Patent ID: 6888787

Claim:
An optical information processor performing at least either one of information recording and information reproduction with respect to an information recording medium, comprising: a light source; an objective lens for focusing light emitted from the light source on the information recording medium; a separation element for separating light from the information recording medium from an optical path to the light source; and first photodetectors for receiving light separated by the separation element, wherein an aperture in a direction almost orthogonal to a track of data string on the information recording medium is formed so that an aperture NA 1 (R) in a first optical path from the light source to the information recording medium and an aperture NA 2 (R) in a second optical path from the information recording medium to the first photodetectors satisfy a relationship of NA 1 (R)>NA 2 (R), and an aperture in a direction almost parallel to the track of data string on the information recording medium is formed so that an aperture NA 1 (T) in the first optical path and an aperture NA 2 (T) in the second optical path satisfy a relationship of NA 1 (T)=NA 2 (T).