Research On Optical Fiber Sensing Technology Based On Microwave Photon Filter

With the rapid development of information technology,researchers have gradually used optical systems to process microwave signals,thus a new discipline--microwave photonics was born,which realized the interaction between microwave signals and optical signals.Microwave Photonics Filter(MPF)is an important research field of microwave Photonics.It mainly integrates optical devices and microwave devices to process rf signals in the optical domain.It features large bandwidth,high resolution,anti-electromagnetic interference,easy reconstruction and high sampling frequency.Among them,because of the tunable advantage of MPF,it does not change the structure of filter,but also can process microwave signals of different frequencies,which makes the application mode of MPF more flexible.At present,MPF has great application potential in military system,radar communication system and optical wireless communication system.Meanwhile,the application of MPF technology in the field of optical fiber sensing is becoming a new research hotspot.For example,the traditional based on Fiber Bragg Grating(FBG)sensors,such as temperature,tension,transverse stress measurements,the signal demodulation is usually use optical spectral analyzer(OSA)in optical domain,by monitoring the FBG wavelength with the temperature and stress changes by measuring sensor.However,the current commonly used OSA has a resolution of about 0.02nm,which is not high,thus affecting the performance of fiber optic sensors.It is well known that a small change in the length of light wave in the optical domain will cause a large change in the frequency in the microwave domain.In the microwave domain,the frequency of MPF can be monitored by using the microwave vector network analyzer(VNA).Since the electro spectrum analyzer has better resolution than the spectrometer,the sensor based on MPF can greatly improve the resolution of sensor measurement.The main research contents of this paper are as follows:(1)Firstly,the principle of MPF is studied deeply,the working principle of single source MPF and multi-source MPF is introduced,and several important factors affecting the frequency response of MPF are introduced,including tap number,weight coefficient and delay difference.This paper introduces several important performance indexes of MPF and the basic principle of two tapped MPF.The principle and main parameters of electro-optic intensity modulator are introduced.Finally,the temperature tuning and stress tuning of FBG are introduced,and the simple structure of FBG based MPF is introduced.(2)A high resolution fiber transverse load sensor based on MPF is proposed.Different from the traditional optical fiber sensor,this sensor uses the electrical spectrum analysis equipment instead of the spectrum analyzer,and the signal demodulation is completed in the microwave domain.The high sensitivity of 9.87MHz/N was obtained in the experiment,and the accuracy and stability of the lateral pressure sensing system were not easily affected by the ambient temperature and axial strain after the experiment.The transverse load sensing system is continuously tunable by controlling the magnitude of the lateral load applied to a polarization-maintaining fiber grating(PMFBG).(3)A high resolution MZI micro displacement sensor based on MPF is proposed.When the difference in the length of MZI's arms changes,so does the free spectrum range(FSR)of MZI,causing the central frequency of MPF to change.By detecting the MPF resonance frequency,the sensor system can obtain the displacement measurement with super high resolution.The high sensitivity of the sensor is 2.75MHz/?m.In addition,the sensor has good stability and reliability.