# US 5,347,503 A · Optical information processing apparatus for correcting linearity of a photosensor output with respect to power of an emitted light beam > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,347,503 A - Document ID: US5347503A - Status: Granted - Kind: A - Application number: 08/154,385 - Filed: 1993-11-18 - Granted: 1994-09-13 - Earliest claimed: 1989-08-04 - Assignees: Canon Kabushiki Kaisha - Inventors: Osamu Koyama; Tadashi Kato; Masayuki Usui; Yoshihiko Watanabe; Hisatoshi Baba; Hirotake Ando; Hideo Nakajima; Shinji Sakai; Kenji Tamaki - Web page: https://patentgrep.com/patent/US5347503A ## CPC - G11B 7/094: {Methods and circuits for servo offset compensation} - G11B 7/0941: {Methods and circuits for servo gain or phase compensation during operation (for initialising servos G11B7/0945)} - G11B 7/126: Circuits, methods or arrangements for laser control or stabilisation - 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 An optical information processing apparatus includes a light source for radiating a light beam onto an optical information recording medium. A first photosensor is provided for partially receiving the light beam emitted from the light source and generating an output, and a second photosensor is provided for receiving either a light beam reflected by the recording medium or a light beam transmitted through the recording medium and generating an output. A control circuit controls power of the light beam emitted from the light source using the output from the first photosensor, and a correction circuit automatically corrects linearity of the output of the first photosensor with respect to the power of the light beam emitted from the light source in accordance with the output from the second photosensor. ## Claims ### Claim 1 An optical information processing apparatus comprising: a laser diode for emitting a laser beam to irradiate an optical information recording medium, and for emitting a monitoring light; a monitor photodiode, attached to said laser diode, for receiving the monitoring light emitted from said laser diode and for generating a photodiode output; a control circuit for receiving the photodiode output, and for controlling power of the laser beam emitted from said laser diode in accordance with the photodiode output; a photosensor for receiving one of a laser beam reflected by the recording medium and a laser beam transmitted through the recording medium and for generating a photosensor output; and a correction circuit for automatically correcting linearity of the photodiode output with respect to the power of the laser beam emitted from said laser diode in accordance with the photosensor output. ### Claim 2 (depends on 1) An apparatus according to claim 1, wherein said correction circuit comprises a digital signal processing circuit for calculating correction data in accordance with the photosensor output and memory means for storing said correction data calculated by said digital signal processing circuit. ### Claim 3 An optical information processing apparatus, comprising: a light source for radiating a light beam onto an optical information recording medium; a first photosensor for partially receiving the light emitted from said light source and generating an output; a control circuit for controlling power of the light beam emitted from said light source using the output from said first photosensor; a second photosensor for receiving one of a light beam reflected by said recording medium and a light beam transmitted through said recording medium and generating an output; a correction circuit for automatically correcting linearity of the output of said first photosensor with respect to the power of the light beam emitted from said light source in accordance with the output from said second photosensor; temperature detection means for detecting a change in temperature in said apparatus; and means for adjusting said correction circuit when the change in temperature detected by said temperature detection means exceeds a predetermined value. ### Claim 4 (depends on 3) An apparatus according to claim 3, wherein said correction circuit comprises a digital signal processing circuit for calculating correction data in accordance with the output from said second photosensor and memory means for storing the correction data calculated by said digital signal processing circuit. ### Claim 5 (depends on 3) An apparatus according to claim 3, wherein said light source comprises a laser diode. ### Claim 6 A method of controlling power of a laser beam emitted from a laser diode in an optical information processing apparatus comprising (i) a laser diode for emitting the laser beam to irradiate an optical information recording medium and for emitting a monitoring light, (ii) a monitor photodiode attached to the laser diode and (iii) a photosensor, said method comprising the steps of: emitting the laser beam and the monitoring light from the laser diode; receiving the monitoring light emitted from the laser diode by the monitor photodiode and generating a first output; receiving one of a laser beam reflected by the recording medium and a laser beam transmitted through the recording medium by the photosensor and generating a second output; correcting linearity of the first output with respect to the power of the laser beam to irradiate the recording medium with the laser beam in accordance with the second output; and controlling the power of the laser beam emitted from the laser diode by using the corrected first output. ### Claim 7 (depends on 6) A method according to claim 6, wherein said linearity correcting step comprises the steps of: obtaining data indicative of a relation between the first output and the second output while varying the power of the monitoring light and the laser beam, emitted from the laser diode; storing the data into a memory; and correcting the first output by using the data stored in the memory. ### Claim 8 An optical information processing apparatus comprising: a laser diode for emitting a laser beam to irradiate an optical information recording medium, and for emitting a monitoring light; a first photosensor, attached to said laser diode, for receiving the monitoring light emitted from said laser diode, and for producing an output; control means for controlling power of the laser beam emitted from said laser diode in accordance with the output of said first photosensor; a second photosensor for receiving one of a laser beam reflected by the recording medium and a laser beam transmitted through the recording medium, and for producing an output; and correction means for automatically correcting linearity of the output of said first photosensor with respect to the power of the laser beam to irradiate the recording medium with the laser beam, in accordance with the output of said second photosensor. ### Claim 9 (depends on 8) An apparatus according to claim 8, wherein said correction means comprises a digital signal processing circuit for calculating correction data from the output of the second photosensor and a memory for storing the correction data calculated by said digital signal processing circuit.