Terumasa ITO, Atsushi OKAMOTO, and Kunihiro SATO¹

Graduate School of Information Science and Technology, Hokkaido University, Sapporo 060-0814, Japan
¹Faculty of Engineering, Hokkai-Gakuen University, Sapporo 064-0926, Japan

(Received February 1, 2007; Accepted April 2, 2007)

We present a novel numerical model for analyzing shift margin in spatial spread-spectrum (SSS) multiplexing, in which the spatial phase of signal beams, not in reference beams, is modulated and demodulated by a random diffuser to multiplex holograms. The shift margin is determined not by the Bragg effect of a thick hologram, but mainly by the phase correlation property of the diffuser used. In our model, we simulate signal data patterns and a smooth rough surface of a diffuser using oversampling and zero-padding, which allows us to cover crosstalk calculations and direct bit-errors calculations, with a fine shift resolution and a wide diffusion angle range. Calculation results revealed that the practical shift margin that ensures a signal to noise ratio more than 3.0 and a bit-error rate less than 10^-2 is in the range of 0.3ω_eff–0.5ω_eff, where ω_eff is the effective autocorrelation length of the diffuser transmission function. This model will be helpful in designing the optimum random diffuser profile for SSS multiplexing.

Key words: holographic recording, multiplexing, spatial spread-spectrum, shift margin