Study On The Linear Transmission Spectrum And The Nonlinear Bistable Characteristics Of Magneto-optic Fiber Bragg Gratings

Magneto-optic fiber Bragg gratings(MFBGs)are photonic crystal fibers possessing a periodic spatial modulation of their optical and magneto-optical properties along the direction of propagation of an optical wave. MFBGs as magneto-optical media possess the Faraday polarization-mode conversion effects to manipulate the polarization state of a beam.MFBGs have become the focus of the fiber gratings field, with great market potential. This paper has done some research on the linear transmission spectrum and the nonlinear bistable characteristics of MFBGs.Firstly, the nonlinear and linear coupled-mode equations for the circular polarization light in MFBGs are derived. The side lobes of the linear transmission spectrum of Gaussian, super Gaussian, rise cosine, cap, hyperbolic tangent, Blackman apodized MFBGs have been restrained by apodization. The nonlinear multistability of several kinds of apodized MFBGs has been analyzed through contrast research. The side lobes of the linear transmission spectrum of inverse Gaussian, inverse super Gaussian, inverse rise cosine, inverse cap, inverse hyperbolic tangent and inverse Blackman apodized MFBGs have been enhanced by inverse apodization, the inverse apodized gratings can be used as flexible dual-wavelength or multi-wavelength bandpass filters.In particular, the transmission blocking band of inverse hyperbolic tangent apodized MFBGs can open up a number of narrow windows with high transmissivity, an inverse hyperbolic tangent apodized MFBG can be used as a comb filter.Secondly, the influence of introducing the Lorentzian function, rise cosine function and Gaussian function perturbation to the magneto-optic coupling coefficient on the linear transmission spectrum and the nonlinear bistable characteristics of MFBGs is investigated numerically. The nonlinear optical transmission of the guided optical waves in the MFBGs is investigated numerically. The origin of the bistability and multistability is the magneto-optical nonlinearity existed in the MFBGs. It is shown that the magneto-optical nonlinearity characteristics lead to specific multistable transmission patterns and the polarization states controlled multistability at constant input intensity. The magnetic field and the length of the MFBGs controlled multistability are also demonstrated at constant input intensity.Thirdly, based on the linear coupled mode theory of the MFBGs and Fiber Bragg Gratings (FBGs), by using the transfer matrix method, the transmission of sectional MFBGs and FBGs is investigated numerically. The transmission blocking band of differently sectional MFBGs and FBGs can also open up multiple transmission windows.