Cylindrical-type nanometer-resolution laser diffractive optical encoder

A new, to our knowledge, design for a cylindrical-type diffractive optical encoder is proposed. The wave-front aberrations induced by the power of the rotation disk in this encoder can be canceled out completely. Wave-front-aberration cancellation and desensitization to the grating misalignment are achieved by means of positioning the virtual point source, which was induced by the cylindrical grating with respect to two sets of modified telescopes with a magnification ratio of one: 1x telescopes. For evaluating the performance envelope of this newly designed optical system a code v-based optical-design software program was adopted to simulate the performance of the optical system. From tolerance-analysis results it was found that this newly developed cylindrical encoder system has the capability to compensate for most aberrations and, in addition, possesses a high tolerance for optical-component misalignment. For verifying the performance of the developed system the cylindrical diffractive encoder system was cross-referenced with a Hewlett-Packard Model HP-5529 laser interferometer positioning signal. The experimental results confirm the merits of this newly developed cylindrical encoder.