Extremely large mode area optical fibers formed by thermal stress.

TLDR: It is reported that a strictly single-mode optical fiber with a record core diameter of 84 microm and an effective mode area of approximately 3600 microm(2) at 1 microm is reported and a record low numerical aperture of approximately 0.013 in an optical fiber is demonstrated.

Abstract: We report a strictly single-mode optical fiber with a record core diameter of 84µm and an effective mode area of ~3600µm2 at 1µm. We also demonstrate fundamental mode operation in an optical fiber with a record core diameter of 252µm and a measured mode field diameter (MFD) of 149µm at 1.03µm, i.e. an effective mode area (Aeff) of ~17,400µm2 at 1.03µm, an Aeff of 31,600µm2 at 1.5µm. All these fibers have near parabolic index profiles with a peak refractive index difference ΔN≈~6×10-5, i.e. a record low numerical aperture (NA) of ~0.013 in an optical fiber. This low refractive index difference was achieved by frozen-in thermal stress as a result of two different types of glass in the fibers. When the fundamental mode was excited in the 252µm core fiber using a 1.03µm ASE source, the output beam was measured to have M2x=1.04 and M2y=1.18.