bluuebunny/crossref_metadata_2025 huggingface dataset:
High-Speed Internet, Financial Technology, and Banking
Authors: D’Andrea Angelo , Limodio Nicola
Published: February 2023

Exploiting the staggered arrival of fiber-optic submarine cables, we show that high-speed internet promotes the role of banks and credit in Africa. Variation within country and across multicountry bank networks indicates that high-speed internet induced a 22% expansion in credit supply. We investigate the role of plummeting telecommunication costs in promoting the bank adoption of new financial technologies and study a specific technology used in the interbank market, the real-time gross settlement system (RTGS). We find that upon connecting to high-speed internet, banks adopt the RTGS more extensively, reduce inside liquidity, and increase interbank transactions and lending. We also observe that high-speed internet particularly strengthens firms in countries with weak preexisting interbank markets.

This paper was accepted by David Sraer, finance.

Funding: This work was supported by a Private Enterprise Development in Low Income Countries (PEDL) of the Centre for Economic Policy Research (CEPR) grant and Università Bocconi.

Supplemental Material: The data files and online appendix are available at https://doi.org/10.1287/mnsc.2023.4703 .
Silver Service
Authors: Martin Jennie , Stone Tom , Dyson Lauren
Published: February 2023

ITS (UK)’s well-known and highly accomplished secretary general Jennie Martin is to retire at the end of 2022 after nearly 25 years in the job. TTi editor Tom Stone caught up with her to talk about how transportation has changed over that time, and to discuss what is coming next in the industry in which she’ll still play an active role
Design of services or designing for service? The application of design methodology in public service settings
Authors: Strokosch Kirsty , Osborne Stephen P.
Published: February 2023

Over the past decade, there has been growing interest in the theory and practice of design in the public sector. Service design aims to improve the experience of public services through a human-centred, iterative and collaborative process of creativity and problem solving. However, there is a lack of empirical research on the application of design approaches in public service settings. This article aims to fill that gap, drawing on service research and empirical illustrations to explore what is being designed, how service design is practised, and the implications of service design. By applying ‘design of services’ and ‘designing for service’ perspectives, the focus of design is discussed, along with its implications for design practice and impact. While the analysis suggests an important shift in the practice of design with a focus on services, it proposes that applying design for service may further the potential of design and support deeper transformation. In this way, the article makes a significant contribution to scholarship on policy design, as well as public service delivery.
Making ‘shiny’ or avoiding ‘sticky’: a cross-cultural comparison of household bathroom cleaning practices
Authors: Isboli Gabriel Henrique Pimenta , Middlemiss Lucie , Coutinho Pépece Olga Maria
Published: February 2023

This article examines how people’s life course and cultural backgrounds impact their consumption practices, particularly in the use, disposal and treatment of water in bathroom cleaning. We explore this through 12 oral histories from Brazilian and English residents, including locals, migrants and cross-national couples. Our findings provide an account of cleaning routines in two cultural contexts, offering insights for those addressing sustainability, consumer behaviour and water governance. Our research suggests that culture, upbringing, expectations of cleanliness, and social and material contexts all shape how people clean bathrooms, and when contexts change, material elements become particularly influential.
Methodological perspectives in Brazilian critical criminology: foundational guidelines and the mapping of its sources
Authors: de Carvalho Salo
Published: February 2023

This research, part of a broader exploration of the sources of current Brazilian critical criminology, aims to map the canonical works in the field, especially the publications and research of the 1970s, in order to identify theoretical guidelines, methodological perspectives, and to which extent there is an alignment with the debate of the Global North. This exploration seeks to identify (a) the theoretical perspectives, (b) the empirical emphasis, (c) how gender and race issues were faced, and (d) whether the boundaries between criminology and criminal law were delimited in the general framework of criminal sciences. The conclusion presents a synthesis of the foundational methodological guidelines and the present state of critical criminology in Brazil.
Soliton Generation through Raman Amplification of Modulational Instability and Sub-Fundamental Soliton Power Pulses
Authors: Gouveia-Neto A. S. , Patrick D. M. , Wigley P. G. J. , Taylor J. R.
Published: February 2023

It was first shown by Hasegawa and Brinkman [1] that as a result of the combined effects of anomalous dispersion and the non-linear optical Kerr effect, amplitude and phase modulations on a c.w. wave in a single mode fibre show an exponential growth rate, with the evolution of sidebands to the central pump frequency, at a frequency separation which is proportional to the optical pump signal. The conditions necessary for the observation of this modulational instability are similar to those required for the generation of envelope solitons in optical fibres. In the time domain, modulational instability manifests itself as an intensity modulational of the c.w. pump signal. "Long" picosecond pulses can be used to observe the effect since, for typical operational parameters, the frequency of the induced modulation is ~1012 Hz and consequently pulses of the order of 100ps effectively appear c.w.
Some fabrication constraints on nonlinear integrated optics components
Authors: Jackel Janet Lehr
Published: February 2023

It is widely recognized that the optical confinement provided by waveguides allows efficient use of optical nonlinearities. With high optical power densities maintained over macroscopic distances by a waveguide, optical nonlinear effects can be seen in materials with smaller nonlinearities and/or using lower optical power than would be possible in bulk material. Waveguide devices have the additional advantage of being compatible with optical fibers, and so may find a place in communications networks.
Second harmonic generation of blue and green light in periodically-poled planar lithium niobate waveguides
Authors: Lim E. J. , Fejer M. M. , Byer R. L.
Published: February 2023

Periodically-poled, planar waveguides in lithium niobate were used to generate 532 nm and 424 nm radiation at room temperature by continuous-wave frequency-doubling with conversion efficiencies of 2.4 − 5% per W-cm2. Quasiphasematching allowed generation of the second harmonic using the d33 nonlinear coefficient.
Two-Photon Absorption as a Limitation to All-Optical Switching Demonstrated in Lead Glass Fiber
Authors: Mizrahi Victor , DeLong K. W. , Stegeman G. I. , Saifi M. A. , Andrejco M. J.
Published: February 2023

In recent years considerable research has gone into the study of all-optical switching devices in waveguides, where the requirements for a material with a large n2 (nonlinear refractive index) may be relaxed by taking advantage of relatively high power densities and long interaction lengths.1 This is particularly true of glass which, while having a relatively small n2, can be conveniently drawn into optical fibers. Already a number of all-optical switching schemes have been demonstrated in silica fibers.2,3 One possibility to reduce switching powers is to use lead glasses,4 which are known to have an n2 an order of magnitude higher than fused silica. We show here that two-photon absorption (TPA) can place a fundamental restriction on such an approach.
Soliton Frequency Shift in Fiber Nonlinear Loop Mirror
Authors: Islam M.N. , Sunderman E.R. , Stolen R.H. , Pleibel W. , Simpson J.R.
Published: February 2023

We observe complete switching of 310fsec soliton pulses in a fiber nonlinear optical loop mirror (NOLM) but find that the transmission is reduced by the soliton self-frequency shift (SSFS) effect. To show that solitons make possible more complete switching, Doran and Wood 1] first proposed the NOLM, which consists of a four-port directional coupler in which two ports on one side are connected by a loop of fiber. The device acts like a Mach-Zehnder interferometer whose two arms correspond to the two counter-propagating directions around the loop.
Linear Dispersion Assisted Amplification, Multimode Instability, and Chaos in Counterpropagating Waves in Nonlinear Fibers
Authors: Law C. T. , Kaplan A. E.
Published: February 2023

Waves with the same frequency counterpropagating in a Kerr-nonlinear fiber (the so-called degenerated four-wave mixing) for the spatially stable eigenarrangement [1] can exhibit temporal instability if the nonlinearity has a finite relaxation time [2]. Here we demonstrate that another fundamental physical parameter, linear dispersion, in combination with third-order nonlinearity can result in temporal instability.
Numerical Modelling of Integrated Optics Doubly Resonant Parametric Oscillators
Authors: Bava G.P. , Montrosset I. , Pelissero R.
Published: February 2023

This paper deals with the numerical analysis of integrated optics doubly resonant parametric oscillators in Ti:LiNbO3 waveguides. In particular the attention has been devoted to the evaluation of output spectrum, power conversion efficiency, etc. in static conditions and varying the device operation parameters such as input pump power and frequency.
Constraints on the Design of Long-Haul Soliton Systems
Authors: Wright J V , Carter S F
Published: February 2023

Erbium doped fibre amplifiers now allow the possibility of deploying optically transparent systems over trans-oceanic and trans-continental distances. However it is now well established that fibre non-linearities cannot be ignored in such systems. For example, when a single channel system is operated in the anomalous dispersion régime, ie. with λ > λ0 where λ0 is the wavelength of zero chromatic dispersion, self phase modulation (SPM) may lead to pulse compression or pulse break up. When operated with λ < λ0, SPM leads to increased dispersion and pulse broadening. A choice may be made to avoid the non-linearities as far as possible; for example by minimising the amplifier spacing, by using the minimum optical power consistent with the required electrical signal-to-noise ratio (SNR) and by careful choice of the operating wavelength with respect to λ0. Alternatively, one may choose to use actively the fibre non-linearity to design a soliton based system operating in the anomalous dispersion régime. This paper attempts to consider some of the design constraints for such a system. In particular it considers a system operating at 5Gbit/s over a total distance L
sys
of 6000km.
Qualitative Dynamics of Modulated Soliton Pulse Trains
Authors: Arnold J. M.
Published: February 2023

The recent advances in the technology of passive optical amplification have brought closer the realisation of optical fibre communication systems using soliton pulses which are not limited by dispersion. This in turn creates a new generation of theoretical problems concerned with the evolution of information-bearing pulse trains along a nonlinear channel. Previously, these theoretical models have been constructed primarily on the basis of the behaviour of isolated 1 - or 2-soliton phenomena, as deduced by perturbation theory carried out on the Inverse Scattering Theory (IST) for the exactly-integrable Nonlinear Schrodinger Equation (NLSE) [1-4] or by direct numerical solution of the NLSE [5,6]. However, there are many circumstances in which the behaviour of a small number of isolated solitons may not properly represent the behaviour of a very long pulse train with neighbouring pulses coupled by a weak nonlinear intersoliton interaction; for example, two isolated solitons in the repulsive phase of the intersoliton interaction will diverge apart indefinitely, but this cannot happen when those two pulses form part of a long train of pulses, since the diverging pulses must eventually meet and interact with other pulses in the same train. Although the IST method is extremely useful for predicting the evolution of initial conditions consisting of a small number of solitons in the absence of an IST continuum, the presence of a large number of solitons or IST continuum in the initial conditions renders the method intractable. Even the simplest case of an infinitely long pulse train of periodically repeated identical solitons involves much more difficult analytical techniques than the conventional IST method and the true physical case of a modulated pulse train containing an infinite number of solitons is not tractable by any known analytical method, despite preserving the integrability of the NLSE.
Ultra long nonlinear fiber optics data transmission using dual-frequency laser sources.
Authors: Mamyshev P.V. , Chernikov S.V. , Prokhorov A.M.
Published: February 2023

In previous papers [1-3] we have shown that it is possible to generate high-repetition-rate (GHz-THz) trains of uninteracting solitons from a dual-frequency signal by using a weak amplification of the signal in fibers. The length of the fiber necessary for the soliton train generation grows quadratically with increase of the generated solitons pulse width. The fiber length varies from 10-300 m for the soliton pulsewidth of about 100 fsec to thousands of km for the case of relatively long (about 50 psec) solitons [3]. At the present state of fiber optics technology there are reasons that relatively long solitons are required for ultra long distance transmission [4.5]. But the discussed method requires too long fibers for generation of such solitons.
A negative contribution to n2 in silica fibers
Authors: Stolen R. H. , Tomlinson W. J.
Published: February 2023

The Raman interaction contributes about 18% of the nonlinear refractive index of silica optical fibers. By numerical simulation we previously demonstrated that this Raman contribution to the nonlinear refractive index is substantially reduced when the optical pulse width is less than the molecular resonance period.[1] A surprising result of those simulations was that the Raman contribution to the nonlinear index was actually negative for pulse widths less than 30 fsec. Here we show that the negative contribution can be traced to the time delay inherent in the Raman response.
Spatial Soliton Propagation Through Periodically Modulated Layer in Nonlinear Medium
Authors: Abdullaev F.Kh. , Abdumalikov A.A.
Published: February 2023

Here we present, a theory which describes the propagation of self-focused channel (spatial solitons) in the media consisting from the twoself - focusing nonlinear media and the periodically-modulated thin linear film separating this media. Recently it was shown that propagation of spatial olitons at an oblique angle of incidence to an interface between nonlinear Kerr-like media may be represented as an equivalent particle moving in the effective potential[1].This theory predicts the nonlinear Snell’s law of reflection and existence of nonlinear surface waves. It is possible to use the design of an all-optical power spatial scanner and an all-optical switch [2]. Existence of periodically - modulated thin film also leads to the new possibilities for such designs.
Erbium Fibre Soliton Laser Pumped by a Laser Diode
Authors: Smith K. , Greer E.J. , Davey R. , Wyatt R. , Doran N.J.
Published: February 2023

We have recently reported on the generation of pulses as short as 1.2 ps from a mode-locked erbium fibre laser pumped by a frequency doubled Nd:YAG laser [1]. Experimental and theoretical evidence strongly supported the idea that soliton pulse shaping played a dominant role in the short pulse formation. In this paper, we review this earlier work and present preliminary data from a simple, compact totally integrated erbium fibre soliton laser pumped by a high-power laser diode.
Electrostrictional Interaction of Optical Pulses in Long Distance Soliton Communication Systems
Authors: Dianov E. M. , Luchnikov A. V. , Pilipetskii A. N. , Prokhorov A. M.
Published: February 2023

Mollenauer et al. have experimentally demonstrated the transmission of optical solitons in a single mode fiber over large distance up to 10000 km [1]. One of the limitations to the transmission rate in the soliton regime of propagation is an interaction between optical pulses. Besides the well studied short-range Kerr-like interaction, Smith and Mollenauer experimentally discovered the interaction of the two periodic trains of 55-ps solitons shifted in time on several dozens of soliton widths for propagation distance of 3000 km [2]. In [3,4] we suggested and developed the theory of a mechanism of long-range interaction of solitons - electrostrictional interaction. According to this theory an optical pulse excites an acoustic wave, propagating in transverse direction to the fiber axis. This leads to the temporal perturbation of the fiber effective refractive index. In consequence, the following optical pulses become phase-modulated and change their carrier frequency. That results in additional temporal shift of solitons. We have obtained a good quantitative agreement [4] with experimental results of [2] on interaction of two soliton pulse trains.
Nonlinearity Near Half-Gap in Bulk and Quantum Well GaAs/AlGaAs Waveguides
Authors: Islam M.N. , Soccolich C.E. , Slusher R.E. , Levi A. F. J. , Hobson W. S. , Young M.G.
Published: February 2023

We present measurements of the nonlinear index n2 and two-photon absorption coefficient β as well as time resolved pump-probe data for both bulk AlGaAs and GaAs/AlGaAs multiple quantum well waveguides near half-gap at 1.68 μm. The figure of merit (2n2/βλ) [1] for the bulk (MQW) material is 17 (1.6), which means that these semiconductors below half bandgap are appropriate for all-optical switching and quantum optics applications. The β value is up to 25 times larger in the MQW. This larger value may result from mid-gap states that act as a stepping stone in two-photon absorption (TPA). The mid-gap absorption should not be fundamental to MQW material provided that caution is exercised during the growth to avoid impurities and interface states. We confirm that n2 is instantaneous on the 300 fs time scale of our pulses from self-phase-modulation spectra as well as time-resolved pump-probe measurements. However, we find an intriguing exchange of energy between the two orthogonal axes with the signal along the probe axis following the negative derivative of the pump. This result may be explained by self-phase-modulation of the pump combined with a low frequency Raman gain between orthogonal axes.
Nonlinear Absorption Processes at Half the Band gap in GaAs Based Semiconductors
Authors: Villeneuve A. , Stegeman G.I. , Scelsi G. , Ironside C.N. , Aitchison J.S. , Boyd J.T.
Published: February 2023

The utility of the ultrafast nonlinearity in semiconductor waveguides operated below the band gap is limited by two photon absorption β (α = βI where I is the intensity) which does not allow a nonlinear 2π phase shift over one absorption length. [1] However, the two photon coefficient should be zero below half the band gap, potentially allowing for all-optical device operation there.[2,3] Here we report the first measurements of two photon absorption in GaAs waveguides in the vicinity of half the band gap.
Measurement of High Frequency Electro-Optic Coefficient in Ferroelectric Liquid Crystal Materials
Authors: Liu J.Y. , Robinson M.G. , Johnson K.M. , Doroski D.
Published: February 2023

Ferroelectric liquid crystals (FLC's) form the thermodynamically stable Smectic C* liquid crystalline phase that is non-centrosymmetric and has macroscopic polar order. The symmetry (C2) implies that FLC materials can exhibit second order nonlinear properties such as the linear electro-optic(EO) effect and second harmonic generation (SHG). In most FLC's designed for optical modulation applications these nonlinearities are small1,2, but in principle could be made, large by specifically synthesizing liquid crystal molecules which self-assemble in such a way that functional groups with large microscopic hyperpolarizabilities, β's, are oriented along the polar axis. By adopting this approach to produce second order nonlinear material, the problems associated with processing organic single crystals are avoided. Furthermore, the flexibility of the liquid crystal technology can be used to design materials with specific refractive indices for phase matching purposes and waveguide design. Waveguides in this material system are particularly interesting as they allow a significant increase in optical propagation length with high electric field generation capability; both important attributes for nonlinear optical phenomena. Preliminary work has already been carried out on waveguide structures whose possibilities are numerous owing to the ability to successfully align FLC's on many different substrates (including Si)3.
Photonic Bloch Waves and Field Microstructure in Nonlinear Gratings: An Intuitive Approach
Authors: Russell P.St.J.
Published: February 2023

Coupled wave theory is commonly used in numerical simulations of reflection from nonlinear grating structures. By contrast, the complementary photonic Bloch wave (PBW) approach has rarely been adopted, perhaps the only example being recent work on gap solitons1,2. Bloch wave theory3,4 offers an alternative physical intuitive picture that encourages one to think in terms of field microstructure, leading to a range of simple explanations for the behaviour of light in linear gratings. In this paper the dispersion relation and field microstructure of nonlinear Bloch waves are found, and used to clarify the physical mechanisms that lead to regions of bistability, instability and oscillation for incidence of a monochromatic plane wave on a nonlinear grating half-space.
Nonlinearity Enhancement in a Four Layer GaAs/GaAlAs Waveguide
Authors: Chen Shaomei , Liao Chaangjun , Jin Huaichen , Huang Zhaohong
Published: February 2023

The photorefractive effect in semiconductor materials is attractive for processing low intensity near-infrared optical signals which are important for optical communication and optical computing. Photoinduced large nonlinearity in GaAs materials has been extensively studied in bulk material. A few is desl with optical waveguide of GaAs materials though the signal amplification in GaAs waveguide eia two wavemixing has been proposed.
Fiber-Optical Element for Ultrashort Pulses Control and Switching
Authors: Khaidarov D.V.
Published: February 2023

Fiber-optical interferometers are outlook for ultrafast all - optical light control and switching. Here the fiber - optical loop is discussed as an element for fundamental soliton self-switching and for ultrashort pulses formation.
Theory of Photo-Induced Second-Harmonic Generation Caused by Phase Transition in Defects System in Silica Glass
Authors: Dianov E.M. , Sokolov V.O. , Sulimov V.B.
Published: February 2023

To describe inducing of non-zero macroscopic second-order susceptibility in a centro-symmetric media such as the glass we suppose that a pump wave excites electrons from certain "donor" states in the middle of the v-SiO2forbidden gap to defect states near the conduction band edge and the conformation of each defect changes significantly owing to pseudo-Jahn-Teller effect with a certain number of electrons placed in the proper state of the defect. Our cluster calculation performed by MNDO method proves the pseudo-effect to occur in Ge and Al atom substituted for the Si one and in =Ge-O-Ge= diatomic center with a certain defect state occupied by two electrons or by one election, respectively. The relaxed conformation of the defects is stable since their spontaneous decay is forbidden. We suppose that a phase transition occurs owing to cooperative pseudo-Jahn-Teller effect in the system of defects created in the glass by the pump wave, that it is described by a vector order parameter

η
→

and that it is caused by small relaxation of each of the defects with non-zero polarizability bω. Under these assumptions macroscopic second-order susceptibility is proved to be

χ

ijk

(
2
)

=

χ

(
2
)

(

η
i

δ

jk

+

η
j

δ

ik

+

η
k

δ

ij

)

where

χ

(
2
)

≡
n

b
ω

δ
R
/
R
,
 
 
 
 
δ
R
/
R

being mean relative atomic displacement in relaxed defect, n being defects concentration. Bloembergen's relations [1] are valid for

χ

ijk

(
2
)

since

χ

xxy

(
2
)

=

χ

xyx

(
2
)

=

χ

yxx

(
2
)

=

χ

(
2
)

′

η
y

,

χ

yyy

(
2
)

=
3

χ

(
2
)

η
y

. So the results of [2] are explained by our theory and therefore those do not prove the SH generation to be caused by strong electrostatic field induced in the glass by the pump wave, as supposed in [2]. Our computer simulation of the defects results in δR/R ~ 0.1. The defect polarizability may be estimated as bω~ (νd)3(ηω)-2with d being mean value of dipole matrix element in the defect, ν being number of the defect states. Since νd ~ le, one finds for wavelength ~ 1 μm: νd ~ 5·10-18CGS and bω~ 10-28CGS . Assuming the mene order parameter to be η ~ 0.1 one obtains χ(2)~ 10-30CGS ~ 10-12CGS for n ~ 1018cm-3in good agreement with experimental data (see review in [3]).
An Ultrafast Multibeatlength All-Optical Fibre Switch
Authors: Finlayson N. , Nayar B.K. , Doran N.J.
Published: February 2023

Considerable effort has been devoted to the development of all-optical switches in the last several years,1 with a view to using these switches in ultrafast telecommunications. In spite of having a very low nonlinear refractive index coefficient (n2 = 3 × 10−20 m2/W), fused silica fibre is probably the best material medium for such switches owing to its extremely low loss (~0.2 dB/km). A severe challenge in using fused silica fibre is designing devices that can take full advantage of the low loss property, since the device length needs to be maximised in order to minimise the switching power. The nonlinear optical loop mirror (NOLM) has proved to be very effective in this respect, and devices as long as 9km have been successfully tested by our group. The NOLM operates on the principle of nonlinear interference between counterpropagating modes of a single fibre. In this letter we report successful all-optical switching with a device which also allows long lengths of fibre to be utilised.
Application of Ultrafast Gates to a Soliton Ring Network
Authors: Soccolich C.E. , Islam M.N. , Hong B J. , Chbat M. , Sauer J.R.
Published: February 2023

We describe the application of ultrafast, all-optical logic gates to a soliton-based local or metropolitan area network. The slotted ring network discussed here serves a few hundred users and uses self routing packet switching with a 100 Gbps peak data rate and a 1.25 GHz packet rate. This is a "light-pipe" system where the data remains in optical format throughout the network, converting to electronics only at the host and destination nodes. The packet header (or address) is selected and decoded using recently demonstrated soliton dragging and trapping logic gates [1,2], which are long latency, ultrafast fiber devices that satisfy all cascadability and logic requirements for a digital optical processor. A ring network is one potential application of these logic devices that requires only a handful of gates per node.
Steering One Spatial Solitary Beam by Another
Authors: Snyder A.W. , Poladian L. , Mitchell D J
Published: February 2023

A beam of sufficient intensity can be made self guiding in a bulk medium1,2,3,4. It is intriguing to speculate that such solitary waves could be the building block for cellmate all optical devices and computing. Here we are concerned with directing one solitary wave by another. In particular, we show that two solitary waves, depending on various factors, can attract, repel, remain unchanged in their initial direction or spiral about each other in a double helical trajectory. Our discussion concerns both bright and dark solitary waves in Kerr and saturating material.
Mode Locking using the Half-Bandgap Nonlinearity in Passive AIGaAs Waveguides
Authors: Su Z. , Grant R. S. , Kennedy G. T. , Sibbett W. , Aitchison J. S.
Published: February 2023

Passive AlGaAs waveguides have been shown to be suitable for ultrafast all-optical switching when used at wavelengths in the vicinity of the half-bandgap (around 1.5-1.7 μm).1,2 Nonlinear phase shifts in excess of π radians have also been observed directly by monitoring self-phase modulation induced spectral broadening of pulses propagating through straight waveguides.3,4 These large phase shifts, caused by nonresonant nonlinear index changes, are possible due to the combination of low nonlinear absorption, coupled with a localised enhancement related to the two-photon band edge.5 In addition, semiconductor waveguides are, in general, polarisation preserving. Taken together, these attributes make passive AlGaAs waveguides attractive alternatives for optical fibres in coupled-cavity lasers operating at wavelengths around 1.5 μm. In this paper, we describe the application of passive AlGaAs waveguides as the nonlinear element in a coupled-cavity KCl:TI colour-centre laser to produce pulses of less than 170 fs in duration. The principal advantage of using semiconductor waveguides over silica-based optical fibres is their low power requirement which offers considerable potential for miniaturisation.
Low-Loss Ultrafast All-Optical Switching in a GaAlAs Integrated Interferometer at 1.55 μm Spectral Region without Multi-Photon Absorption
Authors: Al-hemyari K. , Aitchison J.S. , Ironside C.N. , Kennedy G.T. , Sibbett W.
Published: February 2023

Recent investigations into the origin of the nonresonant nonlinearity, n2, have shown that the magnitude of the effect has a resonance close to the two-photon absorption, TPA, edge [1]. Earlier experimental investigations into ultrafast all-optical switching in semiconductor waveguides have shown that the two-photon absorption TPA imposes severe limitations on the practical operation of a device [2]. Therefore, to avoid the TPA at optical communication wavelengths of around, λ =1.55 μm, semiconductors are selected with a half band-gap energy slightly above the optical communication spectral region. We have already demonstrated ultrafast all-optical switching in waveguide geometries at photon energies below half the band gap of Al0.18 Ga0.82As [3-5]. The previously published results have shown that the switching performance was hampered by the multi-photon absorption MPA effect, primarily the three photon absorption 3PA [4]. We have shown that the nonlinear absorption can be avoided by reducing the switching power which is achieved by employing a longer interaction length to obtain the required phase change for the NLDC to switch [6].
Novel Soliton States and Bifurcation Phenomena in Nonlinear Fibre Couplers
Authors: Akhmediev Nail , Ankiewicz Adrian
Published: February 2023

The study of nonlinear effects in optical couplers has expanded greatly since the pioneering works of Maier [1] and Jensen [2]. One of their possible applications is to all-optical switching [3,4] and logic functions [5]. Recent experiments [6] show that very high switching speeds, e.g. in the femtosecond range, are possible with this kind of device. Extensive theoretical and numerical investigation of soliton switching and propagation dynamics has been reported in a number of publications [7-11]. In all published works, it has been implicitly or explicitly supposed that soliton states consist of two solitons having sech-function shapes. In reality the shape of each component in a coupled soliton state can be quite different from the sech-function. This is particularly important in considering bifurcation phenomena.
Nonlinear Propagation of Partially Polarized Light in Optical Waveguides
Authors: Svirko Yu.P. , Zheludev N.I.
Published: February 2023

One of the main differences between natural light and coherent laser radiation is that natural light is polarized only partially, i.e. it contains a component whose polarization state changes randomly in a time domain, while coherent radiation has a fixed polarized state. Traditionally nonlinear optics deals with polarized light. However during the last few years it has been found that intense laser light with chaotic polarization behaviour may be generated via the non-linear interaction of two coherent polarized light waves in a nonlinear medium [1]. This opportunity to create intense unpolarized light raises the problem of developing nonlinear optics with unpolarized and partially polarized light. In linear optics it is known that unpolarized light may change its degree of polarization as the result of an interaction with an absorbing material, polaroid film, for example. In nonlinear optics the evolution of the degree of polarization is evidently more complicated. Here we intend to address this problem considering self-action phenomena. The approach developed below may be used for consideration of the light polarization stability in optical waveguides and for treatment of the optical communication lines using polarization codding of information.
Pulse Switching in Nonlinear Fiber Directional Couplers
Authors: Lederer F. , Uzunov I.
Published: February 2023

Since a decade a considerable deal of interest has centred on the investigation of nonlinear directional couplers (NLDC) as a basic scheme for all-optical information processing in waveguides. It has been shown that the location of the output signal depends critically on the intensity launched into one input channel or the phase difference between two input signals. Most analyses are concerned with the cw case. This model holds even for pulses provided that the pulse length exceeds considerably the relaxation time of the nonlinearity. Hence, each portion of the pulse will couple according to the cw switching characteristic that in turn depends on the instantaneous power. This leads to a pulse break-up in the course of propagation and limits the achievable nonlinear power transfer.
Lightwave System Implications of Optical Fiber Nonlinearities
Authors: Tkach R. W.
Published: February 2023

The loss in optical fibers can be compensated by optical amplifiers, and fiber chromatic dispersion can be avoided in dispersion-shifted fibers. The overthrow of these two limitations on system length and capacity brings the subject of fiber nonlinearity to the forefront. This presentation will examine the nonlinear processes that occur in fibers used for optical communications, and describe how they affect the performance and design of lightwave systems.
Stabilisation of a 10GHz Mode-locked Erbium Fibre Laser and Its Application in 4×10Gbit/s Soliton Transmission
Authors: Shan X. , Ellis A. D. , Widdowson T. , Wichens G. E. , Spirit D. M.
Published: February 2023

Stable picosecond optical pulse sources working at multigiga hertz repetition rates are highly desirable for applications in soliton communication systems. Mode-locked erbium fibre lasers can produce highly transform limited pulses, but unless synchronisation to specific data rates can be demonstrated, they are of little use in communications experiments. Different schemes to stabilize them have been proposed and realized [1,2,3,6]. One is to stabilise the cavity length and at the same time dither it at a kilohertz rate [1,6]. Another is to insert into the fibre cavity a high finesse etalon whose FSR is equal to the pulse repetition frequency to suppress unwanted supermodes in a harmonically mode-locked ring laser [2]. Yet another scheme is to use a polarisation maintaining ring cavity to avoid detrimental polarisation fluctuations [3]. Fibre lasers stabilised by these methods have been sucsessfully used in soliton transmission experiments [4,5,6]. In this paper, we report a 1 OGHz mode-locked erbium fibre laser, made of all commercial components, stabilized without use of an etalon and PM fibres, and its application in a 4x10Gbit/s soliton transmission experiment.
Measurement of the nonlinear refractive index dispersion of Erbium-doped Y2O3 waveguides
Authors: Offrein B.J. , Hoekstra T.H. , Lambeck P.V. , Hoekstra H.W.J.W.M. , Popma Th.J.A.
Published: February 2023

The intensity dependent refractive index and absorption coefficient are third order optically nonlinear effects which offer the possibility to realise all-optical switching devices. The refractive index change Δn due to the applied field E is expressed as Δn = n2 · |E|2. Important material parameters are the value and relaxation time of the nonlinear coefficient n2, the maximum achievable refractive index change Δnsat and the linear absorption α0 [1]. Rare earth-doped materials are well known for their use in optical amplification but may also be of importance for all-optical switching. By implantation of the rare earth atoms in a (poly)crystalline material it is possible to obtain sharp absorption peaks which are accompanied by a relatively broad dispersive change of the refractive index. This property may be used in a device where a pump beam tuned at the absorption peak changes the refractive index which influences the behaviour of a signal beam tuned just outside the absorption region. The n2 relaxation time of this type of materials is in the order of ms but can be drastically reduced by injection of a short turn off pulse [2]. The Δnsat scales proportional to the rear earth doping concentration and may be increased to about 10-4.
Soliton Dynamics in the Presence of Phase Modulators
Authors: Smith N.J. , Blow K.J. , Firth W.J. , Smith K.
Published: February 2023

There have been many recent demonstrations of soliton behaviour in actively and passively mode-locked erbium fibre lasers [1, 2]. The work described here investigates theoretically and numerically the behaviour of solitons in the presence of electro-optic phase modulators, the essential component in FM mode-locked laser cavities. The topic also has relevance to future soliton transmission systems in that electro-optic amplitude modulators have been shown to control the growth of timing jitter known as Gordon-Haus effect [3, 4]. Here the equivalent results for combined bandwidth filtering and phase modulation are presented.
Polarisation Maintaining Figure-8 Laser
Authors: Taverner D. , Richardson D.J. , Payne D.N.
Published: February 2023

Passively mode-locked, erbium-doped fibre lasers have received considerable recent attention because of their ability to generate ultrashort, transform-limited soliton pulses. Figure-8 [1,2], ring [31 and linear [41 cavity configurations have been developed based on nonlinear Sagnac and polarisation switches respectively. Pulse durations ranging from several picoseconds down effectively to the limit defined by the erbium bandwidth (~ 100 fs) have now been demonstrated directly at the output of such lasers [5,6]. However, questions concerning the practical application of such lasers remain, particularly the question of environmental stability.
Optical Bullet-holes in Semiconductors
Authors: Firth W. J. , Lord A. , Scroggie A. J. , Brambilla M. , Lugiato L. A. , Penco R. , Pregnolato R. , Spinelli L.
Published: February 2023

Stable, robust two-dimensional spatial solitons could act as “bits” for parallel information storage and processing. We present analytic and numerical evidence for the existence of stable 2D soliton-like states in optically driven semiconductor cavities. We consider both free-carrier and excitonic nonlinearity, and use parameters appropriate to VCSEL structures. In output these solitons would appear as transparent disks on an absorbing background, formed by aiming a short pulse of light at the target location: hence our term “optical bullet-holes” (OBH) [1]. We demonstrate a self-correcting 2D OBH array memory based on this concept.
Quantum Picture of Nonlinear Optical Patterns
Authors: Gatti A. , Lugiato L. A. , Marzoli I. , Oppo G. L. , Barnett S. M. , Wiedemann H.
Published: February 2023

The recent investigations on quantum effects in nonlinear optical patterns and spatial aspect of squeezing have focused on the concept of quantum image [1,2,3]. These are very noisy images images, dominated by quantum fluctuations and can be revealed either 1) by high frequency observation, which is able to reveal the fast dynamics of fluctuations, or 2) by low frequency observation, by measuring the spatial correlation function. This displays a regular modulation, which anticipates the stripe pattern that appear above threshold [4], while the intensity distribution is uniform on average.
Nonlinear Optical Microscopy for Imaging Thin Films and Surfaces
Authors: Smilowitz Laura , McBranch Duncan , Robinson Jeanne M.
Published: February 2023

In the electric dipole approximation, an intense laser beam incident on a centrosymmetric material will not generate any even ordered harmonics. In particular, there will be no second harmonic response generated by the bulk of the material. At the surface of a centrosymmetric medium, the inversion symmetry is broken, allowing for a second order response characterized by the second order nonlinear susceptibility, χ(2) 1. Thus, χ(2) has an inherent surface sensitivity which we utilize in order to image surfaces, interfaces, and thin films.
Optical Parametric Device for Efficient Generation of Radiation in the 3.9 Micrometer Range
Authors: Koch Karl , Moore Gerald T.
Published: February 2023

In this paper we describe a device for efficiently converting pump radiation, such as the λ
p
= 1.064 μm radiation from a Nd:YAG laser, to idler radiation at a desired wavelength λ
i
, using an optical parametric oscillator (OPO) which incorporates additional stages of three-wave mixing. In the conventional OPO each converted pump photon produces only one idler photon. We can extract a second idler photon by internally converting a signal photon of frequency ωs = ωp – ωi using difference-frequency mixing (DFM). We suppose that the OPO is singly resonant at ωs and insert a DFM crystal in the cavity after the OPO crystal. The DFM crystal is phase-matched for the process ωs – ωi → ωd. The DFM interaction also plays the role of an optical parametric amplifier (OPA) for the idler radiation. Thus, the ideal output of the OPO-DFM device consists of two photons of frequency ωi and one photon of frequency ωd per pump photon. If ωd > ωi, one or more additional idler photons can be extracted by successive DFM/OPA stages outside the cavity, the first such external conversion being pumped at ωd and generating a frequency ωd2 – ωd → ωi. For conversion of 1.064 μm radiation to 3.9 μm radiation one internal and one external DFM process are possible. The other wavelengths generated are λ
s
= 1.463 μm, λ
d
= 2.342 μm, and λ
d
2 = 5.861 μm. The OPO and internal DFM process can be carried out using two successive quasi-phasematched χ(2) gratings on a wafer of periodically poled LiNbO3 (PPLN). The external DFM process can be carried out using AgGaS2, with the ωd2 radiation polarized orthogonally to the other two waves.
Absolute Scale of the Second-Order Nonlinear Optical Coefficients
Authors: Shoji I. , Kitamoto A. , Shirane M. , Kondo T. , Ito R.
Published: February 2023

The second-order nonlinear optical coefficients are essential material parameters that determine the performance of nonlinear optical devices. Unfortunately, however, there have been considerable discrepancies among their absolute values reported to date [1]. This confusion, we believe, arises from the following factors. First, quite different values have been reported between parametric fluorescence (PF) and second-harmonic generation (SHG) measurements; e.g., d31(LiIO3) measured by PF method is 70 % larger than by SHG method [2. 3]. Second, wavelength scaling of nonlinear optical coefficients has been made based on the constancy of Miller’s Δ, although it has not been experimentally confirmed in what wavelength region and to what accuracy Miller’s Δ is constant. Moreover, the interference effect caused by multiple reflection effect in (nearly) plane-parallel samples has been overlooked in almost all the previous measurements, which can be the source of considerable error.
Dynamics of a fiber laser with two tone modulation
Authors: Newell T. , Kovanis V. , Gavrielides A. , Sukow D. , Emeux T.
Published: February 2023

In addition to their connection with communication networks, fiber lasers provide a rich system for the study of nonlinear dynamics. These lasers are slow in the sense that their relaxation oscillations range in the tens of kilohertz. As a result, we can study in the time domain fluctuations in the output intensity as changes occur in the pump laser. Under the influence of an oscillating pump beam, a neodymium fiber laser shows period doubling bifurcations, quasiperiodicity, chaos, coexisting attractors, and hysteresis [1-3].
Time-dependent optical nonlinearity in silica
Authors: Dajani I. , Mcgillen D. J. , White W. R.
Published: February 2023

We present a model for second-harmonic generation (SHG) in germanium-doped silica and provide results from some numerical simulations. Our simulations examine the temporal evolution of the SHG and do not account for the spatial saturation of SHG along the direction of propagation. In planar waveguides and bulk glass, the effect of the generated second harmonic (SH) wave is negligible as the SHG conversion efficiency is diffraction limited [1]. Certainly in fibers, the generated SH wave plays a part in dictating the saturation of SHG. Nevertheless, even in the case of fibers, our temporal simulations are able to shed some light on the saturation mechanism.
Effect of Raman Gain on Broadband Fiber Optical Parametric Amplifiers and Wavelength Converters
Authors: Marhic M. E. , Park Y. , Yang F. S. , Kazovsky L. G.
Published: February 2023

Recently we have shown theoretically that two-pump fiber optical parametric amplifiers (OPA’s) can exhibit highly uniform broadband gain spectra [1]: for example one can obtain 20 dB of gain over a 45 nm bandwidth, with uniformity of 0.2 dB. These calculations, however, did not include the effect of stimulated Raman scattering (SRS). Here we study the influence of SRS on the uniformity of the OPA gain spectrum, by starting from four-wave mixing (FWM) equations including SRS gain contributions. We show that in general SRS modifies the OPA gain spectrum, but that under realistic conditions the uniformity can remain quite good.
Competition of hexagonal and square patterns in a photorefractive feedback system
Authors: Sedlatschek Markus , Rauch Torsten , Denz Cornelia , Tschudi Theo , Honda Tokuyuki
Published: February 2023

Square and squeezed hexagonal patterns have been observed for the first time in an optical pattern formation experiment very recently by the authors of this presentation [1]. The experimental setup consists of a reflection-grating dominated photorefractive phase conjugator and a feedback path containing an ordinary mirror and a thin imaging lens at distance 2f from the photorefractive crystal and distance 2f + L from the mirror. The schematic of the setup is shown in fig. 1.
Phase Conjugation Based on Thermal Nonlinearity
Authors: Betin Alexander A.
Published: February 2023

The possibility of controlling the spatial structure of laser radiation, and in particular, of forming a diffraction limited beam is the key factor for the majority of laser applications. This problem can be successfully solved by means of a phase conjugation (PC) effect. In principle, PC mirrors allow us to cope with such problems as compensation for highly-inhomogeneous phase distortions, auto-guidance of laser radiation, and phase-locking of individual amplifying channels and segments of optical components. These capabilities are of particular importance for high-power laser systems with dynamically varying inhomogeneities and involving large-aperture optical elements. Accordingly, this report is a review of the history and recent achievements in the development of phase conjugation mirrors (PCM) based on the thermal nonlinear mechanism.