Research On High ?² Themally Poled Fiber Based On Electrical Field Evolution

Currently,thermal poled technology is the most efficient way of breaking the macroscopic center of quartz glass,to induce the Second Order Nonlinearities(SON).Other poled methods,such as UV polarization,corona polarization and electron bombardment,are gradually eliminated due to their unstable SON coefficient and low repeatability.In recent years,optical fibers have developed rapidly own to their low insertion loss,low manufacturing cost and high optical damage threshold.Due to the third-order nonlinear characteristics,optical fiber has been exploited in optical switches,supercontinuum generation,and optical pulses.The themally poled optical fiber has second-order nonlinear effect,which makes them have great applications in soliton generation,Second harmonic generation(SHG),beat frequency generation and all-optical modulation.At present,the mechanism of thermal poled fiber is generally considered the carrier migration trapped in the fiber under the high temperature and high voltage.The induced internal electric field will be combined with the third-order nonliearity,which makes the fiber has the second-order nonlinearity.Based on the two-dimensional carrier dynamics model and the mechanism of the second-order nonlinearity,the factors affecting the second-order nonlinear coefficient of thermally poled fiber have been analyzed.The evolution of the internal electric field of the core relative to the electrode hole has been investigated under three modes of single anode,single anode-single cathode and double anodes.The numerical simulation demonstrates that the maximum second-order nonlinear coefficient can be obtained when the core is distributed at 30° relative to the electrode hole in the double-anode mode.According to this rule,a fourcore thermally poled fiber with a second-order nonlinear coefficient up to 0.46 PM/V has been proposed.Based on the periodic erasing by ultraviolet of the second-order nonlinearity,the first platform for periodically poled fiber grating in China has been illustrated.The second harmonic generation has been realized in the periodically poled fiber.In addition,the effects of temperature and grating period to the specifications of the periodic poled fiber gratings have been studied and optimized in this paper.The main work and the innovation of this paper are listed as follows:1.The development history and the mechanism of thermally poled fiber have been introduced in detail in terms of theory and application.The current structure of thermally poled fiber has been analyzed from aspects of the single core and dual cores.The factors influencing the SON coefficient have been illustrated,which foreshadows the design of thermally poled fiber with high SON.2.Based on the two-dimensional carrier dynamics model,and the second-order nonlinearity of the themally poled fiber has been numerically simulated.The mechanism of the second-harmonic generation has been explained in detail.The second-order nonlinearity of the thermally poled fiber could be periodically erased by ultraviolet.The principle of the periodically poled fiber grating has been introduced.3.Based on the finite element analysis,the evolution of the internal electric field of the fiber core relative to the electrode hole under three different methods has was proposed: the Anode-cathode,the Single Anode and the Double Anode.A four-core thermally poled fiber with high second-order nonlinearith has been designed and optimized.Considering that fourcore fiber structure may have crossover problem,the simulation also slove the energy distribution diagram of the fundamental mode,to verify that feasibility of the high-SON four-core thermally poled fiber.4.Based on the periodic erasing of the themally poled fiber by ultraviolet,the first platform for periodically modulating poled fiber grating in China has been first demonstrated.This periodic poled fiber grating is used to generate the second harmonic wave.