Optical information processing apparatus and method of controlling position of optical spot and reproducing signals

An optical information processing apparatus comprising:

• (a) light source;
• (b) diffracting means provided in an optical path of beams from
• said light source, said diffracting means allowing a part of said beams to pass therethrough as the main beam and producing a couple of sub-beams respectively having positive and negative astigmatisms with two focal lines, respectively in directions at very small angles different from the direction of the main beam;
• (c) an image-forming optical system for focusing said main beam as a main light spot and also focusing said couple of sub-beams as light spots on the information recording surface, said information recording surface has marks for modulating the reflected light quantities of beams emitted thereon, said marks being provided in a large number in the track-advance direction and aligned in directions substantially perpendicular to said track-advance direction for a range of at least several tracks;
• (d) separating optical system for separating out the beams reflected by said information from the optical path of said beams;
• (e) photo-detecting means for receiving said reflected beams separated out by said separating optical system, said photo-detecting means comprising at least a first photo-detecting element for receiving a reflected ray of said main spot and a second photo-detecting element for receiving reflected rays of said couple of sub-beams;
• (f) off-track detecting means for obtaining an off-track signal from output of said first photo-detecting element;
• and
• (g) a focusing error detecting means having amplitude detecting means for detecting the size of the amplitudes, modulated by said marks, of the respective reflected beams of said couple of sub-beams from output of said second photo-detecting element, said focusing error detecting means obtaining a focusing error detection signal from a difference of the amplitudes.

An optical information processing apparatus comprising:

• (a) a diffraction grating for diffracting light beams emitted by a semiconductor laser into at least three beams, said three beams comprising-a main beam and a couple of sub-beams, said diffraction grating giving said couple of sub-beams positive and negative astigmatism having two focal lines, respectively;
• (b) a focusing lens for focusing said main beam and said couple of sub-beams on the information recording surface;
• (c) a separating optical system, arranged between said information recording surface and said diffraction grating, for separating reflected beams from said information recording surface from the incident beams;
• (d) a lens for focusing said reflected beams on three photo-detecting elements, reflected beams of said main beams and said couple of sub-beams being focused respectively on said three photo-detecting elements;
• (e) a sampled servo circuit for detecting a tracking signal from a reflected beam of said main beam;
• (f) a focusing control means for detecting a focusing signal from the reflected beams of said couple of sub-beams, said focusing control means comprises envelope circuits for detecting amplitudes of signals respectively obtained from said couple of reflected beams, and a differential operation circuit for obtaining a difference of outputs of said two envelope circuits;
• and
• (g) an actuator for driving said focusing lens using output of said sampled servo circuit and output of said differential operation circuit.

A method of controlling information processing apparatus comprising the steps of:

• (a) passing a beam of light emitted by a light source through a diffracting optical element having unequally-spaced interval concentric elliptical grating grooves disposed between the light source and a beam splitter to produce a main beam and a couple of sub-beams, said diffracting optical element allowing said main beam to pass therethrough but diffracting said couple of sub-beams;
• (b) focusing said main beam and said couple of sub-beams on an information recording medium, and receiving reflected beams thereof with photo-detecting elements disposed on a plane surface with respect to the information recording medium, said main beam and said couple of sub-beams being focused at different positions in the optical direction;
• (c) obtaining an off-track signal from reflected rays from said main beam;
• (d) obtaining a focusing error signal from reflected rays of said couple of sub-beams;
• and
• (e) feeding said off-track signal and said focusing error signal back to a lens drive means.

An optical information processing apparatus comprising:

• (a) light source:
• (b) diffracting means having unequally-spaced interval concentric elliptical grating grooves disposed between said light source and beam splitter, said diffracting means allowing the main beam to pass therethrough but diffracting a couple of sub-beams;
• (c) an image-forming optical system for focusing said main beam as a main light spot and also focusing said couple of sub-beams as light spots on an information recording surface of an information recording medium, said information recording surface having marks for modulating the reflected light quantities of beams incident thereon, said marks being provided in a large number in the track-advance direction and aligned in directions substantially perpendicular to said track-advance direction for a range of at least several tracks;
• (d) a separating optical system for separating out the beams reflected by said information from the optical path of said beams;
• (e) photo-detecting means disposed on a plane surface with respect to the information recording medium, for receiving said reflected beams separated out by said separating optical system, said photo-detecting means comprising at least a first photo-detecting element for receiving a reflected ray of said main spot and a second photo-detecting element for receiving reflected rays of said couple of sub-beams;
• (f) off-track detecting means for obtaining an off-track signal from output of said first photo-detecting element;
• and
• (g) focusing error detecting means having amplitude detecting means for detecting the size of the amplitudes, modulated by said marks, of the respective reflected beams of said couple of sub-beams from an output of said second photo-detecting element, said focusing error detecting means obtaining a focusing error detection signal from a difference of the amplitudes.