High performance heterodyne detection of weak optical signals using photon-correlated beams

Sheng Feng, Kaikai Wu

Cross correlation heterodyne detectors exhibit the potential for suppression of the detection quantum noise below shot noise without use of optical squeezing for capturing weak optical signals in low frequency bands. To understand the underlying mechanism, we develop a quantum theory to describe the noise performance of cross correlation heterodyne detectors. By calculating the cross spectral density (CSD) of the photocurrent fluctuations from a cross correlation heterodyne detector, we prove that its noise performance can break the shot noise limit and exceed that of a regular heterodyne detector for detection of coherent light. When the detected light signal is in a squeezed state, we show that the corresponding CSD value is negative and discuss how a negative CSD may be explored to improve the output signal-to-noise ratio of the detector contaminated by classical noises through tuning the parameter of the degree of squeezing. This work may find itself useful in space-based gravitational wave searching and a variety of other scientific research activities, such as observation of vacuum magnetic birefringence and telecommunications.

Boya Xie, Dechao He, Peng Yang +1 more

Hongzhou Dong, Mingwu Ao, Xianming Yang +1 more

By constructing an experimental system, the heterodyne detection of the photon counting system is realized. The effects of photon counting rate, sampling rate, background light noise and beam mismatching angle on the single-photon heterodyne detection performance based on power spectrum averaging are studied experimentally. The results show that the power spectrum average results have a saturated signal-to-noise ratio (SNR) at a certain count rate, and the saturation SNR increases with the increase of the count rate. As the sampling rate increases, a higher saturation SNR can be obtained. The local oscillator and signal light mismatch angles have the same effect on single photon heterodyne detection compared to linear detection. The research results in this paper have a promoting significance for the practical application of single-photon heterodyne detection technology.

David R. Selviah, Ricardo C. Coutinho, H.A. French +1 more

Changqing C. Cao, Xiaodong Zeng, Yili Zheng +2 more

A photorefractive adaptive optical heterodyne detection system is proposed. Its principle is introduced and typical numerical calculation is illustrated, which includes the reference beam output power and minimum detectable signal power versus system global power ratio, the effect of crystal coupling strength on reference beam output power and minimum detectable signal power, and the minimum detectable signal power versus nonlinear coupling strength. Several key factors which affect the system characteristics strongly are pointed out. In the proposed system, only one photorefractive crystal is used to attain optical heterodyne detection. The system features simple structure, low noise and high responsibility. It also answers two key questions of heterodyne detection: 1) phase distortion; 2) coherent length of light source.

Ichiro Sakuraba