Generation of three-port splitter by double-layer grating in second-order Littrow configuration

In this paper, a novel double-layer three-port grating is described. The incident grating structure is in the second-order Littrow configuration. The grating region is composed of fused silica and Ta2O5. The designed grating beam splitter has high efficiency under TE polarization and TM polarization, respectively. The efficiency of two polarizations is more than 90%. In addition, compared with a single-layer three-port grating, this new beam splitter has good fabrication tolerance and incident bandwidth. Therefore, the optimized structure has a good application value.

Uncertainty Evaluation for Measurements of Pitch Deviation and Out-of-Flatness of Planar Scale Gratings by a Fizeau Interferometer in Littrow Configuration

Form errors of a planar scale grating, such as pitch deviations and out-of-flatness, are major contributors to the final measurement uncertainty of an interferential scanning-type planar encoder. Following the previous work, in which a method has been proposed to evaluate both the out-of-flatness and the pitch deviations of a planar scale grating by a Fizeau interferometer in Littrow configuration, uncertainty analysis on this method is performed in this paper. Theoretical equations are derived to make quantitative uncertainty analysis while taking possible error factors into account. To overcome the drawbacks of a traditional uncertainty matrix approach, a new procedure is proposed to evaluate the uncertainty in the PV (peak-to-valley) deviation of a surface form, so as to assure the quality of measurement. Experiments are finally conducted to demonstrate the feasibility of proposed uncertainty evaluation method.