The Study Of Propagation And Switching Properties Of The Nonlinear Fiber Bragg Grating Couplers

In the modern communication network, all optical communication is the trendof the times to increase the network speed and upgrade it. The fiber Bragg gratingcoupler(FBGC) which is successfully used in dense wavelength divisionmultiplexing(DWDM)、erbium doped fiber amplifier(EDFA) and sensing system hasboth the grating’s filter properties and the coupler’s multi-ports characteristics, so itis forecasted as an important device in the future of the all optical communication.In this paper, the relevant theory of the FBGC is researched scientifically with thetheoretical basis of the FBGC coupling equations, the main research work andresults are as follows:1. Firstly, the grating and coupler’s structure and the derivation process of thecoupling equations are introduced by the Maxwell’s equations separately. Then therelationship between the coupling coefficients with the transmissivity of the FBGC isrecommended. Lastly, the energy distribution in the FBGC is introduced by thedifferent detuning.2. Secondly, compared to the normal fiber, the doped fibers have highernonlinear coefficient. The doped fiber Bragg grating, which is manufactured by thehigh nonlinear effect doped fiber, can have better switching characteristics withswitching threshold power decreased and contrast enhanced. However, thepolarization strength of the doped fiber must be considered when the coupled-modeequations are analyzed, so the traditional methods, such as the transfer matrixmethod and et al, can not operate. Here, a new algorithm based on Runge-Kuttamethod to analyze the coupled-mode equations is introduced. According to thealgorithm, the relation curve between transmissivity and different input pulse poweris showed. What is more, the self-switching performance is simulated too. Inaddition, the optical bistability can be observed. The self-pulsing phenomenon of thedoped fiber Bragg gratings are analyzed by simulations. Lastly, the self-switchingcharacteristics are analyzed with the different detunings.3. Lastly, using the algorithm described above, a series of numerical calculationabout the switching and propagation characteristics of the FBGC are researched.Firstly, the relation curve between different input pulse powers and the dispersion is showed. Secondly, according to the algorithm and numerical calculation, thenumerical simulations of the self-pulse, bistability and switching characteristics areanalyzed, in addition, the propagation characteristic is also simulated to show thepulse evolution and energy distribution. Lastly, the linearization method isintroduced to analyze the modulation instability of the FBGC.