Design Of Aperdization For Fiber Bragg Grating And Study Of The Slow And Fast Light In Optical Fibers Using Acoustooptic Coupling Between Two Co-progating Modes

Optical fiber grating is one of the most important components in optical fibercommunication and sensing technology, with the advantage of simple structure, smallvolume, high wavelength selectivity, low weld wastage, full compatibility of fiber,can embed intelligent materials etc, and its resonant wavelength of temperature, strain,refractive index, density is sensitive, which has been widely used in frequencyselective of semiconductor laser, optical fiber laser reflector, WDM device in DWDMsystem, the dispersion compensation of high-speed optical communication, etc.Slow light effect is in the high dispersion devices and media that exist in a kindof abnormal physical phenomena. On the one hand, people use this kind of effect, canstructure optical fiber time delay device, light cache, etc., these devices will be thesolution to the path and the full optical fiber communication system and networkexchange problem at the core of the device.On the basis of the coupled-mode theory, the series of side-lobe in simulatedfiber grating reflection spectrum will reflect optical wave of useless band in theoptical communication and then influence the filtering performance. Opticalapodization can remove these side lobes for ideal reflex spectrum. In the paper, thetransmission matrix is introduced to study the influence of transmission characteristicsof FBG by different apodization functions.The mainly work of this thesis are focused on character analysis and optimized designof apodization for fiber gratings and study of the Slow and fast light in optical fibersusing acoustooptic coupling between two co-progating modes:The first part, we summarize the development, classification, applications in thefields of fiber communication system and sensor systems and fabrication of fibergratings.The second part, coupled-mode theory is introduced to understand the diffractionefficiency and spectral characteristics of fiber grating. Based on the transfer matrixmethod, fiber grating is divided into several section, the length of each paragraph is far longer than the original grating, and the refractive index of every section changesgently, we can get the total transmission matrix by multiplying each segment of thetransfer matrix.The third part, design of apodization for fiber grating: based on the theoreticalmodel above and simulation by MATLAB, we analysis the influence of reflectivespectrum of fiber gratings by change of grating length, refractive index modulationdepth, grating cycle. Optical apodization can remove these high reflectivity side lobes.The transfer matrix method can be used to simulate the reflection spectrum and timedelay in different apodization fiber Bragg grating function, which apodizationfunctions include: uniform P type, super gaussian, gaussian, cosine type, Tanh type,Hamming type, Blackman type, Cauchy type, Sinc type, and summarize the influenceof grating spectrum various by different apodization functions and parameters.The fourth part, we can draw the conclusion by the analysis of the apodizationfiber Bragg grating reflective spectrum: apodization can effectively suppress thesidelobes in the reflectivity spectrum. As a matter of fact side-lobe suppression willdeteriorate the band width and the steepness of the band edges. Different apodizationfunction has a different effect to the transmission properties of fiber grating. Wechoose the suitable apodization function and its parameters according to differentneeds. In a word, fiber grating get more extensive application after apodization.The fifth part, we prove that the two common kinds of fiber acousto-optic interactionwith transmission mode can be used to obtain the light of the delay, the single lightarea and two acousto-optic interaction area. We gave almost complete coupling,complete coupling, etc.