The Study Of A Microwave Photonic Filter Based On Stimulated Brillouin Scattering

The filter is an important component in signal processing, however, the requirements of high speed and broad bandwidth signal processing are becoming desperate in recent years with the increasing communication capacity. It’s undoubted that this becomes a great challenge to the traditional electronic filters. Microwave photonic has attracted the researcher’s attention with the merge of microwave communication and fiber communication. It has the advantages of low loss, broad bandwidth, immune of electromagnetic interference and the reconfigurable capacity. Thus it has been attractive in microwave signal generation, transmission, amplitude and phase controlling and filtering.etc. It also becomes an effective way to solve the microwave signal processing problems by flexible tunability and reconfigurability.This paper analyze the application of SBS effect on microwave photonic filtering both in theoretical and experimental based on the study of SBS effect in optical fibers. The filter takes great advantage of the combination of phase modulated signal and dual-sideband suppressed-carrier pump. This filter enables the realization of an ultra-wide and continuous tuning range,single bandpass and narrow bandwidth to be obtained. It also advanced in the following points:(1)Maintaining the frequency stability and suppress noise interference caused by different optical carrier of the signal and pump wave;(2)The signal wave is modulated by the phase modulator while the filtered electronic signal is detected in the photoelectric detector by the interference of sidebands and carrier;(3)This filtering system not only realizes the ultra-narrow filtering function in optical field but also can be reconfigurable of the filtering bandwidth.This paper including four parts:Firstly, a brief summarization of microwave photonic filtering method and the application of SBS have been presented. Secondly, a close attention has been paid to the SBS theory including physical process and couple-wave equations. And a mathematical module has been built to describe the interaction of pump, acoustic and Stokes waves. Thirdly, an introduction of the filtering system used in this paper has been proposed. And this part also focus on the theoritical analyses of filtering bandwidth, source of the sideband noise, out-of-band rejection ratio (OOBR) and influencing factor of the threshold. Finally, researches have been carried out to verify the theory. The effects of pump and signal power levels to the3dB bandwidth have been analyzed experimentally. And the results have demonstrated that the filtering bandwidth varies from15to41MHz by changing the pump power, and the bandwidth is almost immune to the signal power. The reconfigurable ability of3dB bandwidth has been tested by broadening the pump spectra with BPSK noise of20MHz-40MHz. The results illustrates that the filtering bandwidth is changing with BPSK noise bandwidth when the pumper is not very high. Above all, the preliminary work in this paper can give helpful suggestions on designing and optimizing of the SBS filtering system.