Focusing error detection method in microholographic data storage system using polarization characteristics

We present a disk-focusing error detection method for microholographic data storage systems using polarization characteristics. In high-speed optical storage systems, disturbances exist along the vertical direction of a disk. The diffraction efficiency of a readout signal depends on the distance between the focusing point of the reference beam and the vertical center of the microholographic grating. The proposed disk focusing error detection method uses only one laser source, unlike most existing systems, which use two laser sources. By using polarization characteristics, disk-focusing and reading beams are inserted in the media without interference, and the proposed system achieves the simultaneous reading of microholograms and disk-focusing control. By evaluating the focus error signal, we verified the reliability of the optical path and tolerable S-curve (FES) balance (1.8%) for the proposed system. It is possible to achieve a diffraction efficiency of over 90% at the best focus position using the proposed disk-focusing method.