Diffractive laser encoder with a grating in Littrow configuration

In this work, we present a new compact diffractive laser encoder system, which serves as a positional detection apparatus in precision machine applications. The encoder records displacement information in terms of grating period using the Doppler effect. Using the Littrow configuration, the novel encoder provides high alignment tolerances. The design is special such that a change in the gap between the grating and the optical head does not affect the measurements. Therefore, a Michelson interferometer can be added to the system to measure the out-of-plane displacement. This system will be developed as a three-dimensional displacement sensor in the future. Within a measurement distance of 100 mu m, even in the laboratory environment, the maximum error is 53 nm and the repeatability is within +/- 20 nm.