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Theoretical And Experimental Study On Thermal Poling Of Optical Fibers And The Poling Induced Second-order Nonlinearity

Posted on:2019-02-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:L HuangFull Text:PDF
GTID:1318330545952321Subject:Communication and Information System
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Silica glasses have a wide range of applications in electro-optical devices and silica fiber communications due to there excellent properties,such as low cost,low loss,high optical damage threshold etc.However,due to the macroscopic central symmetry of the materials,silica glasses and silica based fibers do not possess optical second and other even order nonlinearities.The technique thermal poling,which applies high voltage and high temperature to the materials could break the macroscopic central symmetry of silica glasses and introduce second order nonlinearities(SON).Generally,the mechanism of thermal poling is accepted as migration of charge carriers during poling,however,thermal poling in fiber is still in need of theoretical guidelines for interpreting the evolution of electro-optic coefficient during poling and its corresponding value after poling,revealing the detailed 2D electric field distribution inside and outside the nonlinear layer,and getting optimal ?(2)in different fiber and electrodes configurations,and more complicated models should be established to study the special phenomenon in thermally poled optical fibers.What's more,thermal poling induced SON is quite small which limits its performance in the application of opto-electrical devices,more works should be done in enhancing SON,designing new structures and finding new applications of thermal poling optical fibers.This thesis is devoted to study the poling induced charge dynamics in optical fibers,propose corresponding models,optimize thermal poling induced SON,simulate and experimentally characterize the poling process in new type optical fibers and find more applications of these kind of fibers.Major works and innovative results are summarized as follows:1.A 2D charge dynamics model for investigating the migration of charge carriers is proposed and validated.The simulated model results revealed the migration and distribution of charge carriers,nonlinear layers,demonstrated the evolution of thermal poling induced opto-electrical coefficient in fiber.The model provides theoretical guidelines for experiments and optimizing the poling results.Additional,simulated results reveal,for the first time,the evolution of opto-electrical coefficient after poling.2.Study on the transmission and poling properties in twin-hole optical fiber.Propagation and polarization dependent losses(PDLs),modal birefringence and the chromatic dispersion of the poling fiber with various fiber configurations are analyzed in detail.We revealed that a single polarization poling fiber with a length of a dozen centimeters could provide a high PDL(beyond 30 dB)and a low propagation loss(in the order of 1 dB).The choice of electrode material plays an important role for optimizing PDL and propagation loss of poling fiber.Based on these results,time evolution of nonlinear layer and SON in core region are investigated with various core-to-hole distances by using the 2D charge dynamics model,a large SON in core can be obtained by decreasing the anode-to-core distance.The influence of fiber configurations on transmission and poling properties can be effectively combined,and a single polarization poling optimized twin-hole fiber is proposed.3.Hindering effect of the core-cladding interface(CCI)in thermally poled optical fiber is investigated based on the two-dimensional charge dynamics model.It is found that lower mobility of charge carriers at the CCI is responsible for the hindering effect of the CCI.The hindering effect of the CCI could either be enhanced by increasing the mobility and concentration of charge carriers in the fiber core or be overcome by decreasing the mobility and concentration of sodium ions in the fiber core,which could increase the ?(2)in propagation mode,The results provide theoretical insight into the underlying mechanism of the hindering effect and may find applications in thermal poling optical waveguides and multilayered structures.4.A new model assuming a two-rate hydrogenated cations migration mechanism is proposed to explain the formation of the narrow SON layer in thermally poled silica fibers.This is technologically significant because of the possibility to highly localize the nonlinearity with the guided mode.Both the migration of H+ and H3O+ are taken into consideration.The H3O+ combines and dissociates with NBO-with a lower mobility,while the H+ hops between the H2O sites in the region where H3O+ has combined with NBO-,with a relatively higher mobility.Good agreement is obtained between the simulation results and the experimental observations.5.Second-harmonic generation(SHG)in double-anode thermally poled fibers is numerically investigated.The poling process is investigated based on a two-dimensional charge dynamics model.We show that SHG efficiencies of HE11,TM01 and HE21 modes are affected by ?(2)distribution in the fiber core,which can be deliberately designed by varying poling parameters.Efficient generation of the TM01 mode at second-harmonic(SH)could be achieved in symmetrically double-anode poled fiber,which provides an alternative method to obtain radial vector beams in compact all-fiber-based devices.SHG of HE11 and TM01(or HE21)modes could also be available at different wavelengths in a single asymmetrical double-anode poled fiber,which can be potentially applied in two-wavelength or ultrabroadband SHG.6.Tunable coupler based on thermally poled twin-core fiber(TCF)with a hole-core-core-hole configuration was proposed.The thermal poling process therein was investigated based on the 2D charge dynamics model.Effective ?(2)in the twin-cores pointing toward opposite directions were introduced.By subjecting the poled TCF to modulating voltage,the tunability of coupling ratio between the twin-cores was investigated.The results indicate that the coupling characteristics of thermally poled twin-cores could be controlled flexibly by modulating voltage,and consequently achieving a stable and highly compacted electrically tunable TCF coupler.7.We demonstrate experimentally poling?50 and?500 tin wire array fiber.The results show the?50 wire fibers are successfully poled such that all rings of wires develop SON layers,and the SON enhances with increased poling temperature.SON layers were also observed surrounding the outer rings of wires in the?500 wire fiber poled at lower poling temperature.The findings extend poling of fiber from two anodes to multi anodes.Our simulation based on a two-dimensional charge dynamics model reveals the charge migration process in the multi-wire fiber,the SON layers develop at the outer rings of wire at first,then the inner rings,and finally all wires are surrounded by an induced SON layer after sufficiently long poling time.This is in accordance with the self-adjustment mechanism in a two-anode poled fiber.Poled multi-wire fiber can be potentially applied for electro-optic modulation or frequency conversion,even a quasi-phase matched structure may be obtained by using the multi-wire glass material from the side if the wires are removed.In addition,these results may also open up possibilities for tunable metamaterials.
Keywords/Search Tags:Thermal poling, Second order nonlinearity, Charge carrier migration, Electro-optical modulation, Second harmonic generation
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