Patent ID: 7259863

Claim:
A grating interference type optical encoder, comprising: a scale board; a diffraction grating located on the scale board; a light receiving element; an illumination optical system for emitting coherent light fluxes to the diffraction grating on the scale board that relatively moves, to produce two diffraction light fluxes having different orders; an arc-shaped grating for re-emitting to the diffraction grating the two diffraction light fluxes having the different orders which are produced in the diffraction grating through a deflection unit; light guiding unit that superimposes rediffraction light fluxes produced by rediffracting the diffraction light fluxes re-emitted to the diffraction grating and that guides the superimposed rediffraction light fluxes to a light receiving element; a phase grating that divides the rediffraction light fluxes superimposed between the diffraction grating and the light receiving element into a plurality of light fluxes; a linear polarizing element having different polarizing directions corresponding to the plurality of light fluxes divided by the phase grating; an origin detecting pattern formed near the diffraction grating on the scale board; a light flux separating element for deflecting a part of the coherent light fluxes to guide the part of the coherent light fluxes deflected onto the origin detecting pattern; and origin signal detecting unit that detects only a reflection diffraction light flux optically modulated by the origin detecting pattern.