Research Of Multi-Clad Dispersion Compensating Fiber

Along with the unceasing development of fiber communication technology, the loss of fibers is not any longer the main obstacle to improve long-haul transmission of the optical signal. On the other hand, dispersion of fibers has a more important effect on fiber communication. In order to control and reduce dispersion of fibers, many ways, such as dispersion-flatted fiber, dispersion-shifted fiber and dispersion-compensated fiber, have been brought forward. Because dispersion-compensated fibers have lots of outstanding characteristics, such as agility, convenience, tending to upgrading of fiber transmission networks and compensating dispersion slope, it has become a pop task. The multi-clad dispersion compensating fiber is researched in this paper. Using the theory of light wave-guide transmission, the latent equation of four-clad, as an example, symmetrical refractive index fiber is acquired through shifted-matrix, and the analytic expression of dispersion is acquired also. Dispersion of other multi-clad fibers can be figured out in the same way. On the basis of analyzing traits of different fiber frame, the multi-clad fiber is used to design dispersion compensation fiber. Though the analytic expression of dispersion of the multi-clad fiber has been given out in this thesis, the process of calculating is very complex. So the way of equivalent single-clad fiber is used to get the dispersion of multi-clad fiber. By solving characteristic equation and unitary frequency equation with computer, the propagation constant and the equivalent refractive index of single-clad fiber which is equal to multi-clad fiber is achieved. Then the propagation constant of multi-clad fiber is obtained too. Finally, the dispersion of multi-clad fiber is acquired. On the basis of a theoretical analysis, Matlab is used to program to realize numerical calculation. Through calculating the refractive indexes of fiber and the propagation constants at a series of certain wavelenghthes, the equivalent refractive indexes of single-clad fiber are proposed. Using the data and relationship between dispersion and propagation constant, the dispersion curve of the multi-clad fiber can be achieved via curve simulation and differential coefficient numerical method.. At last, through repetitious numerical simulations using Fiber-CAD, a software of Optiwave corporation, the dispersion curves of multi-clad fibers is obtained and the effect of structural parameter of fiber to performance parameter of fiber is analyzed, and the dispersion compensation fiber to compensate dispersion of G655 is designed.