Patent ID: 6876480

Claim:
A variable optical attenuator arranged with, in order, a polarizer, a Faraday rotation angle varying device and an analyzer, wherein said Faraday rotation angle varying device comprises: a first Faraday element; a second Faraday element which is different in Faraday rotation direction from said first Faraday element; a pair of permanent magnets operable to magnetically saturate said first and second Faraday elements; and an electromagnet operable to change the Faraday rotation angle on said first Faraday elements; wherein said second Faraday element is only magnetically saturated by said pair of permanent magnets, and the rotation angle of said second Faraday element is not changed by said electromagnet; and wherein said variable optical attenuator further comprises an optical filter functioning part having at least a wavelength-dependent loss which is reverse in sign to a wavelength-dependent loss to be caused by said polarizer, said Faraday rotation angle varying device and said analyzer.