Performance analysis of complex phase-code for volume hologram multiplexing

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% phaseerror 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 1049 address beams, which are relatively higher number than that of the conventional phase codes.