| 摘要 |
PURPOSE:To improve scanning accuracy by controlling the optical quantity of a reflected beam in response to the incident angle of a light beam so as to compensate the luminous amount of the reflected beam changed in response to the change in the incident angle of the light beam to a polarizing device. CONSTITUTION:A bias current I1 is set to a maximum value at the same time when the laser lighting period for light beam position detection is started. A constant current source 107 is applied with feedback control by a photodetector PD and an optical output control circuit 105 so that the light output of a laser diode LD attains a prescribed value in this state. When the laser beam is inputted to a photodetector 300, a synchronizing signal S2 is generated, then the current I2 by the feedback control of the constant current source 107 is fixed. Since the counter subtraction of the circuit 105 is started in this case, the current I1 is decreased and the light output of the diode LD is also decreased. On the contrary, since the reflectance is made large because of the increased incident angle of the light beam to a rotary polygon mirror (not shown), the luminous intensity of the laser beam reflected from the rotary polygon mirror is unchanged. |
