Study On All-fiber Fabry-Perot Interferometer Strain And Ultrasound Sensor

With the advantages of small size,high sensitivity,corrosion resistance,etc.,all-fiber Fabry-Perot(F-P)strain and ultrasound sensors have important applications in structural health monitoring,medical ultrasound diagnosis,underwater acoustic detection and other fields.In this paper,through the research on the development of fiber-optic sensors in recent years,this dissertation proposed three kinds of strain and ultrasound sensors with different structures for the problems existing in the field of strain and ultrasound sensing and the factors that limit the practicality of fiber sensors.Theoretical analysis,experimental preparation and testing,and experimental results analysis were carried out for each type of sensor.Aiming at the low sensitivity of fiber F-P strain sensor,this dissertation proposes an F-P strain sensor based on large lateral offset splicing fiber.By constructing the strain sensitive cavity by offset splicing a section of fiber between single modes fibers,the sensor can achieve high sensitivity measurement of strain.Three sensors with different F-P cavity lengths were fabricated in the experiment,and the strain sensitivity reached 103.3 pm/??.The experimental results verify the theory that the shorter the cavity length of the F-P cavity and the higher the strain sensitivity.Improving the sensor's strain sensitivity by reducing the cavity length of the F-P cavity is technically limited,and the Vernier effect will increase the sensor's cross sensitivity.Aiming at these problems,this dissertation proposes a fiber strain sensor based on the separated F-P cavities and Vernier effect.The sensor consists of two separated air F-P cavities,one of which is used for strain testing and the other F-P cavity is used to generate the Vernier effect and amplify the sensitivity.In the experiment,the magnification factor of the sensor is 18 times,and the strain sensitivity measured in the experiment is as high as 1.15 nm/??,which is the highest strain sensitivity achieved by the fiber strain sensor based on F-P cavity and the spectral demodulation mechanism.Compared to single F-P cavity sensors based on fiber capillary,the strain sensitivity is increased by two orders of magnitude.The separated F-P cavity structure is designed so that only the sensing characteristics of the sensing cavity are amplified,and the sensing cavity is insensitive to temperature,so the proposed sensor has the advantage of low temperature-strain cross sensitivity.Aiming at the problem that the reflective diaphragm of fiber F-P ultrasound sensor is easy to oxidize and the air tightness is poor,this dissertation proposes a high sensitivity ultrasound sensor based on an ultra-thin silica reflective diaphragm.The ultra-thin silica diaphragm is prepared by the arc discharge technology of the fusion splicer.The thickness of the silica diaphragm fabricated in the experiment is less than 1 ?m.The ultra-thin reflective diaphragm makes the sensor highly sensitive to both static pressure(air pressure)and dynamic pressure signals(ultrasound).The sensor's pressure sensitivity at standard atmospheric pressure reached-0.1 nm/kPa.The sensor shows good response to both continuous and pulse ultrasound signals,and the ultrasonic frequency response range of the sensor covers 30-860 kHz.The structural design of all-silica allows the sensor to be used in complex and harsh environments with strong electromagnetic field,high temperature,strong acid and alkali.