Optical Nonlinearities in Chalcogenide Fibres

Optical fibers are obtained by heating glass preforms fabricated via rod-intube type processes [213, 214] or by double-crucible processes [214-216].

Fabrication of single-mode chalcogenide optical fiber is essential for applications such as fiber amplifiers. The rod-in-tube technique has been the most popular process for fabrication of single-mode chalcogenide optical fibers [217, 218]. This technique involves many stretching and overjacketing steps that are not suitable for most glasses because of their thermal instability. To overcome this difficulty, a double-crucible technique has been used to produce single-mode optical fiber. A typical system consists of an inner quartz crucible (tube) concentrically positioned within an outer quartz crucible (tube). Each tube is connected individually to an inert gas source, flow meter, pressure controller, and pressure gauge. The outer diameter of the fiber and core/clad ratio can be controlled by adjusting the gas pressure in the inner and outer quartz tubes independently, by altering the drawing rate, and by adjusting the temperature. The core and cladding glasses are introduced into the inner and outer quartz tubes, respectively. Glasses are remelted, fined, and the temperature is then lowered quickly to the drawing temperature where fiber fabrication starts. Chalcogenide fibers with core diameters ranging from 2 to 400 μm and outer diameters from 50 to 500 μm can be fabricated by this technique under different fiber-drawing conditions.