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We report the observation of planar Y-junction waveguide splitters that are due to the bulk photovoltaic effect. The junctions are generated by multiple dark-soliton propagation in LiNbO(3) by use of low power levels (20 mW) and average intensities of 10 W/cm(2) at 488 nm. The junctions persist in the dark and can be used to divide input beams of less photorefractive sensitivity. We describe some possibilities for generating other waveguide structures in bulk and thin-film media.

We examine the consequences of permanent phase distortions on the replay of transmission volume holograms with a phase-conjugated reference wave. In the absence of Bragg degeneracies and significant Bragg mismatch, for negligible dispersion in the spatial frequency response and for negligible variation in obliquity, phase-conjugated reference waves compensate for the effects of phase distortions and permit cross-talk-free multiplexing by using orthogonal reference waves. Spatial frequency dispersion, however, is a source of image distortion and cross talk.

We report on the observation of planar dark spatial solitons due to the bulk photovoltaic effect in lithium niobate, with intensities of the order of 10 W/cm2 and widths of approximately 20 \ensuremath{\mu}m. Photovoltaic solitons display a characteristic tensorial dependence on their direction of propagation, on their polarization, and on the orientation of the amplitude profile, with respect to the principal axes of the crystalline medium. The index perturbation associated with a dark soliton persists in the dark, and it can trap and guide a second beam.

Dark (bright) planar spatial solitons are predicted for photovoltaic photorefractive materials when the diffraction of an optical beam is exactly compensated by nonlinear self-defocusing (focusing) due to the photovoltaic field and electro-optic effect. These solitons may have steady-state irradiances of microwatts to milliwatts per square centimeter and widths as small as 10 [mu]m in lithium niobate. Optical control is provided by incoherent illumination, and the nonlinear index of a dark soliton may be used to trap a bright soliton by rotating the plane of polarization of the soliton field.

We analyze self-trapping of one-dimensional optical beams in photorefractive, photovoltaic media for open- and closed-circuit realizations. We show that a passive load (resistor) in the external circuit can be used for switching of dark photovoltaic solitons. Dark solitons in a short-circuited crystal can be obtained for a much smaller nonlinearity than in open-circuit conditions. Shorting the crystal affects bright solitons very little.

We derive the relationships for coded wave fronts in volume holography for reference and signal waves coded with two-dimensional wave fronts. We develop estimates for cross talk that is due to grating degeneracy, nonorthogonality, and momentum-mismatch reconstruction. We compare a number of multiplexing techniques on the basis of cross talk and other noise sources in a system.

The selection of reference beams for cross-talk-limited wavelength- and angular-multiplexed volume-holographic data storage is discussed. It is shown that sparse selection of the reference waves can lead to a significant improvement in the cross-talk-limited signal-to-noise ratio in a wavelength-multiplexed system. In a high-capacity angular-multiplexed system sparse selection offers essentially no advantage.

We present a comprehensive analysis of the evolution of a grating envelope, in both transmission and reflection geometry, during the erasure process in various readout configurations in bulk photorefractive media. We derive a single partial differential equation that describes grating evolution. This equation shows that under certain conditions the grating envelope propagates and shares several features with either bright or dark solitons. Details of the grating envelopes directly relate to the dynamics of the observed diffraction efficiency. We derive analytical expressions for diffraction during nondestructive readout. Finally, we discuss the effects of nonzero absorption, finite dark conductivity, fringe bending, fanning, and nonlinear responses on the propagating envelope.

We compare the characteristics of cross talk for angular multiplexing and several phase-encoded multiplexing strategies for volume holography. We discuss the implications of these characteristics for holographic data storage and compare noise arising from cross talk with noise arising from scattering that is due to inhomogeneities within a holographic medium.

A two-center photorefractive model permitting all center-to-band transitions and electron–hole charge transport unifies several models describing subsets of these transitions. Using the quasi-steady-state approximation for low continuous-wave illumination, the model derives the first-order Fourier harmonic of the steady-state space-charge distribution and fields and the corresponding response rates. The model describes electron–hole competition, complementary gratings, double-exponential time-dependent behavior, and nonlinear dependence of response rates on intensity. The model can be used to make new predictions of photorefractive behavior of crystals in which two species of impurity center are present; an example is presented for BaTiO3.

Growth-induced striations in photorefractive media constitute phase gratings that scatter transmitted light and therefore degrade the quality of reconstructed images in holographic applications. A simple angular multiplexed holographic memory arrangement in a striated strontium barium niobate sample is considered. For forward-propagating reconstruction the striations distort the readout images and introduce ghost images. For counterpropagating readout, inhomogeneous image reconstruction and interimage cross talk can occur. We investigate these effects experimentally for different reconstruction methods and demonstrate the cross talk and the ghost images with a simple model based on coupled-wave theory. Readout with a counterpropagating plane wave eliminates the ghost images and the distortions but suffers degradation from cross talk and inhomogeneous image intensity. Only reconstruction with a phase conjugate of the transmitted reference beam eliminates cross talk and distortions. The model indicates that negligible material dispersion is a necessary requirement for high-quality phaseconjugation readout.