《光纤通信课程设计》课件：Class4-03.pptVIP

Fiber Optic Network DesignX. Wu, M. J. Li, H. M. YanDept. of Opt. Engr., ZJU2011Class 3 Outline?FWM: definition origin FWM in fiber, effect on WDMHow to reduce it simulationSolutionsPolarization allocationUnequal channel spacingDispersion management Definition: Nonlinear effect that occurs in nonlinear optical materials such as photonic switch, optical fiber cable, etc. This interaction between waves leads to interaction between channels generates one or more new channels (or harmonics). For instance, when three waves at frequencies fi, fj, and fk traverse a fiber they generate another signal located atThe effects of FWMFour-Wave Mixing (FWM) FiberExample : The input is two signals located at ? 1 and ? 2 traverse a fiber of length (L) and the output is four different signals located at ?1, ? 2, 2?1 - ?2, and 2?2 - ?1 . In general the number of newly generated signals is given by Where Pi , Pj , Pk are the input power of the channels D is the degeneracy factor 3 and 6 for two-tone and 6 for three-tone product Where Aeff is the effective cross-sectional area and Leff is the effective length of the fiber given by The power of of newly generated signals is given by And ? is given by The nonlinear susceptibility ?1111The efficiency η is given by Where ?fmn = ?fm - fn?, (m,n = 1, 2, 3) The following figure demonestrates the effect of FWM when Four signals with equally power 3mw traverses a fiber with the following specifications Description ValuesAttenuation factor (?)0.2 dB/kmEffective fiber cross-sectional area ( Aeff )6.4x10-11m2Third order nonlinear susceptibility (?1111)6x10-15 cm3/ergChromatic dispersion (Dc)1ps/nm.kmDispersion slope ( )?.07ps/km.nm2Refractive-index (n)1.48Length L75 kmWavelength ( ? )1550 nm The Original input signals The newly generated signals and their corresponding power in dBm The newly generated signals and their corresponding power in dBm after filtration The original and the newly generated signals after filtration as