Bidirectional Littrow double grating interferometry for quadruple optical interpolation

Although grating interferometers are considered high-performance optical displacement sensors, higher requirements are being demanded for displacement sensing. Furthermore, the TGIS (traditional grating interferometry system) cannot achieve high-fold optical subdivision in the case of single-diffraction, which restricts the improvement of measurement resolution. In this paper, a BLDGIS (bidirectional Littrow double grating interferometry system) is demonstrated, combining Littrow heterodyne detection technology with the double grating structure and providing a quadruple optical subdivision in the case of single-diffraction. Additionally, the use of planar mirror for beam deflection in the optical path is unnecessary, and the sensitivity to angular error is greatly reduced. The experiment results show that the error of the BLDGIS in the linear displacement range of 10 mm in the X direction is within +/- 15 nm, and the actual resolution reaches 2 nm. Compared with TGIS, the error was reduced by 30 % and the resolution was increased by 50 %.