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We have demonstrated a simple and compact tunable dual-wavelength Yb3+:KGd(WO4)2 (Yb:KGW) laser. The laser is diode pumped through an optical bifurcated fiber and an adjustable beamsplitter. Thanks to two transversally chirped volume Bragg gratings (TCVBG) used as output couplers, the frequency difference between the two collinear waves is continuously tunable from 0 up to 7.8 THz with 110 GHz bandwidth. The frequency range is only limited by non optimized optical components and not by the principle of functioning.

We report a diode-pumped CW Tm:YLF laser at room temperature with a volume Bragg grating (VBG) instead of the conventional mirror. The Tm:YLF laser operated at 1909.5 nm with output power 6.0 W. The optical-to-optical conversion efficiency is 25.7% and slope efficiency is 37.4%. Also, a stable output and a narrow linewidth less than 0.3 nm FWHM are achieved.

A two-step holographic process, in which the diffraction efficiency can be adjusted, for the fabrication of 360° walk-around viewable reflection disk-type multiplex holograms is proposed. In order to increase both the vertical and the longitudinal viewing window, a diffuser and a fan-shaped slit are used in the optical system of the object wave in the first step. This kind of hologram can generate a monochromatic clear image under white-light line-source illumination. An alternative lensless copying system for fabrication of a reflection multiplex hologram, which allows one-shot recording of bigger images, is also described. Both experimental and computer-simulated results for the characteristics of the images from this kind of hologram are presented.

Using modified two-dimensional coupled-wave theory, the diffraction properties of ultrashort pulsed beams with arbitrary temporal profiles are studied with a volume holographic grating. Analytical expressions for the profiles of the transmitted and diffracted beams are obtained. It is shown that the Bragg selectivity bandwidth of the volume grating can be influenced by the geometry parameter. Numerical results are illustrated for three different temporal profiles. For different temporal profiles, the ratios of the diffraction bandwidths to input bandwidths are discussed.

There are two known competitive arrangements for reflection-type coaxial holographic storage systems: the optical layout developed by optware, which is a so-called collinear or "split-aperture system", and the "common-aperture system" developed by the European consortium named athos. We modeled the reference diffraction noise for both arrangements by the beam propagation method (BPM), and compared the results from the M number (M#) consumption point of view. We suggest the use of reference beam apodization for the split aperture system to reduce the diffraction noise caused by the reference beam at the object area.

The imaging characteristics of volume holographic imaging elements (VHIEs) are evaluated numerically and experimentally. To evaluate the imaging characteristics of a VHIE, a volume holographic imaging simulator between one-dimensional regions is fabricated. In the simulator, the propagated light in free space and the diffracted light at the VHIE are calculated by numerical Fresnel propagation and Kogelnik's coupled wave theory, respectively. The imaging characteristics of VHIEs for imaging between point sources and between one-dimensional regions are evaluated. Furthermore, we numerically and experimentally investigate the influences of Bragg-mismatched light on imaging characteristics along the direction of the optical axis of a VHIE.

We obtain analytical solutions of the coupled wave equations that describe the Bragg diffraction of ultrashort pulsed finite beams by a thick planar grating, using two-dimensional coupled wave theory. The diffraction properties for the case of an ultrashort pulsed finite beam with Gaussian profiles in both the time and spatial domains are investigated. The spectral bandwidth of the diffracted beam, the Bragg selectivity bandwidth and the diffraction efficiency of the volume grating are influenced by the geometry parameter and the input bandwidth. Therefore extra attention should be paid to designing optical elements based on volume gratings for use with ultrashort pulsed waves in applications of pulse shaping and processing.

Based on the two-dimensional coupled-wave theory, the wavefront conversion between cylindrical and plane waves by local volume holograms recorded at 632.8 nm and reconstructed at 800 nm is investigated. The proposed model can realize the 90° holographic readout at a different readout wavelength. The analytical integral solutions for the amplitudes of the space harmonics of the field inside the transmission geometry are presented. The values of the off-Bragg parameter at the reconstructed process and the diffracted beam's amplitude distribution are analysed. In addition, the dependences of diffraction efficiency on the focal length of the recording cylindrical wave and on the geometrical dimensions of the grating are discussed. Furthermore, the focusing properties of this photorefractive holographic cylindrical lens are analysed.

In this paper the saturated diffraction efficiency has been optimized by considering the effect of the absorption of the recording light on a crossed-beam grating with 90° recording geometry in Fe:LiNbO3 crystals. The dependence of saturated diffraction efficiency on the doping levels with a known oxidation–reduction state, as well as the dependence of saturated diffraction efficiency on oxidation–reduction state with known doping levels, has been investigated. Two competing effects on the saturated diffraction efficiency were discussed, and the intensity profile of the diffracted beam at the output boundary has also been investigated. The results show that the maximal saturated diffraction efficiency can be obtained in crystals with moderate doping levels and modest oxidation state. An experimental verification is performed and the results are consistent with those of the theoretical calculation.

We investigate the durability of volume holograms in bismuth tellurite crystals, Bi2TeO5. This material enables self-fixing of holograms during the recording process rendering any further fixing technique unnecessary. Therefore the material overcomes the vulnerability of holograms which is a typical inconvenient property of inorganic storage crystals. The quality reduction of reconstructed analogue and digital data pages under permanent read-out is studied. In terms of digital page-oriented storage, the change of the bit error rate is investigated. For comparison, all experiments are also performed on iron doped lithium niobate crystals, LiNbO3:Fe.

We discuss the difficulties and propose a technique to measure the diffraction efficiency of volume holograms exhibiting a high Bragg angular selectivity recorded in samples exhibiting lens-like properties, as is usually the case with photorefractive crystals. We also discuss the use of a laser probe beam for diffraction efficiency measurement.

The use of bleaching techniques is perhaps one of the most popular methods of creating phase holograms from holographic emulsions. In this paper we will study the influence of the different experimental conditions on the refractive index modulation created inside the hologram when bleaching techniques are used. A comparison will be made between three different kinds of bleach: a reversal bleach, a conventional bleach and a fixation-free rehalogenating bleach. It will be demonstrated that the necessary refractive index modulation can be achieved with conventional and fixation-free rehalogenating bleaches. The values of the diffraction efficiency are only limited by the absorption and scattering, which is very high in the case of conventional bleaches. It will also be found that the lowest values of absorption and scattering are obtained when the reversal bleach is used to obtain the volume holograms. In this case, the refractive index modulation stored in the hologram is not high and so the final diffraction efficiency is limited. This work was partially supported by “Ministerio de Ciencia y Tecnología”, Spain, under project MAT2000-1361-C04-04 and by “Generalitat Valenciana”, Spain, project GV01-130. Shirley Condeza and Ana María Campos wish to acknowledge a scholarship granted by the ‘Agencia Española de Cooperación Internacional (AECI)’.

Photographic emulsions are still widely used to record holographic optical elements. In particular, if high diffraction efficiencies are needed, phase volume holograms are preferably recorded on these emulsions. Two particular techniques producing high-quality volume phase holograms are fixation-free rehalogenating bleaching and the use of silver-halide-sensitized gelatin. In this work we compare these two particular techniques applied to three different red-sensitive emulsions: Agfa 8E75 HD, BB-640, and Slavich PFG-01 emulsions. The differences between these emulsions determine the particular experimental conditions needed to record high-quality volume holograms on them. In this work these differences are analysed, and also their influence on the experimental procedure.

In this paper, performance of the complex phase code (CPC) which is recently proposed as a practical phase encoding method for volume hologram multiplexing is analyzed in detail. This new CPC has been known to have not only random and orthogonal properties but also the potential to generate a relatively large number of address beams in a holographic memory. For performance analysis of the CPC in a holographic memory system, four types of phase code, the new CPC, as well as the conventional pure random code (PR), random code with equality (RCE), WHM (Walsh Hadamard Matrix), are generated and used as the address beam. In computer simulations, the size of the address beam is fixed at 32 x 32 pixels and 0%-25% phase-error ratio in a pixel are intentionally added to the ideal phase values to consider the nonlinear phase-modulation characteristics of the practical spatial light modulator. From comparative analysis of crosstalks and signal-to-noise ratios for these phase codes by calculating auto-correlation and cross-correlation, it is found that the new CPC have the lowest cross-correlation mean value of 0.021, the lowest standard deviation of 0.0113 and the highest SNR of 26.9 among the four types of phase code. In addition, from the calculation of the number of all possible address beams for these four types of phase code as the size of the address beam is fixed to 32 x 32 pixels, the CPC is found to have 6.334 x 10 4 9 address beams, which are relatively higher number than that of the conventional phase codes.

Kogelnik's coupled-wave theory has provided a well-established basis for understanding how light propagates inside a volume hologram, giving an accurate approximation of the diffraction efficiency in this type of hologram. In this paper we elaborate on some aspects of the theory. In particular we evaluate the effects of an overmodulation of the refractive index inside the hologram, which results in a particular behaviour of the angular response of the diffraction efficiency. These overmodulation effects are found when fixation-free holograms are recorded on silver halide emulsions. This study was supported by the "Comisión Interministerial de Ciencia y Tecnología (CICYT)" of Spain under project Nº MAT2000-1361-C04-04.

Generation of Stark spectral components in free-running Q-switched Nd:YAP (1064 nm and 1073 nm) and Nd:YAG (1062 nm) lasers is obtained. For this purpose reflecting volume Bragg gratings placed into the laser resonator and permitting to tune the laser emission spectrum were used. Stable generation of Stark components in both lasers is obtained. The possibility of obtaining two-frequency generation in an Nd-glass laser with the help of these gratings is shown.

A quasi-optical approximation without allowance for beam spreading over its envelope is used to show that selection of a conjugate wave occurs in a volume hologram whose dimensions are greater than the longitudinal correlation length of the fields forming the hologram. The condition under which the signal power exceeds the noise power is found. Phase conjugation of a speckle field with a divergence of 2×10-2 by a four-wave interaction with feedback was achieved experimentally for neodymium-activated glass and the efficiency was 5%. The input energy threshold was 100 mJ and the maximum energy in the phase-conjugate wave was 10 mJ.

A transmission volume hologram is evaluated as a quantum projector operating on linear momentum states of individual photons in a four-dimensional state space. A state space is defined by four momentum vectors that are either efficiently diffracted or transmitted by the hologram. The influence of the volume hologram on the complex amplitudes of the basis states is modeled using coupled-wave theory. Measurement probabilities obtained with a second hologram introduced as a state-space analyzer are compared to measurement probabilities associated with a projection operator in quantum mechanics. A compact sequential hologram configuration for projecting superposition states onto all of the basis states is demonstrated for individual photons prepared in all 20 states of the five mutually unbiased bases of the four-dimensional state space. The complex amplitudes associated with superpositions of the basis states are imparted to individual photons via computer-generated holography and a liquid-crystal spatial light modulator. The coupled-wave theory analysis indicates that relative phase relationships in transmitted superposition states can be preserved to within 1/28th of an optical cycle and measured detection probabilities compare favorably to those associated with a quantum projector in a basis of discrete orthonormal states. Small departures of the measured statistics from theoretical expectations are quantified and attributed to imperfections in the hologram and experimental setup.

Analytical shift selectivity equations assume an infinite hologram size. When developing a compact holographic storage system, one uses small holograms. From a practical viewpoint, it is better to use reflection type discs, in which the entire optical system, writing and reading objectives, among others, are on the same side of the disc. For reflection-type holographic discs, it is important to use half-cone-shaped reference beams to avoid generating ghost images caused by phase conjugate readout. Our calculations show significant discrepancy between the shift selectivity curves corresponding to the approximated analytic equation and the numerically calculated shift selectivity curves.

We experimentally demonstrated angular selectivity in a nondestructive readout of a photochromic protein bacteriorhodopsin (bR). bR is a photochromic material which has many unique properties. Especially, its high spatial resolutional recording ability is suitable for holographic applications. From the viewpoint of latching, it is desirable to preserve a hologram after readout. The experimental result shows a weak angular selectivity in a volume hologram on bR.

Transmissive volume holograms are considered as mode-selective optical elements for the de-multiplexing and detecting of optical vortex modes according to the topological charge or mode number. Diffraction of vortex modes by a fundamental mode hologram is modeled using a physical optics model that treats the volume hologram as an angle-dependent transfer function. Diffracted irradiance profiles and diffraction efficiencies are calculated numerically as a function of the incident mode number. The results of the model are compared with experimental results obtained with volume holograms of fundamental and higher-order vortex modes. When considered as a function of detuning between the incident and recorded mode numbers, the measured diffraction efficiencies are found to be invariant with respect to the recorded mode number, provided that the order difference remains unchanged, and in close agreement with the predictions of the model. Measurements are made with a 1.3 mm thick permanent photo-thermo-refractive glass hologram and a 9 mm thick re-writable photorefractive lithium niobate hologram. A liquid-crystal spatial light modulator generates the vortex modes used to record and read the holograms. The results indicate that a simple volume hologram can discriminate between vortex modes; however, adjacent mode discrimination with low crosstalk would require a very thick hologram. Furthermore, broadening of the vortex angular spectrum, due to diffraction at a finite aperture, can adversely affect diffraction efficiencies.

Reflection holograms in thick layers of bichromated gelatin are recorded by using 50-fs pulses of the second harmonic of a Ti:sapphire laser.

One-dimensional photonic crystal band-edge lasing at different excitations was studied experimentally by altering the excitation angle. We considered almost every condition including in-band, out-of-band and near the band edge while keeping the density of states unchanged. Holographic rhodamin 6G-doped dichromated gelatin was used for creating low-threshold photonic band-edge lasing (PBEL). Lasing actions excited near the high-energy and low-energy band edges were observed simultaneously, and their full widths at half maximum were different. The results show that the PBEL intensity and pump efficiency are sensitive to the excitation angle, enhanced obviously at the excitation near the band edge and suppressed distinctly in the band which agreed well with the theoretical prediction. We also demonstrated for the first time that active matters exist not only in the air voids but also in the high-index regions of the gelatin.

On the basis of two-dimensional coupled-wave theory, diffraction properties of ultrashort pulsed beams (UPBs) generated from volume holographic gratings with arbitrary boundaries are studied. The resulting differential coupled equations are solved numerically by a two-dimensional Runge–Kutta method. The effects of the grating boundaries on the intensity distributions of the diffracted and transmitted pulsed beams in spectral and temporal domains are presented, and the effects on the Bragg selectivity bandwidth, the diffracted bandwidth and the total diffraction efficiency of the gratings are also given. Simulation results show that use of a characteristic grating will result in distorted profiles for the diffracted beam and that truncated grating shapes significantly improve the output beam quality. This study presents the possibility of shaping a broadband UPB by controlling the boundaries of local volume hologram gratings.

The wavelength selectivity of volume holographic gratings with different size ratios is presented. The gratings are made in a doubly doped LiNbO3 photorefractive crystal by using the transmissive-writing and orthogonal-readout scheme. The gratings are recorded at the short wavelength of 532 nm and read out at the long communication wavelength, which is tunable between 1520 and 1630 nm. It is demonstrated that the wavelength selectivity of gratings can be improved by choosing larger grating size ratios. A 3 dB bandwidth of 0.43 nm is achieved with the grating size ratio of 2.5. The experimental results agree well with the prediction of two-dimensional coupled-wave theory.

We investigate different classes of organic photosensitive materials in order to optimize the interaction between the material itself and a surrounding optoelectronic system. The focus of investigation is the application to microholographic data storage. Key issues are the dynamic material response, spatial resolution and photoresponse, spectral and temporal grating development, influence of the light intensity distribution, and impact of pre-exposure. The materials under investigation are cationic ring opening and free radical polymerization systems.

We report the results of an extended investigation performed on composite polymeric materials with the aim of obtaining compounds suitable for holographic recording. In order to investigate the material properties a characterization of holographic reflection gratings at different writing wavelength (514.5, 457 and 405 nm) has been performed. The volume grating presents high diffraction efficiency (>60%), high sensitivity (>103 cm J−1) and refractive index modulation Δn≈0.01 even for writing wavelength in the blue range. We show that following a strategy of two basic components leading to phase separation during the photopolymerization process, most of the requirements for holographic data storage are achieved. The one that needs further improvement concerns long term mechanical stability.

We demonstrate holographic recording in surface-modified ZrO2 nanoparticle–polymer composites and their recording sensitivity enhancement in the green by hydrogen donor and acceptor agents, N-phenylglycine (NPG) and 3,3'-bismethoxycarbonyl-4,4'-tert-butyl peroxycarbonyl benzophenone (BT2). It is shown that the refractive index modulation and the recording sensitivity increase by factors of approximately 2 and 9, respectively, at a recording intensity of 10 mW cm−2 as compared to those of our previously reported ZrO2 nanoparticle–polymer composites (Suzuki et al 2006 Opt. Express 14 12712). It is also shown that the incorporation of NPG and BT2 into the new composites does not substantively increase light absorption on recording, but results in a further increase in the recording sensitivity by approximately a factor of 3 at low recording intensities (≤10 mW cm−2).

The measurement of the phase coupling between the two-wave mixed transmitted and diffracted beams behind a photorefractive material is directly obtained using a self-stabilized recording technique. These phase coupling data are used to compute the Debye screening length on an undoped Bi12TiO20 crystal. The diffraction efficiency, which is obtained in two different ways from the same self-stabilized experimental run, is similarly processed to compute the Debye length too. The Debye length is also measured for Pb- and Zr-doped Bi12TiO20 crystals, and from this parameter the corresponding effective density of traps is computed and shown to be lower than for the undoped sample.

We use photoconductivity and holographic techniques to characterize some material and transport properties in undoped and doped photorefractive sillenite crystals, with particular emphasis on photorefractive Bi12TiO20. We show how different dopants are able to modify the performance of the undoped crystals and suggest some possible mechanisms to explain some of their properties.

The effect of the asymmetric expansion properties and random fluctuation in dichromate gelatin on the bandwidth of a volume hologram is studied. It is found that the bandwidth of the hologram greatly depends on the asymmetric properties of expansion. That is to say, the experimental results are mainly controlled by the processing conditions. We can obtain wide band gap photonic structures by controlling the conditions of processing and experiments. The experimental results under different processing conditions are also demonstrated. The width of the band gap can reach about 120 nm by changing and controlling the processing conditions. The experimental results agree with the theoretical analysis. The results can give us some guidance for future experimental design.

A new complex phase code (CPC) is proposed as a practical orthogonal phase encoding method for volume hologram multiplexing. Through comparative performance analysis of the proposed CPC with the conventional phase codes, the CPC is found to have the lowest cross-correlation mean value of 0.019 and the lowest standard deviation value of 0.0102.

We report two-way holographic image storage in azo polymers. Urethane-urea copolymers involve two photochemical reactions, photoanisotropic modification and surface modification. We can realize the recording of two holograms: (polarization volume hologram due to the anisotropy of azo side chain and surface relief hologram) that have different types of information. This is possible because the polarization volume hologram is rewritable while the surface relief hologram is thermally stable. Using the fact that the polarization volume hologram acts like a half wave plate, we can separately readout the different types of information.

We propose a volume holographic device for spherical aberration correction and parallel data readout in three-dimensional optical memory. Since the volume holographic device has high angular selectivity and wavefront conversion property, it is possible for that the volume holographic device can achieve data separation in each layer and the correct the spherical aberration which is generated when the data in deep layers are read or written. We present the theoretical analysis of parallel readout property using Kogelnik's diffraction theory [Kogelnik: Bell Syst. Tech. J. 48 (1969) 2909]. We also demonstrate some experimental results of the volume holographic device.

We present a stereoscopic display system using a volume hologram. The stereoscopic image pairs are recorded into a volume holographic memory with a reference beam. Multiple stereoscopic image pair holograms within common volume is possible using angular multiplexing. The reference beam with Bragg matching condition is scattered by the index grating and the diffracted beams are propagating along the directions of the stereoscopic image pairs. The images are to be suitably projected on the left and right display plane for stereoscopic viewing.

Experimental investigation is presented on an all-optical associative holographic memory with storage of more than one image using an iron-doped lithium niobate single crystal in which memories can be written, erased and rewritten without developing treatment. Several images are multiply stored in the single crystal volume hologram by sequentially changing their own corresponding reference beams. Then using an image input, an output image is read out. This output image most closely resembles the input image. Threshold processing due to the sublinear photorefractive effect in the crystal is used to single out a distinct diffracted beam from the hologram.

The problem of a volume hologram converting a reference speckle field into a plane wave is considered. The angular distribution and the total intensity of a plane wave are calculated for distortions which appear because of the amplitude inhomogeneity of cross gratings and which propagate close to the plane wave direction. The total intensity is found to be proportional to the product of the angle between the signal and reference waves and the divergence of the reference speckle wave.

An analysis is made of the physical basis of the processing of coherent optical signals with the aid of volume holograms. The coupled waves approximation is used to obtain a dynamic equation for the propagation of optical signals and of the associated noise in such holograms. An approximation solution of the dynamic equation is used to calculate the response of a volume hologram, recorded with the aid of a coded reference wave, to an arbitrary reconstructing signal. It is shown that such a hologram belongs to a new class of devies for the filtering of coherent optical signals, which are spatially invariant filters of the spatial frequencies. The main types of noise in a volume holographic filter are considered and the real dynamic range of the filter is estimated. An effective method for minimization of the filter noise is proposed.Methods for synthesis of a generalized filter transfer functions are discussed. A diagram is given for relating the main parameters of matched volume holographic filters recorded in the widely used photographic materials by a variety of methods.

Concentration gradients of the sensitiser in dichromated gelatin films as used in volume holography can produce undesirable variations in the reconstruction wavelength and reconstruction waveband at a fixed angle. These gradients are related to the draining time allowed for the films following sensitisation and a 5 min time limit is recommended to minimise such effects.