bluuebunny/crossref_metadata_2025 huggingface dataset:
Encoding and Decoding of Femtosecond Pulses for Code-Division Multiple Access
Authors: Weiner A. M. , Salehi J. A. , Heritage J. P. , Stern M.
Published: February 2023

We demonstrate spreading of femtosecond optical pulses into low intensity pseudo-noise bursts by performing spectral phase encoding. Subsequent decoding of the spectral phases restores the original pulse. Encoding and decoding of coherent ultrashort pulses is proposed as the basis for an ultrahigh-speed code-division multiple-access communications network, and the bit error rate of the proposed network is evaluated as a function of data rate, number of users, code length, and receiver threshold.
All-Optical Switching in a Fibre Nonlinear Mach-Zehnder Interferometer
Authors: Nayar B. K. , Finlayson N. , Doran N.J. , Davey S.T. , Williams D.L. , Arkwright J.W.
Published: February 2023

All-optical switching is of increasing interest for ultrafast transmission systems and logic applications. Silica fibres are particularly attractive for fabrication of switching devices since the nonlinearity is ultrafast and losses are low. A number of fibre interferometric devices with long fibre lengths have been investigated in order to minimise the switching power. A major constraint is the stability of the device against external perturbations. To date the nonlinear fibre loop mirror (NOLM) is the only interferometer to show insensitivity to external perturbations[1]. However, as the NOLM is a two-port device it is necessary to use additional optical elements e.g. isolators, to improve its functionality[2-3]. In contrast the nonlinear Mach-Zehnder interferometer (NLMZ) is a simple four-port device and can be directly concatenated for all-optical switching/logic applications. However, in the NLMZs reported to date instabilities occurred having time constants of the order of milliseconds[4] and active stabilisation was necessary to maintain the linear operating point. Also, the temporal overlap was not an issue as a CW signal was switched using control pulses
Polarization-Independent Optical Waveguide Switch with Parabolic Potential Quantum Well
Authors: Tada Kunio , Nishimura Shinji , Chan Yuen Chuen , Ishikawa Takuya
Published: February 2023

Carrier confinement in semiconductor quantum wells(QWs) results in extremely large exciton binding energy and oscillator strength when compared with those of bulk crystals. Under an electric field applied perpendicular to the QW layer, the energy of the fundamental absorption edge shifts by a large amount without severe line broadening of the exciton resonance. This well-known quantum-confined Stark effect(QCSE) enables one to utilize QWs for high-speed optical waveguide modulators. Recently, not only QWs with rectangular potential shape, but also several kinds of QWs with modified potential shapes have been studied both theoretically [1,2] and experimentally [3,4], but none of them exhibit polarization-independent electric-field-induced optical effects.
High Speed Wavelength and Spatial Switching with a Y-Coupled Cavity Laser (YCCL)
Authors: Idler W. , Schilling M. , Laube G. , Wünstel K. , Hildebrand O.
Published: February 2023

For photonic switching there is a growing interest in III/V semiconductor based functions. Such components offer the capability of optical and electrical integration with other semiconductor devices even under low cost aspects. Based on interferometric principles /1/ we have developed a new InGaAsP/InP device with a wide range electronic tunability3of 23 nm: the Y-coupled cavity integrated interferometric injection (YCC-I3 laser /2−4/. For optical switching applications we consider this all active Y-shaped waveguide as a basic structure.
A Combined Photonic Time-Division and Wavelength-Division Switching Network
Authors: Kuroyanagi S. , Shimoe T.
Published: February 2023

Photonic switching systems generally can be divided into three categories: space-division (SD), time-division (TD), and wavelength-division (WD). A particularly important target for a photonic switching system is to accommodate large line capacity video information (about 150Mb/s). In order to realize such a system, it is necessary to combine the three methods, because it is difficult for an individual method to achieve sufficient multiplexity. A combined TD and WD switching system is an effective method, however. The multiplexity of such a system is given by the product of TD multiplexity and WD multiplexity. Moreover, it has been reported that a wavelength and time hybrid switch (W&T hybrid switch) can reduce the number of optical memories required compared to the equivalent S-T-S TD switch [1].
A Multistage Reconfigurable Optical Interconnection Network using Polarization Switch Arrays
Authors: Nakagami Takakiyo , Yamamoto Tsuyoshi , Itoh Hiroyasu N.
Published: February 2023

Due to many limitations of the electrical interconnection, optical free-space interconnection is expected to overcome its bottleneck because of the high-bandwidth, high-speed transmission, parallel multi-beam inputs, and the absence of interference among beams. Some of such attempt are found in [1],[2],[3].
Lightwave Interconnections Employing Spatial Addressing: LISA
Authors: Sakano Toshikazu , Noguchi Kazuhiro , Matsumoto Takao
Published: February 2023

The interconnections among processors and memories in advanced parallel processing systems suffer wiring congestion and undesired electromagnetic effects. Multi-processor systems for real time processing especially require high speed and large fan-out interconnections. To overcome these problems, free space optical interconnections are considered to be a promising [1]. To use spatial parallelism, which is one of the inherent characteristics in free-space optics, to its best advantage, many array devices such as laser diode, micro lens, and detector arrays, are being actively researched[2],[3]. As for switching in free-space optics, many switching networks using spatial light modulators have been proposed[4],[5]. However, these devices limit the switching speed of such networks to the microsecond order. Besides, driving the devices requires particular control circuits and interconnections.
Fast Optical Triggering and Wavelength Switching using a DBR Laser with a Saturable Absorber
Authors: De Bouard D. , Loura G. Da , Chauzat C. , Jacquet J. , Benoit J. , Leclerc D. , Gabriagues J.M. , Jacob J.B. , Le Roy G.
Published: February 2023

Recent advances in the field of tunable semiconductor lasers have stimulated research studies on new optical switching concepts and architectures making efficient use of the wavelength domain. In the specific case of ATM-type systems, cells (data packets) can be encoded in the wavelength domain so as to determine a physical path through the switching network (wavelength routing) [1,2]. However, the useful tuning range of semiconductor lasers is still restricted to 10-20 nm and thus the capacity of any switch fabric based on wavelength routing remains somewhat limited, in terms of number of available wavelength multiplexed channels. In order to increase further this capacity, the integrated wavelength converter (IWC), recently demonstrated by Kondo et al [3], is an attractive device which can be used, for instance, as an optical gateway between stages of a multistage wavelength switching network. Basically, the IWC is a tunable laser which is optically triggered by external light; if this external signal is carrying binary data via intensity modulation, the IWC translates the incoming signal into an image signal, the wavelength of which can be tuned by electrical means. The aim of this paper is to present new results on high speed optical triggering and wavelength switching using an IWC based on a new DBR laser featuring a saturable absorber section.
Recent Progress in Wavelength Tunable Semiconductor Lasers
Authors: Ishikawa Hiroshi
Published: February 2023

The wavelength tunable semiconductor laser will play a key role in coherent communication systems and in the future photonic switching systems which utilize the wavelength domain. We need a single wavelength laser with a wide tuning range. In this paper we discuss the recently developed wavelength tunable semiconductor lasers with their up date data.
Flexible and fast switching
Authors: Kung H. T.
Published: February 2023

Summary not available
New Devices and Lasers for Large Scale Photonic Switching Systems
Authors: Sizer T. , Woodward T.K. , Chiu T-H. , Sivco D.L. , Cho A.Y.
Published: February 2023

Large scale photonic switching applications require that one have a switching device which uses one beam of light to switch either the amplitude or direction of another. Free-space imaging architectures are powerful by using large numbers of these devices in parallel. These issues place several requirements on the device parameters. First, the speed of the device must be compatible with telecommunications or switching applications and as such must exceed 100 MHz.[1] The optical energy to switch an individual device must be low in order to drive as many devices as possible with the available optical power. The devices must be cascadable and have a gain of at least two to allow the output of one device to drive two identical devices. The device should have a vertical structure (as opposed to waveguide) to allow for free-space imaging to large numbers of devices.
Optical Bistable Arrays : Prospects for Ultimate Performances.
Authors: Oudar J.L. , Kuszelewicz R. , Planel R.
Published: February 2023

The epitaxial growth of GaAs/GaAlAs structures allows the fabrication of monolithic bistable devices with very appealing characteristics for all-optical applications, such as low threshold power and good thermal stability[1,2]. These devices rely upon the excitonic and band-gap resonant dispersive non linearities of bulk GaAs or multiple quantum wells (MQW)[3,4], which can produce a substantial phase shift over interaction lengths as small as a few micrometers. This results in very compact devices, especially when the mirrors are integrated in the form of AlAs/AlGaAs Bragg reflectors grown during the same epitaxial process[5]. Additional advantages of such Bragg reflectors are that they improve the mirror/active layer interface quality and facilitate thermal dissipation, as these materials have a good thermal conductivity. The recent report of laser emission on optically- or electrically-pumped similar structures seems to be the starting point of a generic type of complementary devices that could share the same basic technology.
Bistable Diode Laser Amplifiers as Optical Repeaters or High Sensitivity Receivers
Authors: Pan Zeqi , Dagenais M.
Published: February 2023

Optical logic devices based on semiconductor laser amplifiers will play an important role in future photonic switching systems. In particular, they will be used for the routing of high data rate optical signals in a network, for high speed interconnections within high speed digital systems which involve distributed and parallel computing, within the telephone switch of an advanced communication system, and in signal processing and digital optical computing. In this paper, we study the sensitivity of a bistable diode laser amplifier when used as an optical regenerator or when used as a high sensitivity optical receiver.
A 4 X 4 Nonblocking Acoustooptic Waveguide Space Switch
Authors: Tsai C.S. , Le P.
Published: February 2023

Optical space switch arrays and matrices in waveguide format constitute vitally important components in wideband multichannel fiber optic communication systems.(1) Most of the existing optical waveguide space switch matrices utilize electrooptic (EO) effects in LiNbO3 and may be cataloged into two types, namely, those utilizing parallel channel waveguide (directional-coupler) switches(2) in one and those utilizing intersecting channel waveguide (TIR-, X- or digital) switches(3) in the other. However, all switch matrices referred to above are configured in stages (or tandem), and require a large number of basic cross-point switches as the size of the switch matrix or the number of input and output ports increase. As a result, the real estate of the substrate and the optical propagation losses and crosstalks as well as the complexity in both electrode layouts and electronic driver circuits greatly increase with the size of the switch matrix. Furthermore, both the optical insertion loss and the crosstalks may vary widely with the route the light takes.
Defects in Undoped and Doped Bi12GeO20
Authors: Tapiero M. , Gies J.G. , Benjelloun N. , Launay J.C. , Zielinger J.P.
Published: February 2023

Optimization of Bi12Ge O20 (BGO) for better photorefractive performance requires a systematic physico-chemical and physical characterization in parallel with material processing, investigation of photorefractive properties and implementation of nonlinear experiments. A main aspect is to analyze the effects of unintentional and intentional doping. We are concerned by the physical characterization of defects. To this end we use novel special thermal and optical spectroscopic methods (1). These survey techniques allow to probe the forbidden gap and to monitor changes in the nature and concentration of the species.
Study on Crystal Growth of BSO and Fabrication of PROM
Authors: Lianying Xu , Biyun Shu , Bing Xiao
Published: February 2023

PROM(Pockels Readout Optical Modulator) is a solid state, rapidly recyclable spatial light modulator, which can be addressed optically and ultilized for storage, write-in and read-out of two-dimensional digital signals as well as analogous images of different grey scales. Up to now it is still regarded to be one kind of the spatial light modulators of practicable use in the field of real-time optical signal processing and optical computing.
The Growth and Characterization of Photorefractive BaTiO3 Single Crystals
Authors: Tongrong Zhao
Published: February 2023

The paper described the growth of bulk BaTiO3 single crystals adopting two synthetic raw materials by top - seeded solution growth (TSSG) technique, discussed the reasons for the formation of defects and their relation to the growth condition.
Theoretical Impurity Levels of Ni and V Ions in BaTiO3 in Relation to Photorefractive Effects
Authors: Moretti P. , Michel-Calendini F.M.
Published: February 2023

An increasingly deal of attention is developping on the photorefractive properties of Barium Titanate. Indeed, its large electro-optic coefficients make it at the present as one of the most promising material in some optical processing applications such as self-pumped phase conjugate mirror or laser resonator1,2).
Spectroscopy of photorefractive centres in Bi12SiO20
Authors: Baquedano J.A. , Cabrera J.M.
Published: February 2023

The spectroscopy of several centres in Bi12SiO20 which are related to its photorefractive behaviour will be presented and discussed. In a recent paper, the spectral dependence of the photorefractive erasure by using the holographic method has been studied [1]. Two major absorption bands producing photorefractive erasure were found, their peak positions and halfwidths respectively being 2.7 eV (0.27 eV) and 3.1 eV (0.4 eV). These bands were obtained by numerically fitting the experimental decay constants for each erasing wavelength to those predicted by a two centre model [2] in which fast carrier exchange between the two traps was assumed. Because of practical reasons related with the fitting process, the geometrical shadow effect (sample selfabsorption) was not taken into account in that paper. Therefore the band parameters obtained from photorefractive erasure are necessarily a first approximation which should be improved with other measurements. In this paper, an analysis of the optical absorption and photoconductivity spectra based in those gaussian components is presented. This analysis is expected to provide a more detailed knowledge of the bands responsible for the optical absorption, photoconductivity and photorefractiorn, although the actual nature of the centres originating the bands remains uncertain. Photochromic effects induced on these bands by low temperature illumination, as well as their thermal annealing, will be also considered.
Light-Induced Charge Transport in BaTiO3
Authors: Holtmann L. , Groll A. , Unland M. , Krätzig E. , Maillard A. , Godefroy G.
Published: February 2023

BaTiO3 has favourable photorefractive properties [1] for applications in fast nonlinear optics such as image processing or self-pumped phase conjugation. Desirable is the optimization of the dielectric response time which is determined by the charge transport mechanisms. Only little is known about the centers involved in the photorefractive effect of BaTiO3. In this contribution we present measurements of photovoltaic effect, photo-conductivity, light-induced absorption and two-beam coupling. The results are consistent with a charge transport model based on the assumption of deep and shallow traps [2].
Subharmonics in BSO
Authors: Au L. B. , Solymar L. , Ringhofer K. H.
Published: February 2023

In 1988, Mallick et al.[1] found self-generated subharmonics in Bi12SiO20 (BSO). They used two coherent almost linear pump beams (wave vectors
k→
p
and
k→
p

′
, see Fig. 1) with grating vector
K→ and frequency detuning Ω, impinging on a 1 cm thick BSO crystal. For a certain frequency detuning, they observed a third beam in the middle between the two pump beams with intensity as high as 40% of the pump beam intensity. The length of the grating vector for the grating written by one of the pump beams and the third beam was approximately K/2 and therefore they called the new beam a K/2-subharmonic.
Shallow Traps Resolve the IX Mystery in Photorefractive Barium Titanate
Authors: Mahgerefteh Daniel , Feinberg Jack
Published: February 2023

In 1984 Ducharme and Feinberg1 showed that the speed of the photorefractive effect in barium titanate was not a linear function of the light intensity I, but varied instead as Ix, with x < 1. This sublinear dependence prevailed over four orders of the light intensity ( 0.01 Watt/cm2 <I < 100 Watt/cm2 ). They also showed that the power x increased with increasing temperature. In 1988, Mahgerefteh and Feinberg2 showed that the speed of the photorefractive effect in barium titanate obeyed the same Ix power law for the case of pulsed illumination as well as for cw illumination, even though the peak intensities used in the pulsed case were 104 times that of the cw experiments. This result suggested that the Ix power law was valid for a range spanning eight orders of magnitude in the light intensity.
Magnetic Circular Dichroism and Circular Dichroism of Doped Bi12GeO20 Crystals
Authors: Briat B. , Laulan C. , Launay J.C. , Badoz J.
Published: February 2023

Crystals with the sellenite structure are used widely in various technical devices because they exhibit photochromie, piezoelectric, electrooptic or else magnetooptic effects. They are also photoconductive and eventually photo- or thermoluminescent.
Photorefractive recording mechanism of acoustic waves in crystals
Authors: Zelenskaya T.E. , Kovalenko E.S. , Padusova E.W. , Sharygina L.I.
Published: February 2023

Now some recording mechanisms of acoustic waves in crystals are known. Photorefractive mechanism, mechanism, connected with nonstationary photoconductivity under impulse radiation of the crystal and also mechanisms connected with nonlinear material equations [1-3] belong to them. Our experiments on recording of acoustic waves with the frequency of about 100 MHz under the radiation of LiNbO3 crystal with subnanosecond light impulses showed that in this case photorefractive mechanism of recording is the main one. On this condition the electrical fields of the recorded grid gets the value like that of electric field of acoustic wave in piezocrystal. As the value of the field is so high one must take into consideration the selfdifraction of the waves while examing the recording process [4]. In this work the recording kinetics of the acoustic waves in photorefractive crystals under the radiation by the ultrashort light impulses with repetition frequency equal to that of sound is considered.
Two-photon Absorption and Transient Energy Transfer in BaTiO3
Authors: White Jeffrey O. , Boggess Thomas F. , Valley George C.
Published: February 2023

We have used ultrashort optical pulses to investigate bound electronic, free carrier, and photorefractive nonlinearities, as well as induced absorption in BaTiO3. A pump-probe technique was used to measure both an instantaneous two-photon absorption and a long-lived induced absorption. Measurements were taken with co-polarized and cross-polarized pump and probe pulses to identify any transient energy transfer associated with free-carrier gratings.
Nanosecond Photorefractive Phenomena in Strontium Barium Niobate
Authors: Monson Brian , Salamo Gregory J. , Miller Mary J. , Mott Andrew G. , Sharp Edward J. , Clark William W. , Wood Gary L. , Neurgaonkar Ratnakar R.
Published: February 2023

Observations and descriptions of two-beam coupling, beam fanning, self-pumped phase conjugation, and double phase conjugation using 15 ns pulses will be presented. These effects begin with the first pulse. The crystal used is Rh-SBN:60.
Picosecond Pulse-Probe, Two-beam Coupling, and Polarization Rotation Switching in Cadmium Telluride*
Authors: Petrovic M.S. , Suchocki A. , Powell R.C. , Valley G.C. , Cantwell E. , Aldridge J.
Published: February 2023

Laser-induced gratings produced by one- and two-photon absorption of picosecond pulses at 1.064 μm were used to examine the room temperature nonlinear optical responses of undoped n- and p-type CdTe crystals. We report what we believe to be the first observation of picosecond photorefractive two-beam coupling in a material that has no cw response. Gains up to 2.5 cm−1 were obtained at fluences of 120 mJ cm−2 for 0.8 μm grating spacing. Polarization rotation switching was also measured with on/off ratios of 6.0 at fluences of 56 mJ cm−2. Pulse- probe degenerate four-wave mixing measurements of grating dynamics on subnanosecond time scales were used to measure the ambipolar diffusion coefficient of charge carriers in the crystals. The value of Dα = 3.0 cm2 s−1 which was obtained is in very good agreement with theoretical estimates. Free carrier lifetimes of 12 ns were measured. A long-lived contribution to the signal consistent with a trapped charge photorefractive effect was observed at large grating spacings for n-type conductivity, and is tentatively attributed to a larger trap density in this sample. Measurements of the relative scattering efficiencies of successive diffracted orders in the Raman-Nath regime allowed for calculation of the laser-induced change in the index of refraction, Δn due to the creation of free carriers. The value of Δn = 4 x 10−4 which was obtained is in good agreement with theoretical estimates. *Research sponsored by DARPA contract MAD972-89-K0001.
Parametric Intermode Scattering in LiNbO3 Planar Waveguides
Authors: Novikov A. , Odoulov S. , Shandarov S. , Shandarov V.
Published: February 2023

Practically all nonlinear frequency degenerate four wave mixing processes reported previously for the bulk photorefractive materials have been observed also in the planar photorefractive waveguides: interaction of two beams with the same (or with the different) mode indices resulting in the developement of the dynamic grating, phase conjugation due to the backward wave mixing, polarization conversion, etc.[1]. Specific properties of the waveguides, as, e.g., the existance of several propagation modes with the same frequency but different propagation velocities, make possible same additional nonlinear wave mixing effects which do not occure in bulk samples. We report the first to our knowlage observation of such effect-the nonlinear parametric mixing of different waveguide mode and parametric intermode scatering.
Route to chaotic structures in a phase-conjugate ring-resonator during self-oscillation
Authors: Blumrich R. , Kobialka T. , Tschudi T.
Published: February 2023

The sytem we investigated is called phase-conjugate ring-resonator (PCR). It consists of a Sagnac interferometer and a phase-conjugate mirror (PCM) realized by four-wave mixing in a photorefractive BaTiO3-crystal. Since the PCM provides nonlinear gain and high amplification, the PCR forms a nonlinear, active feedback system with a large image plane and a high resolution [1].
Observation of Periodic Instabilities in Externally Driven Ring Phase Conjugator
Authors: Królikowski Wiesław , Chen Bo Su , Cronin-Golomb Mark
Published: February 2023

There has been growing interest in the temporal properties of wave mixing processes in photorefractive crystals. Several years ago, temporal instabilities such as frequency detuning [1] and pulsations [2] were observed in self-pumped phase conjugation. Also, there has been considerable interest in the possibility of bistability associated with the multiple solutions of the four-wave mixing coupled wave equations [3]. Especially important was the result of Gauthier et al. [4] where it was shown that instabilities occur for strong nonlinear coupling. As a result, demands for large coupling constants for large energy transfer and high phase conjugate reflectivity may lead to very unstable output. The mechanism responsible for these instabilities was competition among various coupling mechanisms with different time constants [4]. Very recently, a ring oscillator with photorefractive gain and loss was demonstrated experimentally and theoretically for application to associative memories. This system was shown experimentally to exhibit bistability when an external signal beam was injected [5].
Bipolar charge transport and hologram fixing in KNbO3 crystals
Authors: Montemezzani G. , Günter P.
Published: February 2023

The dark decay time of volume phase holograms recorded in photorefractive potassium niobate crystals mainly depends on the dark conductivity of the material. Self-erasure time constants between some microseconds and a few seconds are observed in general in KNbO3. We report dynamical effects during the build-up and the dark decay of photorefractive gratings recorded in nominally pure KNbO3 samples at temperatures higher than 70°C. Under these conditions bipolar charge transport takes place.1 The thermal activation energies of electrons and holes are different and we demonstrate that the storage and fixing of phase holograms is possible by simoultaneous optical recording and thermal treatment. We can increase in this way the storage time of the hologram by more than a factor 105.
Optical Tracking and Motion Detection Using Photorefractive Bi12SiO20
Authors: Hussain G. , Eason R.W. , Khoury J.A.
Published: February 2023

An optical tracking novelty filter that performs the process of optical image differentiation using an interferometric arrangement involving BaTiO3 has recently been demonstrated [1]. This device exploits differential optical phase changes and is therefore restricted to highlighting or tracking phase objects only. Other schemes for coherent optical image differentiation based on two beam coupling in BaTiO3 have also been demonstrated [2, 3]. These two devices rely on destructive interference between reference and signal beams under static conditions but require high optical quality for the BaTiO3 crystal so that the transmitted images do not suffer from any spatial distortion. In this paper we report a novel arrangement for optical differentiation of images in time that uses an optical processor based on the spatial frequency dependent response time of photorefractive Bi12SiO20 in a phase conjugate Michelson interferometric configuration. The device is capable of differentiating both amplitude and phase objects. To our knowledge this is the first time that BSO with its inherent fast response time, some two or three orders of magnitude faster than BaTiO3, has been used for such optical differentiation in time.
Optically controlled fiber interconnection with photorefractive KNbO3
Authors: Amrhein P. , Voit E. , Bachmann M. , Günter P.
Published: February 2023

Optically addressable fiber interconnects can be realized by using light deflection from photoinduced gratings. Such devices using isotropic Bragg diffraction have been proposed e.g. by Pauliat et al.1. Taking advantage of the anisotropic Bragg diffraction technique2,3 we demonstrate an all optical monomode fiber coupler with photorefractive KNbO3 crystals. KNbO3 is a very sensitive photorefractive material with large electro-optic coefficients 4: r42=380 pm/V and r51=105 pm/V. The anisotropic Bragg diffraction takes full advantage of these non-diagonal elements of the electro-optic tensor. With this method a beam deflector in a non-critical configuration has been built5 and investigated.
Investigation of phase shift of holographic gratings in photorefractive materials
Authors: Zha M.Z. , Amrhein P. , Günter P.
Published: February 2023

The fundamental processes occurring during the writing of phase gratings in photorefractive materials have been studied extensively in the past 1,2. Due to different mechanisms of carrier transportation these holograms may be phase shifted with respect to the interference pattern. This phase shift is of fundamental significance for the understanding of the mechanism of the photorefractive effect and for applications. We present a novel method for measuring the phase shift and some experimental results.
Coupling Between Transmission and Reflection Gratings in Photorefractive Phase Conjugators
Authors: Li Guifang , Papen George C. , Saleh Bahaa E.A.
Published: February 2023

In most derivations of the reflectivity of a photorefractive phase conjugator, the contributions from the transmission grating and reflection grating are assumed to be independent. This is in general not correct We show that within the undepleted pump approximation, the transmission and reflection gratings can couple through a grating formed by the two counter-propagating pump waves. We present a general linearized theory including this coupling and show that it significantly alters the response.
Conjugation of Mutually-Incoherent Light Beams in the Geometry of Two Interconnected Ring Mirrors
Authors: Zozulya A.A. , Mamaev A.V.
Published: February 2023

New geometry for conjugation of mutually-incoherent light beams in photorefractive media is proposed. This geometry is realized experimentally and its theoretical description is given. Comparison between theory and experiment is made.
Photorefractive Beam-Coupling in BSO Crystals in Near Infrared
Authors: Sochava S.L. , Stepanov S.I. , Odoulov S.G. , Slussarenko S.S. , Shcherbin K.V.
Published: February 2023

Dynamic holographic recording in sillenite type photorefractive crystals Bi12SiO20 (BSO)1 is very carefully investigated in visible region of spectrum. Two promising techniques (recording by the moving or oscillating light fringes in DC electric field or recording by stable fringes in AC electric field) were proposed to improve the beam coupling efficiency in these materials; the gain factor up to 6.12cm−1 is now obtained2,3. Present paper describes the first study of the dynamic coupling of two light beams in BSO crystals in near infrared. The measured values of the gain factor indicate the possibility of the development of coherent oscillators pumped by semiconductor lasers (including passive phase conjugating mirrors).
Noise-free Photorefractive Image Amplifiers
Authors: Rajbenbach H. , Delboulbé A. , Huignard J. P.
Published: February 2023

When a weak optical signal is injected in a photorefractive crystal illuminated with a strong pump beam, it experiences gain via a two-wave mixing process.(1) A problem common to these amplifiers is the presence of noise sources that corrupt the quality of the emerging amplified optical signal. We propose and experimentally demonstrate the first technique, to our knowledge, capable of very significantly reducing the optical noise while maintaining high gain coefficients. Consider two-wave mixing in a slowly rotating crystal. First, we estimate the influence of a crystal rotation (angular velocity Ω around the point O) on the noise intensity in the output plane (Fig. 1a). A noise source located around point A radiates a complex wavefront whose component along the direction of the injected signal is represented by a plane wave of intensity IN (A is a crystal imperfection or interface). It is essential to note that the noise sources are bounded to the crystal and will consequently move with it. This is the basis for the process of discrimination between the noise gratings and the injected signal grating. In the Ox coordinate bounded to the rotating crystal, the interference pattern responsible for the formation of a noise grating around the point A is given by: IN(x,t) = I0 [1 + mN cos KN(t)x], where KN(t) ~ 2π(θ + Ωt)/λ is the time-dependent grating wave vector (we have assumed that the angles inside the crystal are small), I0 is the total incident intensity (I0 ~ IP0), θ is the angle between the beams inside the crystal, λ = λ0/n is the optical wavelength in the crystal with refractive index n, and mN is the fringe modulation.
Efficient Photorefractive Beam Combining with High-Power Injection-Locked Semiconductor Laser Arrays
Authors: Verdiell J.M. , Rajbenbach H. , Huignard J.P.
Published: February 2023

Much research effort is currently devoted to the improvement of the output power and beam quality of semiconductor diode lasers. One of the most successfull approach is the concept of phase-locked laser arrays [1]. When the individual emitters of such arrays are separated by a distance of the order of a few wavelengths, phase locking between them occurs and coherent, diffraction-limited operation of the array can in principle be achieved [2]. However, when very high power operation is needed, thermal considerations imposes a large separation between the individual emitters or a division of the total array into several uncoupled sub-arrays. This is in particular the case of laser bars [3] and of many two-dimensional arrays [4]. To achieve coherent and diffraction-limited operation in one single emission lobe from such devices, an external control of the phase of otherwise independent elements and a beam combining technique are needed. Injection locking and wave mixing in photorefractive BaTiO3 are good candidates for such functions [5-7]. Energy transfer from an injection-locked array by two-wave mixing in BaTiO3 has been reported in Ref. [8], with a maximum of 1% efficiency. The purpose of this paper is to describe and demonstrate highly efficient energy transfer with an injection-locked array using two-wave mixing in BaTiO3.
Photorefractive incoherent to coherent optical conversion with KNbO3 crystals
Authors: Amrhein P. , Voit E. , Günter P.
Published: February 2023

The high sensitivity of photorefractive materials is very convenient for real time holography and image processing. All optical spatial light modulators using the photorefractive effect have been proposed by different authors1,2,3. These devices can transfer incoherent images to coherent laser beams.
High-Fidelity Dynamic Imaging with Photorefractive Materials
Authors: Vainos N A , Gower M C
Published: February 2023

Photorefractive crystals such as BaTiO3 Bi12SiO20 (BSO) and SrxBa1−xNb2O6 (SBN) have photosensitivities to visible light which are comparable to the best photographic emulsions (~100 μJ/cm2) and are simultaneously capable of recording information of extremely high resolution (~200 nm) with response times as short as 10 psec. Currently the properties of these materials are being thoroughly studied for potential applications in image processing, beam clean up, image amplification and projection.
Influence of the Excited State of Fe2+ on Photorefractive Effect in InP
Authors: Delaye P. , Halter P.U. , Roosen G.
Published: February 2023

Although the excited state of Fe2+ is well known in InP:Fe (figure 1), its influence on photorefractive effect has never been taken into account. We report here a study of this influence and show that the presence of this state induces in the photorefractive effect a new hole-electron competition. This theory well explains the photorefractive coupling gain results obtained on a crystal without any classical hole-electron competition(αn«αp).
Generation of pure torsional wave in Bi12GeO20 crystals
Authors: Gaglione R. , Launay J.C. , Lauban C.
Published: February 2023

Ultrasonic methods of material characterization usually employ α-Quartz crystals to create torsional vibrations1. The mode is not pure, and the crystals exhibit a low electromechanical coupling factor.
Photorefractivity at 1.5 μm in CdTe:V
Authors: Partovi Afshin , Millerd James , Garmire Elsa , Ziari Mehrdad , Steier William , Trivedi Sudhir , Klein Marvin B.
Published: February 2023

CdTe is the least studied of the photorefractive semiconductors known to date (GaAs, InP, and CdTe). This is somewhat surprising considering that the electrooptic coefficient of CdTe is almost four times larger than that of GaAs and InP. CdTe is also one of the most sensitive photorefractive media available. Its photorefractive figure of merit for sensitivity (index change per absorbed photon), n3r41/εr is 2.5 times that of GaAs.
Neutron diffraction — photorefractive materials enter a new research and application branch
Authors: Rupp R.A. , Hehmann J. , Ibel K. , Matull R.
Published: February 2023

Light-induced changes of the refractive index are referred to as photorefractive effect. Thereby it does not matter whether the light causing and the light sensing these changes have different wavelengths—from the infrared to the 7-ray spectral region— or not. In this paper we intend to generalize the notion of a photorefractive effect to cover also light-induced changes of the refractive index for neutron waves (photorefractive effect of a second kind). The scope of possible applications of photorefractive materials is extended towards holographic optical elements for neutron optics.
Multistable and Time Sequencing Photorefractive Ring Resonators
Authors: Anderson Dana Z. , Benkert Claus , Hermanns Anno
Published: February 2023

Our purpose in this presentation is to discuss and demonstrate two multimode photorefractive systems. The first is a multimode oscillator with “winner-takes-all” dynamics. The oscillator has several (in our case five) possible stable steady state solutions. The state of the system can be switched with an injected signal. A slight modification of the resonator gives a system with only one stable steady state, but that state is reached through a time sequence, or chain, of oscillating modes.
Reflection Grating Photorefractive Self-Pumped Ring Mirror
Authors: D’yakov V.A. , Korol’kov S.A. , Mamaev A.V. , Shkunov V.V. , Zozulya A.A.
Published: February 2023

We report on the first to our knowlege experimental realization of a reflection grating passive ring mirror in a photorefractive medium. The experimental arrangement is shown in Fig. 1.
Image Transmission through Multimode Fiber and the Photorefractive Crystal
Authors: Gnatovskii A. , Volyar A. , Kukhtarev N. , Lapaeva S.
Published: February 2023

We describe the results of the image transmission through the multimode optical fiber and photorefractive crystal LiNbO3:Fe.Experiments were done with HeNe laser (λ =0.63μm), with multimode fiber of 70μm diameter, the aperture number 0.17 and 2m long. After passing an optical fiber light wave E1 were mixed with another coherent wave E2 at the photorefractive crystal. Amplitude mask was introduced in E2 wave and a dynamic hologram was recorded in the crystal through photogalvanṁc effect /1/.Retrieval of this hologram was done by another counterpropagating wave E3, which lead to difracted wave E4 conjugated to E1 with 1⊕% difraction efficiency after 3min. of hologram writing.
The Influence of Cobalt Doping on Deep and Shallow Trap Dependent Photorefractive Properties of Barium Titanate
Authors: Garrett M. H. , Chang J. Y. , Tayebati P. , Jenssen H. P. , Warde C.
Published: February 2023

The photorefractive properties of cobalt­doping barium titanate have been recently reported by Rytz et al. [1]. High beam coupling gains were reported therein. Similarly, we have grown a series of cobalt-doped p-type barium titanate crystals, (undoped, 17 ppm, 50 ppm and 75 ppm), that also have relatively large beam coupling gains, e.g. for E||a and kg||c the gain is 7.4 cm−1 at 514.5 nm in the 75 ppm sample. We have further characterized these crystals by determining the sublinear dependence of the response time on intensity, the asymmetry of the beam coupling gain for ±C-axis crystal orientations, (i.e. electrooptic and absorptive coupling), intensity dependence of the gain, and light-induced dark decays. Experimental results indicate that, as the cobalt concentration is increased, the photorefractive character of the crystals change from "type B" to "type A" as defined by Mahgerefteh and Feinberg [2]. Type A crystals have filled hole-shallow traps and type B crystals have partially filled hole-shallow traps and thus low and high dark conductivity respectively.
Hot Carrier Enhancement of Dember Photorefractive Space-Charge Fields in Zincblende Semiconductors
Authors: Schroeder W. Andreas , Stark Thomas S. , Smir Arthur L. , Valley George C.
Published: February 2023

We use a novel, nondegenerate, polarization-sensitive, transient-grating technique1 to monitor the picosecond dynamics of the photorefractive effect in undoped CdTe and InP:Fe at 960 nm. The technique circumvents the limited temporal resolution of the two-beam coupling geometry by using a time-delayed third probe pulse (with a duration of <5 psec) to read the gratings written in the semiconductor. The technique also exploits the crystal symmetry of zincblende semiconductors by using an optically induced anisotropy in the crystal index of refraction2 to separate the photorefractive gratings from the stronger, co-existing instantaneous bound-electronic and freecarrier gratings. In both semiconductors, the photorefractive effect is associated with the Dember field between mobile electron-hole pairs, in contrast to the more conventional photorefractive space-charge field connected with the separation of a mobile carriers species from a stationary, but oppositely charged, mid-gap state. In the undoped CdTe sample, which possesses no optically-active mid-gap levels, the electron-hole pairs are produced by two-photon absorption of 1.3 eV photons across the 1.44 eV band-gap of the semiconductor. The resultant ~1 eV excess carrier energy, which allows hot carrier transport to dominate the initial formation of the space-charge field, causes up to an order of magnitude enhancement in the photorefractive effect on picosecond timescales. After the carriers have cooled and the initial overshoot in the space-charge field has decayed, the photorefractive effect is observed to decay as the Dember field is destroyed by ambipolar diffusion of the electron-hole pairs across the grating period. In InP:Fe on the other hand, the electron-hole pairs are produced predominantly by direct single-photon band-to-band absorption into the band-tail of the semiconductor (band-gap ~1.35 eV), since the iron dopant only dominates the linear absorption at longer wavelengths. This means that the carriers are generated with little excess energy. Consequently, no hot carrier enhancement of the photorefractive effect was observed, and once formed, the Dember space-charge field decayed directly by ambipolar diffusion.
Holographic Storage Capacity Estimate for Photorefractive Media
Authors: Fredericks George , Lahrichi Adil , Johnson Kristina
Published: February 2023

The practical limit on the storage capacity of photorefractive media is estimated for a given bit error rate and read out bandwidth.
Diffraction Efficiency Dynamics in Photorefractive Crystals
Authors: Maniloff Eric S. , Johnson Kristina M.
Published: February 2023

Due to their large potential storage capacity, photorefractive crystals are an attractive medium for a variety of optical computing architectures[1]. The actual capacity of such storage systems is determined by the minimum acceptable diffraction efficiency for a given system design[2] and the maximum number of holograms that can be recorded with this efficiency in photorefractive crystals.
Dynamic photorefractive optical memories
Authors: Sasaki H. , Fainman Y. , Ford J. E. , Taketomi Y. , Lee S. H.
Published: February 2023

The extremely large storage density of volume holographic memories is applicable to numeric and neural network optical computing. Such photorefractive memories can be used to provide optical storage of binary bit-plane or gray scale images as well as weighted interconnects for optical digital and neural network computing. However, success in applying optical memories to computing will strongly depend not only on the memory's large capacity and short random access time, but also on the memory's dynamic characteristics.
Experimental Comparison of the "AC Field" and "Moving Grating" Techniques for BTO and BSO Crystals
Authors: Mokrushina E.V. , Prokof'ev V.V. , Sochava S.L. , Stepanov S.I.
Published: February 2023

There are two techniques of nonstationary holographic recording which are widely used for PRCs with long drift lengths of photocarriers. These are recording of a moving interference pattern in an external DC electric field [1] and recording of a fixed pattern in an AC field [21. Both of them allow the efficiency of the drift mechanism of recording in the external electric field to be increased and the recorded hologram to be transformed into a shifted one. The theory [3] predicts equal efficiencies of two-wave energy exchange for these two techniques. In practice, the "moving grating" technique is traditionally employed for Bi12SiO20 (BSO), but for Bi12TiO20 (BTO), recording in an AC field is in common use. Recent investigations of holographic recording in semi-insulating GaAs:Cr (λ=1.06 μm) [4,5] have demonstrated remarkable superiority of the moving grating mechanism.
Large Signal Gain Effects in Photorefractive Bi12TiO20 at 633 nm
Authors: Klein M.B. , Strohkendl F.P. , Wechsler B.A. , Brost G.A. , Millerd J.E. , Garmire E.M.
Published: February 2023

Bi12TiO20 (BTO) is a photorefractive material in the same structural class (sillenite) as Bi12SiO20 (BSO) and Bi12GiO20 (BGO). However, BTO offers some unique advantages over BSO and BGO: (1) larger electro-optic coefficient (5.7 pm/V)1, and (2) lower optical activity (6°/mm at 633 nm)1, 2. Previous photorefractive measurements3,4 have shown that gain coefficients on the order of 10-15 cm−1 can be produced through the use of an applied AC field. In this work we show that the largest gain values can only be obtained for large values of the pump/probe intensity ratio β. As β approaches unity (large signal regime), higher spatial order gratings become prominent, and the gain is reduced from its large-β value.5−8 Our results are similar to those obtained by other researchers for BSO5 and GaAs6 with an applied field. We have analyzed this and related phenomena using a finite difference method to model the photorefractive grating formation. This method yields accurate numerical solutions which are valid for for all values of β.
Polarization properties of Bi12SiO20 crystals
Authors: Panchenko T. , Kudzin A. , Potapovich Y. , Snejnoy G.
Published: February 2023

Photorefractive crystals Bi12SiO20 (BSO) are particular interest for applications such as spatial light modulators, image amplification and the like. Some properties are connected to distribution of space charge induced in the crystal both by an applied (or intrinsic) electric field and illumination. Many electrical and optical properties as BSO dependence on density and king of localized states. In these paper the results of study of both photoelectret and thermoelectret state (PES and TES) and intrinsic charge distribution as were are presented.