The optimization design of broadband Mid-IR grating

The broadband mid-IR grating is required in the infrared spectrophotometer to keep the instrument compact. In this paper the optimization design of a type of broadband grating is studied by the rigorous diffraction grating electromagnetic theory. As a differential vector method, the rigorous coupled wave analysis (RCWA) has been widely used for the analysis and the design of diffractive structures. In this paper, firstly, the diffraction efficiency properties of the traditional broadband dual-blaze grating were analyzed by RCWA. Then a simple structure grating with broadband spectrum can be obtained to the dual-blaze grating. It is interesting that the designed grating only had one blazed angle which is more easily to made compared to dual-blaze grating. The optimization grating structure parameters were given. According to our design example of broadband, mid-IR metal grating, the grating with grating period 10.0 mu m and blazed angle 22 degree can obtain more than 80% diffraction efficiency within the whole broadest spectrum 8 similar to 18 mu m. The optimization design result demonstrates this simple structure grating is with broadband spectrum and more easily to produce than the dual-blaze gratings.