Recording procedures for high-quality signal readout in self-referential holographic data storage

Two methods are proposed to improve the readout quality of signals in self-referential holographic data storage (SR-HDS), in which no reference beam is required to record and read digital data holographically: the off-the-focus (OtF) method and the oversampling additional pattern (OsAP) method. The focal point is located outside of the recording medium in the OtF method, and the signal pattern is recorded with an additional pattern that possesses a higher spatial frequency than the signal pattern in the OsAP method. Experimental results show that both methods are effective for drastically improving the signal-to-noise ratio (SNR). In addition, through numerical simulation, it can be observed that the readout quality is improved by the achievement of homogeneous hologram distribution.