Toward highly birefringent silica Large Mode Area optical fibers with anisotropic core

We test the development of a silica all-glass optical fiber with a highly birefringent large mode area (HB-LMA). In the fiber, the birefringence and single mode operation are independent of bending and results from the internal nanostructuring of the core, which makes the glass anisotropic. Taking into account technological limitations of the doped silica glasses, we optimized the HB-LMA fiber properties by appropriate selection of germanium and fluorine doping level of silica used in the fiber core and cladding. We demonstrated that the anisotropic glass can be successfully used as a core material in large core area fibres in C-band for polarization components of the fundamental mode. We obtained phase birefringence of 1.92 × 10^-4 in the fiber with the core diameter of 30 µm and the effective mode area equal to 573 µm² and 804 µm², for x- and y-polarization, respectively. The same approach was applied to designing a single mode fiber with 40 µm core diameter and effective mode area over 1000 µm², which supports only single polarization.