| 摘要 |
PURPOSE:To detect exactly an incident optical beam by providing an optical beam splitting optical element for splitting an optical beam which has passed through a scanning lens, into two optical beams, and using one of the split optical beams and the other as a scan use and a monitor light, respectively. CONSTITUTION:A laser beam 2 is emitted from a laser light source 1, passes through a cylindrical lens 4, and thereafter, made incident on a rotary polygon mirror 5, passes through an ftheta lend 6 being a reflected and deflected scanning lens, and thereafter, made incident on a half mirror 8A. The half mirror 8A reflects a laser beam 2a of a quantity required for scanning, and makes the remaining laser beam 2b transmit through. By an action of the ftheta lens 6, the optical beam 2b is focused only in the main scanning direction, therefore, the optical beam 2b becomes an elliptical image or a linear image in which a direction parallel to a lattice of a grid 10 is a longitudinal direction, and even if some dust adheres between the lattices of the grid, a detection of the optical beam is not obstructed. In such a way, a synchronizing signal is obtained exactly and sent to an image information reading circuit 14. |
