Patent ID: 8670127
Filing Date: 2014-03-11
Classification: G01D

Abstract:
1. An encoder system, comprising: a means for deriving a first beam and a second beam from an input beam where the first and second beams have different frequencies, a means for directing the first and second beams along different paths; a means for combining the first and second beams to form an output beam; a diffractive encoder scale positioned in the path of the first beam so that the first beam contacts the diffractive encoder scale at a non-Littrow angle and the first beam diffracts from the diffractive encoder scale at least once; a means for detecting the output beam; and a means for receiving an interference signal from the detector, the interference signal comprising a heterodyne phase related to an optical path difference between the first and second beams, and determining the information about a degree of freedom of the encoder scale based on the heterodyne phase.