Reduction of the polarization sensitivity of grating-based spectrometer using an achromatic quarter-wave plate

Spectrometers are generally sensitive to the polarization state of the measured light, which affects their measurement accuracy. In this study, we developed a method to reduce the polarization sensitivity by using an achromatic quarter-wave plate in a double-pass optical structure. By rotating the polarization state of the second pass beam with an achromatic quarter-wave plate, the diffraction efficiencies of the grating for the s-polarized and p-polarized light become nearly the same. The formulas of this polarization-insensitive system were strictly derived. We designed a double-pass spectrometer with a grating of 1050 lines/mm and a reflective achromatic quarter-wave plate. The results of the numerical simulation show that the polarization-dependent loss of the designed spectrometer is less than 0.5 dB.