By using OptiSystem software and MATLAB, variant types of dispersion compensation techniques used in optical fiber communication have been analyzed. Recent advancement in telecommunication services demands higher bandwidth which can be achieved by lowering the dispersion effect, i.e., pulse spreading. Due to this effect, the system bandwidth decreases. When signal or light pulse is transmitted by the optical fiber, it suffers from some loss due to the attenuation and dispersion. Jay N.In optical fiber, communication signal can be transmitted through one place to another by optical fiber in the form of pulses.Sivarajan, Optical Networks: A Practical Perspective (Harcourt: San Diego, 1998). Again, any random imperfections that break the symmetry would lead to PMD in such a waveguide. For example, a square or equilateral-triangle core would also have two equal-speed polarization solutions for the fundamental mode such general shapes also arise in photonic-crystal fibers. Rather, one requires a core whose symmetry group admits a two-dimensional irreducible representation. Strictly speaking, a circular core is not required in order to have two degenerate polarization states. An extension of this idea is a single-polarization fiber in which only a single polarization state is allowed to propagate along the fiber (the other polarization is not guided and escapes).Ī related effect is polarization-dependent loss (PDL), in which two polarizations suffer different rates of loss in the fiber due, again, to asymmetries. Such fibers currently have practical problems, however, such as higher losses than ordinary optical fiber and higher cost. Since the second polarization is never excited, PMD does not occur. a highly elliptical core) that an input polarization along a principal axis is maintained all the way to the output. Such systems are therefore expensive and complex combined with the fact that PMD is not yet the limiting factor in the lower data rates still in common use, this means that PMD-compensation systems have seen limited deployment in largescale telecommunications systems.Īnother alternative would be to use a polarization maintaining fiber ( PM fiber), a fiber whose symmetry is so strongly broken (e.g. Because the PMD effects are random and time-dependent, this requires an active device that responds to feedback over time. no first-order variation of time-delay with frequency), and applies a differential delay to re-synchronize them. Essentially, one splits the output of the fiber into two principal polarizations (usually those with dτ dω = 0, i.e. Both of these effects can stem from either imperfection in manufacturing (which is never perfect or stress-free) or from thermal and mechanical stresses imposed on the fiber in the field - moreover, the latter stresses generally vary over time.Ī PMD compensation system is a device which uses a polarization controller to compensate for PMD in fibers. Second, there are stress-induced material birefringences, in which the refractive index itself depends on the polarization. First, there is geometric asymmetry, e.g. The symmetry-breaking random imperfections fall into several categories. Δ τ = D PMD L ĭ PMD is the PMD parameter of the fiber, typically measured in ps/ √ km, a measure of the strength and frequency of the imperfections. Because the imperfections are random, the pulse spreading effects correspond to a random walk, and thus have a mean polarization-dependent time-differential Δ τ (also called the differential group delay, or DGD) proportional to the square root of propagation distance L: In this case, the two polarization components of a signal will slowly separate, e.g. In a realistic fiber, however, there are random imperfections that break the circular symmetry, causing the two polarizations to propagate with different speeds. a random superposition of these two polarizations, but that would not matter in an ideal fiber because the two polarizations would propagate identically (are degenerate). The signal that is transmitted over the fiber is randomly polarized, i.e. In this case, the fundamental mode has two orthogonal polarizations (orientations of the electric field) that travel at the same speed. In an ideal optical fiber, the core has a perfectly circular cross-section.