Fabrication and Characterization of a Flexible FBG-Based Shape Sensor Using Single-Mode Fibers

Abstract

Minimally invasive surgical procedures have become the preferable option, as the recovery period and the risk of infections are significantly lower than traditional surgeries. However, the main challenge in using flexible tools for minimal surgical interventions is the lack of precise feedback on their shape and tip position inside the patient's body. Shape sensors based on fiber Bragg gratings (FBGs) can provide accurate shape information depending on their design. One of the most common configurations in FBG-based shape sensors is to attach three single-mode optical fibers with arrays of FBGs in a triangular fashion around a substrate. Usually, the selected substrates dominate the bending stiffness of the sensor probe, as they have a larger diameter and show less flexibility compared to the optical fibers. Although sensors with this configuration can accurately estimate the shape, they cannot be implemented in flexible endoscopes where large deflections are expected.This paper investigates the shape sensor's performance when using a superelastic substrate with a small diameter instead of a substrate with dominating bending stiffness. A generalized model is also designed for characterizing this type of flexible FBG-based shape sensor. Moreover, we evaluated the sensor in single and multi-bend deformations using two shape reconstruction methods.

Shape sensing of optical fiber Bragg gratings based on deep learning

“…We achieved an improvement of almost 2.7 mm in the median value of the tip error, and 1.4 mm in the median value of the RMSE using the proposed model, compared to the previously designed network architecture in [35], which showed a median tip error of 5.8 mm and a median RMSE value of 3.4 mm. Compared to the MFD method [30,34], our proposed model can accurately predict the sensor's shape with an order of magnitude lower tip error.…”

“…The coating layer of the optical fiber can be a bio-compatible material, which makes it suitable for tracking catheters as well [15]. Although different configurations for FBG-based shape sensors have been studied in recent years [16][17][18][19][20][21], the only fiber shape sensors that have been commercialized work based on multicore fibers (e.g. [22,23]).…”

“…To simplify the analysis, the MFD approach assumes that bending-induced birefringence [31] and cladding mode coupling [28,32,33] do not significantly affect the spectral intensity of the eFBGs. Therefore, the shape prediction accuracy can be relatively high [34] when low-cost readout units with grating-based spectrometers are used for eFBG sensor.…”

Current Engineering Developments for Robotic Systems in Flexible Endoscopy

“…45 Therefore, limited studies have been conducted on the endoscopic applications of FBGs. Roodsari et al 46 proposed a singlecore optical fiber comprising a Nitinol substrate as a shape sensor for endoscopic laser osteotomy. The researchers argued that using multi-core fibers with conventional polyamide substrates contributes to a larger sensor diameter and, hence, limited flexibility.…”

Deep learning-based approach for high spatial resolution fibre shape sensing

“…Fiber shape sensors measure off-axis strain, which is then used to compute the directional curvature and reconstruct the sensor’s shape 3 . Various fiber sensor configurations have been investigated for off-axis strain measurement, including multicore fibers with 4 – 6 or without 7 – 9 fiber Bragg gratings (FBG) in their cores, fibers with cladding waveguide FBGs 10 , and fiber bundles made from multiple single-mode fibers that contain FBG arrays 11 – 15 . Accurate shape reconstruction necessitates high spatial resolution in off-axis strain measurement.…”