VARIABLE OPTICAL FILTER

摘要

A variable optical filter comprising, arranged along an optical axis in the order mentioned, a first polarizer, a first phase difference element for causing a phase difference, a variable Faraday rotor for imparting a variable Faraday rotation, a second phase difference element for causing a phase difference, and a second polarizer, wherein when angles formed between the optical axes of the first and second phase difference elements and the transmitting polarization azimuth of the first polarizer are respectively phi1 and phi2, phi1 and phi2are set at different ones. When the rotational direction of the rotation angle theta of the Faraday rotor is positive, an angle delta formed between the polarization transmitting azimuth of the first polarizer and polarization transmitting azimuth of the second polarizer is delta>0, an angle phi1 formed between the poarlization transmitting azimuth of the first polarizer and the optical axis of the first phase difference element is phi1<0, AN ANGLE PHI2 formed between the poarlization transmitting azimuth of the first polarizer and the optical axis of the second phase difference element is phi2<0, AND PHI1 and phi2 are set to be phi1<>phi2.