High-order mode suppression in double-clad optical fibers by adding absorbing inclusions
Svetlana S. Aleshkina, Т. А. Кочергина, Vladimir V. Velmiskin, Konstantin K. Bobkov, Mikhail M. Bubnov, Mikhail V. Yashkov, Denis S. Lipatov, M. Y. Salganskii, A. N. Guryanov, Mikhail E. Likhachev
Abstract
We proposed and experimentally demonstrated a technique for the suppression of unwanted modes in double-clad fibers with a high core-to-clad diameter ratio by introducing high-index absorbing inclusions into the first cladding of the fibers. These inclusions disturb the shape of undesirable modes, and a noticeable part of the power becomes localized inside the inclusion, resulting in an increase in the propagation loss of these modes. Two fiber designs were studied and realized: one with cylindrical symmetry and an absorbing high-index ring as the inclusion and another with high-index absorbing rods inserted around the fiber core. In both cases, the possibility of achieving perfect single-mode propagation was demonstrated both theoretically and experimentally.