Research And Application Of Fiber-optic Sensing Technology Based On Graphene Oxide

In the field of sensing technology,fiber-optic sensing has been favored by researchers all over the world because of its unique excellent characteristics.Fiber-optic sensing has been widely used in various engineering fields through the joint efforts of several generations of researchers,and it plays an irreplaceable role.In recent years,the traditional single-structure fiber-optic sensors are facing the problem that the sensing capacity needs to be further improved with the continuous development of the sensing demand towards to diversification in the field of engineering.It is a great challenge for researchers to invent a new type of fiber-optic sensor to meet the diverse sensing demand.In order to solve this problem,the research on the cross fusion of fiber-optic sensing technology and materials is carried out,which improves the sensing function of fiber-optic sensors.The combination of graphene oxide and fiber-optic has natural advantages in many kinds of materials:the functionalization of graphene oxide can give new sensing function to the traditional fiber-optic,and the fiber-optic as the optical transmission waveguide can provide a stable bearing substrate for graphene oxide.The combination of the two objects complements each other,and the new sensing devices have their respective advantages,which highlight the important research value and application potential.However,as a new research subject of interdiscipline,the sensing devices based on graphene oxide,especially the fiber-optic sensing devices,are still in the experimental research stage,and they are still facing many complicated technical problems when they are used in the actual engineering.Therefore,it is necessary to do lots of work on the structure design,fabrication process,hardware and software implementation and performance optimization of device.Under the support of the program the National Nature Science Foundation of China?NSFC?and on the basis of the team's more than 20 years'research on optical fiber sensing technology,this doctor dissertation has further expanded the research on fiber-optic sensing technology.The fiber-optic interferometric sensing technology based on graphene oxide has been developed.A fiber-optic gas sensor is proposed and demonstrated based on the gases sensitivity of graphene oxide.Furthermore,the sensitivity of graphene oxide to gas sensing is further improved by using the method of surface modification with metal nanoparticles doping.A fiber-optic acoustic sensor is proposed and demonstrated based on the acoustic wave sensitivity of graphene oxide.The structure of the sensor is optimized and the signal demodulation method is improved.These works make the acoustic wave sensor reach the practical level.It has been successfully applied in passive security interception and pipeline leakage monitoring.The main contents and results of this dissertation are summarized as follows:?1?The forming process of graphene oxide film is studied.The graphene oxide/fiber composite waveguide structure is formed on the surface of fiber-optic by liquid phase deposition method.It is successful for combination of graphene oxide and fiber-optic.We have mastered the film forming process of graphene oxide with large area suspension and controllable thickness by improving the process of forming graphene oxide film.These studies have laid a solid foundation for the study of fiber-optic gas sensors and fiber-optic acoustic sensors based on graphene oxide.?2?The sensing characteristic of graphene oxide to gases is studied.A microfiber knot gas sensor based on graphene oxide is fabricated.The sensing characteristic of graphene oxide for different gases is revealed.The detection sensitivity of 0.35 pm/ppm for carbon monoxide and 0.17 pm/ppm for ammonia are achieved.In order to further enhance the sensitivity of graphene oxide to gas,a microfiber gas sensor based on Pt nanoparticle-incorporated graphene oxide is fabricated.Compared with the undoped graphene oxide sensor,the sensitivity of the doped graphene oxide sensor to ammonia is increased by 2 times.The detection sensitivity of 10.2 pm/ppm for ammonia gas is achieved.?3?Graphene oxide thin film is used as acoustic sensing element for the first time.A fiber-optic acoustic sensor has been fabricated based on thin thickness and flexible of graphene oxide film.The micro interference structure based on Fabry-Perot cavity,which formed by fiber and graphene oxide film,can detect weak acoustic signals with high sensitivity.By optimizing the structural parameters of the sensor,the minimum detectable pressure of sensor is reduced to 2.3?Pa/Hz^1/2,which is 25 times higher than that of conventional electroacoustic acoustic sensor.In addition,the dynamic range of acoustic detection can reach-18.7—80.4 dB?ref 20?Pa?.The sensor has characteristics of a linear acoustic pressure response,flat frequency response and full directional sensing.A three-wavelength adaptive demodulation method based on the principle of fiber-optic Fabry-Perot interferometer is proposed.The problems of temperature drift and signal instability in optical signal demodulation are solved.Finally,the prototype of acoustic detection system is developed and successfully applied in practical engineering.?3?The practical application of fiber-optic acoustic detection system in passive security detection field is realized.The detection range for speech signal is up to 50 m².The functional improvement of the system is carried out according to the specific requirements of the application situation.The noise removal function of the detected speech signal is completed by using the off-line Wiener filter algorithm and the real-time software signal processing.The system has the characteristics of passive probe,non-metal probe,anti-electromagnetic interference and so on.It can make up for the natural defects of the current electrical listening equipment and has great application value.The practical application of fiber-optic acoustic detection system in pipeline leakage monitoring engineering is realized.The leakage detection distance of a single sensor can reach 40 m.The monitoring length to the pipeline can be up to 1 km by using the quasi-distributed sensor array scheme.The system has the function of warning only against the leakage situation,which reducing the false alarm rate and greatly improving the working efficiency.The system has the function of quasi-distributed monitoring through the technology of time division multiplexing.The field test results show that the system has great application potential in the field of pipeline leakage monitoring.