The story of the origin of holograms with recording in 3D media is presented. It is pointed out that the capability of a volume photographic picture of an interference pattern of two waves to reconstruct one of the waves when being illuminated by the other one presents a general phenomenon on which holography is based. This phenomenon extends also to the case of a volume picture of travelling waves of intensity resulted from the interference of waves with different frequencies. An alternative method of holographic recording in 3D media presents so-called selectograms. According to this method, the light scattered by an object is split into two components by a diffractive grating that is positioned just in front of a thick-layered light- sensitive material. The interference pattern of these components is record in a 3D light-sensitive medium. The reconstruction of the selectogram is performed by an extended diffuse source of light. An experiment on the recording of the reference-free selectogram are low requirements as to the coherence of the recording and reconstructing light and its insensitivity to the vibration of the set-up during the recording.

Photorefractive rhodium doped barium titanate (BaTiO3:Rh) is now well known for its significant response at near infrared wavelengths .We studied and characterized this crystal at 1.06 j.tm. By twowave mixing experiments in a 45°-cut crystal, we measured a maximum photorefractive gain F of 23 cm1 with cw illumination and 16.6 cm1 with nanosecond illumination, together with a low absorption (0. 1 cm1). Using spectroscopic determinations of the photorefractive sites 2 (Rh3, Rh4, Rh5), we showed that the photorefractive properties of BaTiO3 Rh could be well described by a three charge state model .This enabled to determine the internal parameters of the material using experimental characterizations and to accurately predict its performances at 1 .06 tm. Comparative characterizations of several BaTiO3:Rh samples proved that this material is now well reproducible, which is of prime importance for applications. Reproducibility, high photorefractive gain, low absorption and accurate theoretical description make BaTiO3:Rh a good candidate for realization and optimization of non linear functions like optical phase conjugation. The application we are interested in, is the dynamic wavefront correction of nanosecond Nd:YAG master-oscillator power-amplifier (MOPA) laser sources.

Transition metals in particular increase the photorefractive sensitivity. We have reported in part I of the observed enhancement for the nonlinearity of these crystals due to the single and doubly dopants. In this part, we tried to answer some of the questions about the enhancement of the photorefractive sensitivity due to gamma irradiation. The crystals were irradiated by gamma ray and the EPR spectra were obtained. A new EPR center was observed at 3420G in Mn:Fe:LiNbO3 crystals. The Degenerate four wave mixing experiment was performed for these crystals and we have observed that the intensity of the PC signal from Ni:LiNbO3 crystal was increased by almost 30 percent. By applying the Ar⁺ laser in situ the EPR signal was decreased and the center was bleached after almost nine minutes in the case of LiNbO3:Ni and four minutes in the case of LiNbO3:Fe:Mn crystal. An interpretation for this phenomenon will be given on the light of Kuktarev model.

We report that two beam coupling and response time of reduced BaTiO₃:Rh at wavelengths of 514 nm and 633 nm. For the as-grown, the carriers are holes for both of wavelengths of 514 nm and 633 nm. When reduced at the atmosphere of 10^-10 atm oxygen partial pressure, the carrier is electron for wavelength of 514 nm, and hole for 633 nm. With higher reduction, the carriers are electrons for both of wavelengths. Two beam coupling gain is also dependent on the reduction level and incident wavelength. For the as-grown, the trap density is 23 by 10¹⁶ cm^-3 for 514 nm and 15 by 10¹⁶ cm^-3 for 633 nm. For the sample reduced at the atmosphere of 10^-10 atm oxygen partial pressure, the trap density decreases and is 5 by 10¹⁶ cm^-3 for 514 nm and 2 by 10¹⁶ cm^-3 for 633 nm. With higher reduction, the trap density increases and is 12 by 10¹⁶ cm^-3 for 514 nm and 5 by 10¹⁶ cm^-3 for 633 nm.

We investigate self-organization of a laser beam into a scattering ring in photorefractive potassium niobate when the phase of the coupling constant is arbitrary. We find that for a range of values of the phase and amplitude of the coupling gain, the calculated forward and backward scattered ratios are in reasonable agreement with experimental observations. The phase of the coupling constant is determined by an interplay of both diffusive and photovoltaic nonlinearities, as well as phase shifts in the induced grating profile with only photovoltaic nonlinearities but for strong modulation depths of the intensity grating.

A resonant enhanced phase-conjugate from poly polymer doped with DCM, and Sulforhodamine was observed using the 10P20 CO₂ laser line. The effect of the dye concentration on the phase conjugate reflection coefficient was observed and was found to have an optimum value. The Z-Scan experiment was carried out and (chi) ³ was determined. As, the Z-scan offers a practical method to determine the sign and magnitude of refractive nonlinearities that offers simplicity as well as high sensitivities. The magnitude of refractive nonlinearities was compared from both Z-Scan and DFWM and was found to be in a close agreement. To our knowledge this is the first time PC signal to be observed from PMMA:DCM at 10 micrometers . Also, FTIR was performed for these samples and will be reported as well.

Based on the Li set vacancy model, we analyze the incorporation process of Mg ion in LiNbO₃:Mg crystals with increasing MgO doping concentration. The obtained results are in good agreement with the experimental data reported in the literature. The congruent melting compositions are predicted according to our suggested incorporation model when the (Li₂O-MgO-Nb₂O₅) system is considered as a ternary one.A procedure is suggested to find out the congruent melting compositions of LiNbO₃:Mg crystals.

To exceed the capacity limitation of optical method of data storage, we record and read digital data in 3D in a photorefractive material which is photosensitive for recording and refractile in reading. Optical systems, including a confocal laser-scanning system and a two-photon laser-scanning system, and photorefractive materials suitable for 3D data storage are discussed with current problems for commercial applications. We will show our latest result of two-photon recording in an undoped Lithium Niobate crystal. The comparison between photorefractive digital 3D memory with conventional holographic 3D memory and near-field memory is also discussed in terms of dynamic range, noise, recording density, and accessibility.

Optical signal processing, traditionally employed in the spatial domain, has been experiencing a renaissance with femtosecond laser pulse technology. Temporal optical information can now be manipulated via linear and nonlinear processes, and stored and retrieved, by converting optical signals between the spatial and temporal domains. In this manuscript, we review the state-of-the-art in the spatio- temporal optical signal processing techniques for information data coding, data conversion, signal recording, as well as signal characterization. Applications of these techniques for future computing, communication, storage, and signal processing systems are discussed.

Photorefractive Fe doped LiNbO₃ single crystal has been proposed to be a material for Computer-Generated Hologram (CGH). The diffraction efficiency of the synthesized CGH was experimentally estimated at around 20 percent. In this estimation, several kinds of diffraction grating were constructed in the crystal by a focused laser beam that was manipulated by a laser beam scanner. Also, by using the same system, a well designed digital CGH was synthesized in Fe:LiNbO₃ single crystal. This CGH enable to reconstruct the recorded pattern with the desired intensity in an optical Fourier transformation system.

Here we report our study on Bragg degeneracy in a transmission volume hologram. The Bragg degeneracy generates large crosstalk in an optical storage but nearly 1D shift- invariance in optical correlator. We simulate 2D distributions of the diffraction lights when the reading beam carries a plane wave or an image. The simulation results offer a clear picture of Bragg diffraction for optical storage and optical correlation in a bulk photorefractive crystal.

Photorefractive spatial solitons have recently been the object of intense fundamental research. This paper proposes two applications of this interesting low power phenomenon. Photorefractive self-focusing can indeed be used to enhance nonlinear processes such as wavelength conversion. Furthermore, its sensitivity to low power optical beams makes it a good candidate towards all optical switching and computing, provided the time response issues have been solved. This paper proposes a switching technology with optical powers on the scale of a few mW/cm² and provides strong hints towards solving the photorefractive time response issue.

This paper presents a theoretical and experimental investigation of the self-focusing of a laser pulse in a photorefractive medium on a nanosecond time-scale. For times shorter than the dielectric recombination time, we analyze the space-charge field build-up with respect to time and space and provide strong hints on the short time self- focusing of a narrow powerful beam. In order to validate our theoretical and numerical analysis, systematic investigations were performed on a Bi₁₂TiO₂₀ crystal, to show the effect of the external applied electric field, the intensity of the laser pulse and the beam waist.

We study the cross-talk between the competing holographic gratings in photorefractive cubic crystal Bi₁₂SiO₂₀. The cross-talk technique applies to measure a reduction factor which distinctly appears at low spatial frequency free electron distribution in diffusion regime under conditions so that direct observation of photorefractive gratings can not be performed. We suggest a hypothesis for the reduction factor of the carriers distribution with respect to light modulation is a long-distance photoelectron migration related to a high initial kinetic energy of the free carriers.

The refractive index of Germanium-doped planar waveguides can be changed when it is exposed to UV light. Furthermore, if the waveguide is bombarded by ions during exposure, a negative index change is obtained. If the waveguide is not bombarded by ions, positive change in index results. In a dye-doped polymer fiber, large index change is obtained due to the photosensitivity effect of the dye, in our case, fluorescein. However, the basic material, PMMA, is also photosensitive.

In this paper, a design on intra-chip optical interconnects based on a wavelength multiplexed two layer structure is presented. The key to this approach is the use of one planar waveguide, covering the whole multichip module and its use of unique tunable diffractive optics elements. In the bottom layer, there are multiple modules. In each module, there is a light receiver to receive the clock signal and another to receive information from other individual processing units (IPUs). There is also a light emitter to send information out to other IPUs. The vertical light emitter will send the signal to the upper layer polymer 2D planar waveguide. To determine which IPUs receive information, a set of fast speed wavelength tunable filters will be fabricated on the polymer waveguide and integrated together with each light source. As a result, we can realize arbitrary reconfigurable interconnects between the entire individual processing units. For examples, is the wavelength for the first processing unit is tuned at (lambda) ₂, only the second processing unit can receive this signal because only the second volume holographic grating can diffract wavelength (lambda) ₂. Since all tunable filters can be addressed simultaneously, the whole interconnect system is parallel processing.

Oscillations are observed in mutual pumped phase conjugate emission when two coherent laser beams are incident on the positive C face of a BaTiO₃ crystal in a symmetric configuration. The angle between the laser beams is varied from 30 degrees to 120 degrees. Self-pumped emission and oscillation are also studied with one of the laser beams making angels between 15 degrees and 36 degrees with the crystal. Growth and decay of the mutual pumped phase conjugate signals when either of the laser beams is cut off are also studied. A plausible explanation of the observed features is given in terms of formation and competition between different types of gratings formed in the crystal by the laser beams.

We demonstrate a photorefractive incoherent-to-coherent optical converter using anisotropic self-diffraction (ASD) in BaTiO₃. Only two writing beams are required in the spatial light modulator and no extra readout beam is required. The diffraction efficiency reaches 50 percent. The resolution diffracted image is 22.6 lp/mm with a 6.6 by 6.6 by 7 mm crystal. We can increase the resolution by using a thin crystal without expense of the diffraction efficiency because of the inherent high diffraction efficiency of ASD in BaTiO₃.

In processes of obtaining a new NLO materials, modifying and enhancing the existing materials, various aromatic compounds were synthesized with the intent of comparing their nonlinear optical properties. Different techniques were used to characterize the proton-irradiated N-isobutyl-4-methyl-6- nitro-2-quinolinamine sample. From the electron paramagnetic resonance measurements; the spin concentration seemed to increase significantly when the proton beam increased from 0 to 2.2 Mev and then the spin concentration starts decreasing up to 3 Mev. The EPR signal for N-isobutyl was singlet up to 1.8 Mev then split into duplet around 2 Mev. Then EPR signal for N-isobutyl was singlet up to 1.8 Mev-irradiated-sample. FTIR analysis also shows a dramatic increase in transmission in different bands of the spectra. Due to higher energy proton irradiation, a high significant improvement in the nonlinear characteristics of the sample was observed. A theoretical interpretation for the effect of the proton irradiation enhancement of the nonlinearity of these will be presented as well.

A multi-function optical computing system performing the NOR and NAND operations with two photorefractive BaTiO₃ crystals is proposed. Instead of using the interference between the input signals and local incoherent erasing, we use incoherent erasing techniques in the construction of this system. The multi-function system works with different polarization states of the input optical waves. The system works with different polarization states of the input optical waves. The system is able to accept temporally incoherent and spatially incoherent signals. Optical experimental result with spatially incoherent optical images demonstrating the incoherent parallel processing capabilities and the multi-function logic operations of the system are shown.

We have discovered for mutually pumped phase conjugator (MPPC) with a novel configuration 'ray' in a 0 degree-cut nominally undoped photorefractive BaTiO₃ crystal which phase conjugates two mutually incoherent beams simultaneously. Both beams incident +c face of the crystal make a non-zero obtuse angle to the crystal's +c axis, respectively. This leads to an effective mutual coupling as two fans emanating from the input beam shave a large interaction region. This novel MPPC exhibits phase conjugation with three internal reflection sand is remarkably insensitive to angular and lateral positional changes of the two input beams. We refer to this phase conjugator as 'ray of mutually pumped phase conjugator'. The temporal responses, positional and angular acceptance, and the variations of the phase-conjugate reflectively with input beam power ratio have also been determined. These characteristics make this mutually pumped phase conjugator particularly interesting for practical applications such as for injection locking lasers and for optical free space communications.

To the best of our knowledge, we have demonstrated for the first time that ring waveguides can be written and stored in photovoltaic and self-defocusing photorefractive medium LiNbO₃:Fe crystals. The interactions between the ring solitons, such as the fusion and the birth of ring solitons, have been experimentally observed.

A laser-diode interferometer with a self-pumped (cat) phase- conjugate mirror is presented. The phase is shifted to produce a spatially uniform phase change uncancelled by a phase conjugator between the two beams of an interferometer. An ac interferometer would be realized by means of heterodyne techniques that can be employed by modulating the phase of the conjugate wave by using the wavelength-shifted laser diode (LD). Dynamic response of the phase-conjugate reflectivity of a BaTiO₃ crystal is respond that is illuminated by a sinusoidal-modulated LD. The multigratings inside a cat mirror are taking into account. The time evolution can be solved by the coupled wave equation and the relaxation equation. The experimental results agree fairly well with numerical results.

Three architectures of acousto-optic deflectors performing both spatial and angular multiplexing for holographic memory systems are discussed. The main parameters of such deflectors are determined and analyzed. It is found that increase in one parameter inevitably results in decrease in one or two other parameters. The highest information capacity can be achieved in the two coordinate multichannel variants.

Incoherent optical pattern recognition has been demonstrated with a simple setup using photorefractive BaTiO₃ crystal. The input patterns to be identified can be transmitted into the system with complete incoherent light. The setup does not required pre-fabricated filters for its operation and thus is a real-time system. The working principles of the systems are the photorefractive beam fanning effect and the degenerate four-wave mixing.

Optical holographic correlators can perform many correlations simultaneously. Because the output plane must be divided among the individual templates in the system, for many systems shift-invariance limits the number of correlation templates than can be stored in one correlator. When the system is completely shift-invariant, the correlation peak from one correlator can shift into an area that has been reserved for a different template; in this case, a shifted version of one object might be mistaken for a well-centered version of a different object. This paper describes a technique to control the shift-invariance of a correlator system by moving the holographic material away from the Fourier plane.

Using anisotropic self-diffraction in BaTiO₃, we propose a novel optical symmetry filter which the filter allows us to distinguish a centro-symmetric pattern from a non-centro- symmetric pattern easily with scale invariance. This filter is self-referential, so no extra reference target is required. Both of the theoretical explanation and experimental demonstration are shown.

In this paper, we describe how a photorefractive holographic interferometer may be modified to implement the wavelet transform. By placing phase-only spatial light modulators, such as acousto-optic devices, in the optical path of the sample and reference beams, it is possible to perform correlations on the phase modulated signals and then convert them into intensity modulated signals for detection and signal processing. We discuss a potential application of this architecture known as progressive pattern recognition using the wavelet transform.

Photoinduced anisotropy in terms of dichroism and birefringence was investigated in a series of experiments. Measurements and comparisons were made using samples of wild type bacteriorhodopsin and its mutations 3,4-dehydro BR and 4-keto BR.

Although photorefractive (PR) filter has the advantage of large storage capacity, the thickness of the filter also impairs the target shift limitation. In this paper, we have investigated the thickness requirement, as imposed by the focal depth of the transform lens, and the shift-invariant, as imposed by the Bragg diffraction. The commonly used photorefractive-based correlators are studied, which are VanderLugt, joint transform, and reflective types (RC) correlators. We have shown that PR-RC performance better, in terms of shift-invariant tolerance.

The multi-beam holographic optical head that combines multi- beam with holographic is proposed. This optical head has a light and compact structure, and work with parallel mode. As a result, the data transfer rate of optical disc drive can increase by several or tens times. The designing and fabricating of the key component of the multi-beam holographic optical head based on above designing are discussed also. The mathematical model of this optical head's diffraction is obtained by theory, the simulating of the multi-beam holographic optical head is carried out by computer. As a result, all kinds of signal waveform of each channel are obtained, including data signa, focus error signa, and tracking error signal. It is proved by the result that the multi-beam holographic optical head is a practicable method to realize the parallel reading/writing of optical disc drive.