Xianmin Yi

Hybrid sparse-wavelength angle-multiplexed optical data storage system

We propose, analyze, and demonstrate a hybrid wavelength-and-angle-multiplexed optical data storage system. Our system utilizes multiwavelength information processing in conjunction with angle-multiplexed volume holographic storage, achieving direct compatibility with wavelength-encoded optical logic processors. Such a scheme also allows for rapid recall of high-density data into electronic processing and display systems. Hybridization of wavelength and angle multiplexing relaxes demands on spectral and angle-tuning sources and allows for the use of present-day-available optical sources and components.

Statistical analysis of cross-talk noise and storage capacity in volume holographic memory

We present a statistical analysis of cross-talk noise and consider the cross-talk-limited storage capacity of volume holographic memory. Random-walk approximation is employed to estimate the intrapage interpixel cross-talk noise and the signal-to-noise ratio. We obtain simple expressions of the storage capacity in terms of number of bits per volume for a given signal-to-noise ratio or bit-error rate. The results indicate that the storage density is reduced from the ultimate density of lambda(-3) by a factor related to the signal-to-noise ratio.

Statistical analysis of cross-talk noise and storage capacity in volume holographic memory: image plane holograms

We investigate the cross-talk noise in optical storage based on angle-multiplexed image plane volume holograms. Simple expressions for the signal-to-noise ratio and the storage density are obtained. The cross-talk noise is found to limit the size of the pixels and the number of recorded holograms. The cross-talk-limited storage density of image plane holographic storage is found to be close to that of Fourier plane holographic storage.

Absorption effects in photorefractive volume-holographic memory systems. II. Material heating

We consider how absorption-induced material heating alters the phase profile, the scale, the orientation, and the Bragg matching of volume holograms. We derive theoretical equations that consider the prisming, the lensing, and the Bragg mismatching that occur during material heating and compare these with experimental observations. From our Bragg-mismatching considerations we show how both read beam angle and wavelength need to be dithered for proper compensation of volume holograms for material-heating effects. Our results indicate that material heating in volume-holographic memory systems poses a severe threat to system performance. This threat is shown to be very significant in Fourier plane holograms but only moderately significant in image plane holograms.

Crosstalk in volume holographic memory

Crosstalk noise, due to the finite dimension of the recording medium, is a fundamental limitation to storage capacity in volume holographic memory. We present a general theoretical analysis on the crosstalk noise in angle- and wavelength-multiplexed volume holographic memory systems. Results on storage capacity and its dependence on hologram separation and required signal-to-noise ratio are obtained and discussed. Crosstalk noise may also arise from the expansion or shrinkage of the storage medium during and after the hologram recording process. Its effects, including Bragg mismatch, pixel displacement and impulse broadening, are analyzed for Fourier-plane holographic memories. Complete compensation and optimization to eliminate or reduce these effects are presented and discussed.

Cross-talk noise in volume holographic memory with spherical reference beams

We investigate angle-multiplexed volume holographic memory with spherical reference beams, for which the spherical approximation is made to model the wave-front distortion in general. We find that the angular selectivity and the cross-talk noise with spherical reference beams are close to those with planar reference beams. The results indicate that angle-multiplexed volume holographic memory can be realized in compact systems for which large wave-front distortion is expected.

Absorption effects in photorefractive volume-holographic memory systems. I. Beam depletion

We consider how absorption-induced beam depletion alters the index-modulation profile, the diffracted beam profile, and the Bragg selectivity of volume holograms. We derive theoretical equations that consider beam depletion (in the absence of two-beam coupling) and compare these with experimental observations. We also derive a smart scheduling technique whereby such absorption effects can be compensated for during the scheduled recording of multiple holograms. In our smart scheduling approach, during recording the profile of the input signal beam is modified such that during recall its output profile is uniform.

General solution of contradirectional two-wave mixing with partially coherent waves in photorefractive crystals

Summary form only given. In this paper, we present the results of theoretical analysis and experimental investigation of contradirectional two-wave mixing with partially coherent waves in photorefractive crystals using coupled quasi-monochromatic pump and signal waves. Because the complex amplitudes are stationary random processes of time we can define the corresponding self coherence functions and mutual coherence function. Because the coherence time of a wideband laser source is substantially less than the relaxation time of a typical photorefractive material, the position and profile of the photorefractive grating are nearly temporally constant. As an approximation, the amplitude of the grating is proportional to the mutual coherence of the two waves.

Contradirectional two-wave mixing with partially coherent waves in photorefractive crystals

We investigate contradirectional two-wave mixing with partially coherent waves in photorefractive crystals in the nondepleted pump regime. Equations governing the propagation of the self-coherence function and the mutual-coherence function of the signal wave and the pump wave are derived and simulated numerically. Numerical solutions of these equations are in excellent agreement with the experimental measurements.

Recording of second-harmonic index gratings in photorefractive (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals.

We propose and demonstrate a novel method for recording second-harmonic volume index gratings in photorefractive crystals. The fundamental component of the index grating is eliminated by means of a pi -phase shifted double-exposure process that uses the Mach-Zehnder interferometric technique. Experimental results for (K(0.5) Na(0.5)) (0.2)(Sr> (0.75)Ba (0.25))(0.9)Nb (2)O(6) crystals are presented and discussed.