Ultra-broadband linear polarizer based on subwavelength nanocavity structure in infrared region

A subwavelength nanocavity grating structure designed as a linear polarizer for application in infrared wavelength range with ultra-broadband bandwidth of 3-20 μm is proposed. The structure of the proposed linear polarizer consists of barium fluoride layer as dielectric antireflection layer and nano optical cavity formed by metal aluminum, zinc sulfide (ZnS) and metal aluminum that is prepared on zinc selenide (ZnSe) substrate. It is found that when the total thickness of cavity layer and metal layer is fixed, increasing the number of cavities can significantly improve the extinction ratio of the structure while the transmission of the polarized component remains almost unchanged. Theoretical simulation results show that a transmission of greater than 83% and an extinction ratio of greater than 53 dB in the whole 3-20 μm waveband can be obtained by optimizing the structure parameters with a period of grating of 600 nm and single nanocavity. The proposed cavity structure of the linear polarizer provides a new idea for the design and development of high-performance linear polarization devices.