The air-filled region results in strong wavelength dependence in the characteristics of the fiber and is responsible for the large wave-guide dispersion possible in such fibers. The wave-guide dispersion can be used to enhance or cancel out the material dispersion in the fiber and the flexibility in terms of dispersion profile is therefore much bigger in PCFs than in standard fibers. Changing the design of the microstructure (hole-sizes, pitch, hole structure) strongly influence the wave-guide dispersion and it is possible to design fibers with zero dispersion wavelength (ZDW) in the visible wavelength range or with flat near-zero dispersion over a large wavelength range. By choosing the dispersion profile carefully, the fibers can be tailored to facilitate different nonlinear processes.
For Supercontinuum generation using a femtosecond laser, try Newport's SCG-800 and SCG-800-CARS self contained Supercontinuum Generation Fiber Devices. They consist of nonlinear PCFs contained in a robust, sealed, 25 mm metal housing, without the hassle of fiber handling and cleaving.
These nonlinear fibers are designed with relatively small holes to be single-mode at the operation wavelength. This approach has several advantages compared to multimode nonlinear fibers with large air holes. First, the fibers are easier to splice to solid standard fiber due to the lower air-filling fraction. Second, alignment and focusing with free-space coupling is less critical as light focused on the cladding region will not be coupled, unlike in high-air-filling fraction fibers, where light can be guided in the silica "islands" between the large holes. Finally, a long range of applications requires strict single-mode operation.
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