Abstract: An optical recording and reproducing head wherein light beams emitted from two light sources are combined and applied to a recording medium and the light beams reflected from the recording medium are drawn out in such a way that they are separated from each other. The wavelengths of the light beams from both light sources are different from each other, i.e., .lambda..sub.1, .lambda..sub.2, and the light beams from the light sources are combined by means of a polarization beam splitter, two quarter wave plates and optical filters, and are then simultaneously focussed by a single focussing lens substantially along the optical axis thereof, thereby allowing microspots of focussed light to be disposed on a disc close to each other. The light beams reflected from the disc are drawn out so as to be completely separated from each other by the polarization beam splitter owing to the difference in polarization direction.

Abstract: An optical data recording and reproducing apparatus for recording digital data in a recording track on an optical recording disc. The apparatus includes a light illuminating unit for condensing an output light beam from a light source and for illuminating the disc, a recording-reproducing unit for recording and reproducing the digital data by a recording light beam and a reproducing light beam from the light illuminating unit, a dropout detecting and inspecting unit, and a recording-prohibited sector detecting unit to produce an output signal identifying a recording-prohibited sector where recording is prohibited responsive to an output signal from the dropout detecting and inspecting unit. The sector address of a recording-prohibited sector is recorded at least until recording of digital data in the recording track on the optical disc is begun. A comparator unit compares the sector address of the recording-prohibited sector with a sector address read continuously from the disc.

Abstract: In an optical disc having a file region and a directory region for carrying various pieces of information or data, one or more designated information can be erased by irradiating a laser light beam on a corresponding region in the file region where the light beam is modulated by a superposing writing signal which may be a d.c. or a predetermined a.c. signal. When it is intended to renew the information, designated information is first read out and stored in an external memory prior to performing superposing writing. Meanwhile, the data is renewed and is then written on an unused region in the file region. The directory of the renewed data region is also written so that the renewed information will be read out by searching the new directory. In another embodiment of the invention, the information in the file region is not erased to renew the same, but its directory is erased by superposing writing.

Abstract: The disclosure is directed to an optical recording and reproducing disc in which each track circumference of guide tracks formed into a concentric or spiral configuration is divided into a plurality of sectors for selective recording and reproduction of information in any desired sectors. Sector separating zones of predetermined configuration are provided at starting portions of the respective sectors, while predetermined sector marks indicating the sector separating zones are formed on an index track provided at an outer or inner periphery of the disc in positions corresponding to the sector separating zones so that, during selection of the sectors at recording and reproduction, reproduction signals by the sector marks are used for selection of the sectors, while starting of the recording and reproduction is effected by the reproduced information of the sector separating zones.

Abstract: A modulation and demodulation system for an optical data recording and reproducing apparatus is disclosed in which, in an optical disc having an optical guide track and capable of recording and reproducing optically, the guide track is divided into a plurality of data sectors and the recording or reproduction or reading is effected by data sector. The modulation system for the data field for recording the data is different from that for the identification field containing identification data such as a track address and a sector address in such a way that the identification field is reproduced at high reliability and high demodulation speed while at the same time recording data at high density in the data field.

Abstract: A system for driving a semiconductor laser which is especially adapted for use with an optical recording and reproducing device is disclosed. In the write mode the power of laser light emitted from the semiconductor laser is so raised above a threshold or critical level that the laser beam focused on the surface of a recording medium can cause physical, chemical or electromagnetical changes thereof, but in the readout or reproduction mode, the power of laser light is lowered than the threshold or critical level and focused on the recording medium. A laser light power control loop is provided which is enabled or energized only in the readout or reproduction mode, so that the laser light can be maintained at a predetermined level.

Abstract: A track searching system for an optical information recording and reproducing apparatus in which a disc-like information carrier provided with concentric or spiral guide tracks of a channel-like configuration is used as an information recording and storing means and adapted to be scanned by a light beam for recording or retrieval of information. Light flux reflected by the information carrier and presenting variable distribution of light intensity is received by paired photoelectric elements. A difference signal and a sum signal derived from the output signals from the photoelectric elements or a reproduced RF signal representative of reproduced information undergo phase comparison processing, the result of which is utilized for determining the direction and number of guide tracks traversed by the scanning light beam.

Abstract: An optical information recording and reproducing apparatus for optically recording and reproducing information on and from a disk-shaped information carrier having a guide track is disclosed. A digital track address prerecorded on the guide track is reproduced and the intensity of a recording laser beam is controlled by the reproduced digital track address so that the exposures of the recording laser beam at an inner periphery and an outer periphery of the disk-shaped information carrier rotated at a constant rotation speed are corrected to enable an optimum recording over an entire surface of the disk-shaped information carrier.

Abstract: In the method for scanning light beam in a xerographic recording using a laser light beam spots to scan on a photoreceptor the quality of the recorded image is improved by increasing size of the light beam spot when the irradiation spot scanning on the photoreceptor has neighboring spots to be irradiated. For detecting whether the neighboring spots are the spots to be irradiated or not, three shift registers 12, 13 and 14 and a NOR circuit 15 are used, and the output of the NOR circuit controls analog circuit 161 which switches amount of the laser current.

Abstract: A holographic playback system comprises a turntable adapted to support a record disk which contains a series of holograms recorded along convoluted spiral tracks. Each of the holograms represents a pattern of data bits and synchronization bit, and an optical system for directing a laser beam to the record disk, whereby the laser beam is diffracted by the interference fringes of the hologram to reconstruct the image of the pattern of data and synchronization bits. The turntable is driven so that the holograms are successively shifted in location with respect to the laser beam and illuminated by the beam. A solid-state image sensor is provided which includes a plurality of charge storage type sensing elements each positioned to receive the reconstructed image of each data bit and a non-charge storage type sensing element positioned to receive the reconstructed image of the synchronization bit.

Abstract: An apparatus for separating non-magnetic materials of different densities, which apparatus includes a material separating portion, in which a magnetic fluid is retained in a magnetic field having a gradient in a vertical direction. In this apparatus, a single conveyor is jointly used for the supply, and charging of materials to be separated, into the material separating portion, and the transporting of floating materials of a low density through the magnetic fluid and their recovery outside.

Abstract: The holographic recording system comprises a pair of aligned first and second Fourier transforming lenses, a holographic beam splitter having a series of random phase illumination holograms at a front focal plane of the first lens and arranged to move in a given direction to successively receive a light beam for deffracting it into a zero-order diffracted beam and a first-order diffracted array of sampled, phase shifted beams, and a mask having a first and second apertures disposed at the Fourier transform plane of the first lens. A page composer having electrooptical transducers is positioned in the second aperture to receive the first-order diffracted array of beams to spatially optically modulate the incident beams in accordance with one of successive groups of binary signals.