Mode Coupling in Optical Fibers: Selective Excitation of a Higher-order Mode with a Fiber Bragg Grating

This article discusses how one can effectively couple light from the fundamental mode of a multimode fiber into a certain higher-order mode. This is surprisingly simple: one only requires a fiber Bragg grating with a properly chosen grating period. The physics behind that mode coupling effect are discussed, and the situation is illustrated with some numerical simulations.