bluuebunny/crossref_metadata_2025 huggingface dataset:
Architectural considerations for an optical Extended Generalized Shuffle network based on 2-modules
Authors: Cloonan T. J. , Richards G. W. , McCormick F. B. , Lentine A. L.
Published: February 2023

To efficiently utilize the bandwidth and parallelism offered by free-space optics, new switching network topologies must be developed that can capitalize on the novel benefits of photonics while circumventing its short-comings. In particular, the topologies must (1) take advantage of 3D connectivity between planar arrangements of optical logic devices, (2) use interconnections that are easy to implement in optics, (3) require low fanin and fanout on the logic devices to maintain large noise margins and signals levels, (4) offer a high degree of fault-tolerance for the emerging logic devices, and (5) be flexible enough to adapt to changing technologies. In addition, the topologies should provide very low blocking probabilities and should permit multi-casting operations for switching of broadband video and data traffic in the future.
A wide-wavelength-tunable active filter with a λ/4-shifted DFB structure with independently current-injected tuning waveguide
Authors: Tanaka K. , Inoue T. , Matsuda M. , Yamamoto T. , Kobayashi H. , Wakao K. , Mikawa T.
Published: February 2023

Recently, wavelength division optical communication systems and signal processing ones have attracted attention because of their large capacity of signal processing. Wavelength-tunable lasers, wavelength-conversion lasers and wavelength-tunable filters have been studied by many workers.
On The Capacity of Multiwavelength Optical-Star Packet Switches
Authors: Brackett Charles A.
Published: February 2023

An issue of considerable interest in the field of high-speed network and switch design is to find the practical limits to the achievable bandwidths of switching and routing networks made of passive optical stars and multiwavelength tunable lasers and receivers. In previous work, we[1] and others[2] have discussed the limitations due to power budget limitations and available optical spectrum on the capacity of switches which use such multiwavelength optical star networks at the core of the switch fabric. Henry[2] has given an argument which illustrates a third capacity limit due to the bandwidth available within the switch for communicating the switch control functions to the crosspoint elements of the switch.
Lossless Acoustooptic Permutation Interconnection Network
Authors: Wagner Kelvin , Weverka Robert , Mickelson Alan , Wu Kuang , Garvin Charles
Published: February 2023

A new approach to implementing an optical crossbar using a single acoustooptic device is presented. This novel device configuration can permute an array of single mode fiber inputs to outputs without suffering from fan-in and fan-out losses. Generalized crossbars with broadcast capabilities can also be implemented with the same device by simply changing the driving signals, and this will achieve the minimum possible loss, given by the degree of fanout. The reconfiguration time of the switching network is governed by the acoustic aperture, which is on the order of one microsecond. The device addressing requires only a single driving signal which contains N simultaneous frequencies. This fiber optic switching system avoids optical to electronic conversion permitting the transmission of arbitrary format high bandwidth signals. We will present results of the operation of the switch using a bulk phased-array acoustooptic Bragg cell driven with multiple input frequencies that permutes an array of inputs to an array of outputs. A surface acoustic wave integrated optics implementation of the device optimized for permuting the 12 single mode fibers in a fiber ribbon is being built and tested for application as a switch for digital signals in parallel processors and in video and telecommunication switching environments.
A Proposed Optical Interconnection Technique Employing a Two-Dimensional Waveguide as a Broadcast Medium
Authors: Linke Richard A.
Published: February 2023

Optical techniques can, in principle, provide an interconnection network for complex electronic systems with several important advantages over present electronic interconnections [1]. These advantages include increased interconnection density and bandwidth, as well as the potential for dynamic reconfigurability. In a computing system, for example, an optical data-communications network may allow for the use of massively parallel digital or analog computing schemes by relaxing the restrictions on data transfer imposed by electronic data busses.
Quantum Well Fabry-Perot Electro-Absorption and Refraction Modulators and Bistability
Authors: Boyd G. D. , Livescu Gabriela , Chirovsky L. M. F. , Fox A. Mark
Published: February 2023

Following the demonstration of the absorption reflection modulator [1], many workers [2-10] have used Fabry-Perot resonators to improve the limited contrast ratio of these multiple quantum well light modulators. Most experiments have been in the normally on (Non), spectral region where absorption increases with field. Using field dependent GaAs/AlGaAs quantum well absorption data, we have created a model that calculates the reflectivity and contrast ratio of resonant and non-resonant modulators in both the normally off (Noff), region where absorption decreases with field, and the normally on (Non) spectral regions for use with photonic devices such as the self-electrooptic effect device (SEEDs). The calculations include both electro-absorption and electro-refraction effects.
Demonstration of a Novel Optical Code Division Multiplex system at 800 MChips/s
Authors: Vethanayagam N. , MacDonald R. I.
Published: February 2023

Direct sequence Code Division Multiple Access (CDMA) provides a method of exploiting the wide bandwidth offered by optical fibres without the added complexity of wideband electronics. Each data bit is encoded with a code sequence (of N chips) which represents the destination address of each data bit. The correct selection of orthogonal codes allows the data bit destined for a given receiver to be extracted in the presence of noise (i.e., interference from other users in the system). Due to the uni-polar nature of light, coding schemes used in conventional CDMA cannot be applied directly to optical CDMA. Coding schemes have been proposed for optical CDMA [1] [2] but they have a number of limitations which include high bandwidth expansion factors and significant cross-talk levels. These problems can be overcome by employing complementary correlation detection which generates bi-polar electrical signals from received uni-polar optical ones [3]. Correctly selected codes (Alberta codes) are truly orthogonal for complementary correlation detection.
Measurements of Photorefractive Properties in BaTiO3:Co
Authors: Rytz D. , Wechsler B.A. , Garrett M.H. , Nelson C.C.
Published: February 2023

In the past, the photorefractive properties of BaTiO3 crystals doped with chromium [1] and iron [2, 3] have been described. Iron impurities, present in nominally undoped .crystals at levels between 40 and 150 ppm, have been identified as the microscopic centers correlated with the photorefractive effect [4]. The observed photorefractive effect in high purity crystals, however, with an iron level claimed to be smaller than 0.3 ppm [3], has been interpreted as evidence for another photorefractive species in these samples. The exact role of transition metal dopants in photorefractive BaTiO3 is still unclear.
Photorefractive Properties and Crystal Growth of Doped Barium Titanate
Authors: Godefroy G.
Published: February 2023

The interest of barium titanate has increased during the ten last years for applications in optical data processing and phase conjugate wave front generation. Nevertheless, many of the physical, optical and dielectric properties of this material are not very well inderstood and the microscopic mechanism of the photorefractive phenomena is widely discussed as it is explained in the review paper of M. Klein [1].
Measurement of Electro-Optic and Electrogyratory Effects in BTO (Bi12TiO20)
Authors: Wilde J.P. , Hesselink L. , McCahon S.W. , Klein M.B. , Rytz D. , Wechsler B.A.
Published: February 2023

One group of promising photorefractive materials is the sillenites, which include Bi12SiO20 (BSO), Bi12GeO20 (BGO) and Bi12TiO20 (BTO). These materials are cubic, noncentrosymmetric and optically active. Although BTO shares a common structure with BSO and BGO, it has several advantages over the latter materials for photorefractive applications, including smaller optical activity, larger electro-optic coefficient and improved sensitivity in the red spectral region.1
Photorefractive Holograms In LiNbO3 With Multiple Trapping Species
Authors: Brady David , Kagan David , Raguin Daniel , Psaltis Demetri
Published: February 2023

We have observed in certain LiNbO3 samples that the diffraction efficiency of sufficiently strong volume holograms may increase substantially before eventually decaying when illuminated with a uniform, non-Bragg matched beam. Such an increase is not predicted by the single trap version of Kuktarev’s band transport equations, nor can it be attributed to two wave mixing effects. We believe that the increase is due to the presence of multiple photo-active species in the crystal. In this paper we describe our experimental results and attempt to explain them using a multiple trap band transport theory. Such a theory was first described by Valley [1]. Our analysis differs from [1] in the assumed initial conditions. Specifically, we assume, and observe experimentally, that the temporal derivative of the space charge field is positive at the beginning of the erasure process. We also consider the implications of this effect for multiple hologram storage and adaptive holography.
Effects of temperature on photoconductivity in n-type cubici Bi12SiO20
Authors: Partanen J.P. , Nouchi P. , Cohen-Jonathan J.M. , Hellwarth R.W.
Published: February 2023

In the only study to our knowledge of the photorefractive effect in n-type cubic Bi12SiO20 (n-BSO) at low temperatures (300 to 80 K), optical four-wave mixing via the photorefractive effect was found to decline over one order-of-magnitude as the temperature was lowered from ~ 300 K to below ~ 200 K.1 The mixing returned to normal upon warming. To better understand this unexpected result, we have undertaken both pulsed and dc photoconductivity studies at various temperatures on the same n-BSO crystal, called "CT1" (Crystal Technology, Inc., 1984), as well as on other n-BSO crystals. The photocurrent excited by a nanosecond or picosecond optical pulse is known to decay non-exponentially in time, with characteristic times in the nanosecond and microsecond regimes.2 In CT1 we see further long decay tails (~ seconds) at room temperature. However, in another n-BSO crystal called "SU1" (Sumitomo Corp., 1986), this long tail is essentially absent.
Optimization of DFWM in Crystals of the Sillenite-Family with Respect to the Polarization of the Signal- and Pump-Waves
Authors: Erdmann A. , Kowarschik R. , Wenke L.
Published: February 2023

Over the last years degenerate four-wave mixing (DPWM) has been demonstrated to be a powerful technique to generate a phase conjugated wave. Among the materials used for DPWM the photorefractive crystals of the sillenite-family belong to the most sensitive ones. On the other hand, the anisotropic properties of these crystals result in a strong dependency of the intensity and the polarization state of the phase conjugated wave on the polarization states of the signal— and pump-waves, on the crystal geometry and thickness and on some other physical parameters.
Photorefractive charge migration in BSO: A comparison of the band transport and hopping models
Authors: Krainak Michael A.
Published: February 2023

There is a continued interest in the charge transport mechanism for the photorefractive effect, particularly in the sillenites (BSO, BGO, BTO)1,2. There are two prevalent models for the photoexcited charge migration, namely, the band transport theory and the hopping model3. In this paper we present a detailed comparison of the hopping and band transport models. We place the hopping model in the same framework as the band transport model. The hopping model is then modified to include an external electric field dependent time constant. This allows the development of an expression for the total electric space charge field for the condidtion of an externally applied alternating electric field. This expression is used in the electromagnetic coupled wave theory to predict the two wave mixing gain. Experimental and theoretical results are then compared. AC photoconductivity experimental results and theoretical predictions are also presented and compared.
Seeded Stimulated Photorefractive Scattering
Authors: Mullen Ruth Ann , Vickers D.J. , Pepper David M.
Published: February 2023

Stable phase conjugate reflectivities as high as 60% have been achieved with back-seeded stimulated photorefractive scattering (SPS) in a BaTiO3 crystal having too small a gain-length product for unseeded SPS. The beam-bending and build-up dynamics of the process are demonstrated by the three top-view photographs of the crystal reproduced in Figure 1. In Figure la, there is no external seed and, in this case, no self-pumped phase conjugation; the beam refracts into an a-face of the crystal, fans sharply to an angle of about 20° with respect to the c-axis, then straightens out to exit a c-face of the crystal. In Figures 1b and 1c, the sequence of steps leading to SPS are shown in the presence of a backward seed. In Figure 1b, the fanned light exiting the crystal strikes a non-specular, diffusive-type surface, the scattering from which acts as a back-injected seed and dramatically lowers the gain-length product threshold condition for stimulated scattering. The phase-conjugate reflection in Figure 1b is in the process of building up; pump depletion is already evident in this photo. Figure 1c is a photo of the steady-state beam trajectory inside the crystal.
Self pulsing in a ring resonator with saturable photorefractive gain and loss
Authors: Lininger Diana M. , Crouch David D. , Martin Peter J. , Anderson Dana Z.
Published: February 2023

A ring resonator with photorefractive gain and loss is an active nonlinear system that exhibits self pulsing of the resonator intensity1. The novel feature of this resonator over single crystal resonators2,3 is the addition of a second crystal in our case to couple light out of the resonator providing a saturable loss4. The nonlinearity of a single crystal resonator is manifested in the saturation of the small signal gain. The nonlinearity of the two crystal system is enriched by the interplay between the two crystal time constants and the small signal gain and loss, as well as the addition of the second saturation point The dynamic behavior of the system can be described as a competitive interaction between gain and loss; if the gain wins, the resonator turns on, and if the loss wins the resonator remains off. Self pulsing occurs when the winner is alternately the gain and then the loss, and then the gain again, and so forth. The relative time constants, coupling strengths, and saturation points of the two crystals dictate the details of the competitive interaction. In this communication we include the loss crystal in a theory for photorefractive resonators to address the experimental observations of self pulsing.
Optical Bistability of a Nematic Liquid Crystal with Photorefractively Amplified Feedback
Authors: Ingold M. , Totland K. , Pauliat G. , Günter P. , Schadt M.
Published: February 2023

Light induced changes of the refractive index in a nematic liquid crystal [1] and in a photorefractive crystal (KNbO3) [2] have been used to design an optically bistable device [3]. In the nematic liquid crystal (NLC) light can reorient biréfringent molecules. Therefore the NLC, placed between crossed polarizers, acts as an optically controlled gate. In the KNbO3 crystal photorefractive two-beam coupling is used for light amplification.
Phasematched Three-Wave Mixing in Poled Optical Fibres
Authors: Fermann M.E. , Wells P.J. , Li L. , Dong L.
Published: February 2023

Second-order nonlinear mode-interference gratings are employed for phasematching three-wave mixing processes in excitation poled optical fibres.
Photovoltaic gratings recorded in Praeseodymium doped La3Ga5SiO14 crystals
Authors: Pauliat G. , Slensky A. , Fridkin V. , Roosen G.
Published: February 2023

Because of their unique sensitivity to optical polarization during recording of information, photovoltaic crystals are of particular interest for optical data processing. Light induced refractive index changes in La3Ga5SiO15 : Pr3 + piezoelectric crystals [1] was previously studied. Hereafter, we present and analyse the first recording of holograms in one of these samples. La3Ga5SiO15 belongs to the point group symmetry 32. Our sample was grown by the Csochralski method. Its dimensions along the crystallographic xyz directions are 10.5×8.5×1.4 mm3. This sample presents a green color.
Nonlinear Neurons Using the Fieldshielding Effect in Photorefractive CdTe
Authors: Ziari Mehrdad , Steier William H. , Devine Robert L. S.
Published: February 2023

A key element in the optical implementation of any neural network is the nonlinear neuron. The most common required feature of this device is a saturating response to an activation input. The activation input is the weighted sum of all the incident beams which are routed through an interconnection network to the neuron. We report on nonlinear neurons using the fieldshielding effect in photorefractive crystals which perform an incoherent addition of the incident intensities1,2. The device responds to CW or synchronously pulsed inputs in a variety of saturated, thresholded or bidirectional manners. Using photorefractive CdTe:In, we demonstrate a response to both inhibitory and excitatory inputs with a high sensitivity to incident light in the 1.0-1.4 μm range.
Holographic Recording and Beam Coupling in Photorepractiv Media with Photo-Induced Light Scattering
Authors: Knyazkov A.V. , Lobanov M.N.
Published: February 2023

Hologram recording and beam coupling in photorefractive media are accompanied by photo-indueed light scattering (PILS). The origin of this phenomenon lies in the recording of numerous noisy dynamic phase gratings formed by the original incident waves and by waves scattered from optical inhomogeneities [1]. Each scattered wave forms, with the incedent waves, a stationary interference pattern that produces the so-called noise hologram. These gratings can be spatially shifted that cause the amplification of scattered waves. In consequence the intensity of initial beams are changed essentially and hologram formation may be disturbed considerably also.
Effects of Phase Conjugation and of Coherent and Incoherent Beam Couplings in Reflection and Transmission in BaTiO3
Authors: Venkateswarlu Putcha , Moghbel M. , Sekhar P. Chandra , George M. C.
Published: February 2023

We reported recently1 coherent beam couplings with He-Ne laser in reflection and transmission in electrically poled BaTiO3. We report here effects of phase conjugation on reflection and transmission. The effects of coherent and incoherent beam couplings on reflection and transmission will be compared. The experimental configuration used in the present experiments is shown in Fig. 1a. Two mutually coherent beams A1 and A2 from a He-Ne laser (6328Å) cross in the BaTiO3 crystal at 5°, with A1 and A2 making 73° and 78° with the c axis respectively. A third beam A3 from a second laser (6328Å) makes a crossing angle of 11° with A1 in the crystal. The self-pumped phase conjugate
A←1(t) of the beam A1, its transmitted part A1T1 after one reflection and the specular reflection A1R1 are examined along with the subsequent transmission and reflection beams A1T2 and A1R2 respectively. The development of these five different beams is shown in Fig. 1b. Fig. 2 shows the specular reflection A1R1, being steady for a while, begins to go down as the self-pumped phase conjugate
A←1(t) and the transmission beam A1T1 develop, and saturates at a lower intensity level.
Dynamic instabilities in the mutually pumped ‘bird-wing’ phase conjugator
Authors: James S.W. , Hussain G. , Eason R.W.
Published: February 2023

Recently a novel class of phase conjugator, the Mutually Pumped Phase Conjugator (MPCC), has been demonstrated in which two simultaneous phase conjugate (PC) reflections are generated by the interaction of two mutually incoherent beams within a crystal of BaTiO3[1, 2, 3]. Currently there are three classes of MPCC distinguished by the number of total internal reflections within the crystal, two, one or none, as shown in fig.1.
The Amplification of an Amplitude Modulated Signal Beam Via Two-Wave Mixing in Photorefractive Media
Authors: Webb D.J. , Solymar L.
Published: February 2023

Two-wave mixing in photorefractive media has been studied theoretically and experimentally by a number of researchers, and a wide range of prospective applications of the effect have been demonstrated or proposed. Recently, Hamel de Montchenault et al., have demonstrated the amplification of high frequency amplitude modulated signals via two-wave mixing in BSO.1,2 In this paper we develop a theoretical framework for the analysis of two-wave mixing with an amplitude modulated signal beam. Preliminary experimental confirmation of the theory is provided.
Possible High Effective Pockels Effect for Photorefractive Gain in III-V Compounds by Using the Franz-Keldysh Effect.
Authors: Picoli G. , Gravey Ph. , Wolffer N. , Vieux V.
Published: February 2023

Modest performance of photorefractive III-V semiconductors is expected in experiments such as two wave mixing (2WM) in the absence of external field, due to their low electro-optic coefficient. Nevertheless we have recently shown experimentally and theoretically that InP:Fe exhibits an average gain higher than 10 cm-1 (with maximum of 20 cm-1 in agreement with theory) [1,2]. This gain can be high enough to obtain the Double Phase Conjugated Mirror (DPCM) phenomena at 1.06 μm with a sample no longer than 5 mm [2]. The underlying physics of such high gain is a synergy of hole and electron emissions giving rise to a new mechanism of resonance [1], which will be named here hydrodynamic resonance.
Experimental Studies of Self-Pumped Photorefractive Ring Resonators
Authors: Hříbek P. , Gower N.C.
Published: February 2023

In the setup shown in Fig.1, two-beam coupling with unidirectional oscillation in a ring resonator which contains a photorefractive BaTiO3 crystal was used to create a new type of self-pumped phase conjugate mirror.
A New Photorefractive Material KNSBN:Co
Authors: Jiang Quanzhong , Song Yongyuan , Sun Daliang , Lu Xinliang , Chen Huanchu
Published: February 2023

Potassium sodium strontium barium niobate (KNSBN) has been developed in our country for the first time1. It is a new ferroelectric with A-sites thoroughly occupied by K+, Na+, Sr2+ and Ba2+ ions. Comparing to BaTiO3, KNSBN crystals have no phase transition at room temperature, but have large hardness coefficient and 180° ferroelectric domains that are easy to be polarized. KNSBN will be one of the most prospective photorefractive materials that can be used in holographic storage , image amplification and optical phase conjugation2. The purpose of this paper is to describe the crystal growth and photorefractive properties of KNSBN:Co.
Photorefractive properties of Bi4Ge3O12 crystals in the ultraviolet spectral range
Authors: Montemezzani G. , Pfändler St. , Günter P.
Published: February 2023

To the best of our knowledge, only preliminary studies of photorefractive effects in the ultraviolet (UV) spectral range have been reported up to now, e.g. in KH2PO4 [1], RbZnBr4 [2] (both at low temperatures), and in LiNbO3 [3, 4] and LiTaO3 [5] in the near UV. Photorefractive materials operating in the UV however could be very useful for all types of coherent optical beam interactions, e.g. beam amplification, dynamical holography, phase-conjugation or photolithographic applications where the use of shorter wavelengths leads to an increased resolution.
Observation of the Photorefractive Effect in Semi-insulating CdS
Authors: Tayebati P. , Kumar J. , Barman D. , Scott S.
Published: February 2023

We report the first observation of the photorefractive effect in Cadmium sulfide. The maximum gain coefficient measured is 0.3 cm−1 at 633 nm. The response time is 1 ms at an intensity of 150 mW/cm2.
High sensitivity resonant photorefractive effect in semi-insulating CdZnTe/ZnTe multiple quantum wells
Authors: Partovi A. , Glass A.M. , Olson D.H. , Zydzik G.J. , Short K.T. , Feldman R.D. , Austin R.F.
Published: February 2023

Although the photorefractive sensitivity of the semiconductors is many orders of magnitude larger than the oxides, their small Pockels electro-optic coefficient has been a serious drawback. By taking advantage of the quadratic effects near the band-edge, nonlinearity and sensitivity of semiconductor photorefractivcs can be dramatically improved. Recently, two-beam-coupling gain coefficients of 16.3 cm−1 in GaAs [1] and 26.0 cm−1 in InP [2] have been reported near the band-edge. Quantum confinement of excitons in multiple quantum wells (MQWs) provides an additional enhancement of the resonant electro-optic nonlinearities. We have recently demonstrated how enhanced photorefractive sensitivity can be obtained in semi-insulting MQW devices [3]. These devices were made semi-insulting through ion-implantation to provide sufficient density of traps for the photorefractive process as well as relieving the need for any pixelation.
Increase of mutual coherence of light beams in two-wave interaction in photorefractive crystals
Authors: Bogodaev N. V. , Ivleva L. I. , Korshunov A. S. , Polozkov N. M. , Shkunov V. V.
Published: February 2023

Two-wave mixing allows one to change effectively Intensities, phases, space profiles, polarizations and time evolution of interacting beams [1,21. We will show, that two-wave mixing of partially coherent beams may be used to increase degree of coherence of these beams. The physics of the effect under discussion is as follows: two partially coherent beams write a refraction index grating in a nonlinear medium whose position and profile are practically stationary. Scattering of strong beam on this grating in the direction of the weak one means that this weak beam acquires an addition, that is coherent with the strong beam, thereby increasing degree of coherence of the beams. Similar effects were discussed in connection with scattering of different frequency components at the common running grating [3] and with Interaction of different polarization components [4,5].
Why Light Beams Follow Curved Paths in Photorefractive Phase Conjugators
Authors: Eliseev V.V. , Zozulya A. A. , Bacher G. D. , Feinberg Jack
Published: February 2023

In recent years a variety of photorefractive phase conjugators have been demonstrated that rely on stimulated light beams.1-6 These self-pumped and mutually-pumped phase conjugators are all closely related7 and differ only in the number and angle of their input beams. Here we propose a detailed though necessarily simplistic description of how light beams spring up inside a photorefractive crystal, and why under some conditions these stimulated light beams appear to follow curved paths inside the crystal. We show that these curves are composed of a number of straight line segments which spring up by stimulated scattering in the photorefractive crystal.
Reflection Grating Photorefractive Self-Pumped Ring Mirror
Authors: Kitayama Ken-ichi , Ito Fumihiko
Published: February 2023

Photorefractive crystal waveguide(PCW) is a novel approach to enhance the photorefractive effects.1-4 The waveguide geometry provides a tight optical field confinement and long interaction length of waves, resulting in increasing diffraction efficiency and angular sensitivity of hologram. It also allows to synthesize a high-density matrix array. Key issues to gain the practical applicability are how to overcome the drawbacks of PCW such as the finite aperture and modal phase dispersion which affects both image fidelity and holographic storage capacity.
Absorption Gratings with Multiple Levels
Authors: Cudney R. S. , Pierce R. M. , Bacher G. D. , Feinberg Jack
Published: February 2023

Absorption gratings can cause significant beam coupling in photorefractive crystals;1,2 in the case of BaTiO3, we found gains as large as 1 cm−1.3 This coupling is caused by the variation in absorption created by the spatially periodic distribution of empty and full trap sites throughout the crystal and it requires only one active level. There is also evidence that there are two or more photoactive levels in BaTiO3, as well as in other photorefractive crystals. In BaTiO3, these extra levels explain the sublinear intensity dependence of the photoconductivity,4,5 as well as light-induced absorption.6,7 Here we study the effects that multiple photo-active levels have on absorption grating coupling. We derive expressions for the two-beam absorption coupling gain vs. the magnitude of the grating wavevector k
g
and show that it does not vanish as kg tends to zero, in contrast to the single photo-active level case. This effect is verified experimentally and is used to evaluate the donor-to-acceptor density ratio in a BaTiO3 crystal.
Fundamental Noise Limits in Photorefractive Systems
Authors: Vachss Frederick , Gu Claire , Hong John , Chang Tallis
Published: February 2023

When photorefractive materials are included as elements in image and signal processing systems, the dynamic range of the photorefractive element has a significant impact on the overall performance of the system. Evaluating the Emits on this dynamic range is of particular importance if we hope to provide a realistic comparison of photorefractive devices such as spatial light modulators1,2 or integrating correlators 3 with similar devices based on competing opto-electronic technologies. We must thus determine the range of signal beam intensities which may be used to write a holographic grating with a reference beam of some fixed intensity, or in other words, the maximum beam ratio that will cause a detectable refractive index grating to be written within the photorefractive material.
Photorefractive Noise Suppression using Achromatic Gratings
Authors: Rabinovich W. S. , Gilbreath G. C. , Feldman B. J.
Published: February 2023

We show that achromatic grating techniques can suppress beam fanning while still allowing two beam coupling to occur.
Two-Beam Coupling with Partially Coherent Light
Authors: Kong Hongzhi , Królikowski Wiesiaw , Cronin-Golomb Mark
Published: February 2023

In photorefractive two-beam coupling the interference of two optical beams creates a refractive index grating resulting in energy transfer between the two beams. In models describing this effect it is usually assumed that both beams have perfect spatial coherence. For some applications such as achromatic volume holography [1], multimode fiber gyroscopes and optical phase conjugation through turbulence, spatial coherence effects may become important in the coupling process. Reduced spatial coherence leads to lower contrast interference fringes in an interference fringe region smaller than that of the perfectly coherent case. In recent work, we have made a quantitative study of the influence of these effects on coupling under the assumption that the coherence properties of the interacting beams do not change during the coupling [2]. In the present work, we include the influence that beam coupling has on spatial coherence of the interacting beams. It is worth noting that the problem of spatial coherence in nonlinear wave mixing has been studied earlier [3-5]. However, all of these studies referred to the case of fast Kerr-medium. Photorefractive materials are much slower and cannot follow fast changes of the phases of interacting beams. Thus description of the mixing process will be different.
Multi-mode operations of a holographic memory using orthogonal phase codes
Authors: Taketomi Yoshinao , Ford Joseph , Sasaki Hironori , Ma Jian , Fainman Yeshaiahu , Lee Sing H.
Published: February 2023

Holographic memories offer the advantages of high storage density, distributed storage, and fast parallel access. These characteristics can be important for parallel opto-electronic computers such as neural networks. The memory can be used to hold a training set which is repetitively displayed during learning. In addition, if partitioning is used to solve problems requiring more neurons than the actual number of processors, the memory can also be used to hold connection weight and threshold information. In this paper, we present results from a photorefractive memory using incremental recording scheduling and binary orthogonal phase codes image addressing. We show how this approach allows modification of the content and diffraction efficiency of the stored images, and how multiple images can be combined by complex amplitude addition and subtraction during reconstruction.
Electo-Optic Effects and Domain Reversal in Sr0.61Ba0.39Nb2O6
Authors: Wilde Jeffrey P. , Hesselink Lambertus
Published: February 2023

We present the results of a comprehensive electro-optic (EO) study of Sr0.61Ba0.39Nb2O6 at λ = 633 nm. The experiments are conducted in the transverse field configuration, hence the effective linear EO coefficient rc is measured. Uniformly poled samples yield rc = 230 ± 20 pm/V at 25°C and rc = 1600 ± 150 pm/V at 65°C. However, the EO behavior is found to substantially degrade when attempting domain reversal. Imaging a crystal through crossed polarizers during the reversal process shows a very non-uniform birefringence distribution in the vicinity of the original -c electrode face.
Numerical Analysis of Photorefractive Grating Formations at Large Modulation
Authors: Brost George A.
Published: February 2023

Enhancements in the two-beam coupling gain can be achieved in cubic crystals of the BSO type by the use of nonstationary external conditions such as the application of a dc field along with a moving interference pattern or by the application of an alternating electric field[1,2,3,4,5]. However, for modulation index, m, greater than about 0.1 the performance falls off significantly with increasing m[1,5]. Some success has been achieved in obtaining steady-state solutions of the nonlinear equations in the presence of moving fringes[1,6,7,8]. These numerical calculations were accomplished by expansion of the variables into their Fourier components or by perturbation techniques. In this paper we model the photorefractive grating formation by a finite difference method. This approach is quite general. The numerical solutions predict the photorefractive behavior at large modulation for stationary and nonstationary photorefractive recording techniques.
Optical Damage Resistant Impurities in Lithium Niobate
Authors: Volk T.R. , Rubinina N.M. , Stizza S.
Published: February 2023

Magnesium1-3, zinc4-6 and some other impurities (substituting mainly for the lithium sites) drastically change optical properties of LiNbO3. In particular the value of optical damage (photorefraction) in LiNbO3:Me (Me = Mg,Zn,…) is sharply reduced compared with undoped LiNbO32-6. Similarly Me impurities tend to supress so-called "dark trace” effect4-6 (that means stable darkening under intensive visible laser radiation).
Determination of the Mobility and Transport Properties of Photocarriers in BGO by the Time-of-Flight Technique
Authors: Tapiero M. , Ennouri A. , Zielinger J. P. , Vola J. P. , Moisan J. Y. , Launay J. C.
Published: February 2023

Sillenites are potentially a promising class of photorefractive materials for specific applications provided that crystals, insuring the corresponding optimal and reproducible operating characteristics, could be prepared. The first step in this direction is to measure and to check the reproducibility of the involved properties of the as-grown material obtained by the usual Czochralski technique which in fact works under relatively well defined conditions. In this respect, the determination of the mobility of photocarriers (electrons in BGO) and the knowledge of the mechanism of charge transport are of fundamental importance.
Parametric Oscillation in Photorefractive Crystals with Local Response in Unclosed Optical Cavities
Authors: Mazur A.P. , Novikov A.D. , Odulov S.G. , Soskin M.S.
Published: February 2023

Steady-state coherent oscillation in the ring-loop and double-side mirror geometries is first observed and studied in media with local nonlinear response. The results of calculation are presented stating that the oscillation becomes possible providing two necessary conditions are met: the oscillation waves appear 1) misaligned with respect to strictly backward to pumps directions to restore the phase matching, and 2) they are shifted in frequency with respect to the pump waves. By appropriate choice of frequencies of two incident waves in double-side mirror geometry one of oscillating waves may be done a perfect conjugate replica of an input wave with limited spatial spectrum.
Identification of light induced charge transfer processes in BaTiO3 by combined ESR and optical measurements
Authors: Schirmer O.F. , Possenriede E. , Kröse H. , Jacobs P.
Published: February 2023

What are the defects responsible for the photorefractive effect in BaTiO3? What charge con version processes involving these defects are taking place during illumination? Along which energetic paths are charges transported? These questions have to be answered if one wants to understand the outstanding photorefractive properties of BaTiO3 on a microscopic basis.
Photorefractive and Photochromic Effects in Barium Titanate
Authors: Garrett M. H. , Chang J. Y. , Pollak T. M. , Jenssen H. P. , Warde C.
Published: February 2023

Nominally undoped p-type BaTiO3 was grown that exhibits interesting intensity dependent photorefractive and photochromic properties. When its photochomism is activated the absorption increases at the activating wavelength and there is a concurrent and proportional reduction in photorefractive response time. Three photoactivated and thermally reversible absorption conditions and the difference spectra of the photochromic crystal are shown in Figure 1.
Time-Integrating Self-Pumped Phase Conjugator
Authors: Oldekop Erik , Siahmakoun Azad
Published: February 2023

Huignard et al. presented a speckle-free imaging processor using a BSO crystal and four-wave mixing. The input beam passed through a diffuser screen which was mounted on a step by step rotation motor. Four-wave mixing generated a phase-conjugated beam which was time-integrated with a Polaroid camera [1].
Intensity Dependent Thresholding and Switching in the Photorefractive "Bridge" Mutually Pumped Phase Conjugator
Authors: James Stephen W. , Eason Robert W.
Published: February 2023

The large electro-optic coefficient of photorefractive materials such as BaTiO3 has allowed the observation of exotic phase conjugators such as the Self-Pumped Phase Conjugator (SPPC)1 and, more recently, the Mutually Pumped Phase Conjugator (MPPC), in which two simultaneous phase conjugate (PC) outputs are produced by the interaction of two mutually incoherent beams within a photorefractive crystal. Several generic MPPC configurations have been reported, differing more in their exact beam geometry rather than the physical mechanism responsible for the effect. These geometries include the Double Phase Conjugate Mirror (DPCM)2, the Mutually incoherent beam coupler (MIBC)3, the Bird-Wing Phase Conjugator (BWPC)4, the Frogs Legs Conjugator3 and the Bridge Conjugator6,7. Both the DPCM and MIBC have been shown to possess input beam intensity ratio dependent reflectivities and threshold8,9, and these properties have been utilised in the DPCM for image processing applications8.
Spectral Pulse Distortion from Two-Beam Coupling of Sub-Picosecond Pulses in a Photorefractive Crystal
Authors: Yao X. Steve , Feinberg Jack
Published: February 2023

Consider the coupling between two trains of mode-locked pulses in a photorefractive crystal. Let each optical pulse be so weak that it takes a large number of pulses to built up a quasi-steady-state refractive-index grating in the crystal. In this case the shape of the pulses will change as the result of beam coupling.1 The temporal pulse shape changes for two reasons. First, interference between the diffracted pulse and the transmitted pulse alters the pulse shape, as shown in Fig. 1. Second, only a portion of each pulse's full frequency spectrum is diffracted by the volume photorefractive grating.
Velocity filtering using complementary gratings in photorefractive BSO
Authors: Hussain Ghazanfar , Eason Robert W.
Published: February 2023

Motion detection, velocity filtering and the detection of change in a given scene are all important aspects for optical processing architectures and systems. So far several different techniques have been reported in the literature that use either all optical [1-4], or hybrid (optical plus electronic) [5-6], schemes to implement novelty filter [1] type operations. The electronic techniques however may have only limited applications due to the sequential nature of the process. For essentially all-optical schemes the intrinsic advantages of parallel image subtraction are clear. In this paper we report a different scheme for motion detection and velocity filtering which uses two spatially multiplexed gratings with a relative phase shift of 180 degrees, (known as complementary gratings). Such grating recording has already been implemented in a LiNbO3 crystal [7].
Parametric Buildup of Photorefractive Gratings with Arbitrary Periods in Optical Waveguides on Lithium Niobate at Radiation Mode Pump
Authors: Shandarov V.
Published: February 2023

Optical waveguides on lithium niobate additionally doped by some impurities like Fe, Cu are greatly attractive elements to study photorefractive effect features and transient hologram properties in dependence on photorefractive impurity kind and concentration.
Photoinduced Light Scattering in the Copper Doped Li1-xHxNbO3 Photorefractive Waveguides
Authors: Kostritskii S. M. , Kolesnikov O. M.
Published: February 2023

Photorefractive waveguides (PRW) in integrated optics have been extensively employed for the realization of couples, reflectors beam splitters resonant filters, wavelength-division multiplexers, etc. [1-4].
Intermode Frequency Nondegenerate Four-Wave Mixing in Planar Waveguides
Authors: Shandarov E.
Published: February 2023

INTRODUCTION The intermode parametric light scattering experimentally observed in LiNbOQ planar waveguides [11. The weak scattering beams amplified by the pump beam because of the photorefractive grating formation. The frequencies of the scattering and pump beams may be different [21. The present paper is devoted to the analysis of the intermode four-wave frequency-nondegenerate mixing in planar waveguides.
Phase Sensitivity of Parametric Gain for Seeded Subharmonic in BaTio3
Authors: Odoulov Sergney G. , Jungen Rolf , Tschudi Theo
Published: February 2023

Two copropagating coherent pump waves can produce in BaTiO3 a variety of light-induced scattering patterns [1-3].
Transverse Instability of Counterpropagating Waves in Photorefractive Media
Authors: Saffman M. , Montgomery D. , Zozulya A. A. , Kuroda K. , Anderson D. Z.
Published: February 2023

Small-scale transverse instability of a single beam or two counterpropagating beams in a Kerr-type nonlinear medium has been known in nonlinear optics for some time (see e.g. [1,2]).
Lyapunov exponent analysis of irregular fluctuations in a self pumped BaTiO3 phase conjugate mirror, establishing transition to chaotic behaviour
Authors: Jeffrey P. M. , Eason R. W.
Published: February 2023

The behaviour of the phase conjugate output from a self pumped [1], BaTiO3 ohase conjugate mirror, is known to exhibit temporal instabilities under certain conditions.
Self-Pumped and Incoherent Phase Conjugation in Optical Communication Links
Authors: Medrano C. , Zgonik M. , Sonderer N. , Ginter P.
Published: February 2023

Since the pioneer work of phase conjugation in photorefractive barium manate [1], many experiments have been performed and different configurations have been proposed in order to improve the obtained reflectivities.
Magneto-Photorefractive Effects in a Diluted Magnetic Semiconductor
Authors: Nolte D. D. , Rana R. S. , Oh Eunsoon , Chua K. , Miotkowski I. , Ramdas A. K.
Published: February 2023

Magneto-electro-optic effects introduce a new dimension to electro- optic and photorefractive pnenomena. Diluted magnetic semiconductors (DMS), such as CdMnTe, have pronounced magneto-optic effects that can be tailored by controlling the fraction of the magnetic ion. II-VI semiconductors, such as CdTe, have already been shown to have good linear electro-optic and photorefractive properties.
Photorefractive Gallium Arsenide: Contribution of Absorption Gratings
Authors: Shcherbin K. V. , Litvinov R. V. , Shandarov E. S.
Published: February 2023

The study of photorefractive properties of noncentrosymmetric semiconductor crystals (GaAs, InP, CdTe, CdS, CdSe) still attracts much attention at present because of possible applications for phase conjugation, amplification of coherent light beams, optical processing of information in near infrared (NR) etc.. Gallium Arsenide distinguishes among these materials as a crystal with well developed technology and with a large scope of information gathered on defect and impurity levels involved in space-charge redistribution [1].
Holographic Grating Recorded By Phase-Locked Detection Method in Sillenite and Ferroelectric Crystals
Authors: Chaptsova G. V. , Goltser I. V. , Kataevskii N. G. , Kundikova N. D. , dovich B. Ya. Zel' , Naumova I. I.
Published: February 2023

It was pointed out [1] that the dependence of the amplitude o space-charge field Esc of holographic grating recorded by phase-locked detection method (FLD) on spatial frequency of the grating is connected with the value of µτ.
Optimum Replay Angle for Maximum Diffraction Efficiency of Holographic Gratings in Fe:LiNbO3 Crystals
Authors: Tao S. , Selviah D. R. , Midwinter J. E.
Published: February 2023

Grating formation in a photorefractive crystal is a dynamic process with the writing beams diffracting from the gratings as they form.
Non-steady-state Photocurrents in BaTiO3
Authors: Sochava S. , Buse K. , Krätzig E.
Published: February 2023

Illumination of a photoconductive material with a light interference pattern leads to a charge redistribution between the traps.
Multi-Class Object Recognition in Real-Time using a Synthetic Discriminant Function Filter
Authors: Cartwright C. M. , Gillespie W. A. , Wang Z.
Published: February 2023

An incoherent correlator has been shown to possess a number of advantages over its coherent counterpart.
Record of a running grating by a standing interference pattern in a photorefractive crystal
Authors: Liberman V. S. , Zel’dovich B. Ya.
Published: February 2023

We suggest the resonant record (i.e. excitation) of a running wave of charge density and refractive index in the crystal by a static interference pattern. We suggest the resonant record (i.e. excitation) of a running wave of charge density and refractive index in the crystal by a static interference pattern.
Photorefractive materials, effects and devices topical meeting Kiev - 1993: A PHOTO ELECTRON PARAMAGNETIC RESONANCE STUDY OF VANADIUM DOPED HIGH RESISTIVE CdTe
Authors: Launay J. C. , von Bardeleben H. J. , Mazoyer V.
Published: February 2023

The investigation of photorefractive semiconductors (s.c.) is strongly motivated by the compatibility of their operating wavelengths with s.c. lasers and optics fibers.
Influence of physical parameters on the photorefractive efficiency of semiconductor multiple quantum wells.
Authors: Magaña L. F. , Agulló-López F. , Carrascosa. M.
Published: February 2023

Recently, a theoretical model based on the Dember mechanism has been proposed [1] to describe the quasi-steady photorefractive gratings generated in multiple quantum well structures (MQW).