Tunable Optical Band Pass Filter Using Optically Active and Biaxial Crystals

A tunable optical band-pass filter using an optically active, optically biaxial crystal is proposed. In a biaxial crystal, the direction of the optical axis generally depends on the wavelength. This filter capitalizes on this property and the optical activity. The filter contains a crystal sandwiched between a polarizer and an analyzer which are set in a crossed-Nicol position. The central wavelength can be selected by changing the direction of the light propagation in the crystal by rotating the crystal.