相位调制微波光传输链路特性分析（特邀）

常规的微波光子系统采用强度调制方式实现微波信号的电光转换,由于调制器采用马赫-曾德尔干涉结构(MZI),系统性能不仅受到自身正弦响应特性的制约,而且需要进行偏置点控制,因此存在动态范围受限、系统控制复杂以及3 dB固有损耗带来的效率不足的问题,而采用相位调制可避免该问题。围绕相位调制光传输链路,为了完成相位调制信号的光电解调,文章提出采用薄膜滤波器通过边带抑制与边带选通两种方式实现相位调制到强度调制的转换,并分析了链路射频性能与器件参数之间的映射关系。实测对比了相位调制与常规强度调制链路之间的传输特性,通过分析可知,在相同链路配置条件下,相位调制链路具有更高的传输效率,而且光滤波带来的均衡作用,使得相位调制链路的3 dB带宽比强度调制链路大两倍。

Analysis on Characteristics of Phase Modulated Microwave Optical Transmission Link

Conventional microwave photonic link is realized by using intensity modulation method to complete the electro-optical conversion. Since the Mach-Zender interference structure (MZI) is used for the intensity modulator, the system performance is not only restricted by its own sine-like response characteristics, but also additional bias controller is needed to maintain the bias point. Hence the dynamic range is limited, and also 3dB inherent loss due to quadrature point will decrease the transmission efficiency. Phase modulation can avoid these problems. In this paper, two methods to convert phase modulation to intensity modulation by using optical filter through sideband suppression and sideband passing are proposed, and the relationship between link RF performance and device parameters is also analyzed. Finally, the performance between the phase modulated link and the conventional intensity modulated link are measured and compared. The results show that the phase modulated link has higher transmission efficiency under the condition of same link configuration, and the 3dB bandwidth of the phase modulated link is twice larger than that of the intensity modulated link due to the equalization effect of optical filtering.