基于半导体光放大器的光载微波信号频谱分析基础研究

As the frequency of microwave is 3-5 order lower than that of lightwave, a broadband microwave signal in the electrical domain corresponds to a very narrowband lightwave signal in the optical domain. Therefore, it is very esstential and critical to realize a hyperfine analysis and processing of microwave signals in the optical domain, which is also a technology challenge with scientific and practical signaficance in the research field of microwave photonics. This project aims to propose and demonstrate a hyperfine frequency spectrum analysis for the photonic microwave signals with high subcarrier frequency and large bandwidth. In the case of frequency spectrum analysis, the all-optical frequency downconversion of the photonic microwave signal under test is realized by using the co-polarized dual-pump four-wave mixing in a single semiconductor optical amplifier and the frequency spectrum analysis is obtained from the down-converted immediate frequency signal with the help of a broadband balanced photo receiver and a standard electrical spectrum analyzer. In our research, the ultrafast theoretical model of the four-wave mixing of the SOA will be established firstly to investigate the feasibility of the all-optical frequency downconversion. Secondly, much attention will be paid to the key technology on how to obtain tunable photonic local oscillation, high efficiency frequency downconversion, and frequency response calibration of optical receiver. Finally, the optimization for the whole frequency spectrum analysis will be carried out, as well as the design of the integration solution. Our research covers the theories of the ultrafast semiconductor optoelectronics and the all-optical frequency conversion, which is believed to promote the technology of the hyperfine frequency spectrum measurement of photonic microwave signals, and to provide a useful reference for the photonic millimeter-wave or terahertz signal processing.

微波比光波频率低3-5个数量级，电域宽带微波对应光域窄带光波，在光域实现微波信号的精细分析和处理是微波光子学领域的技术挑战，具有重要的科学意义和应用价值。 本项目旨在提出一种面向高载频大带宽光载微波信号频谱精细测量新方法，拟利用半导体光放大器双平行泵浦四波混频效应进行光域频谱变换，全光下变频到中频，实现光载微波信号频谱分析。首先将建立基于半导体光放大器非线性四波混频超快理论模型，研究实现光域频谱变换的基本途径，其次研究利用半导体光放大器四波混频效应实现光载微波信号精细频谱分析的宽带光学微波本振、高效频谱变换、探测器频响校准等关键技术及实现途径，然后完成频谱分析最佳工作性能的优化，探索集成光学解决方案。 研究方案具有创新性，研究内容涉及半导体超快光子学理论和光域频谱变换基础问题，研究结果将促进宽带微波光子信号高分辨率频谱测量技术的发展，并为探索光载毫米波乃至太赫兹波的分析和处理奠定基础。

本项目面向高载频大带宽光载微波信号频谱精细分析，对基于半导体光放大器四波混频光域频谱变换所涉及的宽带光学微波本振、高效频谱变换、探测器频响校准等关键技术进行了理论研究和实验验证。完善了半导体光放大器四波混频效应中的带间和带内载流子动力学模型，发现量子点半导体光放大器的增益饱和主要是由光谱烧孔引起，其增益恢复时间属于超快恢复过程；而体材料半导体光放大器的增益饱和主要还是超快的带内载流子-载流子散射引起的总的载流子密度的减少，因此体材料SOA的增益恢复主要由载流子复合寿命决定，是慢恢复过程，研究结果为揭示半导体材料中宽带微波与光波相互作用机理、解决微波信号光域频谱变换中的共性问题提供了理论基础。利用半导体光放大器级联四波混频效应实现了波长覆盖1550nm波段、频率步进12.5GHz、频宽162.5GHz的可调式光学微波本振，实验构建了光载微波的高效频谱下变换，信号带宽可达3.125Gb/s，频谱分辨率优于kHz。提出了外差谱映射方法，构造了极窄线宽、超高宽带的光激励源，对光电探测器的频率响应进行测试，频率分辨达到Hz量级，且无需校正光源的功率波动，真正实现高分辨率的自参考测量，而且具有倍频测试能力，这一测试方法为光探测器频率响应提供了追溯基准。项目资助期间，发表SCI/EI论文37篇，其中SCI论文20篇、二区论文12篇，申请专利13项，其中授权6项，项目组成员在国际会议做特邀报告9次。

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