Research On Few Mode Optical Fiber Sensors Based On The Mode Interference

As the interface to the real world and the key component of the Internet of Things,the sensors become more and more important in our life.With the development of the times,our society puts higher requirements on them.In order to improve the sensitivity of the sensors,the researchers have made a lot of explorations and improvements on the sensing part.In the recent years,since the unique advantages such as highly sensitivity,strong ability of anti-interference,low price,small size,and ease of laying,the fiber sensors have been used in variety fields of the society such as aerospace,industry,detection,medical treatment and so on.As for few mode fiber sensor,due to its highly sensitivity,fewer interference modes,the interference shape of it is simple,and is easy to distinguish and apply.Therefore,it is of great significance to study the few mode optical fiber sensors.In order to study the corresponding relationship between the sensor's sensitivity under different mode interference and the constituent modes,so as to provide new ideas for designing more sensitive sensors,Focusing on the mode analysis of the few mode optical fiber and the basic principle of Mach-Zehnder sensors which belong to the phase modulation sensors,we come up with a new mode fiber optical sensor based on mode interference.The implementation method of it,the temperature,refractive index,and curvature sensing characteristics of the sensor have also been studied.The main work of this paper is as follows:Firstly,the domestic and foreign research status is analyzed.The mode theory of the few mode and the main parameters and the refractive index distribution of the few mode used in this paper are introduced.Secondly,the types of the mode interference sensors are introduced,the interference principle of Mach-Zehnder sensors built with few mode fiber is described,which is the theoretical foundation of the sensor system that we have built.Then,Using Comsol and Matlab,the corresponding simulations on the refractive index changes of different modes in few mode fiber sensors are performed.And the interference waveforms of different modes under different temperature,refractive index,and curvature conditions and the simulation results are discussed.Following,the sensing system based on few mode fiber is designed and built.The sensing characteristics like the temperature,refractive index,and curvature of the sensing system which is composed by different modes are studied from theory and experiment.The sensitivity of the sensing system under different mode interferences are measured,verifies the correctness of the theory of the actual value.The reasons for the different results are analyzed.In the experiments of the temperature and curvature,the sensitivity of the interference sensing system of LP01 mode and LP02 mode achieved to 15.7pm/?and 0.8136nm/m^-1.Compared with other modes of the same structure,which has a higher sensitivity.Finally,the main work of this paper is summarized.The feasibility of the sensing structure is analyzed.The optimization of the sensing system and the improvement of the sensitivity are prospected.