This paper develops a high-precision miniature three-dimensional Fiber Bragg Grating (FBG) force sensor designed for detecting and locating hard masses within tissues during Minimally Invasive Surgery (MIS) and robotic-assisted MIS palpation processes. The prototype consists of three FBG-etched optical fibers and an integrated elastomer. The fibers are suspended and parallel to each other within the elastomer, allowing each FBG to be directly compressed or stretched under stress. A novel model, combining segment-by-segment sensitivity and differential decoupling, is adopted for decoupling three-dimensional forces. This approach significantly reduces the crosstalk error caused by spatial forces, avoids the complexity of assembling multiple fibers in previous designs, and reduces the sensor's size, facilitating its integration into MIS procedures. Calibration experiments are conducted to determine the sensor's force sensitivity coefficients, achieving resolutions of 4.35 mN, 3.99 mN, and 3.30 mN in the X, Y, and Z directions, respectively. Through discrete and drag palpation tests on silicone with different types of hard inclusions, the results demonstrate that the proposed prototype has the ability to effectively identify the size, hardness, and depth of hard objects from the contact force information. Additionally, ex vivo porcine kidney palpation experiments are conducted to further verify the feasibility of locating hard masses during MIS palpation.

Objective: To accurately achieve distal contact force, a novel temperature-compensated sensor is developed and integrated into an atrial fibrillation (AF) ablation catheter. Methods: A dual elastomer-based dual FBGs structure is used to differentiate the strain on the two FBGs to achieve temperature compensation, and the design is optimized and validated by finite element simulation. Results: The designed sensor has a sensitivity of 90.5 pm/N, resolution of 0.01 N, and root–mean–square error (RMSE) of 0.02 N and 0.04 N for dynamic force loading and temperature compensation, respectively, and can stably measure distal contact forces with temperature disturbances. Conclusion: Due to the advantages, i.e., simple structure, easy assembly, low cost, and good robustness, the proposed sensor is suitable for industrial mass production.

Wiener deconvolution offers the advantages of effectively suppressing noise, restoring image details, and enhancing signal processing accuracy. It has been successfully applied in image denoising for distributed fiber-optic sensing. However, the effective application of Wiener deconvolution in optical frequency-domain reflectometry (OFDR) systems has not yet been reported. The challenge lies in obtaining an effective point spread function (PSF) or blur function to minimize spatial resolution degradation during image processing. To the best of our knowledge, we first proposed a high spatial resolution OFDR system based on Wiener deconvolution. Crucially, we have theoretically and experimentally validated that the auto-correlation function of local Rayleigh scattering spectrum serves as the PSF for the OFDR system. We have optimized the selection range of the PSF in both spatial and frequency domains to achieve the highest spatial resolution. The effectiveness of this algorithm and its superior denoising performance were validated by comparison with Gaussian filtering. Finally, through multiple experiments, we have demonstrated that the proposed Wiener deconvolution method can restore events at a spatial resolution of 200 $\mu \text{m}$.

Accurate measurement of contact forces between medical instrument tips and tissues is a critical challenge in minimally invasive surgery (MIS), where the lack of tactile feedback can compromise surgical precision and safety. To address this, this article presents a novel miniature high-resolution 3-D force sensor based on fiber Bragg grating (FBG) technology. Compared to traditional methods that use multiple optical fibers and complex structures to decouple forces, this sensor employs a cantilever beam structure for biaxial lateral force sensing, while a hollow cylindrical structure is utilized for axial force sensing. This unique combination allows for the independent adjustment of sensitivity in each segment. Finite-element analysis is used to optimize the structure to approximate isotropy. Experiments demonstrate that the sensor achieves an axial force Z resolution of 3.36 mN and a dynamic measurement error of 2.97% within a range of 0–2 N. Meanwhile, lateral force resolutions for X- and Y-directions within a range of −0.5 to 0.5 N are 4.37 and 3.95 mN, respectively, with dynamic measurement errors of 3.79% and 5.12%. Additionally, porcine kidneys are adopted for ex vivo experiments to simulate tumors, validating the feasibility of the designed FBG force sensor in MIS palpation. The simulated vessel identification experiment further validated the ability to detect vessels at different depths within organs, highlighting the potential of the designed sensor for applications in MIS.

An effective technique based on optical frequency domain reflectometry for analyzing mode coupling events in a few-mode fiber is proposed. Its feasibility is demonstrated both theoretically and experimentally on a two-mode fiber. We elaborate on the process to establish the correlation between mode coupling strength and amplitude of cross-correlation peak by analyzing Rayleigh scattering fingerprint spectra and correlation algorithms. Concurrently, on account of group velocity difference between the two modes, the precise localization of the coupling point can be deduced from the group delay between scattered traces of the two modes, which permits the precise location of coupling events within a fiber link. In the experiments, we induced mode coupling between LP01 and LP11 modes in a two-mode fiber by means of applying transverse stress to the fiber-under-test and achieved good measurement results by employing the proposed method. Moreover, we initiated preliminary research on the location and strength analysis of plural coupling events. As an effective in-situ monitoring technique for mode coupling, this methodology holds significant potential for applications such as defect detection in few-mode fibers and high-power laser chain mode coupling monitoring.