Patent ID: 9488847
Filing Date: 2016-11-08
CPC Classification: G02B

Claim Text:
1. A variable optical attenuator comprising: a polarization beam splitter that splits a beam incoming from the front along one light path into a first linearly-polarized beam and a second linearly-polarized beam, with polarization planes thereof perpendicular to each other as well as outputting the first linearly-polarized beam and the second linearly-polarized beam individually along two parallel light paths going to the back; a variable Faraday rotator that is configured to include a Faraday element composed of magneto-optical materials and a magnetism applying means of variably controlling the direction and the magnitude of a magnetic field to be applied to the Faraday element and rotates each of the polarization planes of the first linearly-polarized beam and the second linearly-polarized beam individually incoming from the polarization beam splitter along the two parallel light paths by controlling the magnetic field to be applied to the Faraday element by the magnetism applying means, outputting them as a third linearly-polarized beam and a fourth linearly-polarized beam, respectively, further to the back; a first analyzer that is configured to have an optical axis of the same direction as that of the polarization plane of the first linearly-polarized beam and modulates the third linearly-polarized beam incoming from the variable Faraday rotator to a component in the direction of the polarization plane of the first linearly-polarized beam for outputting it as a fifth linearly-polarized beam; and a second analyzer that is configured to have the optical axis of the same direction as that of the polarization plane of the second linearly-polarized beam and modulates the fourth linearly-polarized beam incoming from the variable Faraday rotator to the component in the direction of the polarization plane of the second linearly-polarized beam for outputting it as a sixth linearly-polarized beam, the fifth linearly-polarized beam propagating in a first light path and being input to a first 90° optical hybrid without additional splitting before arriving at the first 90° optical hybrid, the first 90° optical hybrid being arranged at a subsequent stage of the variable optical attenuator, the sixth linearly-polarized beam propagating in a second light path and being input to a second 90° optical hybrid without additional splitting before arriving at the second 90° optical hybrid, the second 90° optical hybrid being arranged at a subsequent stage of the variable optical attenuator.