Optical fiber dispersion measurement system based on frequency phase shift and its FPGA implementation

Optical fiber communication has been rapidly developed and applied because of its huge transmission capacity and minimumness transmission attenuation. However, due to the difference in frequency or mode of the transmitted optical signals, dispersion is very likely to occur, causing overlap between pulses, which leads to inter-code interference and affects the judgment of the adjudicator at the receiving end, thus reducing the capacity of communication. In this paper, a high-precision dispersion measurement system based on the clock phase shift method is designed to improve the measurement accuracy and reduce the cost of measurement. The design uses an XILINX's Spartan®-7 series FPGA (Field Programmable Gate Array) chip to achieve accurate measurement of phase difference between counting clocks. The overall modular design idea, using logic control, realized the data communication between modules and register read/write control, and completed the data acquisition and processing. The performance of the system is experimentally verified, and the experimental results show that the measurement error can reach ±500ps for the long-distance fiber of 81km.