Theory And Applications Of Fiber Gratings With Special Structure

With the rapid development of optical fiber communication systems, fiber Bragg gratings(FBGs) have become the key components in all-optical fiber communication technology and the hot topics in current international researches. As a new kind of optoelectronic device, FBG has brought a milestone revolution not only in optical fiber communication technology and optical fiber sensing technology but also in other related fields. Its market has expanded continuously in recent years. In order to improve the performance of fiber grating devices and develop new kind of fiber grating devices, this dissertation focuses on the characteristics of fiber gratings with special structures and their applications in dispersion slope compensations, fiber grating sensors and multiplexing technologies. Some creative contributions have been achieved as follows:1. Using the transfer matrix method (TMM), the reflections and group delay characteristics of 4 types of EIM-FBGs are completely simulated based on the coupled mode equations (CMEs) for EIM-FBG. The effects of grating length and apodization on the EIM-FBG are analyzed as well.2. The linearly effective index modulated uniform fiber Bragg grating (LEIM-UFBG) and the linearly effective index modulated chirped fiber Bragg grating (LEIM-CFBG) are fabricated experimentally by using amplitude mask and phase mask, and their spectral characteristics are analyzed. The experimental results have a good agreement with simulations.3. The characteristics of nonlinearly effective index modulated chirped fiber Bragg grating (NEIM-CFBG) are numerically investigated. A simple model used for calculating the group delay of NEIM-CFBG is proposed. The fabrication method of NEIM-CFBG and dispersion slope compensation scheme based on NEIM-CFBG are given.1. The FBGs with cavities are analyzed theoretically. Their transfer matrixes and reflectivities are showed. We simulate the spectral characteristics of FBGs with cavities and analyze their reflections using fast Fourier transform (FFT). We find that the mismatched Bragg wavelength between sub-gratings can affect the amplitude of Fourier peak-frequency.2. The optical spectra and the Fourier spectra of both FBGs with a cavity and FBGs with two cavities are investigated experimentally. The results agree well with simulations.3. The sensing mechanism of FBG with cavities in differential strain is proposed. The differential strain sensitivity and the effect of wavelength resolution on the demodulation are analyzed. The changes in the amplitude of Fourier peak-frequency and differential strain sensitivity under different wavelength resolutions are researched.4. A novel differential strain sensor based on FBG with a cavity is reported. The sensing signal is demodulated by the amplitude in Fourier domain. The proposed differential strain sensor is temperature insensitive and can be used for spectrally coded multiplexing (SCM) system.5. The SCM technology based on FBGs with a cavity for differential strain sensing is proposed and studied experimentally. We self-develop the demodulation software based on LabVIEW 8.0 and demultiplex the sensing signal. The standard error of measurement results is less than±8με. And we propose two effective methods for processing the crosstalk data from multiplexed systems.