Patent ID: 8068402

Claim:
An optical head comprising: a light source for emitting laser light of 430 nm wavelength or less; a collimator lens for converting the laser light emitted from the light source into substantially parallel light; an objective lens for collecting the laser light emitted from the collimator lens on an information recording medium having plural information recording surfaces; a detecting lens for imparting astigmatism to the laser light reflected on the information recording medium and collected by the collimator lens; and a light receiving element for receiving the laser light subjected to the astigmatism by the detecting lens, wherein the detecting lens is made of a resin material, wherein the detecting lens is disposed on a side of the objective lens with respect to a light collecting position, by the collimator lens, of the laser light reflected on a second information recording surface different from a first information recording surface having a thinnest protection substrate, among the plural information recording surfaces of the information recording medium, during recording or reproducing on or from the first information recording surface having the thinnest protection substrate, wherein the optical head further comprises a light splitting element for separating (i) an incoming optical path along which the laser light emitted from the light source is guided to the objective lens, and (ii) an outgoing optical path along which the laser light reflected on the information recording medium is guided to the light receiving element, wherein the optical head satisfies the following formula: d1/2>d2+td/2 where d1 is a distance between a light receiving surface of the light receiving element and a light exit surface of the light splitting element, d2 is a distance between the light exit surface of the light splitting element and the detecting lens, and td is a thickness of the detecting lens.