Abstract: An optical information recording and reproducing system comprises a light source for emitting a working beam from a front end thereof and a monitoring beam from a rear end thereof, an optical system control circuit, a loop gain adjusting circuit and a photo detector. The monitoring beam emitted from the rear end of the light source is detected by the photo detector, and the loop gain of the servo loop control circuit for the focusing and/or tracking is automatically adjusted by means of the loop gain adjusting circuit according to the detected signal so that a desired closed loop control of the working beam can be performed according to the operation modes and the light beam power variation.

Abstract: A method of detecting defects formed on an optical record medium for use in an optical information recording and reproducing apparatus. The method comprises steps of deriving light output signals reflected from the record medium at the time of information writing, comprising the light output signals with reference signals which are set to a plurality of desired levels, and logically operating the compared output signals thereby detecting and evaluating the defects formed on the surface of the record medium.

Abstract: In an auto-focussing system, an actuator which moves together with an objective lens is vertically movable against a rotating optical disc and radiates a light beam so as to form a light spot on an information plane of the disc. A focus servo unit moves the actuator so that an optical distance between the actuator and the disc is within a proper distance region and performs the focus control of the light spot on the disc. While the actuator is approaching the optical disc, an auto-focus/focus servo controller initially makes the servo unit nonoperative and, when the actuator reaches a too-far position in a suitable servo loop distance region specified by a servo loop of the focus servo unit, the controller temporarily stops the movement of the actuator and then moves the actuator again from the too-far position by only a predetermined distance, thereby causing the actuator to be located within the focus loop distance region.

Abstract: In an optical recording and/or reproducing apparatus for recording and/or reproducing an information signal on and/or from an optical record disc by projecting a light beam spot onto the rotating disc by means of an objective lens, the objective lens is moved linearly in a disc radial direction over a small distance by means of a fine adjusting mechanism and the fine adjusting mechanism is moved in a stepwise manner in the disc radial direction over a large distance by means of a coarse driving mechanism including a pulse motor. The objective lens is moved together with the fine adjusting mechanism at a high speed and during intervals between successive stepwise movements, the objective lens is moved linearly by the fine adjusting mechanism. In this manner, the objective lens can be driven linearly over the large distance and a desired point of the disc can be quickly accessed.

Abstract: An optical disk apparatus has an optical head. The optical head emits a light beam onto an optical disk and forms pits in the optical disk, thereby recording a signal. A detector detects the relative inclination between the optical head and the optical disk and generates a signal corresponding to this relative inclination. A beam intensity correction circuit corrects the intensity of the light beam in accordance with the relative inclination to form proper pits. In one embodiment, the intensity of the light beam is increased when the relative inclination is increased.

Abstract: An optical disk apparatus has an optical disk for recording data into a recording area on an optical disk and reproducing the recorded data from the recording area. The optical disk is provided at the center with a first section with the same reflectivity as that of the recording area and a second section with a different reflectivity from that of the recording area. A photosensor sense detects the first section and produces a signal representing a reflectivity on the first section. The reflectivity data obtained from the signal level is used for controlling a gain of the servo system according to the reflectivity data.

Abstract: A detecting circuit for detecting an operating center of an actuator of an optical head includes a first comparator for comparing a tracking signal based on a reproduced signal coming from the optical head with a reference voltage approximate to zero voltage level, and a second comparator for comparing the tracking signal of which the DC component is removed with a second reference voltage approximate to zero voltage level. A level inversion of a binary output signal of the first comparator is detected at a level inverting point of a binary output signal of the second comparator. The operating center of the actuator is checked with the detection of the level inversion.

Abstract: In a jitter correction circuit for correcting a time base error caused in a color television signal readout from a video disc due to a fluctuation in a disc rotating speed and an eccentricity of the disc, a first closed loop control circuit includes a first phase difference detector for detecting a first phase deviation of a horizontal synchronizing signal of the color television signal and a first variable time constant lag filter for producing a first control signal in response to the first phase deviation and a second closed loop control circuit includes a second phase difference detector for detecting a second phase deviation of a color burst signal of the color television signal and a second variable time constant lag filter for producing a second control signal in response to the second phase deviation.

Abstract: An apparatus for comparing analog signals delivered from a number of light detecting elements with analog signals delivered from a digital-analog converter by means of a plurality of comparator circuits whose output analog signals are supplied as write enable signals to a plurality of digital memories which are controlled by means of digital signals delivered from a central control circuit such that an illumination intensity information of each picture element is read out as the digital signal in the digital memories, thereby obtaining a signal of detecting a focal point of cameras or the like optical devices.

Abstract: A method of comparing analog signals delivered from a number of light detecting elements with analog signals delivered from a digital-analog converter by means of a plurality of comparator circuits whose output analog signals are supplied as write enable signals to a plurality of digital memories which are controlled by means of digital signals delivered from a central control circuit such that an illumination intensity information of each picture element is read out as the digital signal in the digital memories, thereby obtaining a signal of detecting a focal point of cameras or the like optical devices.