US Patent 7570278 Optical scanning device and image forming apparatus

Light beams emitted from a light source, which is a semiconductor laser, are changed to weak diverging rays by a coupling lens, pass through an aperture, and are changed to parallel beams in a main scanning direction and light beams, which focus near a polygon mirror, in a sub-scanning direction by an anamorphic lens forming a first optical system. Further, the light beams are deflected by the polygon mirror and focused on an image surface through a dust-proof glass by a deflector side scanning lens and an image surface side scanning lens. The light source and the coupling lens are fixed to an identical member made of aluminum. Here, all lenses are made of resin, and diffractive surfaces are provided on a light source side surface of the coupling lens and an image surface side surface of the anamorphic lens.