Patent ID: 8710425

Claim:
An encoder comprising: a light source section which emits a light, a wavelength of which periodically changes, in a parallel fashion; a first optical member which receives the light emitted from the light source section and then emits a first light and a second light, the first optical member emitting the first light and the second light from different positions; a second optical member which changes a travelling direction of the first light or the second light such that the first and second lights emitted from the first optical member overlap each other; a diffraction grating member which is disposed at a position where the first light and the second light overlap each other, is displaced relatively with respect to the light source section, the first optical member, and the second optical member, and has a diffraction grating periodically formed along a movement direction by the displacement; a first light receiving section which receives an interfering light of the first and second lights, which is emitted from the diffraction grating member, and detects an interference intensity of the interfering light, wherein an optical path length of a first optical path of the first light from the light source section to the diffraction grating member and an optical path length of a second optical path of the second light from the light source section to the diffraction grating member are different from each other, and the encoder further comprising a transmissive member which is disposed between the light source section and the first optical member in either the first optical path or the second optical path and has a predetermined refractive index.