The effect of groove depth on the polarization behavior of an echelle grating

In order to provide the guidance for the design and application of echelle gratings, the reason why the diffraction efficiency of the echelle grating can be improved by increasing the groove depth or reducing the apex angle is given. The polarization behaviors of gratings with different groove depths were simulated and analyzed via integral theory. To further demonstrate the polarization behavior, gratings with right and acute apex angles for classical and conical-Littrow incidence were simulated. Experimental polarization behaviors of gratings with 5.1-μm and 6.7-μm groove depths for classical incidence were obtained. The polarization degree of the echelle grating with the 6.7-μm groove depth was 6.5% at 405 nm and 2.52% at 632.8 nm, which smaller than 7.89% at 405 nm and 35.74% at 632.8 nm for the grating with a 5.1-μm groove depth. Therefore, the diffraction efficiency of an echelle grating can be improved by increasing the groove depth or reducing the apex angle, mainly because the polarization degree is restrained.