Light distributing apparatus for dividing the light from a light source

Abstract

A light-beam scanning apparatus including a rotatable hologram and a fixed plate, which are provided with diffraction gratings to minimize: either a sum total of values obtained by weighting where a square of an optical path length difference between an optical path of a light flux measured along a principal axis of a light beam incident on and diffracted by a diffraction grating of a rotatable hologram, and incident on and diffracted by a diffraction grating of a fixed plate so as to conduct a scanning and converging on a scanning point on an image formation surface, and an optical path of a light flux measured along a marginal ray distanced from the principal axis; or an absolute value of the optical path difference thereof. Another sum total obtained by weighting requiring minimization is: a square of a sum obtained by adding: an amount of displacement of a light beam convergent on a scanning point on the image formation surface, which displacement is measured along the marginal ray distanced from the principal axis of an incident reconstructing light flux with respect to the principal axis of a phase of the diffraction grating of the rotatable hologram to an amount of displacement of the same light, the displacement measured with respect to the principal axis of a phase recorded on the diffraction grating when the light flux is incident on the fixed plate; or by weighting an absolute value of the sum over every scanning position of the formation surface.