Tunable liquid crystal-resonant grating filters using superimposed grating structures fabricated by nanoimprint lithography

Demonstration of superimposing a short-pitch gratings for aligning liquid crystals onto a larger-pitch subwavelength resonant grating (SRG) is presented, to achieve superior liquid crystal alignment, which leads to drastically improved tuning filter performance and tuning range. The tunable SRG needs a 1 μm pitch gratings for the desired filter resonance frequency, which is in the infrared, and a-shallower gratings with a pitch between 200 nm to 400 nm for aligning liquid crystal, which is used for tuning the resonance frequency of the filter. A tuning range of 21 nm has been achieved.