Electro-optic Device's Simulation And Analysis Based On Finite Element Method And Wave Coupling Theory

Linear electro-optic(EO)effect plays an important role in the field of electric field sensor,and also used in optical communication,laser Q-switch and light deflector.Optical voltage sensor(OVS)is one of the trends of intelligent voltage sensor.Simulation is an efficient means in the process of designing EO devices.We discuss BGO crystal's half wave voltage(HWV)and temperature characteristic,and the electric field's inhomogeneity of OVS based on finite element method(EFM)and coupling wave theory.Such works as follow have important significance for OVS's designing:1)A universal simulation method is proposed,which is applicable to any three dimensional electric field,optical propagation direction and electro-optic crystal.The magnitude and direction of E on the light propagation path in BGO crystal is calculated with EFM.We segment the optical path till each section's electric field is uniform,then calculate the EO effect value of each section with the wave coupling theory's Jones matrix.The output value of OVS can be obtained by multiplying these Jones matrixes.2)The influence of crystal-cutting and light propagating direction on BGO's HWV is studied.More than three times HWV's value can be obtained when the normal direction s1 and s2 of crystal-cuttings are[-0,219,0.219,±0.951]and[1/?2,1/?2,0]respectively.And about 10 times HWV's value appears when the direction angle a and ? are both ±0.4? approximately.These efforts will provide a new way for changing crystal's HWV.3)Influence of temperature and intrinsic birefringence on the OVS's accuracy is discussed.The temperature characteristic of BGO crystal is independent of light propagating direction.The effect of temperature on EO modulation is linear,and 1%error to the sensor is brought by 30? temperature variation.Based on polarization interference of birefringence crystal,0.066°/cm of the intrinsic birefringence is obtained,which brings 0.5%error to the OVS.Taking 50?-90? temperature change into account,1%error appears,which cannot be ignored on the accuracy of OVS.4)The inhomogeneity of the electric field in the sensor is illustrated.Take the simplified structure of the electrode for example,the characteristic of inhomogeneity in the BGO crystal is discussed,and the optimization design for better-distributed electric field in BGO crystal is achieved.Using the simulation method presented in this paper,the influence of the optical path's deviation on the OVS's transverse modulation of the non-uniform electric field is analyzed quantitatively.The error caused by the path's deviation in vertical direction is greater than the one in horizontal direction.For example,the error of 6.05%is brought by ±1 mm path shift and 2.87%by ±0.1 rad a change in vertical direction.At last the maximal shifts of optical path allowed on different accuracy levels of OVS are given.