ROF链路噪声对单频信号相噪的恶化

Effect of additive noise on signal phase noise in radio over fiber links

通过研究光载射频链路(ROF)中系统噪声对射频信号相位噪声的影响,建立了输出信号相噪的理论模型并进行了实验验证。理论模型表明:当输入信号射频信号一定时,链路噪声越小,信号的相噪越难被恶化。实验验证表明:通过加大探测器的平均光电流能显著降低系统的噪声系数,优化射频信号相噪指标。当探测器的平均光电流由0.15mA增加到6mA时,系统的噪声系数可从55dB下降到25dB;2GHz的射频信号相噪在10kHz频偏处从-83dBc/Hz下降到-120dBc/Hz。在ROF通信链路中,为降低射频信号相噪的恶化,在调制器正交偏置的情况下应加大探测器的平均光电流。

The effect of additive noise on the signal phase noise in radio over fiber(ROF) links was studied and the theory model of the output signal phase noise was proposed.The theory model was verified by experiments.The model shows that in the fixed input-RF signal,it is difficult for the phase noise to be degraded at the condition of small noise figure in ROF links.In experiments,the noise was measured by using the spectrum analyzer and the phase noise was measured by the signal source analyzer.Results show that the signal phase-noise performance decreases due to increasing the average photocurrent of the photodiode.When the average photocurrent increases from 0.15 mA to 6 mA,noise figure decreases from 55 dB to 25 dB and the phase noise decreases from-83 dBc/Hz to-120 dBc/Hz at the offset frequency of 10 kHz.In practical applications,in order to reduce the deterioration of reference′s phase noise,it is necessary to improve the average photocurrent when the electro-optic modulator works at quadrature points.