Structural design and optimization of subwavelength grating polarizers for short infrared-wavelengths

Abstract

Subwavelength grating (SWG) is currently the major component being applied in polarimetric detections in infrared wavelengths, owing to its unique advantages in miniaturized dimensions, integrability with the exiting planar focal plane array of photoelectronic detectors, and compatibility with semiconductor technology. However, the obstacle hindering the applications of the SWGs polarizer is the limited polarization performance of both the transmittance and the extinction ratio, despite substantial efforts have been reported. It has been well understood that SWG with short pitch and high aspect ratio is the solution for achieving high performance, which is a daunting challenge to nanofabrication. To overcome the technical bottleneck for highly dense gratings with high aspect ratio, this work proposed a structure with the metallic grating parasitically grown on the sidewalls of replicated dielectric lines/spaces by electron beam lithography, followed by an angled evaporation process of metal. Numerical simulations by a finite-difference time-domain method were carried out to optimize the structural dimensions for achieving both high transmittances and extinction ratios. Electron beam lithography together with angled depositions of an aluminum (Al) film was applied to fabricate the proposed SWG polarizers with the aspect ratio as high as 13:1. Optical characterizations demonstrated enhanced polarization performances in short infrared wavelengths from 1050 up to 1600 nm. The developed SWG polarizer and the fabrication technique possess advantages in the simplified process, lift off free and wafer scale prospect.