EP0045117A2
Expired / Lapsed
EP
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Apparatus and method for writing a signal information track on a disc
Assignee: Discovision Associates
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Filing: 1979-03-27
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Granted: —
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Expires: 1999-03-27
Abstract
Abstract This invention relates to an apparatus and process for writing video information in the form of a frequency modulated signal upon a video disc member and for recovering the video information from the video record is described. The video disc member (10) formed by the writing apparatus is also described. The writing apparatus includes a laser (30) as a source of a laser write beam (29) and a write optical system (40) for directing the stationary laser write beam to a moving video disc member. The video disc member comprises a substrate member carrying a light responsive coating (26) at least one surface. The write optical system focuses the beam to a small spot of light approximately one micron in diameter upon the light responsive layer. The intensity of the focused spot is changeable under the control of a light intensity modulating assembly (44). This light intensity modulator changes the intensity of the write laser beam with respect to a predetermined threshold intensity sufficient to form a first type of indicia (37) in the coating. A read system (165) is employed to retrieve the video signal stored on the video disc member. This read system includes a read laser (150) for generating a read beam, and a motion control assembly for rotating and translating the video disc member relative to the read light beam. A read optical system directs the read beam to impinge upon the successively positioned specular light reflective and non-specular light reflective regions (37, 38) carried by the video disc member. The read optical system also collects the light (150) reflected from these regions. The reflected light beam is intensity modulated by the specular light reflective and non-specular light reflective regions. The read optical system also directed the reflected light beam to a light sensing circuit for changing the intensity modulated reflected light beam to a corresponding frequency modulated electrical signal (165) which is representative of the video signal stored on the video disc member. Circuitry is described for using a triangular frequency modulator (FIGURE 14C) for driving a Pockels Cell (68) and for obtaining a sinusoidal-shaped light modulation output signal from the linear polariser (70). The output from the linear polariser is adjusted such that the half power point from the polariser equals the threshold power level of the material forming the information storage layer. A second harmonic bias circuit (264) is employed for removing the second harmonic intermodulation distortion of the modulated write beam.
Inventors
- 👤 Richard L. Wilkinson
- 👤 John S. Winslow
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-01 20:52
CPC Classifications
G; G11; G11B; G11B7/00; G11B7/12; G11B7/004; G11B7/0045
Claims Analysis
Total Claims: 13
Claim 1
Independent Claim
128 words
Apparatus for writing a signal information track on a disc having a surface capable of responding to a certain intensity of laser or other radiation ( the threshold level) by being converted from having one radiation reflecting characteristic to having a second characteristic, including means for modulating in intensity a beam of radiation directed at a local point along the track as the beam moves along the track, the modulation being in accordance with the signal information and characterised by means for generating a signal responsive to the second harmonic content of the intensity modulated beam at the signal information carrier frequency and a feedback circuit arranged to bias the modulating means in response to the second harmonic signal such that the second harmonic distortion is a minimum.
Claim 2
Dependent Claim
128 words
Apparatus for writing a signal information track on a disc having a surface capable of responding to a certain intensity of laser or other radiation ( the threshold level) by being converted from having one radiation reflecting characteristic to having a second characteristic, including means for modulating in intensity a beam of radiation directed at a local point along the track as the beam moves along the track, the modulation being in accordance with the signal information and characterised by means for generating a signal responsive to the second harmonic content of the intensity modulated beam at the signal information carrier frequency and a feedback circuit arranged to bias the modulating means in response to the second harmonic signal such that the second harmonic distortion is a minimum.
Claim 3
Dependent Claim
48 words
Apparatus as claimed in Claim 1 including a photosensitive device responsive to the modulated radiation and a limiting device for supplying the output of the photosensitive device and the inversion of that output to opposite inputs of a differential amplifier whose output is the second harmonic responsive signal.
Claim 4
Dependent Claim
45 words
Apparatus as claimed in Claim 2 in which the second harmonic responsive means is connected through a high voltage amplifier to a summing circuit which also receives signals responsive to the signal information to be written, and which provides an output to the modulating means.
Claim 5
Dependent Claim
23 words
Apparatus as claimed in any of the preceding claims including wave shaping means for providing the signal information as a continuous triangular waveform.
Claim 6
Dependent Claim
40 words
Apparatus as claimed in Claim 4 including means arranged to adjust continuously the modulating means so that the average intensity of the modulated radiation is at an operating point mid-way between the maximum and minimum states of the triangular waveform.
Claim 7
Dependent Claim
27 words
Apparatus as claimed in Claim 4 or Claim 5 in which the output waveform of the modulating means is sinusoidally shaped in response to the triangular waveform.
Claim 8
Dependent Claim
438 words
Apparatus for storing video information in the form of a frequency modulated signal upon an information storage member, comprising: first means for providing an information signal to be recorded, and said signal having its informational content in the form of a carrier frequency having frequency changes in time representing said information to be recorded; an information storage member including a substrate having a first surface and a light responsive coating covering said first surface for retaining indicia representative of said information signal; means for imparting uniform motion to said storage member; a light source for providing a light beam, said light beam being of sufficient intensity for interacting with said coating while said coating is in motion and said coating is positioned upon said moving information storage member, said light beam being of sufficient intensity for altering said coating to retain indicia representative of said information signal; optical means for defining an optical path between said light source and said record carrier including said coating, said optical means being further employed for focusing said light beam to a spot upon said coating; light intensity modulating means positioned in said optical path between said light source and said record carrier, said light intensity modulating means operating over a range between a maximum light transmitting state and a minimum light transmitting state for intensity modulating said light beam with said information to be stored; said light intensity modulating means being responsive to said frequency modulated signal and changing between its maximum light transmitting state and its minimum light transmitting state during each cycle of said frequency modulated signal for modulatig said light beam with the frequency modulated electrical signal to be stored; and stabilising means responsive to said modulated light beam for generating a bias control signal for biasing said light intensity modulating means; said stabilising means includes a second harmonic detector means for generating a voltage which is linear in the ratio of the second harmonic to the fundamental frequency, said voltage having one polarity indicating that the phase of the second harmonic is in phase with the fundamental frequency, and said voltage having another polarity indicating that the phase of the second harmonic is opposite in phase with the fundamental frequency, said bias control signal being employed for biasing said modulating means at its operating point at which minimum second harmonic distortion is present in said modulated light beam at its average power intensity; and wherein said light passing through said light intensity modulating means and focused upon said coating by said optical means forms indicia in said coating representative of said frequency modulated signal to be stored.
Claim 9
Dependent Claim
438 words
Apparatus for storing video information in the form of a frequency modulated signal upon an information storage member, comprising: first means for providing an information signal to be recorded, and said signal having its informational content in the form of a carrier frequency having frequency changes in time representing said information to be recorded; an information storage member including a substrate having a first surface and a light responsive coating covering said first surface for retaining indicia representative of said information signal; means for imparting uniform motion to said storage member; a light source for providing a light beam, said light beam being of sufficient intensity for interacting with said coating while said coating is in motion and said coating is positioned upon said moving information storage member, said light beam being of sufficient intensity for altering said coating to retain indicia representative of said information signal; optical means for defining an optical path between said light source and said record carrier including said coating, said optical means being further employed for focusing said light beam to a spot upon said coating; light intensity modulating means positioned in said optical path between said light source and said record carrier, said light intensity modulating means operating over a range between a maximum light transmitting state and a minimum light transmitting state for intensity modulating said light beam with said information to be stored; said light intensity modulating means being responsive to said frequency modulated signal and changing between its maximum light transmitting state and its minimum light transmitting state during each cycle of said frequency modulated signal for modulatig said light beam with the frequency modulated electrical signal to be stored; and stabilising means responsive to said modulated light beam for generating a bias control signal for biasing said light intensity modulating means; said stabilising means includes a second harmonic detector means for generating a voltage which is linear in the ratio of the second harmonic to the fundamental frequency, said voltage having one polarity indicating that the phase of the second harmonic is in phase with the fundamental frequency, and said voltage having another polarity indicating that the phase of the second harmonic is opposite in phase with the fundamental frequency, said bias control signal being employed for biasing said modulating means at its operating point at which minimum second harmonic distortion is present in said modulated light beam at its average power intensity; and wherein said light passing through said light intensity modulating means and focused upon said coating by said optical means forms indicia in said coating representative of said frequency modulated signal to be stored.
Claim 10
Independent Claim
110 words
A method of writing a signal information track on a disc having a surface capable of responding to a certain intensity of laser or other radiation ( the threshold level) by being converted from having one radiation reflecting characteristic to having a second characteristic in which a beam of radiation directed at a local point along the track is modulated in intensity in accordance with the signal information, and a signal responsive to the second harmonic content of the intensity modulated beam at the signal information carrier frequency is fed back to provide a modulating bias level such that the second harmonic distortion of the modulated radiation is a minimum.
Claim 11
Independent Claim
110 words
A method of writing a signal information track on a disc having a surface capable of responding to a certain intensity of laser or other radiation ( the threshold level) by being converted from having one radiation reflecting characteristic to having a second characteristic in which a beam of radiation directed at a local point along the track is modulated in intensity in accordance with the signal information, and a signal responsive to the second harmonic content of the intensity modulated beam at the signal information carrier frequency is fed back to provide a modulating bias level such that the second harmonic distortion of the modulated radiation is a minimum.
Claim 12
Dependent Claim
31 words
A method as claimed in Claim 8 in which the fed-back signal is linearly related to the ratio of the second harmonic content to the fundamental frequency of the modulated radiation.
Claim 13
Dependent Claim
50 words
A method as claimed in Claim 8 or Claim 9 in which the fed-back signal has a polarity depending on whether the second harmonic component is in phase with, or in phase opposition with the fundamental frequency, and has an amplitude dependent upon the level of the second harmonic content.
References Cited (Backward Citations)
No citation records indexed.
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