Pickup apparatus for magneto-optical recording medium

Claim 1

A pickup apparatus for a magneto-optical recording medium, which comprises: (i) a light source for irradiating a linearly polarized light beam onto a surface of a magneto-optical recording medium, (ii) an objective lens for converging said light beam onto the reflection surface of said magneto-optical recording medium, (iii) an optical waveguide disposed in such a direction that one surface thereof receives the light beam reflected by said magneto-optical recording medium, (iv) a first focusing grating coupler and a second focusing grating coupler disposed side by side at an incidence position of said reflected light beam on the surface of said optical waveguide so that an axis passing through approximately the center of said reflected light beam and extending on said surface of said optical waveguide approximately normal to a tracking direction intervenes between said first focusing grating coupler and said second focusing grating coupler, said first focusing grating coupler and said second focusing grating coupler respectively making said reflected light beam enter said optical waveguide by exciting either one of a TE guided mode and a TM guided mode, and respectively converging the optical waves, which are thus guided through said optical waveguide in the guided modes identical with each other, to positions spaced from each other with said axis intervening therebetween, (v) a third focusing grating coupler disposed side by side with said first focusing grating coupler and said second focusing grating coupler at the incidence position of said reflected light beam on the surface of said optical waveguide, said third focusing grating coupler making said reflected light beam enter said optical waveguide by exciting a guided mode different from said guided modes of said first focusing grating coupler and said second focusing grating coupler, and converging the optical wave, which is thus guided through said optical waveguide, in said optical waveguide, (vi) a first photodetector, a second photodetector, and a third photodetector secured to the surface or an edge face of said optical waveguide for respectively detecting the optical wave converged by said first focusing grating coupler, the optical wave converged by said second focusing grating coupler, and the optical wave converged by said third focusing grating coupler, (vii) an error detection circuit for carrying out detection of tracking error and detection of focusing error on the basis of outputs of said first photodetector and said second photodetector, and (viii) a differential detection circuit for detecting signals recorded on said magneto-optical recording medium on the basis of a difference between the output of said first photodetector and/or the output of said second photodetector on one hand and an output of said third photodetector on the other hand.

Claim 27

An apparatus as defined in any of claims 1 to wherein said optical waveguide is disposed integrally with said objective lens and is moved together with said objective lens for the purposes of tracking control and focusing control.