Patent ID: 7791986

Claim:
An optical information recording/reproducing apparatus that records or reproduces information using a light spot due to a near field effect, the apparatus comprising: a laser beam source; an objective lens that collects a light flux from the laser beam source; an SIL that is disposed between the objective lens and an optical recording medium; a light receiving device that receives a reflected light flux from the optical recording medium; a splitting device that guides the light flux of an effective numerical aperture NAeff<1 due to the objective lens and the SIL within a pupil among the reflected light fluxes to the light receiving device; a control circuit that focuses the light flux on a recording layer of the optical recording medium based on a focus error signal obtained by the light receiving device; an expander lens, a ¼ wavelength plate, and a polarization beam splitter, which are disposed between the objective lens and the light receiving device; a first photodetector that receives the light flux split by the polarization beam splitter; and a second photodetector that receives the light flux split by a non-polarization beam splitter, wherein one of the objective lens and the expander lens disposed between the objective lens and the laser beam source is driven under control of the control circuit; wherein the expander lens has a collimator function; wherein the expander lens having the collimator function includes one lens or two lenses and is movable in a focus direction; wherein the polarization beam splitter and the non-polarization beam splitter are disposed between the laser beam source and the expander lens having the collimator function, wherein the polarization beam splitter splits a reflected light flux from a bottom of the SIL, and a gap error signal used for controlling a gap interval between the SIL and the optical recording medium is generated according to the reflected light flux, wherein the non-polarization beam splitter splits the reflected light flux from the optical recording medium, and a focus error signal is generated according to the reflected light flux from the optical recording medium, and wherein a distance of the first photodetector from a center of the polarization beam splitter is shorter than a distance between the second photodetector and a center of the non-polarization beam splitter.