140 µm single-polarization passive fully aperiodic-large pitch fibers operating near 2 µm

In this paper the authors demonstrate a single-polarization feature out of passive very large mode area fully-aperiodic large pitch fibers. It has been previously shown theoretically that one of the two polarizations of the fundamental mode is selectively coupled to a cladding mode. This coupling does not require fiber bending, which permits to avoid any decreasing of mode effective area. This coupling is achieved owing to boron-doped silica inclusions implemented into the microstructured cladding and acting as stress applying parts (SAP). This mechanism has been assessed experimentally in this work using fibers of two different core diameters: 60 µm and 140 µm, providing mode field areas of 3637 µm² and 14590 µm² respectively. The tested fibers have a length of 45 cm and an outer diameter exceeding 1 mm, yielding into rod-type fibers. Each sample has been characterized using a un-polarized laser source emitting at 1942 nm. This laser, based on a thulium-doped large mode area step-index fiber, has a spectral bandwidth of about 0.5 nm. After passing through a piece of the passive fiber, a polarization extinction ratio higher than 16 dB has been achieved.