Abstract
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 0.3ωeff−0.5ωeff, where ωeff 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.
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