Study On Electric Field Sensor Based On Phase Modulation And Demodulation

The electric field intensity is the basic physical parameter describing the electromagnetic phenomenon.The research on measuring the electric field is an indispensable requirement in all fields of the research field.The measurement of highfrequency and high-frequency transient electric fields becomes more and more important with the development of high-voltage engineering,electromagnetic pulse technology,and high-energy physics.Compared with the methods realized by electricity in the past,optical realization of electric field detection take the advantage of small volume-,light weight,wide responding bandwidth and insensitive with the electromagnetic interference.So many of mature methods based on integrated optical modulator for electric field sensing have emerged.However,the traditional integrated optical electric field sensor is usually based on the structure of the Mach-Zehnder interferometer and there is a problem of the operation point drift due to the external disturbance.Although many solutions for operation point drift have been proposed,including real-time detection of the device output power,temperature,etc,and then introducing DC bias voltage compensation or using unbalance M-Z fiber interferometer structure.But the former will introduce the disturbance to the detected field while the latter will increase the complexcity of the sensing system.In view of this,this dissertation aims to eliminate the drift of the operating point of the MZI electric field sensor,introduces the electric field sensor capable of responding electric field information in an electric field environment to achieve phase modulation,and uses the unbalance fiber Mach-Zehnder interferometer for phase demodulation.This scheme separates the modulation and demodulation.Only the phase modulation is realized in the electric field environment,and the demodulation part is placed outside the electric field,so that the sensor design is flexible,and the demodulation scheme can be selected according to the specific situation.The main contents in this dissertation are as follow:1.Analyzing and studying the causes of operating point drift of the traditional integrated optical electric field sensor.2.Theoretical analysis and derivation of the modulation and demodulation of the phase modulation signal are carried out.The reason that the phase modulation signal can not be directly detected by the photodetector is explained,and the demodulation scheme of the signal is proposed.The overall scheme is mathematically deduced and verified3.The phase signal is simulated by simulation software.The difference of phase modulation signals with different full width at half maxima and different periodic frequencies and the need of different phase modulation signals for filter performance are summarized.The feasibility of the whole scheme is theoretically analyzed by software.The results verify the feasibility of the scheme.4.In the experiment,the antenna is used to receive the external electric field information and then modulated on the phase of the optical signal.Then,the asymmetric MZI filter formed with different lengths of fiber is used to demodulate the phasemodulated signal,and the result is analyzed by an oscilloscope.The electric field sensing at the MHz level is experimentally demonstrated and the sensing range of the proposed electric field sensor is experimentally investigated,which prove the feasibility of the proposed scheme.Finally,the optical power and electric field frequency that affect the experimental results are analyzed.