Design Of An Electro-optic Modulator Bias Voltage Control Circuit

The distributed sensing system based on Brillouin scattering is a populartopic in the field of optical fiber sensing field. High quality and large extinction ratiooptical pulse is the key to obtain higher signal-to-noise ratio and longer measurementdistance. Mach-Zehnder electro-optic modulator based on lithium niobate (LiNbO3)materials is widely used in optical pulse modulation technique. It has manyadvantages, such as high speed, high extinction ratio, zero chirp, which has beenwidely used in the field of optical communication and distributed optical fibersensors. However, its internal double arm structure makes the working points driftingeasily at the influence of environmental factors, such as temperature and stress. Thequality decline of optical pulses will even lead to the failure of the whole sensingsystem. Therefore, the realization of automatic control of the operating point stabilityis very important in the practical application of electro-optic modulator. The biasvoltage regulation of electro-optic modulator to correct the operating point drift isstudied in this thesis. The main research contents include:1.The Brillo uin sens ing syste m and the importance of the electro-opticmodulator in the Brillouin sens ing syste m is introduced. The n the stud ies ofelectro-optic modulator controlling the working po int drift in recent years areemphatically discussed.2.The interna l structure working princip le and important parameters ofelectro-optic modulator is introduced. Then the work ing point driftpheno menon of electro-optic modulator and the selection of optima l workingpoint electro-optic modulator in the Brillo uin sensing system is discussed,which lays a theoretica l basis for the contro l o f e lectro-optic modulatorworking point drift.3.According to the working characteristic of electro-optic modulator bydetecting the slope of electro-optic modulator’s working point to monitoringworking point drift of e lectro-optic modulator is proposed. The hardware, software and of contro l syste m is b uild up and the contro l a lgorithm isrealized according to the design.4. Measurement of o f contro l s yste m of e lectro-optic modulator iscarried out. Extinctio n ratio and the qua lity o f the output pulse s igna ls ismeasured.