Design And Realization Of Optical Fiber Dispersion Measuring Instrument Based On Time Delay Method

At the advantage of large communication capacity and small signal interference,optical fiber communication has been rapidly developed and applied.It has become one of the most important means of communication in the field of Communications Today.However,due to the complexity of the signal components transmitted in the optical fiber,the light in different mode and frequency is dispersed due to different propagation speeds,causing the distortion of the transmitted signal and affecting the bandwidth.Therefore,it is necessary to measure the dispersion of light.In this paper,we design a optical fiber dispersion measuring instrument based on time delay method to measure the dispersion and bandwidth of multimode fiber.The measuring instrument firstly produces a narrow pulse with a width of about 5ns.Then,it uses the narrow pulse to modulate the laser to generate an optical pulse.After that,it inputs the optical pulse to the multimode optical fiber.Finally,the light receiver converts the optical signal output from the optical fiber into electrical signals to measure.By comparing the broadening of the input and output pulses,we can measure the dispersion and bandwidth of the transmission fiber.In this paper,we firstly analysis the principle and type of fiber dispersion,simulate the transmission of Gaussian pulse in the fiber,explain the principle of delay measurement of multimode fiber dispersion,and modularized design the measuring instrument.Then,we designed each module specifically.In the module of narrow pulse modulating,we experiment on three kinds of generating circuits,and finally choose the crystal oscillator and high-speed NOR gate to generate the narrow pulse.In the light emission module,we analysis the performance of the semiconductor laser diode and the laser module,and design the temperature control circuit and the power control circuit to ensure the stable operation of the laser.In the optical receiving module,we analysis the performance of the photodiode and the optical receiver,and design the optical receiving circuit to amplify the signal.The measurements show that the multimode optical fiber dispersion measuring instrument can effectively measure the dispersion and bandwidth of multimode fiber.