# US 8,542,566 B2 · Holographic recording method detecting displacement of a holographic recording medium, and recording and reproduction apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,542,566 B2 - Document ID: US8542566B2 - Status: Granted - Kind: B2 - Application number: 13/684,435 - Filed: 2012-11-23 - Published: 2013-03-28 - Granted: 2013-09-24 - Earliest claimed: 2010-05-25 - Assignees: Kabushiki Kaisha Toshiba - Applicants: Takashi Usui; Kazuo Watabe; Hideaki Okano - Inventors: Takashi Usui; Kazuo Watabe; Hideaki Okano - Web page: https://patentgrep.com/patent/US8542566B2 ## CPC - G11B 7/0065: Recording, reproducing or erasing by using optical interference patterns, e.g. holograms - G11B 7/083: {relative to record carriers storing information in the form of optical interference patterns, e.g. holograms} - G11B 7/09: with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following - 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 method for recording information in form of a hologram. The method can generate a displacement signal by detecting a displacement of a holographic recording medium. The method can perform an exposure control operation that, if the sampling value of the displacement signal falls within an allowable displacement range, records the information item in the holographic recording medium, and if the sampling value of the displacement signal falls outside the allowable displacement range, blocks or reduces at least one of the information light and the reference light to a light intensity with which the information item is not recorded in the holographic recording medium. ## Claims ### Claim 1 A holographic recording method, comprising: generating a displacement signal by detecting a displacement of a holographic recording medium in which an information item is recorded in a form of a hologram by interference of information light and reference light, the information light being emitted by a coherent light source and including the information item to be recorded, the reference light and the information light being the same wavelength; calculating a frequency distribution information item of first sampling values of the displacement signal, by sampling the displacement signal at a first interval time to obtain the first sampling values and assigning frequencies to classes which correspond to the first sampling values, the classes being a plurality of ranges divided at first intervals; determining an allowable displacement range as an amplitude range of a displacement of the displacement signal based on the frequency distribution information item; and performing an exposure control operation that, if a second sampling value which is a latest sampling value of the displacement signal falls within the allowable displacement range, records the information item in the holographic recording medium, and if the second sampling value of the displacement signal falls outside the allowable displacement range, blocks or reduces at least one of the information light and the reference light to a light intensity with which the information item is not recorded in the holographic recording medium. ### Claim 2 (depends on 1) The method according to claim 1, further comprising calculating a frequency center displacement indicating a central value of the displacement of the displacement signal based on a max class in which a frequency is highest in the classes assigned the frequencies, by detecting the max class based on the frequency distribution information item, wherein the determining the allowable displacement range calculates a first value by adding a positive value of a second value to the frequency center displacement, calculates a third value by adding a negative value of the second value to the frequency center displacement, and determines, as an allowable displacement range, a range defined by the first value and the third value. ### Claim 3 (depends on 1) The method according to claim 1, wherein the first interval time is not longer than a necessary exposure time required to record the information item in the holographic recording medium, and the determining the allowable displacement range updates the allowable displacement range upon receiving a timing signal indicating to start to record information in the holographic recording medium. ### Claim 4 (depends on 3) The method according to claim 3, wherein if starting the exposure control operation upon receiving the timing signal, an accumulated exposure time indicating an accumulated time during which recording is performed for the holographic recording medium is counted, and the performing the exposure control operation blocks or reduces, if the accumulated exposure time reaches the necessary exposure time, at least one of the information light and the reference light to the light intensity with which the information item is not recorded in the holographic recording medium. ### Claim 5 (depends on 1) The method according to claim 1, wherein the coherent light source is a semiconductor laser, and the performing the exposure control operation comprises outputting a modulation signal to pulse-modulate the semiconductor laser, and outputting an current to pulse-drive the semiconductor laser according to the modulation signal. ### Claim 6 (depends on 5) The method according to claim 5, wherein the outputting the current superimposes a bias current not smaller than a threshold current emitted by the semiconductor laser. ### Claim 7 A holographic recording and reproduction apparatus, comprising: a first detector configured to generate a displacement signal by detecting a displacement of a holographic recording medium in which an information item is recorded in a form of a hologram by interference of information light and reference light, the information light being emitted by a coherent light source and including the information item to be recorded, the reference light and the information light being the same wavelength; a calculator configured to calculate a frequency distribution information item of first sampling values of the displacement signal, by sampling the displacement signal at a first interval time to obtain the first sampling values and assigning frequencies to classes which correspond to the first sampling values, the classes being a plurality of ranges divided at first intervals; a determination unit configured to determine an allowable displacement range as an amplitude range of a displacement of the displacement signal based on the frequency distribution information item; and an exposure control unit configured to perform an exposure control operation that, if a second sampling value which is a latest sampling value of the displacement signal falls within the allowable displacement range, records the information item in the holographic recording medium, and if the second sampling value of the displacement signal falls outside the allowable displacement range, blocks or reduces at least one of the information light and the reference light to a light intensity with which the information item is not recorded in the holographic recording medium. ### Claim 8 (depends on 7) The apparatus according to claim 7, further comprising a second detector configured to calculate a frequency center displacement indicating a central value of the displacement of the displacement signal based on a max class in which a frequency is highest in the classes assigned the frequencies, by detecting the max class based on the frequency distribution information item, wherein the determination unit calculates a first value by adding a positive value of a second value to the frequency center displacement, calculates a third value by adding a negative value of the second value to the frequency center displacement, and determines, as an allowable displacement range, a range defined by the first value and the third value. ### Claim 9 (depends on 7) The apparatus according to claim 7, wherein the first interval time is not longer than a necessary exposure time required to record the information item in the holographic recording medium, and the determination unit updates the allowable displacement range upon receiving a timing signal indicating to start to record information in the holographic recording medium. ### Claim 10 (depends on 9) The apparatus according to claim 9, further comprising a counter configured to count, if starting the exposure control operation upon receiving the timing signal, an accumulated exposure time indicating an accumulated time during which recording is performed for the holographic recording medium, and wherein the exposure control unit performs blocking or reducing, if the accumulated exposure time reaches the necessary exposure time, at least one of the information light and the reference light to the light intensity with which the information item is not recorded in the holographic recording medium. ### Claim 11 (depends on 7) The apparatus according to claim 7, wherein the coherent light source is a semiconductor laser, further comprising a generator configured to output a modulation signal to pulse-modulate the semiconductor laser, and the exposure control unit comprises a laser driver configured to output an current to pulse-drive the semiconductor laser according to the modulation signal. ### Claim 12 (depends on 11) The apparatus according to claim 11, wherein the laser driver superimposes a bias current not smaller than a threshold current emitted by the semiconductor laser.