基于双环混频光电振荡器的可调谐微波频率梳产生

随着无线通信的速率提升和微蜂窝趋势，光载微波技术已经成为重要的发展趋势，而光生多载波系统是光载微波的最重要的技术之一.本文提出了一种基于双环混频光电振荡器（OEO）的可调谐光载微波频率梳产生方案，可同时实现多频段微波信号产生，从而高效低成本地为无线节点提供光生微波载波.方案采用混频双环OEO系统，通过工作在增益开关状态的直调激光器，利用其非线性动态特性产生多频率光载微波频率梳信号，并采用双路微波滤波器分别滤出两个相邻频率的微波信号，并利用二者的差频反馈注入直调激光器构成光电谐振.利用偏振双环结构抑制长谐振腔引起的边模问题，提高了输出信号的噪声特性.经过实验分析，得到了低相噪的多路微波信号，并最终实现了间隔797.4 MHz的稳定的微波频率梳信号，一阶载波相位噪声低于-101.7 dBc/Hz@10 kHz，-115.2 dBc/Hz@50 kHz.因此该方案产生的光载微波频率梳信号具有低噪声的优点，适用于光载微波通信系统.

Tunable microwave frequency comb generation based on double-loop mixing-frequency optoelectronic oscillator

With the development of wireless communication technology and micro-cell technology, optical-borne microwave technology, specially optical-borne multi-carrier technology has become one of the most important trends for generating high-quality sources. Therefore, the efficient generation of high-quality microwave signals has always been a requirement in wireless communication systems. Due to its low-noise and high-frequency output characteristics, photoelectric oscillator is widely used to generate high-quality microwave frequency sources in communication systems. Combining the advantages of photoelectric oscillator's low-noise output and direct-modulated laser's gain-switching state characteristics, a tunable optical-borne microwave frequency comb scheme based on dual-loop mixing-frequency photoelectric oscillator is proposed in this paper. And a direct-modulated laser operating in a gain-switching state is used to generate the original optical-borne microwave frequency comb signals. The dual-loop adjacent resonant frequencies are separated by two different high-frequency microwave bandpass filters. The beat frequency of adjacent frequencies mentioned above is injected back into laser to form photoelectric resonance, and thus enhancing the generated original optical-borne microwave frequency comb signals. To suppress the side modes caused by long resonant cavity, a polarized dual-loop structure is used in the system, and thus improving the noise characteristics of output signals. After experimental analysis, the dual-loop filtered resonant microwave signals and low-phase-noise microwave comb signals with a frequency interval of 797.4 MHz are all obtained. The microwave output side-mode suppression ratio after polarized dual-loop adjustment is improved to 47 dB. And microwave comb signal's first-order carrier phase noise is lower than-101.7 dBc/Hz at 10 kHz,-115.2 dBc/Hz at 50 kHz. In addition, higher-order carriers all come from the light multiplication of first-order carrier, they share the same low noise characteristics with first-order microwave comb signal. The output power of first-to-fourth, fifth-to-thirteenth order carriers are balanced to 10 dB by photoelectric resonance injection. And their side-mode suppression ratios are all better than 40 dB. Furthermore, theoretically, the comb interval can be adjusted to any frequencies by changing the center frequencies of two high-frequency bandpass microwave filters. Therefore, optical-borne multi-carrier microwave signals are generated efficiently and cost-effectively by this tunable optical-borne microwave frequency comb scheme, and the generated low-noise multi-carrier frequency sources meet the demand of an optical-borne microwave wireless communication system.