A novel method to measure modal power distribution in few-mode and multimode fibers using tilted fiber Bragg gratings

摘要

In the paper, we present a novel method to measure modal power distribution (MPD) in few-mode and multimode fibers using embedded tilted fiber Bragg gratings (TFBG). The TFBG can couple portion of the guided modes into the corresponding radiation modes, whose powers can be selectively measured through a spatial filter. For few mode fibers, the power coupling coefficients between guided modes and their corresponding radiation modes are obtained by solving a set of linear coupling equations acquired under different launching conditions at the fiber input. For multimode fibers, the power coupling coefficients can be measured separately under single mode-group excitation condition. Then, the powers of guided modes in a few-mode or multimode fiber under any excitation condition can be obtained by simply measuring the powers of radiation modes and calculated using the solved coupling coefficients. The proposed method is successfully demonstrated.