Tunable dual-band infrared polarization filter based on a metal-dielectric-metal compound rectangle strips array

A tunable dual-band infrared polarization filter has been proposed and investigated in this paper. Based on the perfect absorption characteristic of the metal-dielectric-metal sandwich structure, the reflection spectrum shows filter performance. This filter consists of three layers. The top layer is a compound metal nano-structure array composing of an asymmetrical cross resonator and a rectangle strip. The middle and bottom layer are dielectric spacer and metal film, respectively. The calculated results show that the filter property is closely related to the polarization of incident light. When the light polarization parallels to the long direction of the rectangle strip, two resonant wavelengths (1310nm and 2000nm) are filtered, and in contrast only one resonant wavelength (1516nm) is filtered when light polarization vertical to it. Moreover, we found that the resonant wavelength is strongly depended on the length of the rectangle strip which caused the resonant effect. Therefore, the filter wavelength can be tuned freely for different light polarization by adjusting the length of the corresponding rectangle strip. We can change one or two filter wavelengths at a time or change the three filter wavelengths at the same time. In addition, the calculated results show all the intensities at the filter wavelengths are closed to zero, which implies the filter can exhibit good filtering performance.