Low-loss hybrid fiber with zero dispersion wavelength shifted to 1 μm

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We propose a novel cylindrically symmetric hybrid fiber design that allows combining properties of the both fibers guiding light due to total internal reflection (low optical losses) and photonic bandgap fibers (anomalous dispersion at 1 μm). Refractive index profile of these fibers consist of the only few layers: low-index core (ncore-nsilica>0) surrounded with one or more high-index ring layers (nhigh-ncore>0), a depressed layer (ndepress-nsilica<0) and silica cladding. Operating mode is one of the high-order modes (depending on high-index ring layers number) with intensity maximum at fiber axis. Because the other modes (including the fundamental mode LP01) are guided in the high-index ring layer(s) the hybrid mode can be easily excited by splicing hybrid fiber and standard single-mode (λ~1μm) step-index fiber with appropriate mode field diameter. Moreover method of achievement of asymptotically singlemode regime of light propagation (suppression of the high-index ring layer modes) has been proposed. The main idea of it is doping narrow strong absorbing layer where hybrid mode has intensity of electric field closed to zero. Furthermore we have considered possibility to increase anomalous dispersion of the hybrid fiber (up to 100 ps/nm km) by usage more complicated refractive index profile with two high-index ring layers. In this work we have fabricated the technologically simplest hybrid fiber with the only one high-index layer. The hybrid LP02 core mode had dispersion of 13 ps/(nm km) and optical loss of about 6 dB/km. Propagation of chirped pulses through the fabricated hybrid fiber allowed us to compress them from 8ps to 330fs.