Patent ID: 7045770

Claim:
An optical encoder comprising: a light source; a scale having a reflecting portion that is arranged so as to oppose the light source; and a light-receiving element that receives a reflected light beam from the scale, wherein the reflecting portion of the scale has an optical characteristic such that a divergent light beam from the light source is divided into a plurality of wavefronts after a plurality of reflections, and respective light beams obtained as a result of the division are made to overlap each other at an predetermined position, wherein an air conversion optical path length from a light-receiving surface position of the light-receiving element to a reflecting surface of the scale is referred to as gP, a pitch of the scale is referred to as P 1 , one of a center wavelength of an output peak value of a light beam emitted from the light source and a wavelength of a center value obtained through integration of spectral distribution is referred to as λ, gap is set at gP which is determined so that the following relations are satisfied within a range of n<0.5 gP= 2 n ( P 1) 2 /λ.