Patent ID: 7953307

Claim:
An optical circuit, comprising: an optical waveguide having a first state and a second state, the optical waveguide being more transmissive to light of a given wavelength in the second state than in the first state; a first light source coupled to the optical waveguide, and configured to selectively transmit a first optical signal comprising light of a first wavelength through the optical waveguide to place the optical waveguide in the second state; a second light source coupled to the optical waveguide, and configured to selectively transmit a second optical signal comprising light of a second wavelength through the optical waveguide to place the optical waveguide in the first state; a test light source configured to inject a test light signal of the given wavelength into the optical waveguide such that the test light signal counter-propagates through the optical waveguide relative to the first and second optical signals; an output configured to output the test light signal after it has traversed the optical waveguide; and wherein the output and test light source are located on opposite sides of the optical waveguide, and wherein the output is located on the same side of the optical waveguide as the first and second light sources.