Patent ID: 7336418

Claim:
An optical attenuator using a Faraday rotational angle variable device having an optical axis, said optical attenuator comprising a polarizer and an analyzer which are disposed at the incoming side and outgoing side, respectively, on said optical axis of said Faraday rotational angle variable device, said Faraday rotational angle variable device applying an external magnetic field to a garnet single crystal and the like having a Faraday effect, from two directions or more, to vary the combined magnetic field to thereby control the Faraday rotational angle of light passing through said garnet single crystal, wherein let x be an angle, in degrees, which is formed between the plane of polarization of a single incident light to the garnet single crystal after passing through said polarizer, or the plane of polarization of one of two lights, whose planes of polarization intersect each other at right angles, and the direction of the magnetic field orthogonal to said optical axis, applied to said garnet single crystal, and let y be an angle, in degrees, which is formed between the polarizer and the analyzer, then the angle x satisfies {(−z/2)+90×n}−4≦x≦{(−z/2)+90×n}+4 (n=0, 1, 2 or 3), where z=y±90; z is the angle of rotation of the plane of polarization, in degrees, caused by passing through the Faraday rotational angle variable device when the magnetic field is applied, and wherein temperature-dependence of the optical attenuator's dynamic range is reduced responsive to the selection of the angle x.