Patent ID: 7888627

Claim:
An optical encoder comprising: a scale which is installed on one member of which, displacement is detected; and a detecting head which is installed on the other member which moves relatively with respect to the first member, and is disposed facing the scale, wherein a predetermined optical pattern in the direction of relative movement is provided on the scale, and the detecting head includes a light emitting section which irradiates a predetermined light on the scale, a light detecting section which includes a light receiving surface which receives, via the optical pattern, light irradiated on the scale from the light emitting section and which detects distribution of light formed on the light receiving surface, a first light transmitting member which is disposed in an optical path between the light emitting section and the scale, and a second light transmitting member which is disposed separately from the first light transmitting member in an optical path between the scale and the light detecting section, and further comprising: a stray-light reduction element which is interposed between the surface of the first light transmitting member and the surface of the second light transmitting member, and which reduces stray light which does not contribute to signal detection.