This paper reports the performance of an AC-voltage sensor with a LiNbO₃ integrated retroreflective structure based on the Y-junction Mach-Zehnder interferometer. This structure is capable of realizing a low-cost sensor chip because of the small chip size and single optical-fiber connection. In the sensitivity and frequency response evaluation, detection sensitivities of 0.2mV have been measured with a frequency response from 10Hz to 2GHz. These measurement limitations were also analyzed theoretically and compared with the experimental results. This unique sensor enables precise voltage measurement in an EMI environment, even inside a computer.

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