Patent SE-7810130-L (SE)
Inventor: WINSLOW J S
IPC: G11B7/00
Filed: 1978-09-27
Abstract: The invention concerns the method and apparatus for recording video information in the form of a frequency- modulated signal on a video disk element 10 and for recovery of the video information from the video disk element. The recording apparatus has a laser as a source 30 for a laser writing beam 29, 29' and an optical writing unit 40, 41 for directing the stationary laser writing beam against a moveable video disk element 10. The video disk element comprises a substrate 22, which has a coating 26 that can be influenced by light on at least one surface 24. The optical writing unit 40, 41 focuses the beam to a small light spot 42 with a diameter of approximately 1 micrometer on the coating layer 26 which can be influenced by light. The intensity of the focused spot can be altered by control of a light intensity modulation unit 44. The light intensity modulator 44 changes the intensity of the laser writing beam 29, 29' with regard to a predetermined threshold intensity, which is high enough to form a first type of markings 37 in the coating layer. The length of the first type of marking depends on the speed of movement of the video disk element 10 and the time during which the intensity of the writing laser exceeds the predetermined or material-dependent threshold intensity. When the intensity of the laser writing beam falls beneath the predetermined threshold intensity, the formation of the first type of marking 37 ceases. The intervening portions of the coating layer that can be influenced by light, which portions are situated between consecutive markings of the first type, serve as a second type of marking 38. A motion control unit 28 rotates and translates the video disk element relative to the intensity-modulating writing beam. In this way, a linear succession of first and second markings is formed on the substrate. The first and the second markings 37, 38 have variable length and represent the frequency-modulated signal intended for the recording. By making use of the recording method and an apparatus for implementation thereof, video information is stored on the information storage element 10 in the form of a frequency-modulated signal 92, which has its information content in the form of a carrier signal with frequency variations over time, which vary from a central frequency. The frequency-modulated signal 92 occurs as a linear sequence of first and second markings 38 situated in the manner of grooves on the surface 24 of the storage element. In a preferred embodiment of the invention, the linear succession of first and second markings 37, 38 is situated in alternating relationship. The first type of markings reflects light in non-specular fashion. The second type of markings reflects light in specular fashion. The length of the specular light-reflecting regions and the non-specular light-reflecting regions represents consecutive half-periods for each whole period of a frequency-modulated signal. The length of these regions varies in inverse proportion to the momentary frequency of the frequency-modulated signal. In this way, the length of the specular light-reflecting and the non- specular light-reflecting regions is a representation in space of the frequency-modulated signal. A reading system is used to recover the video signal stored on the video disk element 10. This reading system comprises a reading laser 152 for generating a reading beam 150, and a motion control unit 28 for rotation and translation of the video disk element relative to the reading beam. An optical reading system 154, 156 directs the reading beam so that it impinges on regions 37, 38 with specular light reflecting ability and non-specular light reflecting ability situated consecutively one after the other on the video disk element 10. The optical reading system 154, 156 also collects the light reflected from these regions. The reflected light beam is intensity- modulated by the regions with specular light reflectivity and non-specular light reflectivity. The optical reading system also directs the reflected light beam onto a light detecting circuit 158, 164, 162 for changing of the intensity-modulated, reflected light beam into a corresponding frequency-modulated, electric signal, which is representative of the video signal stored on the video disk element. <IMAGE>