Optical head device and optical information apparatus using a lithium niobate hologram with divisional areas to diffract light to corresponding photo detector areas

An optical information apparatus provided with an information storage medium drive means for driving an information storage medium, an optical head device and an optical head drive means for adjusting the positional relationship between the information storage medium and the optical head device, the optical head device comprising:

• a light source for emitting a linear polarized light beam;
• a single component objective lens for converging the light beam on an information storage medium;
• a hologram for receiving the light beam reflected by the information storage medium and generating diffracted light from the light beam, the hologram having such a polarization anisotropy that diffracts light in a second polarization state more strongly than light in a first polarization state which is different from the second polarization state, the hologram allows the light in the first polarization state passing through the hologram substantially without generating diffracted light therefrom;
• a photodetector including a plurality of photodetective sections for receiving a part of the diffracted light and outputting a photocurrent in accordance with the intensity of the part of the diffracted light;
• and
• a quarter wavelength plate, disposed between the hologram and the objective lens, for converting the linearly polarized light beam into a circular polarized light beam when the linearly polarized light beam travels from the light source to the information storage medium and, to the contrary, for returning the converted circular polarized light beam into a linearly polarized light beam in the second polarization state when the circular polarized light beam comes back from the information medium;
• wherein
• the hologram is disposed so that the distance between the hologram and the objective lens is shorter than the distance between the hologram and the photodetector;
• the hologram has a lithium niobate substrate;
• a hologram face of the hologram includes divisional areas H1 and H2;
• the plurality of photodetective sections include a photodetector area P1 and a photodetector area P2 which are provided on the detection face;
• the photodetector area P1 receives diffracted light diffracted by the divisional area H1 of the hologram and outputs an output signal E1 in accordance with an intensity of the diffracted light;
• the photodetector area P2 receives diffracted light diffracted by the divisional area H2 of the hologram and outputs an output signal E2 in accordance with an intensity of the diffracted light;
• and
• wherein a relative positional relationship between the hologram and the objective lens is fixed;
• the hologram is integrated with the objective lens via a supporting member;
• and
• the hologram is disposed between the light source and the objective lens a quarter wavelength plate, disposed between the hologram and the objective lens.