SNR enhancement for single-photon heterodyne detection via phase pairing and balanced differencing

Single-photon heterodyne detection offers ultra-high detection sensitivity at the photon level but is extremely sensitive to noise in weak echo environments, which severely limits the improvement of signal-to-noise ratio (SNR). Among these, phase noise is particularly critical, as the induced phase fluctuations directly weaken the efficiency of coherent signal accumulation and become the core bottleneck restricting system performance. To address these issues, this paper proposes a balanced differential algorithm and conducts experimental verification from two dimensions: 1) Time-domain phase compensation path: Directly invert the initial phase of the signal to construct a virtual reference signal with the opposite phase to the original signal, and cancel phase noise through differential operation. 2) Inter-frame phase pairing strategy: Pair and differentiate signal frames with a phase difference of in full-frame signal processing to suppress noise and enhance signal coherence. Both simulation and theoretical analysis demonstrate that the proposed algorithm can effectively enhance the SNR of heterodyne detection signals, verifying the feasibility and superiority of the scheme.