| 摘要 |
<P>PROBLEM TO BE SOLVED: To prevent the drop of a response-speed of a sensor without additionally providing an optical element for preventing the drop of a response_speed of the sensor. <P>SOLUTION: This device is a head device for a phase-change optical disk which detects focus error signals using a spot-size method. The device comprises a light beam dividing means which divides a reflective laser beam from an optical disk into a zero-th order light beam and ±m-th order diffracted light beam which are a plurality of light beams by diffraction, and which makes the plurality of light beams produce the defocus in the positive/negative direction with respect to the direction of an optical axis. The device further comprises an photo detector for data which is arranged on the optical axis and receives the zero-th order light beam, and a pair of photo detectors for servo which is provided on almost the same plane and in the optical-axis symmetry to the photo detector for data, and which receives the ±m-th order diffracted light beams. The pair of photo detectors for servo is constituted so that different signals are output when they receive the light beams having the equal quantity of light, respectively. Data signals and servo signals are detected based on outputs of the photo detector for data, and the pair of photo detectors for servo. <P>COPYRIGHT: (C)2004,JPO |
