Research On Three-dimensional Strong Electric Field Sensor Of Lithium Niobate Crysta

To detect any electric field in space,three-dimensional（3D）electric field sensor is needed to measure.However,the electrical 3D sensor and integrated optical waveguide 3D electric field sensor contain metal electrode,which will cause interference to the measured electric field and increase the measurement error.Separated electric field sensors do not have metal electrodes,but most of them are one-dimension and two-dimensional electric field sensors,which cannot simultaneously measure 3D electric field in space.Therefore,an all-dielectric lithium niobate crystal3D strong electric field sensor has been developed.（1）The 3D electric field sensor is studied theoretically.The phase difference of light passing through lithium niobate crystal is obtained by deducing the ellipsoid equation of refractive index of lithium niobate crystal under the condition that the applied electric field square is parallel to the axial direction of the crystal.Based on the theory of polarized light interference,the structure of one-dimensional electric field sensor is designed,and the principle of one-dimensional electric field sensor is derived,and the performance index of one-dimensional electric field sensor system is analyzed.Secondly,the length of lithium niobate crystal is designed by the sensor half wave electric field design.Based on the one-dimensional sensor,the structure of the 3D electric field sensor is designed,and the working principle of the 3D sensor is deduced.（2）The structure of the 3D sensor is designed,and the 3D sensor is fabricated.Based on the theoretical analysis of the half-wave voltage of the sensor,the length of the crystal is determined to be 42.2mm.To obtain high sensitivity sensor,the crystal with wide width and thin thickness is used.To suppress the piezoelectric resonance of the sensor,the trapezoidal crystal is used.Then the optical devices and packaging materials of the sensor were selected,and lithium niobate crystal was designed to complete the production of one-dimensional electric field sensor.The static operating point of the developed sensor isπ/2±0.117π.Based on the one-dimensional electric field sensor,three one-dimensional electric field sensors are designed with the measurement direction perpendicular to each other,and the packaging structure of the3D sensor is produced,and then the development of the 3D electric field sensor is completed.（3）The developed sensor is tested.Four one-dimensional electric field sensors are tested with power frequency strong electric field.The sensitivity of the crystal size 3×3×42.2 mm³（x×y×z）,the crystal size 6×6×42.2 mm³（x×y×z）crystal size and 3×18×42.2 mm3（x×y×z）is,respectively 0.243 m V/(k V·m^-1),0.758 m V/(k V·m^-1),0.150m V/(k V·m^-1)and 0.908 m V/(k V·m^-1),when the crystal thickness and length are constant,and the crystal width is increased from 3 mm to 18 mm,the sensor sensitivity is improved by about 3.7 times.When the crystal width and length are constant,and the crystal thickness is reduced from 6 mm to 3 mm,the sensor sensitivity is increased about 5 times.The test results show that the sensor with wide crystal width and thin crystal thickness has high sensitivity when the crystal length is constant.The minimum measured electric field intensity of sensor in time domain is 3.717 k V/m.Lightning pulse electric field was used to test the sensor,and the experimental results showed that:The piezoelectric resonance is suppressed by 60%using the crystal size 3×（1.5～18）×42.2 mm³（x×y×z）sensor compared with the crystal size 3×18×42.2 mm³（x×y×z）sensor.The trapezoidal sensor can be used in lightning pulse electric field measurement because of noise suppression.The frequency response test of the sensor shows that the trapezoidal crystal sensor fluctuates±7.5 d B in the range of 500 k Hz～1 GHz,and has a relatively flat frequency response.The minimum measured electric field is 1810.551d BμV/m in frequency domain of electric field sensor with crystal size of 3×（1.5～18）×42.2 mm³（x×y×z）.The stability of the sensor was tested by setting up a test platform.The test results show that the output optical power of the sensor fluctuates within the range of±3.8%at normal temperature.In the range of 0℃～40℃,the static operating point fluctuates within±11.6°.The sensor has good time stability and temperature stability.The experimental results show that the sensor is most sensitive to the electric field parallel to the y axis and does not respond to the electric field perpendicular to the x-axis.Therefore,the sensor is a uniaxial electric field sensor.The power frequency electric field testing system is used to test the omnitropy of the 3D sensor.The maximum error of measuring the electric field intensity is 4.6%,indicating that the 3D sensor has good omnitropy and can accurately measure any electric field in space.