我们理论上研究了基于热铷原子系综中的四波混频效应实现信噪比优化的系统。我们分析了非相敏放大器与相敏放大器中信号光信噪比的变化情况。在非相敏放大器中,信号光为相干态注入,闲置光为真空态注入,此时信号光在被放大的同时,信噪比降低,其噪声系数大于1。在相敏放大器中,信号光和闲置光均为相干态注入,此时在特定的条件下,信号光在被放大的同时信噪比得到提高,其噪声系数小于1。在注入光束间的相对相位=2 kπ(k为整数)时,信号光的有效增益最大且噪声系数最小。在这样的相对相位下,只要注入闲置光光强高于注入信号光光强的17.2％时,信号光就能够在被放大的同时信噪比得到提高。特别地,当注入闲置光光强同时低于注入信号光光强时,就实现了弱光对强光信噪比的优化作用。

We reseached a system based on four-wave mixing process in hot rubidium vapor to realize the optimization of signal-to-noise ratio (SNR). We also analyzed the change of SNR of signal beam both in phase-insensitive amplifier (PIA) and phase-sensitive amplifier (PSA). In PIA, the input signal was coherent state and the input idler is vacuum state and we find that the noise figure (NF) of the process was greater than 1, i.e. the SNR of signal beam reduces. In PSA, the input signal and idler were both coherent states and found that the NF of the process was less than 1 in some particular areas, i.e. the SNR of signal beam increased in the particular areas. The relative phase between input beams, the ratio of intensity of input signal and input idler, the intensity gain of rubidium cell were represented by ,β, G, respectively. We found that when =2 kπ(k is integer), the effective gain of signal beam was maximum and the NF was minimum. Under the condition of =2 kπ(k is integer), as long as the intensity of input idler beam was greater than 17.2％ of input signal beam, the SNR of signal beam increasesl in amplification process. Particularly, when the intensity of input idler beam was less than the intensity of input signal beam at the same time, the optimization of SNR of strong beams by weak beams was realized.