Design and test of a near-infrared tunable liquid crystal birefringent filter

A near infrared tunable liquid crystal birefringent filter is developed by cascading a series of optical elements including the wide range wire-grid polarizers, the nematic liquid crystal retarders and the quartz retarders. The center wavelength of the filter's bandpass could be randomly selected or scanned in the designed spectral range with almost exactly the same out-of-band suppression by harmoniously adjusting the driving signals. The tuning range of the filter is 900nm similar to 1700m, the clear aperture is over 50mm, and the bandwidth FWHM is about 15nm @900nm. The filter provides more flexible functions such as random wavelength selection and arbitrary spectral scanning step. Due to the excellent imaging quality and the relatively wide angle-of-acceptance with a large aperture, the filter enable snapshot spectral imaging sensors and compact systems without any moving parts, which is of great use in a wide variety of applications such as remote sensing for environmental monitoring, agriculture census, and mineral resources detection.