Patent ID: 7376360

Claim:
An optical device for extracting at least one of first and second optical streams of data from an optical signal at a wavelength λ c wherein the data streams are separated by a predetermined wavelength difference δλ, the device comprising: an input polarization beam splitter including both an input port for receiving said optical signal and first and second output ports defined by respective orthogonal polarization states; an intermediate polarization transformation element coupled to receive orthogonal optical signals output from the input polarization beam splitter at first and second inputs and to polarization transform and cross-over the received optical signals to second and first outputs respectively, the intermediate polarization transformation element further including a polarization maintaining fiber having a primary polarization axis, the fiber being disposed to support contra-directional propagation of the received orthogonal optical signals so that optical signals received at the first input are transformed and supplied at least in part to the second output and so that optical signals received at the second input are transformed and supplied at least in part to the first output, the primary polarization axis at a first end of the fiber being disposed at a predetermined angle relative to first output port of the input polarization beam splitter and the primary polarization axis at a second end of the fiber being disposed at a second angle relative to the second output port of the input polarization beam splitter, the second angle being related to the predetermined angle, the fiber being characterized by a beat length L beat , wherein the fiber has a length substantially equal to (L beat ×λ c )/2δλ; and an output polarization beam splitter having an output port and first and second input ports defined by substantially orthogonal polarization states, the first and second input ports of the output polarization beam splitter being coupled to the first and second outputs of the intermediate polarization transformation element, one of the first and second optical data streams being output from the output port of the output polarization beam splitter.