Study On Spectral Characteristic Of Fiber Bragg Grating

Optical fiber Bragg grating is one of the most important equipments in fiber communication and sensing system, and is a very advanced project all around the world too. It can be used extensively in almost all the links of optic communication because it has many advantages such as low insertion loss, polarization insensitive, easy connection with fiber, controllable and dynamic, contact construction, easy to integrate etc. With the development of optic communication, not only the requirements for the resonant wavelength of the reflection spectrum, peak value and bandwidth will be stricter, but there is still a great deal of work to do about the spectrum analysis and improvement.Firstly, the development, classification and application of FBG have beensimply illustrated. Secondly, the Coupled-Mode Theory which is fit for the Bragg grating was derived from the wave equation and a simple but effective numerical method known as Transfer Matrix Method is also presented. And then, a very useful theory-Multiple Phase Shifts (MPS) theory is discoursed in detail. The reflection characteristic of rectangle sampled, Sinc sampled, Gauss apodized gratings with MPS have been calculated by using the Transfer Matrix Method, the analyzing and discussion were given in the end. Finally, a method for designing a broad spectrum multi-channel optical filter base on FBG is proposed. It was designed according to the practical demand in DWDM and with many different requirements, and the numerical simulation was shown in the end.The results of MPS theory in Sinc sampled grating and Gauss apodized sampled grating indicate that in Sine sampled gratings, the side-lobes and crossfire must be influenced by the index change. After using the MPS, the crossfire will be more severe. In Gauss apodized gratings, the extinction ratio and the ratio of bandwidth to channel spacing all will be changed with the parameter of G. After using the MPS, the change will be cuter.The designing of a broad spectrum multi-channel optical filter shows that the wave band of the reflection spectrum is widened and the channel number is multiplied. What's more, the spectrum flatness is improved with the increasing of refraction index change. Moreover, for the sake of improving the extinction ratio and peak value when MPS adopted in concatenated SFBG, an available designing method based on the cascaded unit is put forward and the optimized results are obtained.