Design and realization of flexible very large mode area pixelated Bragg fibers

Abstract

A new Pixelated Bragg Fiber design showing improved optical performances in terms of single-mode behavior and effective area is presented. The cladding is made of 3 rings of cylindrical high refractive index rods (pixels) in which some pixels are removed to act as a modal sieve for an improved rejection of Higher Order Modes (HOMs). Two half-wave-stack conditions are used to increase the confinement losses of the 3 first HOMs: LP11 and LP02-LP21 guided core modes. The realized fiber exhibits a core diameter of 48.5 μm with an effective single-mode behavior observed from 1000 nm to beyond 1700 nm even for a 1-m-long straight fiber. Losses prove to be low with a minimum value of 25 dB/km between 1200 and 1500 nm. Bending radius of 22.5 cm is reported for this structure without any significant extra-losses above a wavelength of 1350 nm.

Extreme large mode area in single-mode pixelated Bragg fiber

“…The ratio between this diameter and the distance between two adjacent inclusions (Λ) is 0.53. This d/Λ value has been dictated mainly by manufacturing constraints: smaller values (as 0.36 in reference [27]) would lead to fewer resonators and thinner tubes for the low index ring while larger values (as 0.79 in reference [21]) would lead to a very large number of resonators to be stacked into a very small gap. Parametric study of the geometry of the heterostructuration of the two rings was done, starting from the study of a one-ring PiBF (diameter of the first high index ring about 116 µm, so this ring is composed of 16 rods) and then moving to a two-ring PiBF (diameter of second high index ring about 216.6 µm, so the second high-index ring is made of 30 rods) in order to insure robust single-mode behavior.…”

“…PiBF is good candidate for the realization of such single-mode fibers because the use of the appropriate Half Wave Stack (HWS) condition applied to low index ring helps to reject Higher Order Modes (HOM) and make the fiber single-mode [26]. Moreover, high-index rings were heterostructured by replacing some high-index rods by pure silica rods so as to enhance HOM leakage [27]. By combining these two different concepts, we have recently showed that pixelated Bragg fiber can be designed to obtain single-mode guidance and very low attenuation (below 25 dB/km between 1200 nm and 1500 nm) with core diameter as large as 48.5 µm [27].…”

“…Moreover, high-index rings were heterostructured by replacing some high-index rods by pure silica rods so as to enhance HOM leakage [27]. By combining these two different concepts, we have recently showed that pixelated Bragg fiber can be designed to obtain single-mode guidance and very low attenuation (below 25 dB/km between 1200 nm and 1500 nm) with core diameter as large as 48.5 µm [27].…”