The most effective way of increasing the transmission capacity of an optical fiber communication system is to use the extremely wide bandwidth of a single-mode fiber and to feed a large number of channels as is practicable into the fiber. As a consequence of this, the trend has been to extend the communication window from the C-Band to the L-Band and the S-Band so that the communication window covers a total range of about 200 nm.
However, a major obstacle to the development of ultra-wide-band dense wavelength division multiplexing (DWDM) systems are non-linear effects, and in particular the Raman effect, which cannot be managed with dispersion. Non-Linear effects can cause distortion and crass-talk for example. A direct way to manage such non-linear effects is to use a single-mode fiber with a large effective core area, and therefore recently much work has been done on developing such fibers.
At the same time, there is an increasing interest in expanding the bandwidth of a multimode fiber to meet the demand for short-distance broadband applications, such as broadband Internet and local-area networks. For such applications, the very large core size of a multimode fiber proves to be important because it can ease the optical alignment and lower the fiber connection cost (and hence the system cost). Unfortunately the bandwidth of a conventional step-index multimode fiber, especially a large-core multimode fiber, is very limited and cannot meet future, demand. It is desirable to design a multimode fiber that has a very large core size yet provides a sufficiently large bandwidth.