Research On Key Technologies Of Optical Fiber Curvature Sensor

The curvature of a structure is one of the important parameters to measure.However,in practical applications,curvature is difficult to be measured directly.Most deformation sensor measure curvature through detecting strain and calculating strain as curvature.The deformation of thin structure with large bending radius is small.It is difficult to measure strain in this situation.So,developing a high accurate curvature sensor is of great significance for the deformation measurement of thin structures.In this paper,a fiber curvature sensing technique based on intensity modulation is introduced.The field mode of optical fiber is disturbed by introducing rough region on one side of optical fiber.When the fiber is bended in different directions,the distribution of the mode field in the sensing zone will change,and the transmission coefficient and backscatter coefficient of the sensitive area of the fiber will also change.In this paper,the pulse self-reference demodulation technique is used to theoretically suppress the influence of the fluctuation of light source intensity,t optical transmission loss and the system noise.Based on the demodulation technique,a high precision intensity modulated fiber curvature sensing system is developed.We use finite difference beam propagation method to simulate the transmission characteristics of side-polished optical fiber.We use MATLAB to simulate and verify the curve reconstruction algorithm based on curvature.Experiment results based on the cantilever beam show that the sensitivity of the light transmission of the sensor is 0.47/m-1 in the linear region.The backscattering coefficient sensitivity is 6.73/m-1,and the system measurement noise amplitude is2.25 × 10-4.After converting the cantilever displacement into curvature,the curvature resolution of the fiber-optic curvature sensor based on transmitting light can reach 4.75 × 10-4(8)-1).The linearity of the response is good in the curvature interval 0?1(8)-1).Optical fiber curvature sensors based on backscattering light have a resolution of 3.35 × 10-5(8)-1),and linear response is better in the curvature range-1?1(8)-1),which meaning optical fiber curvature sensors based on backscattered light can distinguish the bending direction.The system has the advantages of simple structure,wide response bandwidth and time division multiplexing.At the same time,a two-dimensional cantilever spatial positioning system based on single-point curvature measurement was developed.The maximum relative error of this system was 0.18.The research shows that the intensity-type curvature sensor based on single-mode fiber has the advantages of simple structure,easy demodulation and low cost.It has a good application prospect...