Femtosecond Laser-Fabricated Wavelength Division Multiplexing Sensors for Three-Parameter Robotic Arm Monitoring

To address the growing demands for high-precision pose monitoring and health diagnostics in industrial and medical robotic arms, this paper proposes an integrated wavelength division multiplexing multi-core optical fiber detection system. A triple-core fiber serves as the sensing element for simultaneous strain, bending, and torsion monitoring. Efficient optical waveguides and fiber Bragg grating arrays are fabricated using femtosecond laser micromachining, creating wavelength-decoupled multi-parameter sensing units. Experimental results demonstrate excellent strain sensitivity is 1.78-1.91 pm/με and discrimination in strain tests; significant multi-parameter decoupling and directional identification capabilities in bending/torsion tests; and bending sensitivity enhanced to ±199.2 pm/m-1 through differential calculation. The measurements are supported by systematic uncertainty analysis, indicating combined standard uncertainties of approximately ±2.5 με, ±0.15 m-1, and ±0.8° for strain, bending, and torsion, respectively. This system exhibits extremely high repeatability and stability. Its wavelength drift is less than 0.04 nm, and the intensity fluctuation is less than 0.04 dB. At the same time, it can also achieve distributed multi-point sensing along the robotic arm. Overall, the proposed sensor provides a high-precision and reliable multi-dimensional sensing solution, showing broad application potential in intelligent manufacturing and minimally invasive medicine.