Basic Research On Broadband Photonic Microwave Phase Shifter Based On Stimulated Brillouin Scattering

Microwave phase shifters, which are used to control the phase of the microwave signals, have wide applications in the systems such as coherent detection and electro-optic sampling. In recent years, the high-speed development of the phased array systems requires its key component, i.e., the microwave phase shifters, with a higher performance such as broad bandwidth, large phase shift range, stable output, small volume and light weight. However, these requirements cannot be satisfied by the traditional electronic phase shifter. Photonic microwave phase shifters, which take full advantage of the broad bandwidth and the high speed of the photonic technology, are recognized as an effective technique approach to break the bottleneck of the electronic phase shifter, and have attracted much attention in recent years.In this thesis, broadband photonic microwave phase shifters based on stimulated Brillouin scattering (SBS) are researched. The amplitude-frequency and phase-frequency characteristics of SBS slow and fast light effects are researched in a single-mode optical fiber. A broadband photonic microwave phase shifter scheme based on Brillouin slow and fast light effect is proposed. The phase shift characteristic are theoretically analyzed and numerically simulated through establishing the mathematical model of this proposed scheme. In addition, the experiment platform is designed and set up. It is demonstrated that the proposed photonic microwave phase shifter can realize a full 360° continuous phase tuning in a frequency range of 100MHz-22GHz with a low power ripple. The main work and achievements are listed as follows:1. The performance of the microwave photonic phase shifters are researched based on the analysis of the phase shifter applications. Especially, the research status of the microwave photonic phase shifters based on SBS effect are researched.2. SBS effect in a single-mode optical fiber is researched, and the light-acoustic coupling equations of SBS in an optical fiber are deduced based on wave equations. Slow and fast light effect in a single-mode optical fiber caused by SBS are researched, and the amplitude-frequency and phase-frequency characteristics of Stokes light are analyzed.3. The combination of Brillouin fast and slow light effect in an optical fiber is researched. The amplitude-frequency and phase-frequency characteristics of the signal light are analyzed and simulated. Based on the analysis and simulation, a microwave phase shifter with broad bandwidth, large phase shift range and stable output is designed. The amount of phase shift is proved to reach 360° for 1-4 GHz microwave signals by experiments. Additionally, the phase shift performance of the phase shifter based on two methods (i.e., frequency and power tuning) are researched.4. The factors, which influence the phase shift in the photonic microwave phase shifter, are analyzed. The experimental results show that, in order to get an output microwave signal with a high signal-to-noise ratio (SNR) and a low power ripple, the vestige sideband suppression ratio of the SSB signal should be above 30dB, and the power of the signal light should be in the range of 1-2mW. In addition, the influence of optical fiber group velocity dispersion on the phase shift is analyzed, and the methods for reducing dispersion are researched. Finally, the influence of the light polarization on the phase shift is also studied.