Application Of Optical Fiber Curvature Sensor And Joint Motion Detection With Single Mode-dual Mode-single Mode Structure

Due to the dependence of various production and life styles of human body on joints,as well as the use of mechanical and electronic products caused by the rapid development of science and technology with the progress of society,people’s joints have been continuously damaged.The diagnosis and treatment of joint disease is urgent,and a rapid way to determine the severity of joint disease is to assess the range of motion of the joints.The traditional method of measuring the range of motion of joints has low accuracy and complicated operation,while the fiber optic curvature sensor has the advantages of small size,light weight,easy to fabricate,low cost,anti-electromagnetic interference and high sensitivity,which has been widely reported in recent years.This paper proposes a new kind of optical fiber structure:single-mode dual-mode single-mode fiber（SDS）structure to be used as curvature sensors.By using the commercial form software（Rsoft Incorporation）,we do simulation based on the beam propagation method（BPM）on SDS curvature sensor to analyse how light travels in the structure of SDS before and after bending.The interference peaks（valleys）of the transmission spectra generates red shift.Experiment results shows that red shift increases when bending becomes more serious.In the process of experiment,firstly,we characterized the sensors.The sensors are fabricated with two different type of fusion condition.One is the single-mode fiber and the dual-mode fiber are spliced together with no core-offset,the other one is that one side of the dual-mode fiber is spliced with the single-mode fiber with no core-offset,the other side of the dual-mode fiber is spliced with the single-mode fiber with core-offset.The latter type includes two kinds,one is that the single-mode fiber and the dual-mode fiber are fused with 4μm core-offset,the other is that the single-mode fiber and the dual-mode fiber are fused with 8μm core-offset.In the curvature range of 1.083m^-1-2.165m^-1,we do measurements on every single sensor repeatedly,results shows that,within the wavelength range tested,the curvature sensors fused with no core-offset perform most stably among the three kinds of sensors,with the sensitivity between-32nm/m^-1～-36nm/m^-1.The sensitivity of curvature sensors fused with 4μm core-offset is mainly between-15nm/m^-1～-25nm/m^-1.The curvature sensors fused with 8μm core-offset can reach the highest sensitivity of-46.396nm/m^-1,with the sensitivity between-26nm/m^-1～-46.396nm/m^-1.Since the no core-offset sensors are stable at not only structure but also sensitivity.We choose them to detect the joint movement of the wrist and neck.Since the curvature change of joint movement of the wrist and neck is high,the results by the formula used above deflected a lot,so the method of image is used to correct the formula for calculating curvature and the sensitivity of the sensors are recalculated.In the curvature range of 8m^-1-32m^-1,the sensitivity of curvature sensors fused with no core-offset is-10.624nm/m^-1.During the detection of the joint movement of the wrist and neck,we choose 10and 7 volunteers separately.Results show that the curvature change among different directions of the joint movement of the wrist are between 2.44m^-1-7.56m^-1.the curvature change among different directions of the joint movement of the neck are between 5.04m^-1-9.36m^-1.Results shows that the error between the results by detection and the results by the method of image are dividedly 10%and 6.1%between the joint movement of the wrist and neck,and the error of angle is under 2°in the joint movement of the neck,the sensors can be used to fast evaluate the joint movement,to fast make a simple judgement of joint diseases.Though the accuracy needs to be promoted,this is the first time of fiber curvature sensors used on the detection of the joint movement,the future application is considerable.