Abstract: The apparatus includes optical recording media each of which includes a single plate substrate with recording layers and spiral grooves formed on both sides of the substrate and which are available for recording and reproduction or for recording, erasing and reproduction via irradiation with laser beams. Both surfaces of the recording media are available for simultaneous access, and a plurality of thin floating-type optical heads are provided to irradiate laser beams onto the recording media. The optical heads are respectively provided at each side of the recording media and float, responsive to rotation of the recording media, above the respective surfaces of the recording media at a distance of at most hundreds of microns. The combination of these optical recording media and optical heads makes it possible to stack plural pairs thereof within an ultra-thin space, thus greatly improving the on-line capacity of the optical recording apparatus.

Abstract: The present invention provides a large-capacity stack type optical disk unit capable of information recording and reproducing operation at a high speed and an optical information recording and reproducing apparatus for recording/reproducing information onto/from the stack type optical disk unit. The optical information recording and reproducing apparatus comprises a stack type optical disk unit having N recording faces, the sector starting position on the respective recording faces are displaced by a sector as unit from one face to another, one stationary optical units including a laser light source, a collimator, a reflector and a detector for a reflected beam from the recording faces, N sets of focusing units each for focusing a collimated beam onto respective recording faces, a beam distribution unit for distributing the collimated beam to the focusing units, and a servo unit for focussing outputs from the focusing units onto tracks of the recording faces and for performing tracking.

Abstract: In an optical disc recording-reproducing apparatus using a standard optical disc enclosed in a cartridge, and optical plate for correcting various aberrations generated by a focusing lens is comprised therein in order to allow use of a double recording optical disc enclosed in the standard cartridge of the same size, the optical plate is placed in front of a focusing lens when the double recording optical disc is used, and is removed from the front of the focusing lens when the standard optical disc is used.

Abstract: This invention provides an optical head apparatus in which a grating coupler (8), which is formed on a circular region which has a center on an axis (18) and has a periodical structure with dents and projections in a configuration of concentric circles or spirals around the axis (18), input-couples laser light (7) emitted from a semiconductor laser (5) and turns it into waveguided light (16B) which transmits in a waveguiding layer (15B). The waveguided light (16B) is converted, in a region where the waveguiding layer (15B) and a waveguiding layer (15A) overlap each other, to waveguided light (16A) which transmits in the waveguiding layer (15A). By a grating coupler (9), formed on a ring-shaped area which is located around the axis (18), which has a periodic structure with dents and projections of a configuration of concentric circles or spirals around the axis (18), the waveguided light (16A) is radiated and focused onto points (FA), (FB) and (FC) which are located on the axis (18).