<title>Performance of interferometric rotation encoders using diffraction gratings</title>

Abstract

High resolution optical encoders take advantage of diffraction and interference properties of light. In such components, the scale is a phase grating that diffracts light into several orders; an optical reading system makes two of them to interfere. In state of the art systems, the orders interfere after they have been spatially separated from other orders; this leads to cumbersome reading heads. A compact, fully diffractive optical reading system was designed and realised. This reading system was used for the realisation of rotation encoders. Using the competences of the Eureka EU 922 FOTA project partners, the encoder phase gratings were successfully realised and the reading system was implemented in standard rotation encoder housings. Without interpolation the encoder gives 480'OOO pulses per revolution with a repeatability of 2.5 pulses.

Miniature holistic displacement sensor by immersion diffractive interferometry

“…Highly hydrogenated amorphous silicon has low losses down to the red, therefore it can be used as the corrugated film with low price light sources in the red and near IR spectrum where single crystal silicon detectors can still be used. Different materials are also possible which require not too large a corrugation depth: most high index metal oxides such as TiO 2 , ZrO 2 , HfO 2 , Ta 2 O 5 , Nb 2 O 5 , Si 3 N 4 , iron oxide [8]. A preferred layer material is however amorphous silicon with its very large index and since it is in principle easily etchable by RIE.…”

Flying phase mask for the printing of long submicron-period stitchingless gratings

“…The substrate translates below the phase mask at a speed of approximately 1mm.s -1 and its relative position to the phase mask is given by an optical encoder which reads the reference scale. The incremental optical encoder comprises an optical read head consisting of a readout grating, at least two detectors and a laser diode [7,8]. The reference scale is a grating of 1µm period .…”

The potential of diffraction grating for spatial applications

“…Figure one is the illustration of one of the possible embodiments of the basic principle of diffractive interferometry (2) whereby the collimated beam of a semiconductor laser crosses the readout grating a first time, then gets diffracted into the +1 and -1 reflected orders by the moving measurement grating. The latter are both diffracted into the 0 th and the -1 st transmitted orders of the readout grating.…”