Tilt Compensation Method of Two-Beam Angle Multiplexing Holographic Memory

In a two-beam angle multiplexing holographic memory, there is a problem that the tilt margin is small. Therefore, we propose a radial tilt compensation method (radial tilt is a tilt in the vertical direction to a surface that is made by reference and signal beams). When the radial tilt occurred during the reading, we brought the relative angles of interference fringes and the reference beam near the state at the time of recording. Concretely speaking, we shifted the disc to the circumferential direction slightly to obtain the optimum signal-to-noise ratio (SNR) and then recovered the hologram. In our experiments, we recorded 1 hologram (no multiplexing) and 51 multiplexing holograms, and recovered them using this compensation method. As a result, we confirmed that our method improved the tilt margin markedly in both cases. This compensation method is thus effective for interchangeability without the need for an additional mechanism and making for smaller drives.