| 摘要 |
PURPOSE:To stably detect a track error signal with high accuracy and to make a device compact by sequentially passing a light reflected from an optical information recording medium through the front surface of a double-sided diffraction grating and its rear surface. CONSTITUTION:The double-sided diffraction gratings 9a and 9b, wherein parallel, almost linear diffraction gratings sort out reflected lights into a transmitting light generating astigmatism and one without astigmatism, are provided on front and rear surfaces of a substrate 9 which is disposed in the optical path of a reflected light led to a signal detecting optical system at a fixed angle with respect to the incident optical axis of the reflected light. A photodetector 10 equipped with a quadripartite photodetector 10a receiving a transmitting light formed by passing through the double-sided diffraction gratings 9a and 9b and a bisected photodetector 10b receiving a diffracted light is provided. The transmitting light generating astigmatism is used for detecting a focus error signal, whereas the diffracted light without astigmatism is used for detecting the track error signal. Thus, the tracking error signal can be detected with high accuracy and the device is miniaturized. |
