We present design, fabrication, and characterization results on a novel multi-spectral imaging lens. Our lens design combines a catadioptric geometry with a reflective tunable cholesteric liquid crystal cell. The lens images in a narrow (~50 nm) spectral band and can be continuously voltage-tuned over a broad wavelength range (>;400 nm). The lens works with circularly polarized light. A cholesteric liquid crystal cell reflects light if the incident circular polarization has the correct handedness and the wavelength is closely matched with the liquid crystal pitch. Otherwise, the light transmits unaffected. Our compact optical design converts this reflective mechanism into a transmissive one for the purpose of imaging. In addition, we use corrective refractive lenses to optimize imaging performance over wide field of view. The traditional approach would be to use tunable birefringent filter (e.g. Solc and Lyot filter) in conjunction with a broadband imaging lens, with the birefringent filter itself composed of multiple liquid crystal cells and polarizers. Tunability is provided by adjusting optical retardation of nematic liquid crystal cells through application of appropriate voltages. Our design uses a single liquid crystal cell and a single polarizer and is inherently high in optical transmission, significantly less complex and thus potentially low cost. The applications include forensic imaging, multispectral aerial surveys, dermatology, medical microscopy etc.
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