Optimization of a surface relief grating for band filter application by numerical simulations

We worked out a band pass filter based on a surface relief grating structure. The cross-section of the grating ridges has a T-shape, realizing high-low-high refractive index contrast like in an interference filter. This monolithic filter exhibits outstanding opto-mechanical qualities, thus it can be efficiently used e.g. in low temperature environment or at high laser intensities. The optimized dimensions of the structure is determined by numerical simulations. The RCWA (see Section 2.2) and MoL (see Section 2.1) methods were used to calculate the transmittance of the filter. It is shown that the filter has very good transmittance at the center wavelength and suppress other wavelengths in the NIR range (1200 - 1900 nm). The stability of the simulations is checked by monitoring energy conservation. The correctness of the results was assured by applying two independent methods (RCWA and MoL) and comparing the results.