Research On Curvature And Strain Sensing Properties Of Waist Enlarge Few Mode Fiber Sensor

Optical fiber sensors have many advantages,such as small size,light weight,and anti-electromagnetic interference,so it attract the attention of domesic and foreign research scholars.In order to obtain the high sensitivity,some methods can be performed,including the preparation of new optical fiber,fiber or sensor structure changes.It has become a research hotspot for domestic and foreign scholars.Because of the controllable few mode fiber(FMF)mode and the simple preparation of fiber waist enlarge structure,the combination of the two aspects has important research significance.Based on the research background of optical fiber curvature and strain sensor with different structures at home and abroad,a new FMF sensor is proposed in this paper.The FMF is used as the sensing unit in this sensor.And three types of waist enlarge optical fiber strain sensors are fabricated and their curvature and strain sensing characteristics are deeply studied.The main contents are included as follows.Firstly,the transmission mode of FMF and multimode interference principle are analyzed,the formation of the transmission interference spectrum,and the influence of curvature and strain on the sensor are analyzed in detail.Secondly,a symmetrical waist enlarge FMF sensor is designed and prepared.The effects of different FMF lengths on the transmission spectrum are analyzed.The curvature and strain characteristics of the prepared sensor are measured.And different FMF length sensors sensitivity are obtained and analyzed.Thirdly,an asymmetric waist enlarge FMF sensor is designed and fabricated.The effect of different cone size on coupling efficiency is analyzed.The effect of different FMF length on the transmission spectrum of the sensor is analyzed.The curvature and strain characteristics of the sensor are measured.The curvature and strain sensitivity of different FMF length sensors is obtained and analyzed.Finally,the cascaded waist enlarge FMF sensor is studied.The sensors with different number of waist enlarge cones are prepared.The curvature and straincharacteristics of the prepared sensor are measured.The influence of the number of waist enlarge cones on the curvature and strain sensing characteristics of the sensor is analyzed.