Polarization maintaining large mode area photonic crystal fiber
  We report on a polarization maintaining large mode area photonic crystal fiber. Unlike, previous work on polarization maintaining photonic crystal fibers, birefringence is introduced using stress applying parts. This has allowed us to realize fibers, which are both single mode at any wavelength and have a practically constant birefringence for any wavelength. The fibers presented in this work have mode field diameters from about 4 to 6.5 micron, and exhibit a typical birefringence of 1.5e-4. 
J.R. Folkenberg, M.D. Nielsen, N.A. Mortensen, C. Jakobsen, and H.R.   Simonsen