| 摘要 |
PURPOSE:To make the entire apparatus compact and to realize an encoder which can be readily manufactured, by specifying the incident angle of coherent luminous flux into a diffraction grating, and arranging a light condensing system having the reflecting plane in the vicinity of the focal plane. CONSTITUTION:When luminous flux from a polarized light beam splitter 9 is inputted into a diffraction grating 3, the luminous flux is inputted so that diffracted light in mth order is reflected from the grating 3 approximately vertically. Namely, an incident angle thetam is set by an expression thetam sin<-1>(mlambda/ P), where P is the pitch of the grating, lambda is a wavelength and (m) is an integer. A reflecting film 12 is provided in the vicinity of the focal plane of an optical member 11. The inputted luminous flux is reflected to the diffraction grating 3. The reflected light is diffracted again and overlapped on the original diffracted light. The resultant light is returned to the original light path and received with photodetectors 81 and 82 through a beam splitter 6. The movement of the grating 3 is obtained from the number of interference fringes. Therefore, a roof prism and the like are not used, and the configuration can be compacted.
|
