Enhanced and Suppressed Birefringence in Fiber Bragg Gratings

We demonstrate theoretically and experimentally that the two orthogonal polarizations of light see an unequal index constrast in a UV induced fiber Bragg grating. We find that in a Bragg grating the phase velocity mismatch is a function of detuning, and hence we can introduce an effective birefringence. The description of the polarization dynamics we develop is confirmed by a set of experiments on a fiber grating. We show theoretically that by adjusting the value of the unequal index contrast relative to the average birefringence it should be possible to eliminate the phase velocity mismatch between polarizations at a given frequency.