Research On Microwave Photonic Filter Technique Based On Multi-wavelength Optical Source

Microwave photonics is a new interdisciplinary subject that is infiltrated and closely integrated with microwave technology and fiber technology.The basic concept of microwave photonics is to use optical methods to generate,transmit and process high frequency microwave signals.Microwave photonic filter is an important research direction of microwave photonics.It uses photonic devices or optical subsystems to perform the same processing functions as traditional microwave filters,not only overcomes the "electronic bottleneck" problem in traditional filters,but also has the advantages of high bandwidth,low loss,light weight,anti-electromagnetic interference,etc.Meanwhile,it has good compatibility with optical fiber transmission systems.Microwave photonic filter has been widely used in the fields of Radio over Fiber systems,radar systems,optical phased array antennas,universal mobile communication systems and digital satellite communication systems.In recent years,it has become a research hotspot in the field of microwave photonic signal processing.This paper focuses on microwave photonic filtering technology based on multiwavelength light source.The main contents include the following aspects:(1)We have introduced the research background and research significance of microwave photonics and microwave photonic filter,classified microwave photonic filter according to the differences in structure and performance,introduced the application fields of microwave photonic filter in detail,and summarized the research status of microwave photonic filter at home and abroad.(2)We have elaborated the mathematical model of the microwave photonic filter,theoretically analyzed the working principle of the microwave photonic filter based on phase modulation,and introduced the main performance parameters of microwave photonic filter,which lies the theoretical foundation for the subsequent research work.(3)A tunable and reconfigurable microwave photonic filter based on multi-wavelength fiber laser is proposed.An erbium-doped optical fiber amplifier and a semiconductor optical amplifier are cascaded to generate a hybrid gain,and a Sagnac loop is used as a frequency selective device.Then,a stable multi-wavelength laser output can be obtained,which serves as the optical tap of the microwave photonic filter.By changing the length of polarizationmaintaining fiber in the Sagnac loop,the wavelength spacing of the multi-wavelength laser output can be changed,thereby achieving the tunability of the free spectral range of the microwave photonic filter;in addition,by changing the bias current of the semiconductor optical amplifier,the number of laser lines is altered,thereby achieving the reconfigurability of the passband bandwidth of the microwave photonic filter.In summary,the designed filter exhibits good tuning and reconfigurability characteristics.(4)A switchable microwave photonic filter based on broadband source slicing is proposed.Firstly,the in-line birefringence fiber filter or the reconfigurable Lyot loop is used to slice the spectrum of the broadband source independently.Combining with photonic devices such as phase modulator and dispersion compensating fiber,a single passband microwave photonic filter or a switchable dual passband microwave photon filter can be generated,respectively.Next,the spectrum of the broadband source is sliced by cascading the in-line birefringence fiber filter with the reconfigurable Lyot loop.By adjusting the polarization controllers in the two stage slicing devices,the spectrum of the sliced broadband source exhibits different periodic characteristics,corresponding to the microwave photonic filter with different number of passbands.The experimental results show that the frequency response of the microwave photonic filter can be switched in four states: single-passband state,dual-passbands state,triple-passbands state,and quadruple-passbands state.The microwave photonic filter obtained in the experiment shows good filtering performance,and the switching between the passbands is flexible and stable.