基于线性光子鉴相器的宽带、大动态射频光前端技术研究

Radio-frequency (RF) front end digital receivers are essential tools for RF sensors and wireless communication systems due to their ability to perform complex algorithmic tasks on captured RF information. Owing to inherently large time-bandwidth products and attractive size and weight features, microwave photonics technology has long been recognized as valuable for its potential ability to extend sensing and signal processing performance and capabilities. However, traditional microwave photonic techniques have been unable to meet the high performance requirements of military RF systems due primarily to the low efficiency optical mixer and inherent nonlinearity of the transfer functions. After specifying the new requirements and challenges, in this project, two scientific issues will be mainly addressed. By reason of low energy conversion efficiency of optoelectronic mixer,the first aim of the project is investage the physical mechanism of RF/LO-IF energy conversion in optical spectrum domain.And the implement method of RF/LO-IF power linear and high efficient delivery is also reseached. The second major area of this project is the design and demonstration of a strictly linear optical phase demodulator to be used in conjunction with a linear optical PM transmitter. Furthermore, optical additional intensity noise, the non-ideal characteristics of the I/Q demodulation signals, and phase ambiguity problems in the architecture are considered and to be corrected based on DSP. Finally, the research is expected to provide important theoretical evidence and technical basis for future application of the military RF photonic front systems.

射频前端数字接收系统可将捕获到的射频信号转换至数字域，以便进行后续复杂的信号处理，是射频感知及无线通信应用中必不可少的设备。由于微波光子技术固有的大处理带宽及其在尺寸、重量上的潜在优势，一直被认为是推进射频信号感知和信号处理方面发展最具价值的潜在技术。然而，由于光域混频效率低下和系统固有非线性传递特性等缺陷，现有微波光子技术还远未达到军用射频装备的性能要求。基于以上新的需求和挑战，本项目将围绕两个方面的科学问题开展研究:第一，针对光域混频中能量转换效率低下的问题，探索光谱域RF/LO-IF能量转换的物理机制，并研究RF/LO-IF能量线性、高效传递的实现方法。第二，设计并研究用于相位调制架构中的线性光子鉴相技术。并着重探讨线性光子鉴相器中光电附加噪声抑制、非理想正交解调、鉴相相位模糊对线性鉴相的影响及改进方法。本项目将为射频光前端的发展和应用提供重要的理论依据和技术支撑。

射频前端数字接收系统可将捕获到的射频信号转换至数字域，以便进行后续复杂的信号处理，是射频感知及无线通信应用中必不可少的设备。由于微波光子技术固有的大处理带宽及其在尺寸、重量上的潜在优势，一直被认为是推进射频信号感知和信号处理方面发展最具价值的潜在技术。.射频前端中最重要的部分是频率变换，基于微波光子的变频方法已进行了大量的研究，但绝大部分是针对超外差结构的接收系统进行的研究。相比于超外差系统，零中频直接转换系统不存在镜像干扰的问题，简化了对放大器和滤波器的设计要求，尤其适合多频段、软件无线电系统中的应用。更重要的是，微波光子系统天然的端口隔离度高的特性，解决了零中频直接转换系统的核心瓶颈问题。同时，本项目利用IQ正交调制器实现了单边带抑制载波调制，相比于普通的马赫曾德型调制器省去了光滤波器的使用。.最后，为了验证射频光前端的应用价值，本项目进行了基于光子和数字结合的灵活有效载荷原理样机演示验证，验证了该样机将L、S、Ku、Ka不同频段上下变频至一个固定中频，以便后续的数字采样和处理，并同时利用光和数字结合的交换方式，实现了不同粒度信号的灵活转发，相比于传统的弯管转发方式具有更多的灵活性。该系统可提供频率规划灵活性和不同粒度信号转发的灵活性，是现有微波系统所不能实现的。