Research On The Key Technology Of Curvature Fiber Optic Sensor

Optical fiber sensors have been widely used in various complex environments due to their advantages of anti-electromagnetic interference,corrosion resistance,and high sensitivity,and have received extensive attention in recent years.Curvature sensor technology is widely used in the field of building structure health monitoring,intelligent structure bent angle measurement and so on.Curvature is an important parameter of optical fiber,and it is also an important detection content of sensors.With the development of existing optical sensor technology,it is imperative to reduce the cost of curvature sensor and simplify the fabrication process.Plastic optical fiber has emerged in curvature sensor technology due to its advantages of flexibility,easy connection and fabrication.In this paper,we have studied various kinds of curvature sensors,and designed a novel side-throwing sensitized curvature fiber sensor,which is not only simple to manufacture,but also sensitive.Moreover,a macro-bend coupling system is built to measure the curvature and to discriminate the bent direction to extend the application range of the sensor.The main work of this paper is as follows:(1)Firstly,we theoretically elaborate the key technology of curvature sensor.Based on the light theory and mode theory,the influence of mode field distribution on transmission power in the curved fiber is studied by theoretical research and simulation analysis.We detailedly analyze the mode coupling characteristics of fiber transition from straight segment to curved segment,which lays a theoretical foundation for the fabrication and research of the side-throwing sensitized curvature sensor.(2)Secondly,we propose a new type of side-throwing sensitized curvature sensor system based on plastic multimode fiber.Based on the ray tracing method,the light transmission mechanism of fiber bending is studied.We analyze the influence factors of transmission loss and the relationship between transmission loss and curvature in this paper.The advantages of the sensitized plastic curvature measurement method compared with the conventional plastic curvature sensor system are verified by experiments.This technology is expected to be applied to liquid level detection,bridge structure curvature detection and so on.(3)Lastly,we build a novel macro-bend coupling system based on the effect of radiation loss on the optical power of a single-mode fiber in a curved region,which realized the optical power coupling of a common single mode fiber and a side-throwing sensitized plastic optical fiber when bent.We experimentally tested the coupling characteristics of the system and the sensitivity of different bent directions.The result shows that the bent technology can not only discriminate the bent direction,but also can be used for non-destructive optical signal extraction and non-intrusive fiber eavesdropping.Compared with the prior art,the method has simple structures,easy operation and a good application prospect.