Research On Technology Of Microwave Photonic Filter

Microwave photonics is a combination of microwave technology and optical technology.Compared with traditional electrical technology,microwave photonics technology has the advantages of large bandwidth,tunable,small volume,low energy consumption,and anti-electromagnetic interference.Microwave photonic filter technology is one of the key techniques of microwave photonic signal processing,it has the incomparable advantages in the frequency tuning and bandwidth reconfigurability compared with traditional electrical filter technology,and has great application potential in the field of radar,reconnaissance and communication.This paper mainly focuses on the microwave photonic filter with time-delay structure,and the main work is as following:Firstly,the research background of microwave photonics and the significance of microwave photonic filter are introduced,and the research status of microwave photonic filter is summarized.The main devices related to microwave photonics filters are introduced,and their related characteristics and working principles are described.Then commonly used modulation methods are deduced and analyzed theoretically based on relevant modulators,including double-sideband modulation,single-sideband modulation,suppressed-carrier double-sideband modulation and suppressed-carrier single-sideband modulation.In addition,several typical microwave photonic filter schemes are studied,and their working principles,advantages and disadvantages are analyzed theoretically after introducing the principle of microwave photonic filter.Secondly,a microwave photonic filter scheme with variable coefficients based on PM and Sagnac loop is proposed and experimentally verified.The center frequency of the filter can be tuned,and the positive and negative coefficients can be switched by tuning the optical tunable delay line(OTDL)and the polarization controller(PC),which makes the filter more flexible in practical application.In addition,the scheme is relatively simple and easy to implement because it doesn't need bias control.In the experiment,the response of the microwave photonic filter with positive and negative coefficients is verified when the free spectrum range is 0.8 GHz and 1.18 GHz respectively.Finally,a microwave photonic filter scheme with complex coefficients based on dual-polarization modulator is proposed,which solves the problem that the pass band shape changes when the positive and negative coefficient microwave photonic filter tunes its center frequency.Besides,the scheme can not only realize the microwave photonic filter with complex coefficients,but also achieve the phase shift,the frequency conversion of RF signals,and suppress the clutter signals of other frequency in the frequency conversion process.In the simulation,we verify the phase shift of 10 GHz RF signal in the range of 0-360°.By adjusting the OTDL,we verify the response of the microwave photonic filter with complex coefficients when FSR are 200 MHz and 400 MHz respectively.The tunability of the center frequency is verified by adjusting the PC.The frequency conversion of 1.8 GHz and 2.4 GHz signal is realized by using 10 GHz local oscillator signal,and the signal of 1.8 GHz is suppressed more than 30 dB.