A low-noise, high-SNR balanced homodyne detector for the bright squeezed state measurement in 1–100 kHz range**Project supported by the National Natural Science Foundation of China (Grant Nos. 11654002, 61575114, 11874250, and 11804207), the National Key Research and Development Program of China (Grant No. 2016YFA0301401), the Program for Sanjin Scholar of Shanxi Province, China, the Program for Outstanding Innovative Teams of

Abstract

We report a low-noise, high-signal-to-noise-ratio (SNR) balanced homodyne detector based on the standard transimpedance amplifier circuit and the inductance and capacitance combination for the measurement of the bright squeezed state in the range from 1 kHz to 100 kHz. A capacitance is mounted at the input end of the AC branch to prevent the DC photocurrent from entering the AC branch and avoid AC branch saturation. By adding a switch at the DC branch, the DC branch can be flexibly turned on and off on different occasions. When the switch is on, the DC output provides a monitor signal for laser beam alignment. When the switch is off, the electronic noise of the AC branch is greatly reduced at audio-frequency band due to immunity to the impedance of the DC branch, hence the SNR of the AC branch is significantly improved. As a result, the electronic noise of the AC branch is close to −125 dBm, and the maximum SNR of the AC branch is 48 dB with the incident power of 8 mW in the range from 1 kHz to 100 kHz. The developed photodetector paves a path for measuring the bright squeezed state at audio-frequency band.