Mechanism Analysis of Thermal-Induced Periodic Fluctuations in Electro-Optic Sensor

Electro-optic (EO) sensors have a wide range of applications in power systems, but their output stability is significantly affected by temperature, limiting their practical performance. To understand the temperature stability of EO sensors, this article experimentally studies the stability of Bi4Ge3O12 (BGO) and z-axis light-transmitting LiNbO3 (LN) sensors at different temperatures. It is found that both the static working point and the EO modulation signal of the sensors fluctuate periodically with temperature changes. The temperature period and fluctuation amplitude of the two sensors are different. We propose a mechanism for the periodic fluctuations in EO sensors. The EO crystal can be regarded as an optical resonator. The laser undergoes multiple reflections and transmissions at the two light-transmitting interfaces of the crystal, resulting in the actual output light being formed by multilevel transmission light interference. The optical thickness of the crystal resonator changes due to the thermo-optic effect and the thermal expansion effect under temperature changes, leading to periodic fluctuations in output light intensity. A mathematical model of sensor thermal periodic fluctuation is established. The calculation results agree well with experimental data.