Optimizing design of high-resolution optical encoder using a point-source light-emitting diode with slits

We discuss an interference fringe type encoder using a point source LED equipped with a slit; this encoder offers high resolution, a wide temperature range, and high reliability. To optimize the design of this encoder, we develop a simulator for an interference-fringe-type encoder using the Fresnel-Kirchhoff diffraction formula, and we analyze the following elements of the optical system of the encoder: (1) the effect of the LED wavelength band, (2) the effect of the size of the LED radiation area, and (3) the effect of the shape of the diffraction grating surface. The interference fringes of this encoder are generated with 60% greater efficiency than an encoder using an LD featuring a very narrow slit width.