Holographic storage optical system and beam calibrating method thereof

A holographic storage optical system, comprising:

• a storage medium which comprises an address layer and a recording layer,
• wherein the address layer is composed of a plurality of optical tracks, each optical track is provided with a plurality of data holographic positioning marks and a plurality of calibration holographic positioning marks, each data holographic positioning mark is configured to position a data hologram for recording data, and each calibration holographic positioning mark is configured to position a calibration hologram for calibrating optical paths of the holographic storage optical system;
• a recording unit, which is configured to generate a signal light beam and a reference light beam, and introduce the signal light beam and the reference light beam into the storage medium at a certain angle respectively to generate the data hologram by interference and exposure on the recording layer of the storage medium, the recording unit comprising an optical path for the signal light beam, an optical path for the reference light beam, and a relay lens group for adjusting the signal light beam and the reference light beam,
• wherein the relay lens group comprises a fixed first Fourier lens and a movable second Fourier lens, and an irradiation position and an angle of the signal light beam and the reference light beam are adjusted by moving the second Fourier lens;
• an imaging unit, which is configured to convert a reproduced signal light beam formed by diffraction of the reference light beam into a data page image, and collect the same, the imaging unit comprising a fourth Fourier lens for imaging and an image sensor for collecting the data page image and analyzing a diffraction efficiency and a signal-to-noise ratio of the data page image;
• and
• a servo unit, which is configured to ensure that an optical head of the recording unit is constantly away from the storage medium during movement relative to the storage medium and to ensure that the signal light beam and the reference light beam moving along each optical track, and is configured to accurately position a recording position or a reproducing position on the storage medium,
• wherein the servo unit comprises
• a servo laser, which is configured to generate a servo light beam;
• a beam splitting module, which is configured to transmit the servo light beam to enter the storage medium from the servo laser and reflect the servo light beam returned by the storage medium to a signal detection module;
• a calibration lens, which is configured to adjust a servo light spot of the servo light beam in the horizontal and vertical directions to the data holographic positioning marks or the calibration holographic positioning marks;
• and
• the signal detection module, which is configured to detect and analyze the servo light beam returned by the storage medium, and obtain a servo signal.