Patent ID: 7557820

Claim:
A multi-beam optical scanning device, comprising: a single optical deflecting device; a plurality of photoconductor drums; a pre-deflection optical system that allows light beams from a plurality of LD arrays which form electrostatic latent images on each photoconductor drum corresponding to each image for each of the LD arrays, to enter the optical deflecting device; a post-deflection optical system that focuses each reflecting light beam from the optical deflecting device on a scanned surface of each light beam, wherein the pre-deflection optical system includes a polarizing beam splitter that synthesizes optical paths of light beams from two LD arrays, whose height and incident angle in a sub-scanning direction on incident surfaces of the polarizing beam splitter are different, and polarization direction changing means for changing a polarization direction to be provided as a P wave and an S wave on a polarization beam splitter surface with respect to each light beam on two incident surfaces of the polarizing beam splitter, wherein a polarization direction of the LD arrays inclines with respect to the P wave and the S wave on the polarization beam splitter surface, wherein the plurality of LD arrays are disposed so that an absolute value of an inclination from a sub-scanning direction has the same angle in a polarization direction of the light beam from the plurality of LD arrays, the plurality of LD arrays emitting light beams whose light paths are combined by the polarizing beam splitter and wherein the polarization direction is at an angle not in the sub-scanning direction nor in a direction perpendicular thereto; and at least one of a half-wave retardation plate and a quarter-wave retardation plate that change a polarization direction of each component light in a combined light beam from an emitting surface of the polarizing beam splitter of the pre-deflection optical system, in case of the half-wave retardation plate, two beam polarization directions of the light beam are +/−45 degrees from the sub-scanning direction and the tilt directions are opposite, and in case of the quarter-wave retardation plate, the rotation directions of the polarization are opposite at the optical deflecting device.