Experimental research of low-noise and high-gain balanced detectors in the mHz-MHz band

Balanced detectors are fundamental components for the precise measurement of quantum state fluctuations, particularly quantum noise, which is crucial for future quantum-enhanced interferometric gravitational wave detectors utilizing squeezed light. Based on the transimpedance amplifier (TIA) model core to balanced detection, we conduct a detailed theoretical and practical analysis of the electronic factors influencing detector performance in the target ultra-lowfrequency band. The TIA stage was meticulously designed using a highperformance integrated operational amplifier characterized by low offset voltage drift. To ensure gain stability critical for ultra-low-frequency operation, the design incorporated low temperature-drift metal foil resistors. Subsequent voltage amplification was achieved using a noninverting amplifier configuration to attain the necessary high electrical gain while strictly managing overall electronic noise. Recognizing the criticality of common-mode noise rejection for quantum noise measurements, we analyzed and optimized the photodiode (PD) nonlinear response compensation mechanism. This was achieved through the innovative implementation of a differential fine-tuning circuit (DFTC) coupled with an adjustable bias voltage (ABV) compensation scheme. Experimental validation confirmed the effectiveness of the optimized design. The compensation scheme utilizing DFTC and ABV successfully achieved a high common mode rejection ratio (CMRR) exceeding 75 dB@500 Hz. Crucially, the detector achieves an electronic noise spectral density of 3.5×10⁻⁵ V/Hz1/2 within the 1 mHz–1 Hz band, surpassing the space-based gravitational wave detection requirement for laser intensity noise (1×10⁻⁴ V/Hz1/2). Furthermore, the detector demonstrated high gain capability and bandwidth: with an incident detection light power of 4 mW, the balanced detectors achieved a gain of 20 dB maintained across a wide frequency range from 1 mHz to 1 MHz. This work presents the design, detailed analysis, and experimental realization of optimized balanced detectors specifically tailored for high-sensitivity measurements in the millihertz gravitational wave frequency band. The achieved low electronic noise floor below 1 Hz and high CMRR fulfill the critical requirements for detecting squeezed states of light in future space-based gravitational wave detectors. This optimized balanced detector provides vital components and technical support for next-generation space-based gravitational wave detection and millihertz squeezed light characterization.