Research On The Spectral Characteristics Of Sampled Fiber Bragg Grating

A fiber grating is a new type of optical devices emerged in 70ths of the 20th century. It has played a key role in various fields of optical fiber communication, optical fiber sensing and optical information processing. Because it has many advantages such as small bulk, low cost, low insertion loss, good filtering performance and easy connection and compatibility. With the further research, in addition to uniform Fiber Bragg Grating (FBG), we also found a variety of fiber grating in different structures. In particular, Sampled Fiber Bragg Grating (SFBG) is attracting people's attention in recent years. This is because the sampled grating has excellent wavelength selectivity and it's reflective spectrums have multiple channels, the spaces between the channels are stable, the bandwidths are narrow. These advantages make the sampled grating has a broad application prospects in the all-optical communication network.Based on SFBG, this thesis discusses the various grating parameters affect on the spectral characteristics of SFBG, and launch an in-depth research on the optimization of the reflection spectra. Meanwhile, it also proposes a new type of the grating re-exposure technique. The main works are as follow:1. This dissertation introduce the development of optical fiber communication and the basically theory of Fiber Bragg Grating. Meanwhile, the theoretical analysis of fiber Bragg grating, such as Coupling Mode Theory (CMT), Transfer Matrix Method (TMM) and Fourier Transform Method (FTM), were deduced in details.2. According to the CMT, this thesis have researched the spectral characteristics of uniform fiber Bragg grating, and have verified the rules how grating length & coupling coefficient influence the reflective spectrum.3. The effect of Rectangular SFBG's grating parameters on reflective spectrum was analyed. Parameters include the reflective index modulation amplitude, sampled period and sampled rate.4. This dissertation proposed and studied an optimization, which was to eliminate the side lobe interference, on the reflective spectrum of the rectangular SFBG by using the apodization function. Additionally, it also summed up the best range of the apodization coefficient and the advantages and disadvantages of the apodization. Apodization function include: Gauss apodization, Hamming apodization, Sinc apodization, Blackman apodization, etc. On this basis, we selected three apodization functions to optimization the reflective spectrum of 8-channel and 16-channel Sinc SFBG, and summed up the best range of the apodization coefficient.5. According to the phenomenon of missing orders, this paper proposed and studied the re-exposure technology of fiber grating. This technology's basic principle was written another section grating, whose sampled period and center wavelength of the grating can be changed, on the non-exposed areas of the same SFBG. After the numerical simulation analysis, the rules how the written location, duty cycle and center wavelength influence have been got. The purpose of this method is to increase the number of channels, improve the efficiency of grating, so as to establish the foundation for research on application of multi-channel filters of SFBG.