We studied the behavior of filaments that are formed in the beam of ultrashort laser pulses via self-focusing effect. A refractive index change of 0.01 was confirmed by three independent image-analysis techniques. The waveguide structures were a few to 500 micrometers long depending on the numerical aperture (NA) of the ultrashort pulses. All the diameters were approximately two micrometers. We identified the conditions to produce one filament in one beam and produced waveguides using this single filament. By moving the focus along the optical axis, a longer straight waveguide can be produced. We also demonstrate that one can seize and translate voids formed by ultrashort laser pulses inside silica glass and can also merge two voids into one. We further present a clear evidence of a void and its surrounded region by showing scanning-electron-microscopic image of cleaved voids: we cleaved through the glass along a plane that includes the laser-ablated thin line on the surface and the voids formed inside.

The diffraction of ultrashort laser pulses from static gratings in photorefractive multiple quantum wells (PRQW) has been investigated for use as a diffractive optical elements in information processing systems with ultrashort laser pulses. The PRQW used in this experiment was specially designed to exhibit broad bandwidth. The desirable spectra of the diffracted pulses from the PRQW was observed experimentally. The bandwidth for one of the PRQW devices was 13 nm.

We report enhanced photorefractive sensitivity in Mn, Ce doped LiNbO₃ at 514 nm and 633 nm under ultraviolet illumination at 365 nm. Without ultraviolet sensitization, the crystal showed very weak diffraction efficiency and self-erased behavior. The accumulation of charged states by ultraviolet light is observed even after the hologram is erased because of the asymmetric process of recording and reading. The concentrations of doped ions and the intensity ratio of ultraviolet and recording light are important factors to improve sensitivity in this material.

All known polarizers operate via a separation of orthogonal electric field components, one of which is subsequently discarded. As a result, 50% of the unpolarized incident light is wasted in the process of conversion to polarized light. We demonstrate a new method by which the optical power in the ordinarily discarded component is used as the pump to amplify the retained component in a nonlinear amplifier. We achieve greater than 50% throughput. These new polarizers are self-organizing in that they form internal gratings which, based only on the phase relationship between the two components, best optimize the transfer of power to the desired component.

We show that using a simple two-beam coupling geometry and higher (non-Bragg) diffracted orders, one can obtain triple correlation between objects. The objects correlated here are microorganisms such as algae and can be used for identification of these microorganisms and their concentration in the solvent. The material used for correlation is a photorefractive organic polymer with no bias voltage.

We review the main properties and the potential applications of photorefractive solitons. Several different types of photorefractive solitons are referred, but a special attention is paid to one type: the photorefractive screening soliton. Both bright and dark screening solitons, together with the corresponding induced waveguides, are identified and discussed. The main characteristics of soliton interactions and the more recent topic of incoherent solitons are also reviewed.

The nonlinearity of phase-conjugate beam reflection with four-wave mixing in BSO crystal by the moving grating at large fringe modulation formed by the incident-beams ratio is investigated. The experimental results have shown that the optimum fringe velocity is the incident-beam ratio and the total-light-intensity dependent, the reflectivity at the optimum fringe velocity is the incident-beam ratio and the fringe-spacing dependent. Based on these nonlinear properties, the edge-enhancement of an object is achieved.

Laser-diode phase-conjugate interferometry with self-pumped phase-conjugate mirrors (SPPCMs) is presented by using a frequency-modulated continuous-wave (FMCW) technique. The phase is shifted to produce a spatially uniform phase change uncancelled by a phase conjugator between two beams of an unbalanced interferometer. The phase-modulated conjugate wave with the frequency-ramped laser diode (LD) is stable since the frequency-modulated LD can decrease the grating contrast due to the average action of moving gratings inside a crystal. A wavefront-matched interferometer has been constructed with two BaTiO₃, SPPCMs instead of usual two mirrors. The wavefront-matched unbalanced interferometer does not depend on the distortion of input wave, but can only detect the spatially uniform phase change introduced by the displacement of one cat mirror in two phase-conjugate mirrors. The FMCW technique can be applied to a tunable-LD wavefront-matched interferometer for distance measurement that is not significantly dependent on the phase distortion. The distance introduced by the displacement of one cat mirror in the interferometer can be measured by detecting the carrier beat frequencies with an rf spectrum analyzer.

Four kinds of lithium niobate crystals doped with Cu:Ce, Mn:Cu:Ce, Mn:Fe, and Mn:Fe:Mg processed under oxidation or reduction conditions are studied experimentally for the photorefractive non-volatile holographic storage with the first scheme, i.e with ultraviolet light sensitizing and red light recording. On the condition of non-volatile holographic storage with high signal-to-noise ratio, the non-volatile diffraction efficiency of the oxidized LiNbO₃:Cu:Ce crystal is the highest among all studied samples. The non-volatile holographic storage in the oxidized LiNbO₃:Cu:Ce crystal is performed with the second scheme, i.e with blue light sensitizing and red light recording, and the intensity of the blue light is optimized.

We use the scalar diffraction theory to analyze the grating detuning effect in a volume holographic data storage system. The general formulas for describing the two dimensional distribution of retrieved image under the detuning effect have been derived. In terms of the image uniformity and the pixel shift of the retrieval image, computer simulations are used to perform a quantitative analysis.

We present our studies on the temperature effect of the grating recorded in a phenathrenequinone (PQ) doped poly(methyl methacrylate) (PMMA) photopolymer. The characteristics for recording a strong single grating have been studied. We find that the main limitation of full utilization of the refractive index modulation of the hologram is caused by the scattering effect. Experimental demonstration of using dark enhancement to enhance diffraction efficiency of a grating is presented.

Fiber communication networks utilize wavelength-division- multiplexing (WDM) to enhance the transmission capacity of fiber-optical networks. This technique requires narrowband wavelength filters for multiplexing and de-multiplexing of the channels. We report on realization of an advanced multiplex/demultiplex device based on superimposed volume- phase gratings in lithium-niobate crystals. The gratings are recorded via the photorefractive effect by interference of two green laser beams. Thermal fixing is employed to increase the lifetime of the recorded gratings. Infrared light in the telecommunication wavelength region around 1500 nm is diffracted from the gratings. Each grating reflects light of a certain WDM channel. The selected wavelengths and the propagation directions of the diffracted beams are determined by spatial frequency and orientation of the gratings in the crystal. We will present the basic concept of this technology as well as recent advances : (1) construction and testing of a two-channel demultiplexer prototype (fiber to fiber insertion loss 5-6 dB, crosstalk less than -25 dB, channel spacing 0.8 nm), (2) simultaneous demultiplexing of 8 channels (separation 0.8 nm).

Two-wave coupling between orthogonally polarized beams in a Cerium doped potassium sodium strontium barium niobate crystal is studied. The coupling gain coefficient, the response time and the saturation diffraction efficiency of the volume grating are measured with respect to the angle (phi) between the polarized direction of the pump beam and the c-axis of the crystal. It is found that they have the similar variation behavior. In our experimental condition, the maximum coupling gain coefficient is 3.2 cm^-1, the maximum response time is about 55 seconds and the maximum saturation diffraction efficiency is about 18.5%. The maximum values are obtained at (phi) =20 degree(s) and (phi) =160 degree(s). Numerical calculated results from the couple-wave equations are given, which are coincident with the experimental data.

Volume holographic storage combines fast, parallel readout (because each hologram stores a large data page) with high density (because many holograms are multiplexed within the same volume). Phase-conjugate readout has been proposed as a way to eliminate the precision optics that recent demonstrations have relied upon to image the pixels of the input spatial light modulator (SLM) onto those of the output detector array. However, hologram multiplexing with the phase-conjugate approach requires multiple pairs of phase- conjugate beams, which are extremely difficult to create and maintain. We have developed a two-step recording process which combines the advantages of phase-conjugate holography with the simplicity of using the same multiplexed reference beam for recording and readout. The data-bearing object beam first passes completely through a long storage crystal, and is then temporarily stored in a second holographic storage material. This buffer hologram is immediately read with a phase-conjugate reference beam, reconstructing a phase- conjugate object beam which travels back into the storage crystal. This new object beam can now be recorded, and then later reconstructed, with a multiplexed reference beam at any of the spatial storage locations. We describe the advantages and limitations of this technique, the materials requirements for the buffer hologram, and describe a test platform designed to implement this technique.

The use of spatial solitons to effect optical interconnects is being actively studied by a number of researchers. Perhaps unjustifiably overlooked in this work is the formation of a grating where two solitons intersect, and the diversion of light into a new path through the resulting Bragg diffraction. An experiment is conducted in which solitons, formed from two mutually coherent argon beams, collide at an angle of several degrees in the Strontium Barium Niobate (SBN-60) crystal. Up to 35% of the intensity of one beam is transferred into the other; if one beam is interrupted, a significant rise or drop in intensity is observed in the other. Using the two solitons, the control over their own paths, and the exchange of information between them at their intersection, an interconnect system is established. Experimental and theoretical results pertinent to those concepts are presented, and a possible interconnection system based on these ideas is discussed.

Photosensitive optical fibers provide great potential for development of many important devices. The application of photosensitivity of optical fibers has profound impact to telecommunication at the 1550nm window and, increasingly, to optical fiber sensing as well as other systems. Large tunability in fiber grating is of great significance for future dense wavelength division multiplexing where channel selectivity and reconfigurability are of prime concern. The group in University of New South Wales has recently investigated the photo sensitivities of various polymer optical fibers and has demonstrated that polymer optical fiber Bragg grating based on poly(methyl methacrylate) could be made and tuned over a range of more than 70nm, far exceeding that could possibly achieved in conventional silica fiber Bragg gratings. More recently, the photosensitivity of a low loss new polymer fibre material- CYTOP has been demonstrated. These research activities and results unfold the great potential of realizing a new class of fiber Bragg grating for various photonic applications. This paper will review the recent developments and will discuss some of the important prospects and remaining challenges in polymer fiber Bragg gratings and related topics.

Three dimensional shifting sensitivity of volume holograms based on random phase encoding using a ground glass has been theoretically analyzed. There are different shifting tolerances in different shifting directions, which include laterally horizontal, laterally vertical, and longitudinal directions. The shifting sensitivity depends on the diameter of the illumination region on the random phase plate, the thickness of the hologram and the distance between them. We apply the theoretical calculation to a degeneracy condition, a point object, and theoretically analyze the shifting tolerance of shifting multiplexing in holographic storage and holographic confocal microscope.

Here we propose our study in the temporal and spatial uniformity of a phase conjugate wave generated from photorefractive self-pumped phase conjugators. The phase perturbation of the conjugate wave is caused by the thermal effect in the crystals. We find that beam size and intensity is the key parameters for controlling the uniformity.

An all-optical fiber sensing system with interconnection in volume holograms through random phase encoding has been demonstrated. The random phase is generated from the speckles of a multi-mode fiber. The experimental and stimulation results are also presented.

The possibility to use the third dimension of the medium for data storage and extraction in memory devices is accessible in a wide sense only if a holographic method of data recording and reconstruction is used. However, this possibility has many limitations part of which is inherent just to the holographic devices. Among them one can find significant influence of a limited dynamic range, quadratic dependence of power expenses on the amount of stored information, limitations of the number of selective positions which can be used for the hologram multiplexing as well as some geometric limitations which are significant in 3-D holographic memory. On a level with that, such phenomena exercise influence on holographic memory device information capability as diffraction limits of information input and storage, spatial information losses in a complex system, limitations of rate of information input and output in holographic memory devices etc. The limitations caused by each of the listed factors have been compared and analyzed. It has been found that some of these factors do not influence on information capability limitations provided by the other reasons.

Two-dimensional periodic waveguides have been made by depositing colloidal crystals on top of a planar waveguide. We present a fabrication technique and discuss applications of 2D periodic waveguides in optical coupling, filtering, and wavelength demultiplexing.

We describe an ultrafast all-optical processor for time-to- 2-D-space conversion by using a second harmonic generation. We show the proposed technique for ultrafast all-optical processor that can convert a modulated ultra-short optical pulse sequence into a 2-D spatial distribution for ultrafast spatial information processing with ultra-short pulse laser. Experimental results show the proposed processor can achieve the throughput of conversion over Tbps.

In this paper, a broadband tunable long period grating (LPG) with an ultra-thin cladding layer using liquid crystal is presented. By chemical etching the long period grating to a very thin diameter (approximately 30micrometers ), the long period grating becomes extremely sensitive to the surrounding refractive index change so that a wide range tunable filter is realized. By using liquid crystal material (18523) that has a n_o less than the refractive index of cladding, a resonant band of the LPG is tuned by controlling the temperature of the liquid crystal. We obtained a tuning range of 87nm with a temperature change of only approximately 22 degrees. It is believed that this filter has the largest temperature-dependent tuning effect ever reported. Further experiment will be focused on photo- induced reorientation of the liquid crystal molecules, so that another type of tunable filter via photochemical effect can be realized.

The prospects for a thin film amorphous silicon based integrated photonic technology spanning materials, devices, and physics are described. Impurity implantation is an effective technique for the preparation of permanent refractive index patterning due to the very high solubility limits of the amorphous phase. Methods of preparing films of the requisite thickness and smoothness for photonic application have been identified. Other experiments suggest that there is a light induced refractive index change of sufficient magnitude for patterning light adaptive and/or light defined optical elements. Two light induced refractive index changes, one fast and one slow, were observed in amorphous silicon materials. These changes were observed over temperatures ranging from room temperature to 250 degree(s)C and do not appear to diminish with increasing temperature over this range. Simulations were used to elucidate the physics of light induced change. Several classes of thin film devices were developed which span a wide range of functionality.

Speckle patterns from optical fibers can be used as reference beams in holographic storage. Quasi-random patterns from multimode or tapered single mode fibers enhance hologram selectivity. The storage and retrieval of near-field photorefractive hologram using a near-field scanning optical microscope is also discussed.

The application of photorefractive materials has shown remarkable promise over the last two decades for various computation-intensive information processing applications such as pattern recognition. In this paper, we explore various two-beam coupling and four-wave mixing architectures and algorithms for all-optical implementation of real time pattern recognition techniques suing photorefractive materials. The application of novel concepts such as the incoherent-erasure fringe-adjusted joint transform correlation, obscured target detection, heterogeneous correlation and nonlinear compansive noise reduction for enhancing the correlation performance are discussed in detail. The trade-offs between various performance criteria such as correlation peak intensity, efficiency and noise performance has been investigated.

The devices entering an input information signal into an optical processing scheme are the most important elements in optical information and measurement systems. For a number of applications, acousto-optic cells are the most preferable such devices. The parameters of the devices entering the initial signal into optical processing schemes determine the maximum and operation characteristics of the entire system. The questions of the design, manufacturing, and characterization of acousto-optic cells for information and measurement systems are discussed.

By using a self-pumped conjugator (Cat conjugator) it is demonstrated to produce the phase conjugate reflection of double signals, induced by the self-pumped phase conjugation, in a 16 degree(s) cut Cu-doped KNSBN photorefractive crystal. On various experimental conditions, the phase conjugate reflectivities of signals were measured versus the pump-signal beam ratio. A comparison was made between the signal's reflectivities in and without the presence of the other signal beam. The multi-region four-wave mixing model within the same crystal has been employed to explain the geometry performance and the experimental results.

In this paper, we show two optical storage and retrieval techniques: a technique to record/readout data in serial format with real time detection, and an orthogonal-code multiplexed recording/readout system with nonlinear gated detection. Both of these techniques are based on femtosecond optical short pulses. In the former storage and detection technique, a train of pulses is recorded via spectral holography into a photorefractive crystal at wavelength 460 nm and the recorded hologram is read at the wavelength 920 nm, allowing nonvolatile readout of information from the photorefractive crystal. For detection and demultiplexing of a femtosecond pulse sequence whose time duration is much longer than the pulse width, a new pulse correlation technique is developed that is capable of real-time conversion of a femtosecond pulse sequence into its spatial image. Our technique uses a grating at the entrance of the system, thus introducing a transverse time delay (TTD) into the transform-limited reference pulse. The shaped signal pulses and the TTD reference pulse are mixed in a nonlinear optical crystal, producing a second-harmonic field that carries the spatial image of the temporal shaped signal pulse. In the orthogonal-code multiplexed recording technique with spectral holography, a signal pulse that contains a 1-D spatial information is recorded with a unique spectral phase-coded reference pulse, and multiplexing is performed by orthogonal phase-coding of reference pulses. Information readout is performed employing a nonlinear time- grating technique with the use of wave mixing in nonlinear optical crystals. We present the basic principles and experimental results for those femtosecond optics systems.

We present several encryption techniques for holographic data storage, using orthogonal phase-code multiplexing and random phase encoding. Our system is capable of storing page-oriented data based on the selectivity of orthogonal phase-codes in a photorefractive LiNbO₃ storage crystal. In order to encrypt data, random phase multiplexing is added to the system. We proof that the combination of deterministic and random phase code multiplexing is possible with low cross-talk and take advantage of this technique for an extremely secure data encryption. Moreover, the potential of phase-code multiplexing to realize arithmetic operations is exploited for data encryption purposes.

The paper considers the methods of computation and fabrication of focusing phase optical elements that operate in the visible spectral range and produce specific light patterns in the near field. We determine the relationship between the dimension of the quantization grid used in computations and the performance of the optical elements and parameters of corresponding light patterns. The paper gives the results of computation of 1D and 2D HOEs and describes the fabrication methods and experimental samples.

We propose a new holographic memory scheme based on random phase-encoded multiplexing in a photorefractive LiNbO₃:Fe crystal. Experimental results show that rotating a diffuser placed as a random phase modulator in the path of the reference beam provides a simple yet effective method of increasing the holographic storage capabilities of the crystal. Combining this rotational multiplexing with angular multiplexing offers further advantages. Storage capabilities can be optimized by using a post-image random phase plate in the path of the object beam. The technique is applied to a triple phase-encoded optical security system that takes advantage of the high angular selectivity of the angular-rotational multiplexing components.

Degenerate four-wave mixing in a cerium doped potassium sodium strontium barium niobate photorefractive crystal is studied. The transmission grating is dominated in our experimental geometry that the bisector of the pump beam and the signal beam is normal to the c-axis of the crystal. As the fringe modulation depth of this transmission grating varies, the variation of the conjugated beam intensity forms a loop. Based on this nonlinear property, real-time optical image edge-enhancement processing as well as real-time edge- enhanced optical correlation is obtained without the reverse of the signal-to-pump beam intensity ratio. The full-width- at-half-maximum intensity of the auto-correlation peak is one fifth of that without the edge-enhancement operation. The computer simulation results are given, which are coincident with the experimental data very well.

The photorefractive grating formulation is a dynamic process which means that the interference light intensity of the two coherent beams inducing a phase grating through photo- induced refractive index variation and the phase grating changing the intensities of the two beam through beam- coupling take place at the same time. The analytic solution for such a grating formulation can be only obtained by simultaneously solving the material equations and the coupled wave equations. In this paper, using the Moharam's space-charge field function and the coupled wave equations, we first obtained the exact and approximate analytic solutions to the photorefractive grating with any light modulation depth and any constant light excitation efficiency. Here three step calculation idea has been used. These solutions help to understand the two-beam coupling effect and the interacted grating formulation process in physics more straightforward and in quantity more exactly.

A CO₂ laser beam has been suggested to heat the Fe:LiNbO₃ to thermally fix a recorded hologram. This optical/thermal method permits to spatially locally and selectively fix, erase or update photorefractive holograms in-situ and in real time. The thermal field distribution in LiNbO₃ induced by the heating of a CO₂ laser beam is in fact nonuniform, which has an effect on the fixing efficiency for the recorded hologram. In this paper, we developed the relation between the fixed space charge field amplitude E_sc and the fixing temperature T_f. Then to evaluate the performance of the recorded and fixed local but nonuniform photorefractive holograms, two parameters of the localization coefficient (Psi) and the average space charge field amplitude E_sc^ave are defined, respectively. The relations among local hologram amplitude and locality and the nonuniform temperature field are discussed. An optimum temperature field caused by the CO₂ laser heating is achieved. The developed method is suitable for the other boundary conditions and laser beam profiles.

A novel photorefractive demultiplexer for dense wavelength division multiplexing (DWDM) applications has been experimentally demonstrated for the first time, by using the narrow-band filtering and demultiplexing properties of a volume holographic gratings formed in lithium niobate crystal. For the multiple recording of the 16-wavelength channels with equal diffraction efficiency, the rotation multiplexing and the exposure time schedule are used. The 1x16 photorefractive DMUX is designed to work with a channel spacing of 0.5nm range from 670nm to 677.5nm and a bandwidth of 0.16nm. From the experimental results, the measured diffraction efficiency of each channel is 8.3+/- 0.62%. The 3dB bandwidth of 0.16+/- 0.005nm and the channel spacing of 0.46 approximately 0.5nm, with optical loss from Fresnel reflection and absorption in the crystal of 2.22dB/cm, are measured.

We propose an all-fiber nonreciprocal component that allows strongly nonreciprocal power transmission. The component is made of a mechanical fiber mode converter and an asymmetric fiber. The asymmetric fiber made of a few-mode fiber and a single mode fiber is fabricated by the fuse-and-tapering technique. The mechanism of the nonreciprocal transmission is based on the polarization isolation of the mechanical fiber mode converter. The strongly nonreciprocal power transmission of the proposed device operated at 980nm is experimentally demonstrated.

Germanium-doped silica glasses have been fabricated and the UV induced refractive index change have been studied. An order of 10^-3 refractive index change has been obtained. With the use of silver ion exchange before UV exposure, much greater refractive index change has been observed. The silver ion exchanged germanium-doped glass has a 10^-2 refractive index change when it is exposed to 248 nm excimer laser. This procedure allows the fabrication of integrated optical components in a convenient way.

The volume holographic memory in the photorefractive crystal is considered to be an efficient approach for high throughput data storage and retrieval. Among different techniques for data multiplexing, the hologram with speckle reference beam is a potential approach for high-density holographic information storage. However the existing research are mainly focused on the selective properties of volume holograms with speckle reference beam rather than on the capacity of data storage. So it is necessary to analyze the diffraction efficiency of speckle holograms that can be measured by dynamic range metric of storage medium. In this paper, an analytical expression of the effective dynamic range metric of storage medium for speckle volume holographic memory is derived. The effective grating modulation ratio is considered in the dynamic range metric owing to the appearance of speckle. The variation relationship of grating modulation ratio with speckle characteristics is described theoretically. The influences of speckle characteristics on the dynamic range performance are discussed by use of the numerical simulation.

A phenomenon of phase Coulomb crystallization on the charged liquid dielectric polymer in the field of corona discharge is investigated. The condition is obtained under which the deformations of hexagonal and square symmetry amplitudes of surface relief appear and become competitive.

We have studied the effect of adsorbed water on the primary photocarrier-generation process in Y-form titanyl phthalocyanine (Y-TiOPc) by using ground-state absorption and time-resolved fluorescence spectroscopy. The water adsorption is the unique feature of Y-TiOPc , that is not observed in the other polymorphs of TiOPc. We report for the first time the water-induced change of the absorption spectrum, that is, the hydrochromism of Y-TiOPc. The fluorescence lifetimes and amplitudes of Y-TiOPc are greatly influenced by adsorbed water. We have found that the mechanism of the fluorescence quenching of Y-TiOPc caused by water adsorption is the same as that by an electric field. Adsorbed water enhances the photocarried generation of Y- TiOPc in the same way as an electric field does in the picosecond time regime.

Electron and hole drift mobility in N-picrylarylamine doped polycarbonate films has been studied by the conventional time-of-flight technique. The charge transport molecules contain both electron acceptor and donor functionalities. Electron mobility is similar in value for all the systems as the electron acceptor functionality is the same in all the molecules. Hole mobility depends on the donor functionality. The results can be fit well into a correlated disorder model when energetic features of the transport molecules are also taken into account. For quantum-chemistry calculations, the semiempirical PM3 and ZINDO/S methods were used.

According to coupled wave theory, when a volume holographic grating (VHG) is used as dispersion device, the Bragg wavelength selectivity indicates that only in narrow spectrum range can VHG have definite diffraction efficiency. Therefore, volume holographic dispersive device with broad spectral coverage can be realized by means of multiplexing. The key technique is based on wavelength multiplexing holographic recording. Each VHG is corresponding to a narrow spectral range with variant center wavelength. In this paper, the Bragg compensatory multiplexing recording (BCMR) is reported, which can realize multiplexing volume holographic device written with a single wavelength and working under multi-wavelength without using a tunable laser. This key technique can be realized based on the reciprocally compensatory relationship between the wavelength of incident light and the Bragg angle when Bragg matching. In this paper, a BCMR experimental system is constructed to prove the practicability of this recording method.

Aiming at the non-linear dispersion of single grating dispersive device, in this paper, a novel dispersive device based on volume holographic multiplexing storage principle is reported. According to this principle, more than one volume holographic gratings are recorded in the same photorefractive material. The Bragg wavelength selectivity of volume hologram indicates that a volume holographic grating (VHG) with certain thickness can have definite diffraction efficiency only under the design center wavelength. Therefore, in order to make the whole device realize the needed distribution of spectral lines, a number of VHGs must be multiplexed on the device and each volume grating is corresponding to variant center wavelength. This multiplexing volume holographic dispersive device (MVHDD) can be realized by means of wavelength-angle mixed multiplexing recording (WAMMR). Through adjusting recording parameters of each VHG and multiplexing number, all design center wavelengths can be reasonably distributed in operating spectrum coverage, accordingly the dispersive characteristic of the MVHDD can be reasonably determined. On the base of coupled wave theory, this paper describes spectral characteristics of the MVHDD, discusses the relation between the main parameters of spectral device and the recording parameters of WAMMR, and then gives results of theoretical analysis.

Self-pumped photorefractive phase conjugators only work with extra-ordinarily polarized waves (e-waves) with respect to the photorefractive crystal used in the conjugator. This is because photorefractive effect is prominent only with e-wave in crystals. Ordinarily polarized waves (o-waves) do not only give rise to this kind of photorefractive effect but often suppress the e-wave photorefractive effect when both of them are directed into the crystal. In this paper, we propose another photorefractive phase conjugator, which although works with e-waves too, is very insensitive to the suppressing effect of a beam of o-waves occupying the same propagation channel.

We have demonstrated a double phase conjugator with orthogonal incident polarizations that generates both extraordinary and ordinary polarized conjugate waves simultaneously in the same photorefractive crystal, with its polarization state preserved. The e-conjugate waves are yielded by photorefractive backscattering in the crystal, and the o-conjugate waves take place due to the coupling of the incident e-waves and o-waves through circular photogalvanic effect.