Research On Optical Fiber Pressure Sensing Technology Based On Microwave Photonic Filter

In the 1950 s,one of the most important achievements in the field of electronics was applying microwave technology to the field of radar and communications,among which satellite communications were regarded as cutting-edge achievements.In the early 1960 s,laser technology came out.Regarding the problems encountered in communication and information science,people began to explore the combination of laser technology and microwave technology.The successful development of semiconductor device and integrated circuit is not only an important milestone in the field of electronics,but also a starting of photonic technology to mature.Owing to the boom of technology,researchers have begun to use the basic principles and techniques of photonics to solve the difficult problems in conventional electrical signal processing,resulting in a new interdisciplinary-microwave photonics.Microwave photonics contains many research directions,Among which microwave photonic filter is one of the important research fields.For the rate bottleneck problem existing in the traditional electrical domain,microwave photonic filter(MPF)offers a brand-new solution.The working principle of MPF is to modulate the input microwave signal onto the optical signal through the electro-optical modulator(EOM),The microwave signal is processed in the optical domain,and then the photoelectric conversion is performed by photoelectric detector(PD),at last,demodulated microwave signal is achieved which leads to the realization of filtering function.MPF usually has excellent characteristics that traditional microwave filters do not possess,such as wide bandwidth,anti-electromagnetic interference,and low loss.Therefore,it has great application prospects in the fields of RoF communication system and radar communication.At the same time,the optical fiber sensing technology based on MPF demodulation has also been highly valued by researchers.For the optical fiber sensor demodulation technology,if the microwave photonic filtering technology is used to convert the sensing information carried by the optical signal to the microwave domain for measurement,not only the measurement accuracy can be improved,but the demodulation speed can also be improved.The main research content of this paper is the research of optical fiber pressure sensing technology based on MPF.The structure of the paper is as follows:(1)The composition type,working principle and research status of MPF are introduced.Several core components of MPF,such as lasers,electro-optic modulators and photodetectors,are briefly analyzed,and their working principles and main parameters are discussed.Finally,several important performance indicators of MPF are introduced,and the application of MPF in the field of optical fiber sensing is briefly introduced.(2)A high-resolution polarization-maintaining photonic crystal fiber(PM-PCF)pressure sensor based on MPF is proposed.Different from traditional fiber optic sensors,this fiber optic sensor is based on microwave photonic technology to demodulate signals and measure the sensing signals in the microwave domain.In this experiment,COMSOL software is used to simulate and analyze the theoretical characteristics of PM-PCF,and the relationship between the birefringence and lateral pressure of PMPCF was obtained.Using PM-PCF as the sensing unit,when the lateral load imposed on the PM-PCF changes,the frequency response of the MPF will change accordingly.The vector network analyzer(VNA)can be used to monitor the change of MPF frequency response to achieve sensing measurement.The experiment has obtained a high sensitivity of 15.625MHz/N.(3)A Sagnac pressure sensor based on MPF is proposed.The Sagnac optical fiber interferometer is also composed of PM-PCF,and since the Sagnac interferometer can act as a comb filter,which can cut the input light signal into a wide-spectrum light source.When the lateral load imposed on the PM-PCF changes,the free spectral range(FSR)of the Sagnac interferometer will also change,according to the working principle of the spectral slice type single passband MPF,it can be known that the center frequency of the single passband MPF will change accordingly.Using VNA to monitor the frequency shift of the center frequency,the magnitude of the applied lateral load can be obtained by calculation.The experiment obtained a high sensitivity of 12.28MHz/N.In addition,the sensing system also shows good stability and reliability.