Laser scanning system

Abstract

A laser scanning system formed by injection molding first and second scanning lenses by using a plastic substance for correcting field curvature at a scanned surface, minimizing focus shift and eccentricity due to a temperature variation and degradation of optical performance due to a tilt error, and providing a relatively simplified lens shape while facilitating mold processing and injection molding includes a light source for emitting a modulated beam from a laser diode, a collimator lens for forming the beam from the light source into parallel beams, a slit for partially passing the parallel beams from the collimator lens, a cylinder lens for converging the parallel beams passed through the slit in a sub scan direction, a polygonal rotating mirror rotated at high speed for deflecting the incident parallel beams at a prescribed angle, and a scanning lens system for receiving the deflected beams from the polygonal rotating mirror to form an image on the scanned surface by converging the incident beams in the scan and sub scan directions, in which a first scanning lens and a second scanning lens of a plastic substance constitute the scanning lens system. A first surface of the first scanning lens is formed with a spherical surface, a second surface of the first scanning lens and third and fourth surfaces of the second scanning lens are formed with an a spherical toric surface having a rotating axis in the scan direction. The shape around the optical axis of the scanning lens is concave, convex and concave from the first surface in the scan direction and concave, convex, concave and convex in the sub scan direction.