In digital copying machines and laser beam printers, a laser beam, turned on and off based on characters or patterns of images is applied on a charged photoconductor drum, to write an electrostatic latent image which is made visible by applying toner onto the electrostatic image with electrical force. A laser optical scanning system which guides the laser beam onto the photoconductor drum is composed of a laser diode, various types of lenses and a polygon mirror.
A laser beam emitted from the laser diode is collimated by a collimator lens into parallel light beams, and is further converged on the polygon mirror by the cylinder lens to be linear. The laser beam is reflected on the polygon mirror, and uniform rotation of the polygon mirror enables the laser beam to function for scanning. The reflected laser beams are converged on the photoconductor drum by the scanning lens.
Konica Minolta has succeeded in realization of a unified resin-made light source optical system which has been composed of several glass lenses. Use of resin-made light source optical system for color as well as monochromatic laser beam printers contributes to downsizing of such printers.
To avoid an influence of changes in the refractive index of resins caused by temperature changes, a reflecting surface is used instead of a refracting interface. Shifting of the light-convergence position generated slightly even when the reflecting surface is used, is eliminated by also using a diffraction surface. Owing to this, shifting of the light-convergence position due to temperature changes can be controlled to be smaller than in the case of conventional optical light source systems, and contributes to stabilization of image quality of prints produced by laser beam printers and digital copying machines.