An Arrayed Liquid Crystal Fabry–Perot Infrared Filter for Electrically Tunable Spectral Imaging Detection

Abstract

An arrayed electrically tunable infrared (IR) filter based on the key structure of liquid crystal Fabry-Perot (LC-FP) working in the wavelength range from 2.5 to 5 μm is designed and fabricated successfully. According to the electrically controlled birefringence characteristics of nematic LC molecules, the refractive index of LC materials filled into a prefabricated microcavity can be adjusted by the spatial electric field stimulated between the top and bottom aluminum (Al) electrodes. As a crucial component of the filter, the Al film with a typical thickness of ~30 nm acts as the electrode as well as the reflective mirror. The particular functions, including key spectral selection and spectral adjustment, can be realized by the developed LC-FP filter driven electrically. Our experiments show that the maximum transmittance of the transmission peaks is ~24%, and the transmission spectrum can be shifted remarkably through applying different voltage signals with a root mean square value range from 0 to ~21.7 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> . The experimental results are consistent with the simulation according to the model constructed by us. As a 2 × 2 or four-channel IR filter, the top electrode of the device is composed of four same sub-electrodes. Each channel in the device is powered separately and synchronously to select desired transmission spectrum, which means that the device can be used to obtain spectral sub-images in different spectral bands in one shot.