| 摘要 |
Light beam emitted from a laser light source is focused by an objective lens and applied in this state to an optical information recording medium. In the optical path between the laser light source and the objective lens is disposed a diffraction grating inclinedly with respect to the optical axis. This diffraction grating not only reflects the light beam emitted from the laser light source but also separates it into zero order as well as +1st order and -1st order diffracted light beams. Thus, this diffraction grating functions not only as a diffraction grating but also as a mirror. The thus-separated light beams are applied to an optical disc and the reflected light beams from the optical disc are converted to electric signals by means of a photo detector. The +/-1st order diffracted light beams are used as track servo beams for following the track on the disc. The zero order diffracted light beam is used for reproducing information signals provided from the track on the disc. The diffraction grating has unequally spaced, curvilinear grooves in order to solve the problems of wave front aberration and light spot aberration which are induced by letting the diffraction grating function as both a diffraction grating and a mirror. |
