Research on roughness estimation using phase noise of single-photon heterodyne detection

Phase noise exerts a significant influence on the performance of single-photon coherent heterodyne systems and can severely degrade the system signal-to-noise ratio (SNR). This paper first analyzes the characteristics of intrinsic system phase noise (clock jitter) and phase noise induced by rough targets. Under a homologous clock configuration, the system is only affected by radio frequency (RF) random jitter and chopping random jitter, with the initial phase fluctuating around a constant value. In contrast, a heterologous clock configuration leads to phase noise originating from RF time-base error, RF random jitter, chopping time-base error and chopping random jitter, resulting in initial phase characteristics of both random jitter and linear drift. The phase noise caused by rough targets is a superposition on the basis of the intrinsic system phase noise; accordingly, the relative roughness of targets can be inverted by the fluctuation characteristics of the initial phase. Both simulation and experimental results verify a positive correlation between the fluctuation degree of the initial phase and the roughness of the target. In practical measurements, the standard deviations of phase residuals are 1.3 rad for the reflective tape, 1.8 rad for the mirror, and 11.3 rad for the diffuse reflectance panel.