Research On Key Devices In Optical Fiber Sensor Network

Optical fiber sensor network plays an important role in military security,bio-sensing,environmental detection,and urban construction.Fiber laser and fiber-optic sensor are key components in optical fiber sensor network,which have received extensive attention and research.Fiber lasers have features such as higher output power and optical signal to noise ratio.Therefore,fiber lasers have great advantages in long-distance fiber sensor network.Multi-wavelength fiber laser can output multiple wavelength lasers at the same time,which has the advantages of low cost and compact structure,and it occupies an important role in long-distance,multi-point sensor network.At the same time,multi-wavelength fiber laser is ideal light source for multi-channel communication in high-speed optical communication network.The optical fiber sensor has the advantages of compact structure,anti-electromagnetic interference,low cost,high sensitivity,corrosion resistance,etc.It plays an important role in a miniaturized,Multi-functional sensor network.In this paper,we study multi-wavelength fiber laser and optical fiber sensors based on the principle of interference in fiber-optic sensor network.The main research results are listed as follows:1.On the basis of previous work,based on the sampling fiber grating filter and liquid nitrogen cooling technology,four kinds of multi-wavelength fiber lasers are tested by using polarization-maintaining erbium-doped fiber and common erbium-doped fiber,and their output characteristics were respectively and polarization characteristics are analyzed.A multi-wavelength fiber laser is used as light source of the sensing system,combined with a wavelength division multiplexer,and a refractive index sensor is fabricated by utilizing the reflection characteristics of the end face of the fiber.According to the experimental results,the sensing system has refractive index sensitivity of 132.52 dB/RIU.At the same time,the sensing system has the potential for multi-point refractive index measurement.2.Based on no-core fiber,hollow-core fiber and bent single mode fiber,three mode interference fiber sensors are proposed and fabricated.Under different refractive index solutions,no-core fiber radius and no-core fiber length,the influence of solution liquid level on the transmission spectrum of no-core fiber mode interferometer are analyzed.Based on the no-core fiber mode interference structure,high air pressure sensitivity is fabricated.The relationship between the cavity length of different air cavities and the sensitivity of the sensor has been studied experimentally and theoretically.The maximum pressure sensitivity of the sensor is 266.6 nm/Mpa.A compact sensor with a no-core fiber hollow-core fiber no-core fiber structure is fabricated.Two segment of no-core fiber are respectively fused at both ends of the hollow-core fiber to serve as a beam combiner and beam splitter.In the experiment,the influence of different lengths of hollow-core fiber on the transmission spectrum of the mode interferometer is analyzed,and the stress response characteristics and temperature response characteristics of the sensor are studied.A high force sensitivity sensor of a bent single mode fiber is fabricated,and the mode interference structure is formed by bending a single-mode fiber with coating stripped.The influence of different bending diameters on the transmission spectrum of the mode interferometer is analyzed by experiments.The maximum force sensitivity of the sensor is 24.9 pm/pN.3.A fiber senor based on asymmetrical twin core fiber and multimode fiber is proposed.From both experiment and coupled-mode theory,the uncoupled characteristics of twin core fiber is analyzed.Two segments of multimode fiber used as beam splitter and combiner are embedded on the two ends of the twin core fiber,and the extinction ratio of the comb transmission spectrum of the fiber sensor is about 15 dB.In the experiment,the fiber sensor is applied to the measurement of curvature and strain.The experimental results show that the maximum curvature sensitivity of this sensor is 103.35 nm/m-1 and the maximum strain sensitivity is-4.01pm/??.4.An asymmetric Fabry-Perot interferometer for simultaneous measurements of temperature and curvature is proposed.The Fabry-Perot interferometer is comprised of a low reflective fiber Bragg grating with narrow bandwidth and a no-core fiber with broadband Fresnel reflection.From both experiment and theory,the curvature response and temperature response characteristics of the interferometer are analyzed.The results show that the temperature variation will affect the peak wavelength of the interferometer shift and has no influence on the extinction ratio.While the change of curvature will cause the extinction ratio of the interferometer change and has no effect on the peak wavelength.According to the measurement results,the temperature sensitivity of the sensor is 10.2 pm/?,and the curvature sensitivity is 9.57 dB/m-1 in the range of 0.8844 m'1 to 1.0995 m-1.