High-speed Polarization Control In Optical Fiber And Polarization Encoding Communication

Polarization effect is a nonnegligible problem in the field of fiber technology.On the one hand,a large number of polarization problems in fiber system,for example, polarization dependent loss,polarization mode dispersion(PMD),depolarization,ect., become very serious,which result in the degradation of system performance and become a main bottleneck for rate upgrade of high-speed fiber communication systems. On the other hand,the advantages of polarization effects in high-speed optical signal processing impel various novle technologies develop rapidly such as polarization optical switch,polarization optical encoding,polarization optical logic,ect..Whether for solving the polarization problems or application of polarization effects,polarization control is a key technology.High-speed polarization control can quickly compensate the massive polarization dependent damages in fiber systems,and greatly improve the system performance,while ensure the performance of high-speed polarization related devices,which is one of the core research issues in the field of fiber technology.Encoding format is a difficult problem for 40Gb/s and above high-speed fiber communication.In the communication systems with present encoding formats,the bit rate upgrade to 40Gb/s gives rise to intensive damage of signal by nonlinear effects, while causes double increase of PMD penalty,serious deterioration of signal-to-noise ratio,and lower spectrum efficiency.Therefore looking for new encoding format becomes an urgent task in present high-speed fiber communications.Polarization encoding is a novel format and has more advanges such as natural power equalization, better polarization characteristics,less power penality,and so on,which can greatly reduce the nonlinear effects,suppress the PMD,and improve the spectrum efficiency,so its realization will accelerate the development of high-speed fiber communications.In this dissertation,based on detailed investigation of various polarization effects in the fiber and communication systems,including properties of polarization controller and semiconductor optical amplifier(SOA),under support of the "863" project and the National Nature Science Foundation,high-speed fiber polarization control and polarization encoding communication with the signal source are deeply researched, while a few kernel technologies are proposed,then the high-speed polarization control and polarization encoding communication are demonstrated experimentally.The main innovative achievements of this dissertation are presented as following: 1.Based on polar decomposition of Mueller matrix,the polarization effects in the fiber and SOA are investigated in detail,and a precise differential rotation method is proposed to obtain the PR or birefringence vectors,which is applicable to long time measurement of fiber in complicated environment with great perturbation,therefore greatly improves the precision and anti-interference capability of Mueller matrix method.Furthermore a practical parameter model is established which can describe three kinds of effects including polarization rotation(PR),polarization dependent gain, and polarization independent gain in the SOA,while it is successfully used to obtain the necessary conditions for SOA-based orthogonal PR(OPR),and to solve the problems in the applications of SOA-based polarization rotation.2.A theoretical approach is proposed to compute the stress function and its distribution in the circular single mode fibers(SMFs) under press,and the analytical solution of stress distribution is obtained for the fiber and core,while the elastic deformation and limitation of pressure stress have been discussed in detail.Then the stress birefringence is gained for circular SMFs by vector perturbation approach,and the theoretical result is proved by precise experimental measurement.Moreover the functional relationship between press vector(magnitude and direction) and birefringence vector is studied and disclosed,while a fiber-based sensing method is presented which can obtain not only the magnitude but also the direction of press.3.A generated concept of principal state of polarization(PSP) is introduced to analyze the elastic-optic effect in the fiber caused by PZT squeezing,and then the concept of multicomponent PSP is proposed,while the PSP model which describes the output state of polarization function with relation to driving voltage is obtained for the piezoelectric polarization controllers(PPCs) with two and three units,thus an open-loop high-speed polarization control method is proposed,which improves the control speed of present PCs to 2～3 order of magnitude and reach the microsecond magnitude. Furthermore a high-speed polarization state generator is demonstrated experimentally based on 3-unit PPC.The method of open-loop high-speed polarization control is appraised as "great work" by commentators of "Optics Letters".4.A new method of optical pulse differential is proposed based on cross polarization modulation of the SOA,and then it is demonstrated for extracting the pulse front edge by single-side differentiation and both edges by double-side optical differentiation.Thus a high-speed all-optical differentiator is implemented based on double-side differentiation,where the differential signal is much shorter than that obtained by SOA's cross gain modulation.Furthermore based on double-side differentiation,the low-rate clock of 5 Gb/s is successfully multiplied up to 40Gb/s,and then a high-speed signal source is achieved.The SOA-based double-side all-optical differentiator is appraised as "a novel technology" by commentators of"Optics Letters".5.A novel scheme of digital polarization encoding is proposed based on orthogonal polarization rotation(OPR) of the SOA by optical pump control,and the experiment of 12.5-Gb/s polarization encoding communication is successfully carried out with differential polarization decoding receiver.The polarization shaking of output signal from the SOA in polarization encoding is observed by experiment,and the pump wavelength with the highest efficiency for OPR is obtained,while a power equalization method is presented to overcome the influence of cross gain modulation.By numerical simulation of the polarization encoding transmission in 40 Gb/s single channel and 4×40 Gb/s multichannel fiber communication systems,where it is convinced that the polarization encoding communication employs less transmission power then overcome the nonlinear effects in the fiber and greatly reduce the bit error rate.The method of polarization encoding bansed on OPR of the SOA is appraised as "a significant contribution" by commentators of "Optics Letters".