Patent ID: 9601147
Date: 2017-03-21
CPC Classifications: G03H,G11B

Claim:
1. An optical information recording and reproducing apparatus, which branches a light beam into a reference light and a signal light to cause interference and records an obtained interference fringe as a hologram on an optical information recording medium and also reproduces the recorded hologram by applying the reference light onto the optical information recording medium, the optical information recording and reproducing apparatus comprising: a pickup having a light source which emits the light beam, a branching element which branches the light beam into the reference light and the signal light, a spatial light modulator for adding information to the signal light, a spatial filter having an aperture through which the signal light with the added information passes, an objective lens which applies the signal light passing through the aperture onto the optical information recording medium, an optical system which applies the reference light onto the optical information recording medium, an image pickup element which detects reproduction light passing through the aperture when the reference light is applied onto a hologram of a reproduction target formed on the optical information recording medium and generates a reproduced signal therefrom, and a photo detector different from the image pickup element, the photo detector detects the reproduction light applied on a periphery of the aperture; and a processor connected to a storage medium that stores instructions that, when executed by the processor, cause the processor to compute a position error signal indicating a deviation in position of the optical information recording medium with respect to the objective lens based on an output from the photo detector, wherein the aperture is disposed to prevent diffracted light coming from a hologram other than the reproduction target formed on the optical information recording medium from being guided to the image pickup element, wherein the spatial filter has a reflective area on the periphery of the aperture on a side where the reproduction light enters, wherein the photo detector is provided at a position different from the image pickup element and the optical information recording medium, and wherein the reflective area is tilted by a predetermined amount with respect to a surface of the spatial filter so as to guide the reproduction light applied on the periphery of the aperture to the photo detector.