Abstract
The characteristics of a point light source diffraction have great differences from that of a parallel light source diffraction. Namely, a diffraction image of the former case moves in accordance hith the movement of a diffraction grating, however, a diffraction image of the latter case does not move. The former pattern is magnified by the optical lever effect and a very small displacement of the grating produces a great movement of the diffraction pattern suitable for the detection of a very small displacement. An optical encoder composed of a laser diode and a diffraction grating with 3μm pitch was made trial. The encoder has a high resolution and reliability for a mechanical shock in spite of a very simple structure.
