OPTICAL POSITION DETECTOR

PURPOSE:To obtain a position signal of good S/N by providing a position detection mark where projecting parts having a width l/2 and recessed parts having the width l/2 different in depth by about 1/8 of the wavelength of light or integer-fold 1/8 wavelength of light are arranged alternately in a checkered pattern. CONSTITUTION:The luminous flux from a semiconductor laser 3 is made incident on a collimator lens 4 and is discharged as parallel rays of luminous flux. This luminous flux is made incident on a polarizing prism 6 having a polarizing film 5. The luminous flux is made incident on a reflecting film 10 on a fixed scale 1 while being converged by the action of the film 5. The film 10 consists of a rugged mark different in optical depth by about 1/8 of the wavelength of the laser 3; and if a two-divided photodetector 9 is arranged in a far field with respect to the luminous flux reflected on the film 10, outputs from elements of the photodetector 9 are obtained with about 90 deg. phase difference, and this difference is taken to detect the position.