Patent ID: 6631238
Filing Date: 2003-10-07
Classification: G02B,G02F

Abstract:
A variable optical attenuator comprising:a) a light input port having a configuration to deliver input light to a first end of a birefringent crystal, wherein said birefringent crystal has a structure and orientation to separate said input light into a first ordinary beam and a first extraordinary beam and cause said first ordinary beam and said first extraordinary beam to emerge from the opposite second end of said first birefringent crystal separated by a walk-off distance; and, b) a half-wave plate located such that said half-wave plate intersects said first ordinary beam and said first extraordinary beam, wherein said half-wave plate has a structure and orientation so as to rotate the plane of polarization of said beams by 45Â°; and, c) a variable polarization rotator located so as to intersect said first ordinary beam and said first extraordinary beam following said half-wave plate, wherein said variable polarization rotator rotates the plane of polarization by an angle in the range from greater or equal to âˆ’45Â° to less than or equal to +45Â° in response to an externally applied control signal; and, d) a retroreflector having a structure and orientation so as to return said first extraordinary beam onto said second end of said birefringent crystal as a second extraordinary beam, and to return said first ordinary beam onto said second end of said birefringent crystal as a second ordinary beam, wherein said second ordinary beam and said second extraordinary beam impinge on said second face of said birefringent crystal separated by said walk-off distance and wherein said second ordinary beam and said second extraordinary beam emerge from said first end of said birefringent crystal recombined to a variable extent determined by said externally-applied control signal applied to said variable polarization rotator.