ENCODER

PURPOSE:To execute the cost reduction and the improvement of reliability and to contrive to make the encoder further small in size and light in weight by transferring and radiating a light wave onto a scale from a coherent light source and detecting an arbitrary diffracted light from a diffracted light by the scale, and allowing it to interfere. CONSTITUTION:A light wave generated from a laser diode 6 is inputted to an asymmetrical X branch path 4 from a terminal I, and divided into terminals III, IV by the same phase light and by an equal quantum. This light wave is propagated in a slab type optical waveguide 9 as a divergent light. Subsequently, this luminous flux is emitted from a substrate 3 as a collimating light by optical input/output couplers 5a, 5b, respectively, radiated to two different points on a scale 1, and diffracted by a diffraction grating provided on the scale 1. Next, a + primary diffracted light in the light wave radiated to the scale 1 by the coupler 5a and a - primary diffracted light in the light wave radiated to the scale 1 from the coupler 5b are reflected by mirrors 10a, 10b, respectively, made incident on the scale 1 from the reverse side, diffracted again, and thereafter, reach the couplers 5a, 5b. Thereafter, the luminous flux is propagated in the waveguide 9 and made incident on the terminals III, IV.