Birefringence of femtosecond written fiber Bragg gratings for linear polarized fiber lasers

We present an investigation of birefringence in ultrashort pulse and phase mask written fiber Bragg gratings (FBGs). Polarization dependent loss and shift of the resonance wavelength as well as the polarization extinction ratio of the FBGs was determined. As expected, we could find a significant dependency connecting the grating strengths and the birefringence . For high reflector gratings, birefringence of up to 10^-5, corresponding to a resonance wavelength shift of up to 10 pm was measured. The results show excellent suitability for usage of the FBGs in linear polarized fiber lasers.