Multiband notch filter based guided-mode resonance for mid-infrared spectroscopy

摘要

A dielectric guided-mode resonance (GMR) notch filter with multiple channels was designed to operate in the mid-wave infrared (MWIR, 3 similar to 4 mu m). The transmission characteristics of filters were analyzed using a finite difference time domain (FDTD) method. In the structure of notch filter, two different periodic (p(1) = 1.6 mu m and p(2) = 2.0 mu m) silicon (Si) grating waveguide layers (GWLs) are constructed on the CaF2 substrate. Si waveguide layer thickness and CaF2 cladding layer thickness were designed based on optical interference principle to give maximum transmission across the MWIR. The transmission spectrum presents two narrow band located at 3.410 mu m and 3.833 mu m with not only a high bandstop coefficient (>99%), but also a broadband high transmission (>90%) off-resonance. The resonant wavelengths can be flexible modulated in wide range by changing grating periods or filling factors, and it is proved that filter is stable and useful in actual atmospheric conditions. Because of the good performance in the bandstop features, the multiband GMR notch filter designed in this method may have a potential for a variety of imaging or detection applications.