| 摘要 |
PURPOSE:To always detect a focusing state with high accuracy by making reflected light incident from an irradiated object to two light reception parts so as to be mutually reversed and detecting the focusing state based on this output by using light emitting and receiving elements for which a generation part and the two light reception parts are provided on the same semiconductor base. CONSTITUTION:The light emitting surface of a laser diode 51 in light emitting and receiving elements 54 and the light receiving surfaces of photodiodes 52 and 53 on the both sides of the laser diode are arranged between respective two focal points of + or -1st diffracted light and the + or -1st diffracted light is received by the diodes 52 and 53. Thus, when an irradiated object 57 is set at the focal position of an objective lens 56, the beam shape of the diffracted light is made mutually equal and when the object 57 is made close to the lens 56 side rather than the focal position of the lens 56, however, the beam shape is changed. Reversely, when the object 57 is separated from the lens 56, the beam shape is reversely changed and accordingly, by detecting output difference between the diodes 52 and 53, a focus error signal can be obtained to express the focal state of the lens 56 to the object 57. |
