Research On Working Point Stability Of Integrated Optical Waveguide 3D Electric Field Sensor

The integrated optical waveguide electric field sensor based on the electro-optic effect of lithium niobate crystal has been widely used in the field of pulsed electric field measurement due to its advantages of small size,fast response speed,wide measurement bandwidth and strong anti-electromagnetic interference capability.But in the actual application process,the Mach-Zehnder interferometer electric field sensor based on lithium niobate crystal as the core material will cause the optimal operating point of the sensor to slowly drift due to changes in environmental conditions,such as temperature,humidity or pressure.The working point is the key to the measurement of the space electric field signal.It has a great impact on the detection sensitivity,linear dynamic range,and time-domain waveform of the system.Therefore,the working point of the sensing system needs to be controlled to make the device change in a complex The environment is stable in a state suitable for sensing.The thesis first introduces the structure,working principle,the influence of external factors on the drift of the operating point,and the basic theory of the elasticoptic effect of the integrated optical waveguide three-dimensional electric field sensor.Aiming at the problem of the drift of the operating point of the sensor caused by the change in the refractive index of the optical waveguide caused by the elastic-optic effect,the magnitude of the strain in the optical waveguide of the sensor was simulated and numerically calculated using COMSOL finite element software and the theory of the elastic-optic effect.The thermal stress at the interface of the buffer layer-lithium niobate substrate will form a complex strain distribution in the waveguide.This phenomenon will change the refractive index of the lithium niobate crystal and cause the sensor operating point to drift.Then,the lithium niobate substrate was calculated by Matlab The strain distribution of the optical fiber is analyzed,and the internal refractive index of the optical waveguide is analyzed with temperature to verify the simulation results.Finally,it was found that a buffer layer can be deposited on the bottom of the lithium niobate substrate to offset the stress in the top buffer layer.This measure can effectively reduce the stress in the waveguide and improve the working point drift.Besides,the operating point drift that occurs when an electric field sensor measures an electric field is a complex physical process,and it is not realistic to suppress the operating point drift only from within the device.Therefore,an external control method that tunes the wavelength of the light source can also be used to steadily adjust the working point,a three-dimensional sensor working point control system is designed,and the hardware and software implementations in the system are introduced separately.Besides,the transmission characteristics of the three-dimensional electric field sensor are tested,the best wavelength of the three-dimensional electric field sensor is found according to the test results,and the optimal wavelength selection algorithm is designed.Because the control system uses a pure light control technology,it will not interfere with the measured electric field.Finally,an experimental platform for the electric field sensing system was built,and the sensors were tested in the time domain,linear dynamic range analysis,and evaluation of the control capability of the control system.