Direct and accurate measurement of insulator near-surface electric fields in gas-insulated equipment is critical for understanding charge accumulation and insulation failure

yet it has been technically challenging. Optical sensing technology is renowned for its high sensitivity

wide dynamic range

strong resistance to electromagnetic interference and high integrability

providing a new approach. This study developed an integrated optical electric field sensor (IOES) based on the electro-optic effect of thin-film lithium niobate. By coupling an auxiliary micro-ring on one waveguide arm

the linearity of the sensor exceeded 99%

the dynamic range surpassed 84 dB and the packaging size was optimised to the millimetre scale. A finite element simulation was conducted on the electric field distribution of a 126 kV cone-type insulator to verify the reliability of IOES measurement results through comparison. Experimental verification showed the consistency of the electric field distribution above the insulator with the simulation. The high-field section demonstrates high accuracy with an error margin of just 1.56%

whereas the low-field section shows some deviation due to simulation parameters and the calibration curve. These results indicate that this optical electric field sensor holds great potential for measuring electric field distribution inside electrical equipment.