Four-level phase pair encoding and decoding with single interferometric phase retrieval for holographic data storage

We propose four-level phase pair encoding and decoding with single interferometric phase retrieval for holographic data storage. Inherent with phase pair encoding, phase shifting is generated by assigning a certain phase difference between two pixels of the phase pair. Multiple phase shifting operations are not required. In addition, a phase-readout reference beam can be a plane beam with an arbitrary phase in our method because phase shifting can be encoded on the phase-only spatial light modulator easily and accurately. Therefore, our method can not only increase the data transfer rate, but also improve the robustness of the holographic data storage system. Although the code rate of our method needs to be sacrificed by half, the code rate is still twice that of amplitude code when four-level phase encoding is used. We demonstrated experimentally that there is only a 1 × 10^-2 order of bit error rate before error correcting, which is acceptable. We believe our method will further advance the phase-modulated holographic data storage technique.