Research of two-wavelength filter based on guided-mode resonance of two-dimensional gradient-period grating

Abstract

Guided mode resonance (GMR) gratings are used as filters due to the narrow bandwidth and high efficiency at the resonance wavelength. In this paper, a two-dimensional gradient-period GMR grating with rectangular array structure is proposed. Ta2O5, HfO2 and SiO2 are selected as grating materials. Double reflection peaks are obtained by matching the guide modes in two orthogonal planes of diffraction to different wavelengths. The rigorous coupled wave analysis (RCWA) are used to analyze the resonance characteristics of two-dimensional GMR grating. By comparing the resonance behavior, the resonance wavelengths of two-dimensional GMR grating can be approximated as the superposition of two one-dimensional GMR gratings, the periods of the two one-dimensional gratings are respectively equal to those of the two-dimensional GMR grating along x and y direction (Λx and Λy). Thus, we can control the two resonance wavelengths by changing the periods of Λx, Λy. According to the result of design, when the two resonance peaks are both in the spectrum range of 850nm-1050nm, the efficiencies of the two peaks are greater than 90%, and full width at half-maximum (FWHM) less than 1.5nm. This two-wavelength tunable filter will be a good two-dimensional displacement sensor. The effects of duty cycle, groove depth and other parameters on the resonance wavelength are also studied.