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建立了双平衡式外差探测IQ解调的数学模型,通过旋转λ/4波片来改变IQ信号间的相位差。从本振光强度过剩噪声、散粒噪声和热噪声三个方面对平衡式外差探测系统的信噪比(SNR)进行了仿真。仿真结果表明,当旋转λ/2波片使分束比在(0～0.272)和(0.728～1)范围内时,单源探测信噪比比平衡式探测的信噪比高;而分束比在(0.272～0.728)时平衡式探测的信噪比高于单源探测。搭建了2μm双平衡式外差探测实验系统,当分束比为0.5时,平衡式外差探测的信噪比比单源外差探测的信噪比提高10dB以上,从而证明了双平衡式外差探测系统在微弱信号检测中的可行性和优越性。
A mathematical model of IQ demodulation for double balanced heterodyne detection is established, and the phase difference between IQ signals is changed by rotating the λ / 4 plate. The signal-to-noise ratio (SNR) of balanced heterodyne detection system is simulated from three aspects: local light intensity excess noise, shot noise and thermal noise. Simulation results show that single-source detection signal-to-noise ratio is higher than that of balanced detection when rotating the λ / 2 waveplate so that the splitting ratio is in the range of (0-0.272) and (0.728-1) The SNR of balanced detection is higher than that of single source detection (0.272 ~ 0.728). A 2μm double-balanced heterodyne detection system was set up. When the splitting ratio was 0.5, the signal-to-noise ratio of balanced heterodyne detection was increased by 10dB or more compared with that of single-source heterodyne detection, Feasibility and Superiority of Detection System in Weak Signal Detection.