An effective phase modulation in the collinear holographic storage

Almost all current collinear holographic storage systems record and reproduce the amplitude information but ignore the phase information. To utilize phase information as the useful data is a significant study. Instead of amplitude modulation, using phase encoding and decoding to get phase information is one way to raise storage density. By adding phase encoding to the amplitude encoding, we realized the phase modulation. To reduce the computation load we simplified multilayer phase-scale model to binary 0 and π phase model. By controlling the proportion of 0 and π phase, different phase modulation models can be represented. In the simulation, we use the angular spectrum theory to build the system mathematical model. We got an effective range of the phase modulation called degree of freedom curve of phase encoding, which can promise both low bit-error-rate (BER) and high code rate. Using this curve, we can make phase encoding more efficiently. Once the dynamic response range of the materiel, the gray levels of phase encoding, and the demanded BER determined, we can calculate the degree of freedom curve to prepare for the followed phase encoding.