Laser printer scan lens with diffractive optics

A scan lens for a laser printer system consists of an F-θ lens and a scanning element, typically a polygon mirror. Due to mechanical wobble and facet-to-facet misalignment, a polygon mirror tends to steer the focused beam out of the intended scan line and therefore requires some form of optical compensation. The most common method1 makes use of anamorphic optical elements. Traditionally, lenses based on this approach contain either a toroidal surface or a reflective cylindrical field lens, both of which are relatively expensive. It is possible to use a diffractive surface to replace the need for either of these surface types. Non-toroidal hybrid scan lenses have been discussed previously2,3. These designs were limited to rotationally-symmetric geometries and therefore could not be used with polygon mirrors. This paper discusses the design, fabrication, and testing of a prototype diffractive scan lens for a 600 dpi laser printer system.