Experimental characterization of the photonic bandgap holey fiber with residual core ellipticity

We report on experimental characterization of the photonic bandgap holey fiber operating at 830 nm and having residual birefringence induced by elliptical shape of the core. Using specially developed technique, we measured in this fiber the spectral dependence of phase and group modal birefringence as well as the susceptibility of these parameters to elongation and hydrostatic pressure. All measured parameters are highly dispersive. Our result, show that the group modal birefringence crosses zero value at the bandgap center, while the phase modal birefringence depends parabolically upon wavelength.