Peschel T. , Lederer F.
Published: February 2023

Temporal optical solitons may exist in media where the dispersion-induced chirp is balanced by nonlinear self-phase modulation due to the Kerr effect. Usually, the parabolic approximation is employed for the frequency dependence of the wave vector (dispersion relation) resulting in the nonlinear Schrödinger for the field envelope. The propagation of temporal solitons in optical fibers can be reasonably described by this provided that the mean frequency is not too close to the zero-dispersion point. But, if the parabolic approximation fails higher-order terms of the expansion must be taken into account [1, 2] or the dispersion relation of the material must be approximated in a different way. Here we choose the latter option.
Plethora of soliton-like pulses in passively mode-locked fiber lasers
Authors: Akhmediev N. N. , Soto-Crespo J.M.
Published: February 2023

There is a great interest in soliton generation in actively and passively mode-locked fiber lasers [1, 2, 3, 4]. The mode-locked soliton fiber lasers can generate pulses with a wide range of durations, pulse powers, and repetition rates. Theoretical studies of the soliton fiber lasers are based on the complex Ginzburg-Landau (CGLE). Different forms of this have been used, including the cubic GLE [5], cubic CGLE with saturation [6, 7], quintic CGLE [8, 9, 10, 11, 12], and more complicated models. All these models (except the cubic CGLE without saturation) have solutions in the form of stable pulses. In this study we have found two new forms of pulse-like solutions which have been missed in previous works. In particular, we discover that besides the well-known solution in the form of bell-shaped pulse (plain pulse), and two other forms found in [13], the quintic CGLE has two additional branches of stable stationary solutions in the form of wide composite pulses with a dual-frequency spectrum. These two solutions can co-exist with known pulses but exist for a narrower range of value of the parameters.
Optimal use of the Raman effect for transmission of narrow solitons through sliding-frequency filters
Authors: Malomed Boris A. , Tasgal Richard S.
Published: February 2023

Sliding-frequency filters (SFFs) are currently the most standard and proven means of suppressing the degrading effect of the Gordon-Haus jitter on data transmission in soliton-based optical communication systems. In the current state of technology, solitons are usually broad enough (10-20 ps) so that the Raman effect is insignificant; but for shorter solitons (which can support a greater bit-rate), the Raman effect, scaling as (width)-4, more strongly than the non-Raman effects, becomes significant. The Raman effect shifts (downward) a soliton’s frequency, one of the SFF’s essential tasks. We therefore conjecture that if the SFF’s frequency ramp and the Raman frequency-sliding rate are properly matched, the frequency-sliding of narrow solitons can be generated by the Raman effect, and the SFF, liberated from its task of generating the solitons’ frequency-sliding, may be chosen to minimize unnecessary SFF-associated losses, minimizing the (detrimental) compensatory gain and degradation of the signal.
Modulation instability in a nonlinear dispersive fiber cavity including stimulated Raman scattering
Authors: García-Mateos Jorge , Canal Fernando , Haelterman Marc
Published: February 2023

Modulational instability (MI) involves the growth of initially weak sidebands at the expense of a continuous wave. The existence of MI in the anomalous group-velocity dispersion regime of an optical fiber is well known [1]. Modulation instability in a synchronously pumped fiber loop was recently predicted even in the normal dispersion regime [2] and has been proposed as the mechanism to generate pulses in the modulational instability laser [2,3]. On the other hand, modulation instability in cavityless propagation has been used as seed for later Raman ultrashort pulse generation [4]. In the present work, we analyze the role played by stimulated Raman scattering in the modulational instability dynamics of a synchronously driven fiber cavity. Starting from this study, we propose applications of our device as a low threshold Raman amplifier and as a modulation instability Raman laser.
Modulational Instabilities in Fibres with Periodic Dispersion
Authors: Smith N.J. , Doran N.J.
Published: February 2023

It is widely recognised that nonlinear optical phenomena are of crucial importance when understanding the operation of long haul optical communication systems[1]. The Kerr effect (power dependent refractive index) leads to the exchange of energy between the different frequencies present in the fibre, a process known as four wave mixing. These interactions may be between the different channels of a wavelength-division-multiplexed (WDM) system, between the different frequency components of a single channel, or between a signal and a.s.e. noise introduced by optical amplifiers.
Ion-implanted photorefractive waveguides
Authors: Fluck D. , Brülisauer S. , Günter P. , Beckers L. , Buchal Ch.
Published: February 2023

The fabrication of photorefractive (PR) waveguides is particularly desirable because it provides compatibility with other miniaturised waveguide devices in common use today, in particular with optical fibres and laser diodes. Additionally, the use of guided wave structures in PR media has the inherent advantage of optical confinement and its consequent reduction in response times. For planar waveguides of typical thickness of 1-10 μm, this reduction is approximately two orders of magnitude.
Subpicosecond pulse propagation in dye doped polymer slab waveguide
Authors: Yamakawa Shiro , Yamashita Hiroki , Kinoshita Takeshi , Sasaki Keisuke
Published: February 2023

Beam propagation analysis in a nonlinear planer waveguide have been a subject of intense investigation in recent years[1-4]. In a Kerr type material with a two-dimensional structure, stable spatial soliton was observed under the balance between diffraction and self-focusing due to field-induced nonlinear index increase [5].
Two-Photon Absorption in Hydrogen–Loaded Optical Fibers
Authors: Mizunami Toru , Hashimoto Masato , Yamashiro Mamoru , Gupta Sanjay , Shimomura Teruo
Published: February 2023

It is well known that hydrogen loading1 drastically enhances the photosensitivity of germanosilicate glass. Hydrogen loading has made it possible to write strongly reflective gratings even into standard telecommunication fibers. However, the mechanism is not yet clearly known. On the other hand, photosensitive absorption band (~240 nm) of germanosilicate fiber can be excited by two-photon absorption (TPA) of blue-green light. It has been known that Hill gratings2 are formed by TPA of 488 (514) nm Ar-laser light. TPA in the blue-green region has been studied by index change, induced loss, and electron-spin resonance. However, effects of hydrogen loading on TPA have not been reported. Such studies are expected to contribute to clarify the mechanisms of hydrogen loading, and possibility of enhancement of photosensitivity in the blue-green region. Although one-photon absorption in hydrogen-loaded germanosilicate glass has been measured, the TPA obeys a different selection rule. Hence, TPA should not be determined by an analogy with one-photon absorption and therefore should be determined by direct measurement.
Wavefront Reconstruction via Backward Stimulated Raman Scattering in a Multimode Graded-Index (GI) Optical Fiber
Authors: Islam Naved R. , Sakuda Kyohei
Published: February 2023

Wavefront reconstruction (WFR) in stimulated scattering was discovered by Zeldovich et al. in 1972 [1]. WFR is attributed to the intensity cross correlation among incident and backward scattered light beams in each transverse cross section of the interaction region, both in the case of stimulated Brillouin scattering (SBS) [1] and stimulated Raman scattering (SRS) [2]. The phenomenon of reconstruction of the wavefront of a light beam during SRS had also been detected experimentally by Kudryavtseva et al. [3] and Sokolovskaya et al. [4]. Till now, all the experimental investigations related to WFR via backward stimulated Raman scattering (BSRS), have been done using multimode waveguides, where the presence of a large number of modes in the transverse interaction region, results in effective WFR via stimulated scattering.
All-Optical Switching in Integrated Directional Couplers and Mach Zehnder Interferometers with Cascading
Authors: Schiek R. , Baek Y. , Krijnen G. , Stegeman G. I.
Published: February 2023

The second-order nonlinear interaction between a fundamental light wave and its second harmonic causes energy transfer between the interacting waves (second harmonic generation (SHG)) and modifies their phases nonlinearly (cascaded nonlinearity) [1]. This implies that all-optical switching can be implemented on the basis of cascading in phase-sensitive waveguide structures [2].
Solitary Waves and Ring-Formation in Polydiacetylene para-Toluene Sulfonate
Authors: Lawrence Brian L. , Torruellas William E. , Stegeman George I.
Published: February 2023

Spatial solitary waves propagate in a nonlinear medium by balancing diffraction with a self-focusing nonlinearity. These waves are of fundamental interest, but are also of technological interest if they are stable under propagation. For diffraction in one transverse dimension (ID) a Kerr nonlinearity is sufficient to form stable beams.[1] However, a Kerr nonlinearity does not lead to stable self-trapping in two transverse dimensions (2D).[2] Methods proposed for stabilizing 2D beams have included saturating mechanisms and quintic nonlinearities. [3,4] Until recently, self-trapped beams had only been observed in vapor systems.[5] Current progress in cascaded second-order nonlinear systems has also demonstrated self-trapped beams, which tend to mimic a saturating nonlinearity. [6] However, our recent measurements indicated that polydiacetylene para-toluene sulfonate (PTS) has n2>0 and n3<0 with low linear loss and negligible nonlinear loss at 1600 nm.[7] We now report preliminary experimental demonstrations of 2D spatial solitary waves and ring formation in PTS. The results are supported by numerical simulations of beam propagation in PTS, using measured values for n2 and n3, interpreted in the context of the variational model of nonlinear Gaussian beam propagation. These results confirm, for the first time, the existence of the combination of a third-order and a fifth-order nonlinearity, independent of saturation, in a solid-state material, and the ability of this material to support stable self-trapped beams.
Nonlinear phase shift and all-optical switching in quasi-phase-matched quadratic media
Authors: Kobyakov Andrey , Lederer Falk , Bang Ole , Kivshar Yuri S.
Published: February 2023

Parametric wave mixing in quadratic (or χ(2)) nonlinear materials has attracted a growing attention because of its perspectives for all-optical switching devices [1]. Many of the theoretically predicted effects, such as large nonlinear phase-shifts and dichromatic spatial solitons (mutually trapped fundamental and second harmonic beams), have already been observed experimentally in bulk crystals and slab waveguides [1]. Switching devices based on the non linear phase shift in quadratic materials such as integrated Mach-Zehnder interferometers and directional couplers have also been experimentally demonstrated [2]. However, most of the switching effects require a small wave vector mismatch between fundamental wave (FW) and second harmonic (SH). Quasi-phase matching (QPM) is a promising technique, since it allows, at least potentially, to achieve phase-matching in any material over a wide range of wavelengths [3]. As a consequence the largest component of the second-order susceptibility tensor can be used, allowing for a decrease in operating power. The idea of QPM is to periodically modulate the χ(2) coefficient where the pertinent grating vector can compensate the mismatch. Although the physics of QPM has been known since 1962 [4] technological difficulties have been overcome only recently and stable QPM structures have been developed [5].
Measurement of the non-uniformity of the wave-vector mismatch in waveguides for second-harmonic generation
Authors: Schiek R. , Fang H. , Treviño-Palacios C. G. , Stegeman G. I.
Published: February 2023

For maximum second-harmonic generation (SHG) in a non-linear crystal
the wave-vector mismatch along the interaction length should be
uniform. However, in some applications a non-uniform wave vector
mismatch along the propagation distance improves the performance. For
example, in quasi-phasematched (QPM) waveguides with variably-spaced
phase-reversed QPM gratings the acceptance bandwidth for SHG was
increased. Recently, intensity-dependent phase shifts of the
fundamental due to the cascaded second-order nonlinearity in SHG were
observed. Due to a non-uniform wave-vector mismatch large fundamental
phase shifts were measured in regions of negligible fundamental
depletion with low wavelength and temperature depencence. Here, we
report on measurements of the non-uniformity of the wave-vector in
waveguides for SHG.
Mixing of a laser beam and a spectrum of light in a birefringent optical fiber
Authors: Chiang Kin Seng , Lor Kar Pong , Chow Yuk Tak
Published: February 2023

Four-wave mixing (FWM) in optical fibers has been widely investigated as a technique of realizing wavelength tunable light sources,1–3 and, at the same time, as a source of noise that must be eliminated in wavelength-division-multiplexed transmission systems.4–6 FWM has also been demonstrated as a means of measuring fiber properties, such as the third-order nonlinearity in a fiber,7 the intermodal dispersion in a two-mode fiber,8 and the refractive-index profile of a graded-index fiber.9 Recently, we observed a new FWM process in a birefringent fiber, where a distinct frequency-shifted beam was produced as a result of mixing a laser beam with a spectrum of superfluorescent light.10 In this paper, we outline a theory to explain why this process is possible, and present experimental results to compare with the theory.
All-optical regenerative memory with full read/write capability
Authors: Poustie A. J. , Kelly A. E. , Blow K. J. , Manning R. J.
Published: February 2023

The function of ‘memory’ is one of the key building blocks to implement advanced information processing in future ultrahigh-speed photonic networks. Previously, we have described an all-optical regenerative memory in which stable storage of data is obtained for several hours [1]. In addition, the memory architecture provides amplitude restoration for the stored pulses and the ability to set a threshold storage level [2]. Here we demonstrate an important extension to this design which not only allows optical pulses to be written to the memory but also permits optical pulses to be selectively read from storage. This additional capability greatly extends the usefulness of the memory as a sub-system in more complex processing operations [3]. To achieve the ‘read’ function we incorporate a third nonlinear optical switching element (TOAD/SLALOM [4,5]) to act as an all-optical modulator for the data stored in the regenerative memory.
Three channel directional coupler with an optically induced grating
Authors: Weinert-Rączka Ewa
Published: February 2023

Directional couplers are important elements of the integrated optics systems. The efficient power exchange between waveguides in the directional coupler occurs when the propagation constants of their guided modes are equal. The coupling between different waveguides can be obtained with the help of a grating formed by periodic changes of the refractive index along the coupler [1-5]. The grating constant K=2π/Λ (where Λ is the length of the grating period) should be equal to the difference between waveguides modes propagation constants (K=βA−βB). The gratings in the traditional grating-assisted-couplers (GAC) are usually formed during the fabrication processes and have constant, immutable parameters, what limits the operation of the coupler to one, strictly defined frequency. An optically induced grating proposed in [6] was formed by the interference of two counter-propagating external beams in a nonlinear layer separating two slab waveguides. Parameters of such grating depend on the external waves properties and can be varied during the work of the device. In particular the grating constant can be tuned to the guided modes propagation constants difference by changing the external waves frequencies or propagation directions.
Bright and dark discrete solitons in waveguide arrays with quadratic nonlinearity
Authors: Lederer F. , Darmanyan S. , Kobyakov A.
Published: February 2023

Now it is widely accepted that nonlinear optical waveguide arrays (NOWAs) exhibit interesting phenomena which can be exploited in all-optical signal processing. Many investigations were devoted to NOWAs with cubic nonlinearities. The existence of self-localized states where only the amplitude in a few waveguides differs considerably from that of the background have been demonstrated and their properties were systematically analyzed (see e.g. [1,2] and refs, therein). Another aspect in contemporary nonlinear optics is connected with quadratic or χ(2) - nonlinearities which are believed to possess a genuine potential in all-optical device concepts [3,4]. However, the most studies in that field dealt with continuum rather than discrete media.
Existence and stability of dark solitary waves in the presence of third-harmonic generation
Authors: Sammut Rowland A. , Buryak Alexander V. , Kivshar Yuri S.
Published: February 2023

We show that parametric coupling between the fundamental and third-harmonic frequencies in Kerr media may lead to either modulational instability or other instability mechanisms for dark spatial solitary waves.
Optical Bullet-Holes
Authors: Firth William J.
Published: February 2023

Spontaneous spatial structures have recently been predicted and observed in many nonlinear optical systems [1]. Among such structures are localised bright spots in driven optical cavities [2, 3, 4, 5, 6, 7]. They share certain properties with spatial solitons, and are thus to some extent counter-parts of the soliton pulses being developed as bits for long-haul fibre-optic communications. Cavity spatial solitons could be natural bits for parallel processing of optical information, especially if they exist in semiconductor micro-resonators. Recent work [5, 6] is quite encouraging in that respect.
Optical Bloch oscillations and solitons in nonlinear arrays with linearly varying wave number
Authors: Peschel U. , Pertsch T. , Lederer F.
Published: February 2023

It is well appreciated that arrays of coupled optical waveguides exhibit a similar dynamic as classical discrete systems, for example a chain of interacting molecules, but on an accessible spatial scale. However, besides such fundamental aspects very practical issues as e.g. the optimization of semiconductor laser arrays have moved into the focus of interest. It is known that in waveguide arrays effects can be re-established that are familiar from planar waveguides as the formation of spatial solitons. But owing to discreteness they show various features that are completely unknown in continuous optical systems. Here we report on an optical analog to the so-called Bloch oscillations of the electric current in semiconductor superlattices with an applied DC voltage [1,2,3]. The corresponding optical system reveals peculiarities of the transition from a quasi-continuos to a discrete model.
Dispersion-Managed Soliton Systems
Authors: Carter Gary M. , Jacob John M.
Published: February 2023

Dispersion-managed solitons arise from the nonlinear propagation of pulses along a periodic dispersion map with alternating signs of dispersion. The path-averaged dispersion is anomalous to balance the optical nonlinearity, as is the case for standard solitons. However, when the local dispersion within the map significantly broadens the pulse, the dispersion-managed soliton (DMS) has characteristics that differ from a standard soliton. In single channel experiments, these characteristics have permitted error-free transmission at 10 Gbit/s × 24,500 km [1], 20 Gbit/s × 14,000 km [2], and 40 Gbit/s × 5,000 km [3] without the use of active retiming or sliding frequency filter techniques.
Dispersion management in optical fiber links: a differential equation for the eigenmode(s)
Authors: Paré C. , Bélanger P.-A.
Published: February 2023

In some respects, the periodic nature of dispersion-managed optical communication systems bears a close analogy with the problem of optical resonators. Requiring that the pulse shape of a stationary solution reproduce itself at every period of the dispersion map (Fig. 1) is reminiscent of the self-consistent analysis of the modes of an optical cavity. A question that comes naturally to mind, then, is the following: is it possible that dispersion managed systems support higher-order "modes" (or quasi-higher-order modes) ? In this paper, we present numerical evidence of a positive answer to that question. We propose a simplified analysis leading to quantitative predictions suported by numerical simulations of dispersion-managed systems.
Dispersion-managed solitons with average normal dispersion
Authors: Evangelides Stephen G. , Kutz J. Nathan
Published: February 2023

As a result of their excellent performance characteristics, dispersion-managed communications systems have become increasingly important in recent years. Consequently, a growing research effort has focused on understanding the nonlinear dynamics observed in experiment1,2 and numerical simulation3-7. In particular, many studies have been made of so-called dispersion managed solitons: RZ signals propagating in periodic dispersion maps. These investigations have focused on dispersion maps with a path-average dispersion in the anomalous regime where solitons are expected based on perturbative theories. Using the variational approach, we show that over a small range near the mean-zero dispersion point, there exist stable periodically fluctuating soliton like pulses for dispersion maps with a normal average dispersion. This work confirms recent observations by Nijhof et al8 and explains the mechanism which allows the propagation of these pulses.
Dispersion management in optical fiber links: self-consistent solution for the RMS pulse parameters
Authors: Bélanger P.-A. , Paré C.
Published: February 2023

It is now widely recognized that the so-called technique of dispersion management represents a major headway for both NRZ and soliton communication systems (for a recent review, see [1,2]). Thanks to a low average dispersion, the Gordon-Haus timing jitter, deleterious to soliton systems, can be minimized and the observed enhancement of the pulse's energy implies a better signal-to-noise ratio, hence improving the bit-error rate at the reception. The main predictions of numerical simulations having been confirmed experimentally [3,4], it now seems natural to look for simple design tools in order to optimize future dispersion-managed soliton communication links.
Soliton propagation in the vicinity of a two-photon resonance
Authors: de Oliveira J. M. , Cavalcanti Solange B. , Hickmann J. Miguel
Published: February 2023

We investigate the effects of frequency dispersion of the nonlinear susceptibility associated to the two-photon resonance, obtaining the necessary conditions for a solitary wave solution, even in the presence of a self-steepening term.
Robust solitary waves in fiber transmission lines with semiconductor optical amplifiers
Authors: Gölles M. , Uzunov I. M. , Lederer F.
Published: February 2023

Owing to their robustness solitons are attractive as basic units of information in long- and medium-haul optical transmission lines. This robustness prevents the soliton from being destroyed by various perturbations occurring in practical fiber networks. The European network is peculiar because it consists almost entirely of standard fibers with a high dispersion at the preferred communication wavelength of 1550 nm. Thus the large peak power required and the short dispersion length do not permit an increase of the bit rate beyond 2.5 Gbit/s. Recently two options for upgrading the network are in the focus of interest, viz. dispersion management in the soliton regime and the operation of the network near the zero dispersion point at λ≈1300 nm. With regard to signal transmission at λ≈1300 nm semiconductor optical amplifiers (SOA) are mostly used for periodic signal amplification. In contrast to erbium-doped fiber amplifiers SOAs introduce an own nonlinear dynamics into the line. Thus, even in the case where attenuation is neglected the resulting evolution equation does not admit soliton solutions. However it is worthwhile to look for solitary wave solutions because they may represent some stable attractors in parameter space. Thus it might be expected that one can save, at least to some extend, the robustness familiar from solitons. The aim of this contribution is to identify such solitary waves in a fiber line with losses and bandwidth-limited saturated amplification.
Observation of temporal solitons in second-harmonic generation with tilted pulses
Authors: Di Trapani P. , Caironi D. , Valiulis G. , Dubietis A. , Danielius R. , Piskarskas A.
Published: February 2023

By eliminating the group-velocity mismatch and enhancing the group-velocity dispersion via pulse-front tilting, we obtained the formation of temporal solitary waves in phase-mismatched second-harmonic generation.
Soliton Gas: Bright and Dark
Authors: Mitschke F. , Schwache A.
Published: February 2023

It is well known that the propagation of light pulses in optical fiber under conditions of anomalous dispersion leads to the formation of bright solitons. In this contribution we report on an experiment in which not a single soliton but rather a whole ensemble of solitons is created. The experiment is straightforward: A train of picosecond pulses from a modelocked laser is launched into a piece of fiber. The fiber forms a ring resonator; its round trip time is adjusted to be synchronous with the repetition time of the laser pulses. Thus there is interference between both contributions to the fiber input light on every round trip. In combination with pulse shaping in the fiber due to dispersion and Kerr nonlinearity, femtosecond substructure in the picosecond pulses is created. This substructure, for the case of anomalous dispersion, has been identified as an ensemble of bright solitons [1]. Mutual interaction leads to constant relative motion of all solitons in the ensemble so that the impression of a gas of particles is created (hence the name ‘soliton gas’ [1]), but under certain conditions (low drive power), the solitons also form a regular array [2]. The soliton gas is a unique test bed for the study of soliton interactions.
Improving the performance of reference-frame-independent quantum key distribution with advantage distillation technology
Authors: Jiang Xiao-Lei , Wang Yang , Li Jia-Ji , Lu Yi-Fei , Hao Chen-Peng , Zhou Chun , Bao Wan-Su
Published: February 2023

The reference-frame-independent quantum key distribution (RFI-QKD) has the advantage of tolerating reference frames that slowly vary. It can generate secure keys between two remote users with slowly drifted and unknown reference frames. However, the drift of reference frames may inevitably compromise the performance of QKD systems. In the paper, we employ the advantage distillation technology (ADT) to the RFI-QKD and the RFI measurement-device-independent QKD (RFI MDI-QKD), and we then analyze the effect of ADT on the performance of decoy-state RFI-QKD and RFI MDI-QKD in both asymptotic and nonasymptotic cases. The simulation results show that ADT can significantly improve the maximum transmission distance and the maximum tolerable background error rate. Furthermore, the performance of RFI-QKD and RFI MDI-QKD in terms of the secret key rate and maximum transmission distance are still greatly improved when statistical fluctuations are taken into account. Our work combines the merits of the ADT and RFI-QKD protocols, which further enhances the robustness and practicability of QKD systems.