Patent ID: 7409157

Claim:
An optical switch comprising: an optical waveguide loop circuit for dividing a signal light, propagating the divided signal lights in opposite directions along a loop-form light path formed from an optical nonlinear medium, and then re-multiplexing the divided signal lights; control light input means disposed at a point on said optical waveguide loop circuit for inputting a control light into said optical nonlinear medium to alter the refractive index of said optical nonlinear medium, thereby serving as phase control means for controlling the phase of the signal light propagating through said optical waveguide loop circuit; a wavelength demultiplexing/multiplexing circuit provided at a point on said optical waveguide loop circuit for equalizing the respective contributions made by two orthogonal polarization components of said control light to the phase control amount of said signal light through said refractive index alteration of said optical nonlinear medium; and a phase bias circuit disposed at a point on said optical waveguide loop circuit for removing a phase bias component added to said signal light, wherein said phase bias circuit is disposed at a point on a polarization-maintaining single-mode fiber constituting said optical waveguide loop circuit through which said signal light is guided, wherein said phase bias circuit comprises a first polarization plane rotation element for rotating a polarization plane of said signal light 45 degrees, a phase compensation element for correcting a phase shift between polarization components orthogonal to said signal light, and a second polarization plane rotation element for rotating a polarization plane of said signal light 45 degrees, and wherein said first polarization plane rotation element, said phase compensation element, and said second polarization plane rotation element are arranged in series in that order.