An optical device extracts an information bearing sideband such as an FSK or SCM signal (label) from a composite signal that includes the sideband and an orthogonally modulated signal such as an intensity modulated signal (payload) by splicing the composite signal into a polarization maintaining fiber at a desired angle so that the composite signal is separated into two orthogonal polarizations that experience differential group delay in the fiber. The polarized output signals from the fiber are then coupled to a polarization beam splitter at an equivalent or complementary angle to the desired angle so that one sideband of the composite signal appears at a first output of the beam splitter while another sideband appears at a second output of the beam splitter. The sidebands can then be converted to an electrical data signal by using an appropriate receiver, such as a balanced receiver for FSK signals. In one embodiment of the present invention, an input polarization beam splitter is coupled to the polarization maintaining fiber which, in turn, is coupled to an output polarization beam splitter. The coupling at each end of the fiber is made at approximately 45.degree. to one polarization axis of the fiber. The fiber is characterized by a beat length L.sub.beat and the fiber is designed to have a length substantially equal to (L.sub.beat.times.f.sub.c)/2.delta.f, wherein the sidebands of the composite signal are separated by a wavelength difference .delta.f and f.sub.c is the nominal center frequency of the composite signal. This device has been shown to be useful for extracting GMPLS LSC level wavelength labels from either an FSK/IM composite signal or an SCM/IM composite signal.