Efficient bending compensation of large mode area fiber

Abstract

While much research has been developed to achieve very large mode areas (LMA) fibers, many difficulties arise, such as bending losses, mode deformation, and high order modes suppression. The main obstacle which remains difficult to confront in LMA fibers is bending distortion. When a conventional LMA fiber is coiled, it will generally suffer large bending distortion, and the mode area will contract accordingly, which would significantly affect laser or amplifier performances for some LMA fibers. In this report, we proposed a simple and efficient way for bending compensation in LMA fiber. A periodically etching structure is proposed to compensate the deformation, bending loss, and mode-coupling effects in large mode area fibers. The numerical simulation results showed that the design not only efficiently improves the effective area, but also the fundamental mode bending loss is resistant. Without the structure, the bending losses are very low at large bending radius. When the bending radius reduces, there is a rapid increase of losses. In particular, for smaller bending radius (less than 20 cm), the fundamental mode deforms severely, and cannot normally transmit in the core. The numerical simulation results showed that the design not only efficiently improves the effective mode area, but also the fundamental mode bending loss is resistant. Even at bending radius as small as 5cm, the fundamental mode can transmit normally in the fiber with an increased mode area scaling. Furthermore, the LMA fiber with the structure can be flexibly manufactured by conventional fiber manufacturing approaches and recent etching technologies.