Nanowire grid polarizers for mid- and long-wavelength infrared applications

摘要

High contrast wire grid polarizers on silicon suitable for mid-wavelength infrared (MWIR) and long-wavelength infrared (LWIR) applications have been developed using wafer-scale aluminum nanowire patterning capabilities. The 144 nm pitch MWIR polarizer typically transmits better than 95% of the passing polarization state from 3.5-5.5 microns while maintaining a contrast ratio of better than 37dB. Between 7 and 15 microns, the broadband LWIR polarizer typically transmits between 55 and 90% of the passing state and has a contrast ratio better than 40 dB. A narrowband 10.6 micron polarizer shows about 85% transmission in the passing state and a contrast ratio of 45 dB. Transmission and reflection measurements were made using various FTIR spectrometers and compared to RCWA modeling of the wire grid polarizer (WGP) performance on antireflection-coated wafers. Laser Damage Threshold (LDT) testing was performed using a continuous wave CO_2 laser for the broadband LWIR product and showed a damage threshold of 110 kW/cm~2 in the blocking state and 10 kW/cm~2 in the passing state. The MWIR LDT testing used an OPO operating at 4 microns with 7 ns pulses and showed LDT of 650 W/cm2 in the blocking state and better than 14 kW/cm~2 in the passing state.