为了优化微波光子下变频的无杂散动态范围, 结合带反馈控制的强度调制器和相位调制器, 提出并验证了基于强度和相位级联调制的微波光子下变频方法。通过理论推导和仿真分析了下变频原理以及本振功率对系统性能的影响, 搭建了强度-相位级联调制的微波光子下变频系统, 利用自行研制的直流偏置反馈控制模块确保强度调制器的工作状态稳定, 对系统进行了性能测试。实验结果表明, 增益和无杂散动态范围分别为-6.65 dB和108.62 dB/Hz2/3, 与传统的强度调制器级联下变频链路相比, 增益和无杂散动态范围分别提高了3.56 dB和19.87 dB。基于强度和相位级联调制的下变频方法仅需要单个偏置电压, 且可通过反馈模块实现工作状态的稳定控制, 系统结构简单、性能稳定, 可实现大动态范围的微波光子下变频。

In order to optimize the Spurious Free Dynamic Range (SFDR) of microwave photonic frequency down-conversion, a microwave photonic down-conversion method based on intensity and phase cascaded modulation was proposed and verified by using a Mach-Zehnder modulator (MZM) with feedback control module and a phase modulator (PM). The principle of frequency down-conversion and influence of power of local oscillator on system performance were derived theoretically and analyzed in simulation. The MZM-PM cascade microwave photonic down-conversion system was built, in which a self-developed DC bias feedback module was applied to enable the MZM at a stable operating state. Then the performance of system was tested experimentally. The results demonstrate that the gain and SFDR are -6.65 dB and 108.62 dB/Hz2/3 respectively, which have been improved 3.56 dB and 19.87 dB respectively compared with the conventional MZM-MZM cascade down-conversion system. In addition, microwave photonic down-conversion method based on intensity and phase cascaded modulation only requires a single DC bias voltage, and the stability of operating state can be controlled by the feedback module. The system can offer microwave photonic frequency down-conversion in high dynamic range with a simple structure and stable performance.