Study On Wideband Tunable Optoelectronic Oscillator Based On Stimulated Brillouin Scattering

With the development of microwave system, such as radar and satellite communication, the research of high frequency band, low phase noise and wideband tunable microwave signal source has received a great deal of attention. Optoelectronic oscillator (OEO) using microwave photonic technology to produce microwave signal, can effectively overcome the limitations in microwave frequency band and tuning flexibility of the traditional electrical technology based microwave signal source, and has a broad application prospect in high frequency, wide bandwidth microwave system.In this thesis, a wideband tunable OEO based on stimulated Brillouin scattering (SBS) is designed and experimentally demonstrated. The optoelectronic oscillation loop is constructed by putting the output RF signal of the SBS based filter system back to the electro-optic modulator, and incorporating the polarization multiplexed dual loop structure, It has the following advantages:(1) The frequency selection is achieved by using Brillouin scattering effect in optical domain, which has a narrow bandwidth (only 10 MHz) and avoids the electronic filter; (2) The frequency of the output microwave can be tuned in a wideband range by changing the wavelength of signal or pump light; (3) The polarization multiplexed dual loops, not only effectively suppress the side modes but also decrease the introduction of phase noise due to avoiding the active devices and the orthogonality of the two polarizations.Firstly, the background of microwave photonics and the research advance and applications of OEOs are summarized briefly. The second part focuses on the basic theory of OEO based on Yao-Maleki model, and the concept of oscillation mode, threshold condition, power spectrum and phase noise are explained by using mathematical deduction. The third part indroduces the principle of the wideband tunable OEO based on SBS, analyzes the wideband tunability of output microwave frequency. The phase noise characteristics of the OEO is investigated. The mathematical relationship between noise floor of the system and signal light power is established, while by using the Q value theory the relationship between the optical power distribution in the dual-loop structure and the phase noise of the system is explained.Finally, an experimental system of the OEO based on SBS is established, and the output spectrum characteristics, side mode suppression ratio and phase noise characteristics are measured and analyzed. In the experiment, the microwave signal output of stable single-mode oscillation within 2MHz span is obtained, and a wideband tunability of oscillation frequency from 4 to 16GHz is demonstrated. Measurement and comparative analysis of the signal phase noise at the different frequency, different signal optical power, different power distribution in the two loops. The results show that the noise floor of the system decreases when the signal light power increases. And the phase noise at 100 Hz to 50 kHz offset frequency is lower when the optical power is distributed more in the long loop, The research work gives a good foundation for the further optimization of the OEO performance.