We have developed novel bismuth-based photonic crystal fiber which exhibits high nonlinearity γ ~ 780W-1km-1
and relatively low group-velocity-dispersion D ~ -25 ps/nm/km at 1560 nm. The new fabrication process was
also developed for this novel photonic crystal fiber with 6-fold symmetric structure. The core diameter 2.7 μm
of this fiber was designed to have modelately decreased normal dispersion and high nonlinearity. Spectral broadening
induced by self-phase-modulation by 1550 nm fs-pulse propagation shows that the high nonlinearity and dispersion reduction is simultaneously achieved.
Bismuth oxide based highly nonlinear fiber (Bi-NLF) enabled by glass composition and small core fiber design was successfully fabricated. There's much expectation for the development of high nonlinearity optical devices along with the large volumetric and speed increase of the information traffic in recent years. In order to achieve higher nonlinearity, it is necessary to enlarge the nonlinear refractive index n2 and make the effective core area Aeff smaller, as g is γ=2πn2/(λAeff). Much effort has been put into the development of small-Aeff holey fiber, as its high nonlinearity and dispersion can be controlled to a certain extent. However, holey fiber has issues such as large propagation loss, high connection loss with silica single-mode-fiber (SMF) because of their particular structure, and higher fabrication cost. We performed the fabrication of a conventional step-index-type SMF with high nonlinearity and low propagation loss using Bi2O3-based glass. First, we fabricated Bi2O3-based glass with high refractive index of >2.2 at 1550 nm by a conventional melting method. This glass exhibited extreme thermal stability for fiber drawing. Then in order to make Aeff smaller, cladding glass composition was designed so that the difference with the refractive index of the core glass must be large. Finally the core diameter was controlled to satisfy the single mode condition, and fiber drawing was performed. Typical Aeff of this fiber is less than 5 um2. The nonlinearity g of the fiber can be estimated to be >600 W-1km-1, as large as the value reported in holey fibers using non-silica glass. Bi-NLF with step-index-type structure would become the best candidate for short length and highly nonlinear optical devices.