Controlling the chromatic dispersion of soft glass highly nonlinear fiber through complex microstructure

Soft glass highly nonlinear fibers have high nonlinearity and a broad transparency range, but their chromatic dispersion is far from being freely tailored until now due to the immaturity in fabrication technology. In this research, the chromatic dispersion of soft glass highly nonlinear fibers was controlled by using the complex microstructure in the cladding. A tellurite glass fiber which had a 1.8 μm core surrounded by four ring holes was fabricated. The preform was fabricated by the method of cast rod in tube and stack. The chalcogenide–tellurite glass composite fibers which had a 1.5 μm core surrounded by tellurite microstructure cladding were demonstrated. Their preform was fabricated by the method of stack and draw. In the fiber-drawing process of both types of fibers an inflation pressure of nitrogen gas was pumped into the holes of the preform to overcome the surface tension and to reshape the microstructure. The tellurite complex microstructured fiber has a chromatic dispersion much more flattened than that of step-index air-clad fiber. The chalcogenide–tellurite glass composite fibers have the zero dispersion wavelength (ZDW) in the near-infrared range. Having the ZDW in the near-infrared has not been realized before for the fibers made from chalcogenide glass. Meanwhile, the composite microstructured fiber with large holes in the cladding has the highest nonlinearity of all highly nonlinear fibers if the tapered fibers are excluded. Supercontinuum spectra covering over one octave, free of fine structures, were demonstrated by the fabricated fibers.