Broadband Vis-NIR Circular Polarizer with Cascaded Aluminum Wire-Grid

A universal design and fabrication scheme is proposed for a cascaded aluminum wire-grid-based vis-NIR circular polarizer. The aluminum wire-grid is designed as a broadband circular-linear polarization converter and a broadband linear polarizer, which is further cascaded to form a circular polarizer with strong circular polarization transmittance difference (CPTD) and circular polarization extinction ratio (CPER) in vis-NIR. By increasing the distance between the circular-linear polarization converter and the linear polarizer, the redshift of the CPTD and CPER peaks is realized and used to design a novel circular polarizer to work better in the operating wavelength. Anisotropic thin-film interference is revealed to be responsible for the redshift phenomenon. Furthermore, the circular polarizer is fabricated by nano imprint lithography and nano transfer printing with the merits of relatively low cost, and high production efficiency. With such flexibility in the design and fabrication, cascaded aluminum wire-grid may serve as a tunable compact circular polarizer, and it is also easy to integrate with the wire-grid-based linear polarizer to realize the fabrication of the division-of-focal-plane full Stokes polarimeter.