Microwave Photonic Filter Based On Frequency Comb And Stimulated Brillouin Scattering

With the development of microwave communication, high frequency carrier andbroadband communications are required. However, owing to the limitation of electronictechnology, the circuit structure of traditional microwave filter is very complex andexpensive. Microwave photonic filter (MPF) is a product of the combination ofmicrowave technology and optical technology. Where the microwave signal is loaded inoptical carrier and then transferred back to electric domain by a photo-detector after theoptical-domain process. The advantages of MPF include high frequency filtering band,broadband, small size, electromagnetic immunity and easy access to the optical fiber,and the MPF even can realize some functions which are limited to traditional electronicfilter. In this thesis, a widely tunable and reconfigurable single pass-band microwavephotonic filter is theoretically analyzed and experimentally demonstrated based on thefrequency comb technique and stimulated Brillouin scattering (SBS). The contents ofthis work are as follows:Firstly, the mathematical model of microwave photonic filter using the opticalfrequency comb and stimulated Brillouin scattering was built and theoretically studied.The frequency comb and the Brillouin gain spectrum were studied and the Brillouinamplification transfer function of the frequency comb was deduced. To broaden thepass-band of the microwave photonic filter, the method of increasing the frequencynumber and frequency interval of the comb was proposed.Secondly, the microwave photonic filter based on the optical frequency comb andstimulated Brillouin scattering was established. The frequency comb spectrum, theBrillouin gain spectrum and microwave photonic filter pass-band were measured, andthe reconfigurable pass-band of microwave photonic filter was tested. The parameters ofmicrowave photonic filter pass-band including tuning range, shape factor and out ofband rejection were observed, and the characteristics of the microwave photonic filterpass-band such as the top fluctuation, ladder type amplitude and uneven bottom werediscussed. Factors including high-order sideband, pump power and vector networkanalyzer output power, which have influence on the out of band rejection, wereexplored.In the end, the experiment results show that the3-dB bandwidth of the MPF can bereconfigurable from34.5MHz to306.8MHz through changing the frequency numberand the frequency interval of the combs. By tuning the pump laser wavelength, a lagercontinuously-tuned range from3GHz to20GHz with a stable pass-band isdemonstrated, with the out-of-band rejection over40dB.