The Study And Analysis Of Polarization Effect In Single-mode Fiber

One of the most serious limits to high bit-rate optical transmission systems is polarization-mode dispersion (PMD). PMD arises from the perturbations that are unavoidably induced in a real fiber by the production process and the external environment. Segment-dividing model is appropriate for research on PMD. Mathematical deduction is made to change it into iterative model. It is easy to find the new model gives clear meaning in physics and reveals the process of PMD accumulation in fiber. It is applicable for being transplanted to analysis on PMD. Theoretic analysis gives the reason for error in Numerical calculation.Iterative model can be attained by concatenated model and is applied to analysis on first order PMD. It is pointed out that some problems should be paid attention to in the simulation. Second order analysis on PMD is made on the basis of first order. Numerical simulation shows the method is clear and brief. It provides direct technique for research on the two orthogonal parts of second order PMD. Statistical calculation accords with theoretical result.In numerical model for PMD research, the number of the whole segments N and the length of each segment L are basic parameters, which affect the randomicity of PMD. The choice on them is complex. Analysis is given on randomicity of PMD on the basis of the basic concatenated model in this paper, and it is pointed out that treatment for N and L determines the analytic result. By analysis and exploration on the choice of these two parameters, it is found that appropriate N and logical L are very important in PMD modeling and determines the distributing character of first-order PMD. Numerical simulation shows the character of parameters is the decisive element in concatenated model. On the other hand, the concatenated model shows character of randomicity and this element should be taken into account for analysis on character of probability for PMD. Simulation results show randomicity of first-order PMD, which is laid out by the three orthogonal parts. On the basis of first order, calculation for second-order PMD is put in practice. Simulation results tally well with theoretic curve. It is known second-order can be decomprised of two orthogonal parts: parallel part and vertical part. Simulation for the two vectors is given, which guides analysis on the character of probability for second-order PMD comprehensively.Polarization dependent loss (PDL) is the other limit to optical communication system. Interaction between PMD and PDL affects performance of communication system. On basis of characteristic transfer matrix of PMD and PDL, analysis and simulation is executed on the interaction between PMD and PDL. Results show that increase of PDL can change the value of PMD in single direction. The value of PMD may increase or decrease. But affected PDL shows complex relationship with PMD according to variational value of PMD: while PMD increase, the value of PDL fluctuates.Measurement of polarization mode dispersion is one of the most popular topics. On the basis of Poincarésphere, theoretical analysis is given on the measurement of second order PMD. Research shows that error in measurement of first order PMD influence second order. While the effect of PDL is weak and can be neglected, a new polarization-mode dispersion measurement technique is described that allows the determination of second order PMD (SOPMD) vectors in optical fibers. SOPMD can be directly measured, not derived from first order PMD. If the effect of PDL should be taken into account, a generalized method is provided to measure the DGD. The algorithm requires the launch of three polarizations per wavelength and uses large rotation angles as well as interleaving to attain low-noise high-resolution PMD data. On the other hand, we derived the equation for measurement of PDL and obtained an easy method to measure PDL. The measurement process is fast.Questions discussed above are focused on the domain of frequency. However on the domain of time, a combination of PMD and PDL in optical fiber may lead to anomalous pulse broadening. It raises the issue for more complete assessments when studying the pulse propagation in the presence of polarization-dependent loss. A mathematical description is put forward to including the effect of PMD, PDL and chirp. Simulation shows the delay of a chirped Gaussian pulse depends not only on PDL, but also on the chirp of the pulse itself. To some degree, effective PMD can be controlled by PDL and chirp.At last, we discuss the conception of DOP and method of depolarization. In a non-depolarizing optical system, Mueller-Jones matrix can be used to describe the relation between input Stokes vector and output Stokes vector. However, even if the input light is quasi-monochromatic, effect of depolarization can not be neglected in practical optical fiber system. Mueller-Jones matrix should be modified to have the depolarizing effect included. The newly formulated equations are generalized for input light with arbitrary degree of polarization in optical fiber system where effect of depolarization is seriously considered.