Light beam scanning apparatus using a rotating hologram and a fixed

Abstract

A high-resolution light-beam scanning apparatus utilizing only mass-producible holograms instead of utilizing auxiliary optical systems such as an optical lens or a mirror having curvature, and capable of compensating for disadvantages including scanning beam thickening and variation, failure of a rotatable hologram to rotate at a constant velocity, displacement of a scanning beam position in the scanning direction and the cross scanning direction due to a mode hop of a wavelength of a semiconductor laser, and deviation of a base of a rotatable hologram from a parallel state, which disadvantages are detrimental to efforts for increasing the resolution of a hologram scanner and lowering the cost thereof, the light-beam scanning apparatus being characterized in that provided in the rotatable hologram (1) and the fixed plate (2) are diffraction gratings for minimizing: either a sum total of values obtained by weighting: a square of an optical path length difference between a) an optical path of a light flux measured along a principal axis MA of a light beam incident on and diffracted by a diffraction grating (1a) of a rotatable hologram (1), and incident on and diffracted by a diffraction grating (2a) of a fixed plate (2) so as to conduct a scanning and converging on a scanning point k on an image formation surface (4), and b) an optical path of a light flux measured along a marginal ray M1 distanced from the principal axis MA; or an absolute value of the optical path difference thereof, the weighting being conducted at every scanning position covering an entire range of the image formation surface (4), or a sum total of values obtained by weighting: a square of a sum obtained by adding: an amount of displacement of a light beam convergent on a scanning point k on the image formation surface (4), which displacement is measured along the marginal ray M1 distanced from the principal axis MA of an incident reconstructing light flux with respect to the principal axis MA of a phase of the diffraction grating (1a) of the rotatable hologram (1); to an amount of displacement of the same light, which displacement is measured with respect to the principal axis MA of a phase recorded on the diffraction grating (2a) when the light flux is incident on the fixed plate (2); or by weighting an absolute value of the sum, the weighting being conducted at every scanning position covering an entire range of an image formation surface.