Diffraction Efficiency of Enhanced Phase Grating

In order to improve the measurement accuracy of a phase grating position measurement system, it is necessary to reduce the diffraction efficiency of diffraction signals of the zero order and even diffraction orders, and enhance the diffraction efficiency of high odd order diffraction signals. At present, the known diffraction efficiency model of enhanced phase gratings restricts the range of values of the structural parameters. A special high odd order diffraction signal is used as the optimized target in the design. Therefore, in order to design the phase grating structure with diffraction enhancement and zero and even order diffraction missing for multiple high odd order diffraction signals, the diffraction efficiency of the enhanced phase grating is deeply studied. In this work, based on the scalar diffraction theory, the theoretical models of the phase grating structure and diffraction efficiency are established; the influences of grating structure parameters such as groove depth, grating ridge width, and grating ridge position on diffraction efficiency are analyzed. According to the constraints of phase grating position measurement system, the enhanced grating structure with multiple odd diffraction orders is obtained. This kind of structure not only makes the zero and even order diffraction missing, but also improves the diffraction efficiency of the 5th, 7th, and 9th order diffraction. This study is helpful to understand the diffraction principle of the enhanced phase grating and provides support for grating design.