US Patent 7557820 Optical multi-beam scanning device and image forming apparatus

The present invention can be adapted to improve optical efficiency even when a light source is disposed without restricting a polarization direction or an orthogonal direction with respect to an optical axis of a light beam from the light source. A multi-beam optical scanning device of the present invention includes a single optical deflecting device, a pre-deflection optical system that allows light beams from a plurality of light sources to enter the optical deflecting device, and a post-deflection optical system that focuses each reflecting light beam from the optical deflecting device on a scanned surface of each light beam. The pre-deflection optical system includes a polarizing beam splitter that synthesizes optical paths of two light beams, and the first half-wave retardation plate and a second half-wave retardation plate that change a polarization direction with respect to each light beam on two incident surfaces of the polarizing beam splitter. In this case, it is preferable to include a half-wave retardation plate or a quarter-wave retardation plate that changes a polarization direction of each component light beam in a combined light beam from an emitting surface of the polarizing beam splitter.