Strong LP11-Mode Splitting in UV Side-Written Tilted Fiber Gratings

Dual-mode fiber gratings are promising components for mode converters and reflectionless band filters. In order to be able to use standard telecommunication fibers, which are single-moded at the wavelengths of interest, one can increase the refractive index by UV laser-beam side-writing such that higher modes propagate through the grating region. We show here that UV side-writing is an efficient method to increase the refractive index to allow higher modes to propagate. In addition, the problems of multiple resonant peaks due to weakly broken higher-mode degeneracy [1] is circumvented by breaking the degeneracy such strongly that the resonant peaks are spectrally widely separated.