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Study On The Cross-section Structure Information Extraction Of Actual Microstructured Optical Fiber And The Characteristics Of Ultra-short Pulse Propagation

Posted on:2017-05-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:J S LiFull Text:PDF
GTID:1108330503982344Subject:Condensed matter physics
Abstract/Summary:PDF Full Text Request
Due to the flexible structure design, photonic crystal fibers have many excellent properties(such as: highly adjustable dispersion and high nonlinearity), which opens a new chapter in the field of the nonlinear fiber optics. While, in the process of drawing the optical fiber, due to the gravity, drawing temperature control, drawing speed and other factors, the collapse and position deviation of many irregular air holes frequently appear in the cross-section of MOF. The traditional modeling method tends to be helpless in the face of these MOFs, and that make it more difficult to obtain the characteristic parameters of fibers and further reveal the nonlinear mechanism while the pulse transfers in the MOF. An integration scheme to exact, process and modeling the cross-section of MOFs is proposed based on digital image processing technique, which can provide the structure of fiber completely loyal to the actual structure. On this basis, the numerical simulation for the MOF manufactured by laboratory is done. The nonlinear phenomena while the femtosecond pulses are pumped at the normal-dispersion regime is explored by experiments, and the special nonlinear mechanism is revealed. The main contents are described as folowes:Firstly, in view of that the actual cross-sections of MOFs are complex, the noise sources are wide diverse and so on, we propose a set of solutions based on digital image processing technology. It is widely applied to the “weakening” treatment of the common noise in the MOF cross-section image, which is convenient to obtain the ideal treatment effect image and thus providing the structural modeling with the complete loyalty to the physical features for the applying of the finite element method. Specifically, Butterworth high-pass filter and threshold processing method are successfully introduced into the cross-section image processing scheme. The multi-parameter combined setting method is provided to optimize the treatment effect in the scheme. It provides a perfectly reasonable possibility for handling complex images and a good compatibility to process all sorts of images taken by different types of microscopes. The evaluation criterion of image processing effect is given. Furthermore, it provides the comparison between the original image and the superposition of the holes edges after processing and the original image, these further improve the evaluation intuition of the processing effect and the accuracy of the modeling of the cross-section. The effects of selection of the thickness of perfect matched layer and curve fitting conditions on the dispersion coefficient simulation are also analyzed in this paper. Extracting the cross-section structure to model and simulate the dispersion coefficient of the sample fiber, after comparing with the experimental data, the verification shows that the simulation and experiment are in good agreement, which proves the method to be high effective and scientific reliable. The result show that, not only in the high adaptability to deal with the cross-section image of optical fiber from wide sources or high tolerance to image complexity, but also in the treatment effect of high evaluation and accuracy, our scheme has obvious advantages.Secondly, experimental study is made for the MOF manufactured by laboratory while femtosecond pulses pumping at normal-dispersion regime far away from the zero dispersion wavelength. It revaels the soliton effect mechanism that when pumped pulse at normal-dispersion regime and discovers the Four Wave Mixing(FWM) effect caused by negative fourth-order dispersion. The characteristic parameter of the MOF is obtained by simulation, and then the numerical simulation and theoretical analysis are made on the experimental phenomena, further compared with the experimental phenomena in the references. At last, we reasonably explain the formation mechanism of each wave band. The study shows that the soliton effect and FWM can generate by pumping the normal-dispersion regime in MOFs. The FWM is is dominated by negative fourth-order and negative sixth-order dispersion which is satisfy the noncomplete phase matching. This provides an important evidence and implementation idea for the rational use of the nonlinear effect of micro structure optical fiber. At the same time, through the contrast study, the influence of the sign change of the third-order dispersion on the direction of the dispersive wave is deeply analyzed.Finally, we reported that the FWM induced by three-order dispersion can generated with femtosecond pulses pumped at 0.822 μm by a home-made solid-core silica-based MOF with a simple structure in experiments. The fiber characteristic parameters are obtained by the extraction technology for the information of the cross-section MOF in our paper. Based on the simulations of FWM phase matching curves, the variation curve of time domain amplitudes in the different dispersion orders along with the transmission distance, and the output spectrums with the Pump operating at zero dispersion wavelength and at anomalous-dispersion regime, it is proved that FWM can also be induced by the third-order dispersion under certain conditions, a conception of stimulated FWM effect is proposed in this paper. This is not only the experimental proof of the theoretical derivation by J.Santhanam and P.Agrawal Govind, but also the subversive understanding and recognition about traditional mechanism of FWM effect germination. Research is very meaningful for the in-depth understanding of the nonlinear effects in MOFs, actively carrying out the frequency shift, the development of fiber lasers and other works.
Keywords/Search Tags:microstructure optical fiber, digital image processing, cross-section structure extraction, finite element method, phase matching, four-wave mixing, optical soliton
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