Design Of Adaptive Equalizer Based On FPGA For Pmd In Optical Fiber Communication System

With the development of optical fiber communication systems which are large-capacity ,the polarization mode dispersion(PMD)is a big limitation for long-distance optical fiber transmission systems.The compensation technology in electrical domain can eliminate the inter-sysmbol interference caused by PMD with low-cost,and reduce the effect of the fiber non-linear,it can compensate adaptively. Modern FPGA families provide more I/O port and DSP arithmetic support with fast-carry chains that are used to implement multiply-accumulates (MACs) at high speed.So the DSP arithmetic in Parallel processing systems can be implement fastly on FPGA.Especially,some advanced chip provide the gigabit I/O which is used to receive signal of ethernet at high speed,as a result,it can be used to implement PMD electrical equalizer.In this article,MLSE equalizer is selected for PMD compentation in 10Gbit/s IM/DD system by the comparision among LE,DFE and MLSE. Histogram method is used as the channel estimate method by the analysis of optical fiber channel characteristics and the theory,the structure of MLSE equalizer.The branch metrics transforming from the channel estimating result is used as the input of viterbi decoder.And result of the decoder can be treated as the output of the equalizer.For the high transmission rate of optical fiber communication systems and the low processing speed of FPGA, the signal with PMD in 10Gbit/s IM/DD system is divided to 80 channels for parrallel processing in order to reduce the maximum freqence to 125MHz.Traditional MLSE equalizer is improved to the structure with parallel input and parallel output by pipelining technology for the parallel processing system. The MLSE equalizer is implemented on the chip of EP2SGX130GF1508C3 in Altera(?)StratixⅡGX family.The simulation implement by modelsim.The result shows that the equalizer is in stable performance,and the eye diagram height is obviously better than that before equalizing,as well as the Q factor.