Optical pickup using diffracted light

Claim 1

An optical apparatus which emits a beam of reading light to an optical information recording medium having a pit in which information is stored and reads the information by means of the zero order reflected light reflected from the pit and the diffracted light generated on the pit by diffraction effect, comprising: light generating means for generating the beam of reading light; first photoelectric conversion means provided so that the zero order reflected light is incident thereto for generating a first electric signal corresponding to the intensity of the zero order reflected light incident thereto; second photoelectric conversion means provided so that the diffracted light is incident thereto for generating a second electric signal corresponding to the intensity of the diffracted light incident thereto; light focusing and guiding means, having a first grating lens of a first central optical axis and a second grating lens of a second central optical axis unequal to the first central optical axis, the first grating lens focusing the beam of reading light on the pit, the first and second grating lenses associating with each other to separate the zero order reflected light and the diffracted light, the first grating lens guiding the zero order reflected light to the first photoelectric conversion means and the second grating lens guiding the diffracted light to the second photoelectric conversion means; and operating means for generating an output signal corresponding to the information stored in the pit by taking difference between the first and the second electric signals.