Optical encoder and scale for encoder

An optical encoder comprising:

• an optical sensor section in which a scale and a detecting optical system are disposed so as to be one of relatively movable and relatively rotatable, and an optically anisotropic region, which diffracts incident laser light and selectively rotates a polarization direction of diffracted light of a predetermined order in a predetermined polarization direction, is formed at the scale, and the detecting optical system includes a light source irradiating laser light onto the scale, a polarized light separating means separating a polarized light component of the predetermined polarization direction from diffracted light which has been one of transmitted through the scale and reflected by the scale, and a light intensity detecting means detecting light intensity at a predetermined position of an interference pattern due to the polarized light component which has been separated;
• and
• movement amount computing means for computing an amount of movement of the scale on the basis of a change in the light intensity detected at the optical sensor section.