# US 8,787,136 B2 · Holographic memory apparatus and method for adjusting incident angle of reference beam > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,787,136 B2 - Document ID: US8787136B2 - Status: Granted - Kind: B2 - Application number: 13/875,687 - Filed: 2013-05-02 - Published: 2014-01-30 - Granted: 2014-07-22 - Earliest claimed: 2012-07-30 - Assignees: Hitachi-LG Data Storage, Inc.; Hitachi Consumer Electronics Co., Ltd. - Applicants: Hitachi-LG Data Storage, Inc.; Hitachi Consumer Electronics Co., Ltd. - Inventors: Kenichi Shimada - Web page: https://patentgrep.com/patent/US8787136B2 ## CPC - G11B 7/0065: Recording, reproducing or erasing by using optical interference patterns, e.g. holograms - G11B 7/08564: {using galvanomirrors} - G11B 7/13: Optical detectors therefor - G11B: INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER (recording measured values in a way that does not require playback through a transducer G01D9/00; recording or playback apparatus using mechanically marked tape, e.g. punched paper tape, or using unit records, e.g. punched or magnetically marked cards G06K; transferring data from one type of record carrier to another G06K1/18; circuits for coupling output of reproducer to radio receiver H04B1/20; gramophone pick-ups or like acoustic electromechanical transducers or circuits therefor H04R) ## Abstract A holographic memory apparatus includes an optical detector which receives reflected light of reference beam from the surface of a hologram recording medium. An incident angle of the reference beam is estimated on the basis of information on a focused position on the optical detector. When the incident angle is different from a target incident angle, the incident angle of the reference beam is adjusted according to a difference between the incident angle and the target incident angle. ## Claims ### Claim 1 A holographic memory apparatus which causes interference between a reference beam and signal beam, records an obtained interference pattern in a hologram recording medium as page data by angularly multiplexed recording, and reproduces the recorded page data, the apparatus comprising: an optical detector which receives reflected light of the reference beam from the surface of the hologram recording medium; an angle changing unit which changes an incident angle of the reference beam with respect to the hologram recording medium; a detection circuit which detects a focused position of the reflected light on the optical detector; an incident angle calculation circuit which estimates an incident angle of the reference beam with respect to the hologram recording medium on the basis of information on the focused position; an angle shift generation circuit which generates a difference between the incident angle of the reference beam and a target value thereof; and a control circuit which controls the angle changing unit according to the angle shift. ### Claim 2 (depends on 1) The holographic memory apparatus according to claim 1, further comprising a light quantity detection unit which detects a light quantity of at least a P polarized light component in the reflected light of the reference beam from the surface of hologram recording medium. ### Claim 3 (depends on 1) The holographic memory apparatus according to claim 1, further comprising a phase difference detection unit which detects a phase difference between an S polarized light component and a P polarized light component of the reflected light of the reference beam from the surface of the hologram recording medium. ### Claim 4 (depends on 1) The holographic memory apparatus according to claim 1, wherein the angle changing unit has a first angle changing unit which changes an angle of the reference beam in a Bragg angle direction and a second angle changing unit which changes an angle of the reference beam in a degenerate direction vertical to the Bragg angle direction. ### Claim 5 (depends on 1) The holographic memory apparatus according to claim 1, further comprising a storage area which stores a focused position of the reflected light on the optical detector. ### Claim 6 A method of adjusting an incident angle of a reference beam with respect to a hologram recording medium in a holographic memory apparatus which causes interference between the reference beam and signal beam, records an obtained interference pattern in the hologram recording medium as page data by angularly multiplexed recording, and reproduces the recorded page data, wherein the holographic memory apparatus comprises: an optical detector which receives reflected light of the reference beam from the surface of the hologram recording medium; an angle changing unit which changes an incident angle of the reference beam with respect to the hologram recording medium; a detection circuit which detects a focused position of the reflected light on the optical detector; an incident angle calculation circuit which estimates an incident angle of the reference beam with respect to the hologram recording medium on the basis of information on the focused position; an angle shift generation circuit which generates a difference between an incident angle of the reference beam and a target value thereof; and a control circuit which controls the angle changing unit according to the angle shift, and wherein the incident angle of the reference beam is estimated on the basis of the information on the focused position of the reflected light, and then the incident angle of the reference beam is adjusted by the angle changing unit according to a difference between the incident angle and the target value thereof when the incident angle is different from the target value. ### Claim 7 (depends on 6) The method according to claim 6, wherein the target incident angle is sequentially changed according to a multiplex number. ### Claim 8 (depends on 7) The method according to claim 7, wherein previously storing the focused position of the reflected light of the reference beam on the optical detector in the storage area in recording, taking out information on the focused position from the storage area, and the incident angle of the reference beam is adjusted such that the focused position of the reflected light of the reference beam coincides with the focused position in reproducing.