基于PDM-MZM的线性模拟光链路设计

The Design of Linear Analog Optical Link Based on PDM-MZM

模拟光链路因其大带宽、低损耗等优势,在宽带无线通信、多基地雷达、卫星载荷信号馈送、电子战存储转发中极具应用前景,成为了当前微波光子领域研究的热点。然而由于电光调制和光电探测的非线性,模拟光链路的动态范围受限。基于偏振复用马曾调制器的线性模拟光链路,通过改变两个RF信号的电功率比及两个子调制器的直流偏置点,可以分别改变调制指数比和光功率比,从而构造了两个相位相反的非线性失真信号以抵消链路的三阶交调失真,改善系统的无杂散动态范围。实验结果表明,与基于单个马曾调制器的常规链路相比,基于偏振复用马曾调制器的链路三阶交调失真被抑制33.7dB,无杂散动态范围提高17.6 dB,宽带射频信号的星座图和误差矢量幅度改善明显。

The key advantages of analog photonic links(APLs)include large bandwidth,low loss and so forth.Due to those advantages,APLs have attracted great attention in many applications in terms of broadband wireless communication,multi-static radar,satellite payload signal distribution,electronic warfare storage and forwarding,and thus become the research hotspot in the field of microwave photonics.However,owing to the nonlinear characteristics of the electro-optic modulator and photodetector in APLs,the dynamic range of APL is limited.Aiming at this problem,in this paper,a simple and linear APL based on a single integrated polarization division multiplexing Mach-Zehnder modulator(PDM-MZM)is proposed.By properly selecting the electric power ratio of radio frequency(RF)signals and dc bias angles in the two sub-modulators,the modulation indexes and optical power ratio are changed and thus two nonlinear distortion signals with opposite phases are constructed to cancel out the third-order intermodulation distortion(IMD3)of the link.Therefore,the spurious-free dynamic range(SFDR)of the system can be improved.Experimental results show that compared with the conventional link based on a single MZM,33.7-dB reduction of IMD3 and 17.6-dB enhancement of SFDR can be obtained.Also,the constellation diagram and error vector magnitude(EVM)of wideband RF signals are significantly improved.