Optical system for torsion oscillator laser scanning unit

Abstract

An optical apparatus compensates for imaging errors associated with the sinusoidal angular scan rate of a light beam reflected from a bidirectional scanning torsion oscillator. The compensation is achieved by a combination of pre-scan optics positioned between the source of the light beam and the scanning torsion oscillator, and post-scan optics positioned between the scanning torsion oscillator and an imaging surface of an imaging device. Based on the optical characteristics of its components, the post-scan optical system causes deflection of the light beam in the scan direction. To compensate for the sinusoidal scan rate, the deflection caused by the post-scan optical system is greater at the opposing edge positions of the imaging surface than at a central position. In this manner, the scan rate of the light beam at the first and second edge positions is substantially equivalent to the scan rate at the central position. The pre-scan optical system directs the light beam onto the reflective surface of the torsion oscillator in a manner that compensates for divergence of the light beam in the scan direction caused by the post-scan optical system.