POSITION FEEDBACK SYSTEM FOR VOLUME HOLOGRAPHIC STORAGE MEDIA

摘要

A method of holographic recording in a photorefractive medium wherein stored holograms may be retrieved with maximum signal to noise ratio (SNR) is disclosed. A plurality of servo blocks containing position feedback information is recorded in the crystal (200) and made non-erasable by heating the crystal (300). The servo blocks are recorded at specific increments, either angular or frequency, depending whether wavelength or angular multiplexing is applied, and each servo block is defined by one of five patterns. Data pages are then recorded at positions or wavelengths enabling each data page to be subsequently reconstructed with servo patterns which provide position feedback information. The method of recording data pages and servo blocks is consistent with conventional practices. In addition, the recording system also includes components (e.g. voice coil motor) which respond to position feedback information and adjust the angular position of the reference angle of a reference beam to maximize SNR by reducing crosstalk, thereby improving storage capacity.