Assymptotically single-mode hybrid fiber with a high anomalous dispersion in the 1 μm wavelength region

Cylindrically symmetric hybrid fiber proposed by our group recently allow one to achieve high anomalous dispersion (13-100 ps/nm/km) in the 1 mu m spectral range. Refractive index of such fibers consists of one or two high index ring layer surrounding the core and depressed layer placed outside the ring layer. The drawback of the realized designs was presence of modes, localized in high-index rings, which tails nevertheless spread over the hybrid fiber core. Excitation of the operating hybrid mode LP03 in the two high-index ring design (or LP02 in the one high-index layer design) was accompanied by weak excitation (10-20% of total propagating power) of the modes, located in the high-index rings, that has non-zero electric field at fiber axis (mainly LP02 mode for two high-index-layers design and LP01 for one high-index layer design). In the present work we have experimentally demonstrated possibility to suppress all the propagating modes except the operating hybrid one (LP03 for two high-index-layer design). The main idea is based on introduction a thin ring layer with an extremely high optical loss to the position of electrical field minimum of the operating hybrid mode. Analysis of the mode composition carried out by off-center hybrid mode excitation confirms the asymptotically single-mode propagation regime.