| With the development of optical fiber and optical information technology,optical fiber sensors are widely used in machinery industry,environmental monitoring,structural health and biochemistry.With the continuous research of fiber optic sensor,fiber optic sensor has gradually become an indispensable device in various fields,which is used to perceive various physical quantities in the environment.Compared with traditional electrical sensors,optical fiber sensors have the advantages of anti-electromagnetic interference,low cost,simple production and other unique advantages.This paper focuses on the optical fiber interferometer sensor based on bending structure.Three kinds of optical fiber interferometer sensors with bending structure are designed and manufactured,and their sensing response characteristics are analyzed experimentally.The main contents of the study are as follows:(1)A compact balloon bending fiber Mach-Zehnder interferometer(MZI)sensor for refractive index(RI)and temperature measurements is proposed without special fiber or sensitizing coating.In order to improve the sensitivity and structural stability of the sensor,a spherical structure is fabricated on both sides of the spherical single-mode fiber(SMF).The optical fiber length between the two spherical structures is L.Three kinds of spherical MZI with different L are prepared and their sensing properties are studied.The experimental results show that RI and temperature sensitivity of the sensor increase with the increase of L.When the RI range is 1.3350 to 1.3965,the maximum sensitivity is 965.1 nm/RIU(refractive index unit).The temperature sensitivity is 178.6 pm/℃ in the 30 to 80 ℃ temperature range.Compared with other balloon-shaped sensors,the sensor has higher sensitivity and stronger structural stability,which is conducive to promoting the development of balloon-shaped fiber MZI to meet the actual demand.(2)A high sensitivity fiber MZI liquid level sensor based on bending effect is proposed.To make a fiber optic MZI sensor,the SMF stripped of the coating layer is bent into a balloon.The sensor is attached to a rigid bracket and connected by a thin wire to a buoyancy ball floating on a liquid surface.The change of liquid level will bend the optical fiber,and the bending effect causes the wavelength shift of the transmission spectrum.It is a new method of liquid level measurement based on strain.The sensing performance of the sensor is studied comprehensively,and the ridge regression algorithm is used to optimize the fitting results of experimental data.The maximum sensitivity of liquid level and temperature measured in the experiment is 5.245 nm/mm and 40.3 pm/℃,respectively,and the temperature cross sensitivity of the sensor is as low as 0.00768 mm/℃.In addition,the sensor has the advantages of realtime response,convenient manufacturing,low cost and high reliability,which broadens the application range of balloon MZI and is suitable for liquid level sensing.(3)A two-parameter optical fiber sensor based on parallel vernier effect is designed and fabricated for simultaneous measurement of temperature and transverse load.The new sensor consists of a compact fiber optic Michelson interferometer(MI)and a closed cavity Fabry-Perot interferometer(FPI),where MI consists of an SMF and a short hollow silicon tube(HCST),with the HCST fused between the two SMFS to form the FPI.By optimizing the length parameters of fiber MI and FPI to achieve vernier effect,the detection sensitivity of the sensor is further increased.The experimental results show that the temperature sensitivity of the sensor with vernier effect is increased by 8.97 times to 83.29 pm/℃.The lateral load sensitivity is increased 9.89 times to 2.46 nm/N.In addition,the sensor has the advantages of small size,low cost and ease of manufacture for temperature and lateral load sensing applications. |
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