Abstract
The paper presents a novel three-dimensional quasi-continuous shape sensor based on an FBG array inscribed by femtosecond laser pulses into a 7-core optical fiber with a polyimide protective coating. The measured bending sensitivity of individual FBGs ranges from 0.046 nm/m-1 to 0.049 nm/m-1. It is shown that the sensor allows for reconstructing 2- and 3-dimensional shapes with high accuracy. Due to the high value of the core aperture and individual calibration of each FBG we were able to measure the smallest reported bending radii down to 2.6 mm with a record accuracy of ∼1%. Moreover, we investigate the magnitude of the errors of curves reconstruction and errors associated with measurement of curvature radii in the range from 2.6 to 500 mm. The main factors affecting the accuracy of measurements are also discussed. The temperature resistance of both the inscribed FBG structures and of the protective coating, along with the high mechanical strength of the polyimide, makes it possible to use the sensor in harsh environments or in medical and composite material applications.
Highlights
Multi-core optical fibers (MCFs), with both straight and twisted cores, are being actively studied for creating compact distributed bending sensors or shape sensors [1,2]
The first approach involves the method of high-resolution backscatter reflectometry; the second is based on the analysis of the resonance spectra of 3-dimensional arrays of fiber Bragg gratings (FBGs), inscribed in different cores along the multi-core optical fibers (MCFs)
A temperature resistant fiber 3D shape sensor based on a polyimide coated custom-made 7-core optical fiber was fabricated and tested
Summary
Multi-core optical fibers (MCFs), with both straight and twisted cores, are being actively studied for creating compact distributed bending sensors or shape sensors [1,2]. In a number of applications, an important factor in the operation of shape sensors based on MCF is their mechanical and temperature “endurance” This requirement applies both to the protective coating material of the fiber, as well as to the modified part of the MCF, in which the FBG array is inscribed. The temperature resistance of sensors involving FBGs is an important factor in the sterilization of a medical device by heat treatment in an autoclave At these high temperatures, degradation and destruction of such protective coating as acrylate take place [11]. By using the direct femtosecond inscription method, an array was created with a total length of 72 mm, consisting of 24 FBGs inscribed in 6 cross-sections (nodes) of the MCF For this array, 2- and 3-dimensional shapes are reconstructed.
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