Optical Band-Pass Filter Using Accidental Isotropy and Optical Activity of AgGaSe2

AgGaSe2 is an optically active and birefringent crystal, and has a specific wavelength at which an optical isotropy happens to occur. An optical band-pass filter with polarizer-AgGaSe2 crystal-polarizer sandwich structure is fabricated by using these properties, in which the central wavelength lies in 811 nm and the band width is 3.8 nm. In this type of filter, the change in the band width is made possible by considering the crystallographic orientation of crystal plate used, and suppression of the side-bands can be done by piling the same type of filters. Also in this paper, a change in the central wavelength from 497 nm to 811 nm effected by using AgGaS2-AgGaSe2 alloy is predicted.