Measurement of fiber birefringence by wavelength scanning: effect of dispersion.

Scanning the wavelength in high-birefringence fibers inherently measures the group delay difference, and not the phase delay difference, between the two polarization modes. Dispersion of the birefringence will result in a 10-20% error in fiber beat lengths interpolated from such measurements, even if only stress birefringence is present. Geometrical dispersion can introduce even larger errors in some fibers.