Bending effect characterization of individual higher-order modes in few-mode fibers.

We propose an approach to directly measure the bending effect on individual modes in few-mode fibers using a wavelength-scanning spatially and spectrally resolved imaging technique. By collecting a fiber output beam profile with a scanning wavelength at different bending diameters and analyzing the peaks of its Fourier transformation, we have distinguished higher-order modes (HOMs) of the fiber and investigated their group delay, beam profile, bend loss, and mode splitting individually. We have experimentally verified with a multilayer core fiber at 1-8 cm bending diameters that its HOMs experience more loss compared to lower-order modes, but delay at approximately the same speed as the bending diameter decreases. Mode splitting of the LP11 mode at a small bending diameter due to bending-induced birefringence is also observed and discussed. This method provides an efficient tool to study the bending effect on individual HOMs in fibers and could be extended to studying fiber stretching and twisting.