Optical head device

Details Optical head device Optical head device

G - Physics

11

B

88/0.11, 352/32.

G11B 7/18 (2006.01) G02B 27/44 (2006.01) G11B 7/09 (2006.01) G11B 7/12 (2006.01) G11B 7/13 (2006.01) G11B 7/135 (2006.01)

Patent

CA 2018314

The invention discloses an optical head device having:- a diffraction grating element divided into a first diffraction grating and a second diffraction grating by a plane including an optical axis that connects a light emitting point on a semiconductor laser to a focal point on a recording medium such as an optical disk, so that the first and second diffraction gratings have a substantially equal diffraction angle, a substantially equal optical utilization efficiency, and different focal distances of first order diffracted lights, each of the first order diffracted lights being produced from a reflected light from the recording medium, at the respective diffraction gratings; and a photodetector positioned at a mid-position between two focal points produced when there occurs no focusing error, the photo-detecting means having a plurality of photo-detecting parts juxtaposed in a direction substantially orthogonal to an average diffracting direction of the diffraction grating element. In this optical head, the first diffraction grating and second diffraction grating are designed such that lights diffracted at the first diffraction grating and second diffraction grating are guided into the photo-detecting means to form light spots in the vicinity of centers of the corresponding photo-detecting parts, and the light spots are aligned in a direction substantially orthogonal to the average diffracting direction of the diffraction grating element. The above arrangement enables to produce a small size optical head device and improve the detection of focusing errors and tracking errors. The invention also discloses an optical head device having:- a diffraction grating element divided into first to forth diffraction gratings by two planes including the optical axis which connects the light emitting point of the semiconductor laser to the focal point on the recording medium. In this diffraction grating element, the first to forth diffraction gratings are paired off so that each pair is symmetrical. When focal points of first order diffracted lights in the first to forth diffraction gratings are plotted in three dimensional orthogonal coordinates on condition that a direction Z parallel with the optical axis is plotted as the Z-coordinate, at least the Z-coordinates of the focal points of first diffracted lights in diffraction gratings in each pair are substantially identical, and the Z-coordinate of the focal point for first order diffracted lights in a first pair of diffraction gratings differs from the Z-coordinate of the focal point for first order diffracted lights in a second pair of diffraction gratings. The optical head device further has a photodetector disposed at a mid-position between the focal points of the first order diffracted lights produced in the first pair of diffraction gratings and the focal points of the first order diffracted lights produced in the second pair of diffraction gratings, the photodetector having a plurality of photo-detecting parts which correspond to the first to forth diffraction gratings respectively. In this optical head device, the diffracted lights produced in the pairs of diffraction gratings are guided to the photodetector so as to respectively form light spots in proximity to a center of the corresponding photo-detecting part. The above arrangement enables to produce a small size optical head device and improve the detection of focusing errors and tracking errors.

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