US Patent 7929007 Optical scanning device and image forming apparatus

In an optical scanning device of opposite scanning type, two target surfaces for scanning are scanned in opposite main scanning directions by using a single optical deflector. End portions of a scanning lens arranged in a scanning optical system are configured not to have refractive power in the main scanning direction. A synchronization light beam passes through the end portions of the scanning lens and falls on a light receiving element via a synchronizing optical system. The synchronizing optical system includes a first synchronizing lens, a synchronizing fold mirror, and a second synchronizing lens. The synchronizing fold mirror and the light receiving element are arranged to be in a conjugate relation with the second synchronizing lens.