Polarization-Maintaining Large Mode Area Fiber Design for 2- μ m Operation

Large mode area polarizing maintaining (PM) photonic crystal fiber (PCF) designs, for 2-μm operation, are studied. A commercial PM-PCF optimized for 1-μm operation has been scaled to obtain an 80-μm-diameter core, and then numerically analyzed with the help of a finite-element method-based software to investigate its behavior at different values of bending radius. From the problems emerged by this design, a new optimized design has been proposed and numerically simulated. The new fiber consists in a thulium-doped 19-cell core with a diameter of 80 μm. The holes lattice, which follows the stack-and-draw scheme, has been modified to include two boron-doped stress applying parts, in order to induce a consistent birefringence. The results show that it is possible to achieve a single mode, single polarization operation, efficiently suppressing one of the fundamental mode (FM) polarization and the most significant higher order modes, in a range of bending radius from 33 to 40 cm. A remarkable value of 2600 μm2has been registered for the effective area of the survived FM polarization.