Abstract: An apparatus for recording information on an optical type recording medium alternately generates a binary signal of a first frequency and a binary signal of a second frequency lower than the first frequency, applies radiation to the medium and writes the binary signals of the first frequency and the second frequency into the medium, reproduces the binary signals of the first frequency and the second frequency written into the medium and converts them to electrical signals, AC-amplifies the electrical signals, detects the difference between the amplitude of the output of the AC amplifier of a level higher than a reference level, which corresponds to the first frequency and of a level lower than the reference level, which corresponds to the first frequency and outputs a detection signal, and responds to the detection signal to control the intensity of the radiation applied to the medium for writing.

Abstract: Apparatus for reproducing recorded information applies a linearly polarized light beam to a recording medium having first and second recorded information tracks. The recording medium is formed so that the intensity of reflected light relative to the incident light varies in accordance with the information recorded in one of the tracks, and the plane of polarization of the reflected light relative to the linearly polarized incident light varies in accordance with the information recorded in the other track. The reflected light is divided into two components having different planes of polarization. A recorded magnetooptic signal is reproduced from the difference in intensity between the two components, and a recorded light intensity signal is reproduced from at least one of the two components.

Abstract: In an apparatus for irradiating a magnetooptical recording medium with a linearly polarized light beam and detecting the light from the medium, the light from the magnetooptical recording medium is divided, depending on the degree of the plane of polarization, into two light beams of different intensities which are respectively converted into electrical signals for supply to a differential amplifier, wherein an electrical signal corresponding to a light beam is amplified in order to eliminate the noise component in the output signal of the differential amplifier. In addition, the apparatus is so constructed that the amplification of the electrical signal corresponding to a divided light beam is controlled in response to the electrical signals corresponding to the divided light beams.

Abstract: An optical head system for accurately detecting the relative positions of a spot of Gaussian beam and a recording track. The optical head system includes an objective lens adapted to be moved in a tracking direction for the tracking of the recording track by the beam spot, a light detector arranged stationary, and movable optical means arranged between the objective lens and the light detector such that the beam spot reflected from the recording track and projected on the light detector through the objective lens is held stationary on the light detector with respect to the movement of the objective lens.