Dispersion shifted optical fiber (DSF)

Optical fibers are now widely used as sensors, for communication and data transmission. Commonly used fibers are made of either glass or plastic. PCS fibers have glass core and plastic cladding. Based on modes of propagation, there are two types of fibers. They are single mode and multimode. Cross sectional refractive index profile yield two varieties of optical fibers. They are step index fiber and graded index fiber. Dispersion shifter fiber is a special type of single mode fiber where core-cladding index profile is tailored to shift the zero-dispersion wavelength from the natural wavelength (1300 nm) in silica fibers to 1550 nm. In such fibers controlling material dispersion is not easy. But it can be varied marginally by proper doping of core and cladding regions. Waveguide dispersion can be varied appreciably in dispersion shifter fibers and this allows shifting the zero dispersion wavelengths into 1550 nm range. Chromatic dispersion is almost zero in dispersion shifted fibers at wavelength 1550 nm. Nonzero dispersion shift fibers are used in wavelength division multiplexing systems. This is to avoid four-wave mixing which may cause intermodulation of the independent signals. In zero dispersion fibers, point of zero dispersion can be shifted by increasing material dispersion. This fiber is more regularly used in systems like dense wavelength division multiplexing (DWDM) systems and Erbium doped fiber amplifiers (EDFA).