Research On Fiber Low-Coherence Interferometry And Its Application

The research on fiber low-coherence interferometry (LCI) is originally for measuring the Rayleigh backscatter and for characterizing the loss and locating the defect of optical fiber, and is gradually transferred to other technical fields. Deliberate investigation of various key techniques of LCI makes profound sense for its generalization and application.Chirped fiber Bragg grating (CFBG), a passive fiber element formed by producing in the fiber core a periodic index micro-disturbance, has a broad application prospect for the chromatic dispersion compensation of optical communication systems. For this reason, it is of specific importance for the chromatic dispersion characteristic of CFBG to be measured with high accuracy.Focusing on the characterization of the dispersion of CFBG, this dissertation researches theoretically fiber LCI, especially concerning with the shape and the widening of the LCI interferogram obtained during the measurement of the dispersive medium; researches the noise of fiber LCI system and its suppression; designs and sets up a fiber LCI system for measuring the dispersion of CFBG, and by using of this system, completes measurement experiments and data manipulation. Distinguished and creative achievements of the dissertation are concluded as:1,According to partial coherence theory and Fourier Transform Optic Spectrometry, researches theoretically the fiber LCI technology for the characterization of the dispersion of CFBG, analyzes the relationship between the widening of the LCI interferogram obtained during the measurement of the dispersion of CFBG and the dispersion mechanism of CFBG, and for this purpose, builds a model for simulation calculation;2,Performs theoretical analysis to the noise of fiber LCI system, pointing out that, in the cases of the spectrum characteristics of two interference arms being seriously mismatched, the beat noise is not negligible and is the dominant noise component, accordingly, proposes and implements a method for matching the spectrum by way of a tunable fiber filter to suppress effectively the beat noise;3,Designs and sets up a fiber LCI system for the characterization of the dispersion of CFBG, which system features large OPD (optical path difference) scanning range, high frequency domain resolution, high measurement speed, high accuracy and low cost, with the repetitiveness of the group delay of CFBG being 5ps and the relative accuracy better than 5%, and, analyzes the measurement error of the system.Finally, the contents of the dissertation are summarized and the directions for further endeavor are provided.