Novel Multi-tap Complex Coefficient Microwave Photonic Filter

Microwave photonics is the fusion of microwave and optics which uses optical systems to process and transmit microwave and millimeter wave signals in the optical domain.Microwave photonic filter(MPF)is one of hotspots in the field of microwave photonics.Compared with the traditional microwave filter,MPF not only has characteristics of good anti-electromagnetic interference capability,low loss and strong flexibility in design,but also has no electronic bottlenecks.Positive coefficient MPF has a large limitation in practical applications because it is limited to low-pass filtering.In order to meet the needs of scientific research and technology development,the design of bandpass MPF has become a research hotspot.A reasonable choice of MPF tap sources can effectively improve the performance of filter.Cut broadband sources,laser array of multiple single-wavelength lasers,and multi-wavelength fiber lasers(MWFL)are commonly used as MPF tap sources.When tap sources of filter are selected as cut broadband source,the filter system introduces great noise;when the tap source is an independent laser array,the filter systems are more complicated and expensive;Quality of the light source will be improved,cost of the system will be effectively reduced when MWFL is selected as tap source.In this paper,a MWFL adopted high erbium-doped fiber is used as the tap source of MPF The stimulated Brillouin scattering(SBS)effect in quartz fiber is used to introduce a phase shift to realize the complex coefficient,and then a multi-tap complex coefficient MPF is designed.The magnitude of the phase shift amount can be controlled by adjusting the SBS pump optical power and the frequency detuning amount,so that the MPF center frequency can be continuously tuned.The effect of the tap source and SBS gain medium on the response characteristics of the MPF is studied when the tap source is a tunable multi-wavelength fiber laser signal.The main contents are as follows:1.Firstly,the mechanism of additional phase shift introduced by SBS effect in quartz fiber is deeply studied.The influence of SBS pump optical power and frequency detuning on the phase shift are discussed in detail.2.The SBS gain medium length,the wavelength interval of the tap source and the number of taps on the performance of the MPF are studied by simulated,in order to optimize the overall design of the complex coefficient MPF.3.The experimental platform of MWFL based on high erbium-doped fiber is built,and the main performance parameters of the laser are optimized.The stable multi-wavelength laser signal with wavelength interval of 0.338nm and 16 wavelengths are obtained through experiments.4.The multi-wavelength laser signal obtained in the experiment is used as the tap source.A multi-tap complex coefficient MPF is designed by using the phase shift produced of SBS.The performance parameters of different tap sources and different types of quartz fiber of complex coefficient MPF are studied by simulation.