epub A STUDY ON FEW MODES INTERMODAL DISPERSION FREE OPTICAL FIBERS

Single mode fibers were introduced in the second half of l 970s which are now well established as the transmission medium in an optical fiber telecommunication network due to zero intermodal dispersion. These fibers have extremely small core diameter ranging from 5 to1Oµm. Any optical telecommunication network shall involve junctions or splices between two single-mode fibers. Thus, due to smallness of core diameter, splicing of two such fibers posed a big problem in those days. To overcomethisdifficulty, inthesecond halfof1970sand first half of 1980s, dual mode fibers were proposed by researchers as a larger core diameter alternative to single-mode fibers. In a dual mode fiber, by a suitable choice of the fiber parameters, the group velocities of the fundamental mode (LP 01) and the first higher order mode ( LP11 propagating in it could be equalized resulting in intermodal dispersion free propagation. Since two modes propagate, the cordiameter of the dual mode fiber would be obviously larger than that of the single-mode fiber which facilitated jointing of two such fibers. However, with the subsequent introduction of fusion splicing technique, the jointing of two single-mode fibers became very easy. Thus, research on dual mode fibers eventually stopped. During the last few years, interest ha grown in the study of few-mode fibers (FMFs) which allow first few modes to propagate. Such fibers are generally used in astronomical telescopes, for dispersion tailoring, for dispersion compensation and in photonic devices. A few-mode fiber can replace a single-mode fiber as transmission medium if it is made intermodal dispersion free. The group velocities of the propagating modes are sensitive to the refractive index profile of the fiber. Investigating theoretically, we have proposed a refractive index profile for which the group velocities of the first four modes (LP 0I , LP1I , LP02 and LP1)propagating in this fiber become equal at an appropriate value of the V­ parameter of the fiber. This profile is found to be a composite two-q profile regions insidethecore havingdifferent power law refractive index variations. We have also proposed a numerical method for the solution of scalar wave equation and computation of group velocities of these four modes.Thisfibermayfindapplicationinfutureas transmission medium in optical telecommunication system as a larger core diameter alternative to the conventional single-mode fiber.