Tilted Fiber Bragg Grating Vector Bending Sensor

Due to its advantages of anti-electromagnetic interference,stable chemical properties,low cost and small size,fiber Bragg grating technology is widely used in aerospace,petroleum exploitation,civil engineering,chemical medical and other fields.Tilted fiber Bragg grating is a special fiber Bragg grating whose grating plane is at an angle to the axial direction.Vector bending sensors have huge demands in VR data gloves,electronic control toys,intelligent machines,human health testing,etc.Many fiber-optic sensors cannot perform vector bending measurements due to the circular symmetry of the fiber,which limits the large-scale practical application of the sensor.In the paper,we propose a vector bending sensor based on tilted fiber Bragg grating by wavelength demodulation and intensity demodulation,respectively.The main research contents of this paper are as follows:?1?We observed the cut-off phenomenon in the air and used the software Mode Solutions to simulate the bending of the fiber mode.A vector bending sensor based on 2°tilted fiber Bragg grating is proposed and studied according to the cut-off mode of low-order cladding mode.Since the tilted fiber Bragg grating destroys the circular symmetry of the fiber,the sensor realizes vector sensing in four directions of 0 degrees,90 degrees,180 degrees,and 270 degrees.Curvature measurement range is 0¹7.03 m^-1.The resonant wavelength of cut-off mode has a good linear response to the curvature.Among them,the sensitivity is the smallest in the 0 degree direction,which is-0.171 nm/m^-1;the sensitivity is the largest in the 180 degree direction,which is-0.086 nm/m^-1;In the 90 degree and 270 degree directions,the sensitivity is-0.154nm/m^-1 and-0.149 nm/m^-1,respectively.Wavelength demodulation has good repeatability and is not susceptible to the stability of the light source.?2?We have proposed and studied transmissive and reflective vector bending sensors based on tapered fiber and 2 degree tilted fiber Bragg grating,using intensity demodulation method.Taper fiber technology is a fiber post-processing technology that attenuates modes and increases sensor sensitivity.Transmissive vector bending sensor realizes vector sensing in four directions of 0 degrees,90 degrees,180 degrees and 270 degrees.The strength of the cladding mode and the curvature are basically linear between 6.36m^-1 and 17.03m^-1.The sensitivity is the smallest in the 0 degree bending direction,with-0.989dB/m^-1,and the sensitivity is the largest in the 180 degree bending direction,which is-0.607 dB/m^-1.Reflective vector bending sensors also implement vector sensing in four directions:0 degrees,90 degrees,180 degrees,and 270 degrees.The core mode strength and curvature are basically linear between 6.36m^-1and 17.03m^-1.It has the lowest sensitivity in the 0 degree bending direction,-1.667dB/m^-1,and the highest sensitivity in the 180 degree bending direction,which is-1.492dB/m^-1.Reflective sensing systems have greater attenuation than transmissive sensing systems,which are 1.6 to 2.4 times more sensitive than transmissive sensors.In this paper,the optical fiber vector bending sensor with wavelength demodulation is constructed and realized by combining the vector sensing characteristics of tilted fiber Bragg grating and the mode cut-off phenomenon in air.It has the advantages of large measuring range,high sensitivity and good repeatability.The vector sensing characteristics of the grating and the mode attenuation of the tapered fiber structure construct and realize the optical fiber vector bending sensor for intensity demodulation,which has the advantages of high sensitivity and good flexibility.