Design And Implementation Of Optical Fiber Optic Acoustic Sensor Based On Thin Film Structure

The optical fiber acoustic sensor has the advantages of small volume,light weight,flexible,and electromagnetic insulation,therefore,it is widely used in gas detection,water detection,biomedical ultrasonic imaging and ultrasonic distance measurement.In optical fiber acoustic sensing technology,thin film structure as a direct contact with the measured dielectric objects,the structure of the thickness uniformity will directly affect the accuracy of experimental results.Therefore,it is necessary to conduct in-depth research the optical fiber acoustic sensor,which plays an important role in the study of optical fiber acoustic sensor.This paper mainly completed the following aspects of the work: 1.Two schemes of optical fiber photoacoustic transmitter and detector are proposed respectively.The composite material is coated on the surface of the optical fiber microbubbles to generate ultrasound,the planar thin film FP cavity is used for ultrasonic detection.2.Based on the design scheme,two kinds of structures is prepared and analyzed.Two kinds of optical fiber film structures,microbubble film and planar film,are fabricated by using commercial single-mode optical fiber and glass tube as materials,through fiber-optic welding machine and pneumatic pump.The temperature characteristics of oil-filled and non-oil-filled microbubble films are measured,the pressure characteristic of planar film as well.Through the analysis of the experimental results,it can be concluded: The thickness of the structure film is only several microns and the uniformity is good.With the increase of temperature,the spectrum peak of the microbubble film shifts to the left.The temperature sensitivity of the sensor is 6pm/?.When the microbubble film structure is encapsulated in a fully sealed metal cylinder with dimethyl silicone oil,the same temperature increases and the spectrum peak shifts to the right.The temperature sensitivity of the sensor reaches 36pm/?.The increase of sensitivity shows that the thermal expansion coefficient of silicon oil is higher than that of optical fiber at the same temperature,the relationship between temperature and wavelength is linear.With the increase of the pressure,the spectrum of the planar film shifts to the left.The pressure sensitivity reached 932pm/KPa,and the corresponding pressure is nonlinear related to the wavelength.