| 摘要 |
PURPOSE:To prevent an error signal from deterioration even when a spot position is moved by a change in a wavelength by a method wherein a very small optical detection area is formed in the center of two sensors which photodetect diffracted beams of light of two directions. CONSTITUTION:A beam of light 109 reflected by a recording film is incident on a hologram element 101; it is diffracted to a + first-order diffracted beam of light 103 and a - first-order diffracted beam of light 104. At the same time, the phase difference of the element 101 is controlled, and the intensity of a zero-order diffracted beam of light 105 is set to 1 to 3% with reference to the intensity of the incident beam of light 109. The long side of detection sensors 106, 107 for the + first-order and - first-order diffracted beams of light is arranged parallel with a diffraction direction; a very small sensor 108 is arranged on the same plane as the sensors 106 and 107 and at an equal distance from the individual sensors. Thereby, the condensed light spot of the zero-order diffracted beam of light 105 can be detected. Thereby, it is possible to prevent an error signal from deteriorating even when the wavelength of a semiconductor laser is changed due to a temperature change or the like. |
