Bismuth based erbium doped fiber and highly nonlinear fiber exhibit inherent features which cannot be realized with silica based fibers. Extend L-band amplification, high gain C+L band amplification for coarse WDM and short pulse amplification can be realized using bismuth based EDF. On the other hand, step-index type fiber using bismuth based glass whose refractive index of 2.22 at 1.55μm is fabricated. This fiber exhibits high nonlinearity (γ=1360 W-1km-1) because of the high nonlinearity of the glass material and the small effective core area.
Naoki Sugimoto, Naoki Sugimoto,
"Er-doped fiber and highly nonlinear fiber based on bismuth-oxide-based glasses", Proc. SPIE 5723, Optical Components and Materials II, (4 April 2005); doi: 10.1117/12.590676; https://doi.org/10.1117/12.590676