FPGA-Based Optical Frequency Domain Reflectometry for Real-Time Fiber Shape Sensing

A real-time fiber shape sensing system using a field-programmable gate array (FPGA) in an optical frequency domain reflectometry (OFDR) was firstly demonstrated. At a spatial resolution of 10 mm, the refresh rates for strain demodulation based on weak fiber Bragg grating array (WFBGA) inscribed multicore fiber (MCF) using parallel computing and serial computing were 30 and 17 Hz, respectively. Here, a multi-channel data caching DDR4 module, a large-point fast Fourier transform module and a wavelength shift calculation module were designed and transplanted into the FPGA to achieve fast strain demodulation for shape sensing. And the strain accuracy of serial computing was higher than that of parallel computing due to the maximum sliding window sizes of 8192 and 2048 for serial computing and parallel computing after zero padding. Under the curvature radii of 15.0, 12.5, 10.0, 7.5, 5.0 cm and infinite, the root mean square errors (RMSEs) using serial computing were 0.2831, 0.2760, 0.1529, 0.1323, 0.1869, and 0.1806 cm, respectively, corresponding to distribution volumes of 0.0084, 0.0048, 0.0043, 0.0118, 0.0098, and 0.0013 cm3, respectively. And the 3D shape was also reconstructed with an RMSE of 0.5905 cm and distribution volume of 0.0011 cm3.