Investigation On Mechanisms And Rules About Lapping & Polishing Process For End-faces Of Optical Fiber Connectors

Optical fiber connector(OFC)is the most typical optical passive device at present and its categories and structures are very rich.As optical fiber communication requires better quality devices,many problems about mechanisms and rules of lapping & polishing process for OFC manufacturing must be investigated more profoundly,and then make a breakthrough in the manufacturing technology of OFC.This dissertation was supported by NSFC key project "Sub-micron manufacturing theory and key technologies of Optical fiber devices".To address the problems about manufacturing process of OFC,the light-wave transmission and aberrance rules on the silica fiber link-interfaces and the lapping & polishing process for end-faces of OFC were investigated systematically by theoritical analysis,experimental study and finite element analysis,the syncretic models and numerical-value rules between optics theory and structure parameters,manufacturing precision and technologic parameters of OFC were established.The main innovative research works and conclusions are listed as follows:(1)Based on the optics theory,the mathematical models about optical performances of OFC and the air-gap between silica fiber end-faces. surface roughness,damaged-layer,were established.Results show:when the air-gap between silica fiber end-faces is eliminated,the damaged-layer of fiber end-faces induced by lapping & polishing process is the uppermost factor that counteracts improvement of optical performance of OFC,and restraining damaged-layer is an important approach for improving the optical performance of OFC.(2)The relationships between the lapping & polishing process for end-faces and optical performance of OFC were researched.After the endface geometry and surface quality of OFC were observed by interferometer,SEM,WYKO,the influence rules between the lapping & polishing process for end-faces and optical performance of OFC were summarized.Also,a group of optimal technological parameters of OFC end-faces lapping & polishing was obtained.The refractive indices and depths of damaged-layer were tested by ellipsometer,the refractive indices of damaged-layer increased about 4.4%,3%,2.5%comparing with the one of as-received silica fiber by lapping with 3μm,1μm,0.5μm diamond films respectively,and the depths of damaged-layer were about 0.167μm, 0.09μm,0.063μm respectively.The return losses by calculating according to damaged-layer were basically consistent with the ones obtained by return loss tester,which proved that the established models between optical performances of OFC and manufacturing process factors are correct.(3)The material removal modes of silica fiber during lapping & polishing the end-faces of OFC were studied.The matter of lapping process of silica fiber in plastic mode was found by indentation experiments,and according to the Bifano law,the critical cut-depth of brittle-plastic transition for silica fiber was calculated,namely, d_c=0.023μm;based on the Hertz contact theory,the calculation model of cut-depth which an abrasive imposed on silica fiber when the combination endface consisted of both ceramic ferrule and optical fiber machined by lapping process,was established,and the lapping process condition of silica fiber in plastic mode was obtained.The fiber surfaces topography machined by lapping process with different grain size diamond abrasive films were observed by SEM,it was discovered that there were 3 material removal modes when lapping silica fiber,namely,brittle-fracture mode, semi-brittle & semi-plastic mode,plastic mode.The experimental results reported here are consistent with the ones from theory analysis.(4)The changes on microstructure of the damaged-layer on silica fiber end-faces induced by lapping & polishing process were investigated, and the essential formation reason of damaged-layer was also discovered. Based on the infrared spectrum theory,according to the relationship between the wave number of infrared spectrum characteristic peak of silica fiber and the bond angle of Si-O-Si between the silicon-oxygen tetrahedron[SiO₄]cells,the mathematical models on the 1100cm^-1wave number of infrared characteristic peak and molecular volume,refractive index of silica fiber,were set up.The damaged-layer on silica fiber end-faces induced by lapping & polishing process were tested by micro infrared spectrum tester,comparing with the 1100cm^-1wave number of infrared characteristic peak of the as-received silica fiber,the ones of damaged-layer induced by various lapping & polishing process decrease, so,the bond angle of Si-O-Si of damaged-layer material decreases, accordingly molecular volume of damaged-layer is compressed,and the refractive indices of damaged-layer increase.The molecular volume compressing degree and refractive indices of damaged-layer nearly correlated with lapping & polishing process,from semi-fine lapping,fine lapping to waterish polishing,the molecular volume compressing rate of damaged-layer decreased from about 10%to about 5%,the increasing ranges of reractive indices of damaged-layer obtained by mathematical model were compared with the ones tested direct by ellipsometer,both were basically matched,which verified the accuracy of the testing models on micro-structure of silica fiber with infrared spectrum.(5)The yield criterion obeyed by silica fiber during lapping was researched,and the formation about damaged-layer on the silica fiber end-faces induced by lapping process was investigated by FEM.According to the deformation characteristics that there were plastic shear deformation and plastic bulk compression simultaneously on silica fiber end-faces during lapping,it was discovered that the yielding action of silica fiber is that both effective shear stress and bulk stress act together,and the elastic-plastic constitutive model of silica fiber to conduct the plastic bulk deformation induced by the bulk stress was established.Based on the back EULER law,the stress-update arithmetics of constitutive equations for silica fiber applied to lapping process were educed.The stress-update arithmetics were imported into ABAQUS(an universal finite element analysis software)through UMAT interface program,and the applied to the analysis of lapping course of silica fiber,simulating the formation about damaged-layer on the silica fiber end-faces.The simulating results of the bulk compressing rate and the depth of damaged-layer are found to be in good agreement with the experimental results,which proved that the established constitutive model of silica fiber can describe the real rule of lapping silica fiber process.The method can also provide some valuable reference for researching the quality of surfaces machined by plastic mode for other brittle material.The conclusions obtained in this dissertation can provide some valuable theoretic references for optical fiber devices design and manufacturing.It is also expected that the study can be benefit to the development of optical fiber devices.