Electro-Tunable Optical Cavity Filters in the Mid-Infrared Regime: A Polarization-Independent Solution for Hyperspectral Imaging

The development of tunable optical filters in the mid-infrared (MIR) region is crucial for a variety of applications, including environmental monitoring, medical diagnostics, and communication systems. This paper presents the design, fabrication, and characterization of a novel Twisted Liquid Crystal (TLC) electro-tunable optical cavity filter for the MIR region 3–5 μm. The filter is based on a Fabry–Perot interferometer configuration, which includes a polarization-independent TLC to achieve electrical control over the filter’s transmission characteristics. Two distinct filters were fabricated, differing in their substrate materials: silicon and glass. The silicon-based filter demonstrated an impressive 80% transmission with a tuning range of ∼13.6 nm and ∼14.64 nm in two separate bands, achieved by varying the applied voltage from 0 to 20 V. In contrast, the glass substrate filter exhibited a slightly higher transmission of 82% with tuning ranges of ∼10.5 nm and ∼7.2 nm across the spectral band when the voltage was adjusted from 0 to 27 V. Experimental validation showed a strong alignment between the simulations and results, demonstrating the feasibility of integrating tunable liquid crystals into mid-infrared optical cavities. This advancement highlights their potential for applications that require precise and dynamic control of the mid-infrared spectrum.