Analysis Of Spectral Characteristics Of Long Period Fiber Grating And Its Application In EDFA Gain Flattening Equalizer

Long period grating is optical passive device, succeeding Bragg grating. Comparedwith Bragg grating, Long period grating has many different characteristics, so it cancompensate for the inadequacies of the Bragg grating in some aspects of the application.At present, long period grating is used to design a variety of spectral shape of the filter,thus, the transmission spectrum not only can be precisely controlled, such as resonantwavelength, bandwidth, peak and so on, but also can be devised varies kinds of spectrumshape, which is the base of the subject of my thesis.Firstly, transmission spectrums of long period grating are calculated theoretically bymatlab on the basis of coupled mode theory and transfer matrix method, and its variationswith the changes of the structural parameters are studied.Then, the transmission spectrums of non-uniform long period grating are calculatedtheoretically, the impact of structural parameters(phase shift position, phase shift quantity,change of average refractive index, phase shift magnitude) on the transmission spectrumof phase-shifted long period grating are discussed, and the variations of transmissionspectrum of cascaded long period grating are discussed, the formation of the interferencepattern is resolved, how to prevent the interference pattern is explained.Lastly, on the basis of analyzing the spectrum of long period grating, two EDFA gainflattening filters based on phase-shifted long period grating and cascaded long periodgrating are devised, Maximum fluctuation of flattened gain spectrum of EDFA does notexceed±0.7dB and±0.3dB in the range of 34nm, although the filter based onphase-shifted long period grating is not as good as the later, it has favorable marketprospects due to containing one device, small size and ease of manufacturing andpackaging.