A new, to the best of our knowledge, hollow-core optical fiber based on a tube lattice geometry is proposed. The fiber cross section is formed by eight tubes with five different thicknesses, and the guidance mechanism is based on the inhibited coupling phenomenon. As such, its transmittance spectrum displays low-loss windows intercalated with high-loss regions, each of the latter related to specific core-cladding modal couplings. The spectral behavior of the straight and bent waveguide is numerically analyzed. Simulations on different curvature radii and directions (angles) show the core mode displacement toward the outer side of the curvature and its impact on the spectral shift of the high-loss wavelengths. The different response of each tube resonance is investigated and discussed. The proposed structure identifies a new and promising path for the development of directional curvature sensors.

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We propose and theoretically study a new hollow-core fiber-based curvature sensing approach with the capability of detecting both curvature radius and angle. The new sensing method relies on a tubular-lattice fiber that encompasses, in its microstructure, tubes with three different thicknesses. By adequately choosing the placement of the tubes within the fiber cross-section, and by exploring the spectral shifts of the fiber transmitted spectrum due to the curvature-induced mode field distributions’ displacements, we demonstrate a multi-axis curvature sensing method. In the proposed platform, curvature radii and angles are retrieved via a suitable calibration routine, which is based on conveniently adjusting empirical functions to the fiber response. Evaluation of the sensing method performance for selected cases allowed the curvature radii and angles to be determined with percentual errors of less than 7%. The approach proposed herein provides a promising path for the accomplishment of new curvature sensors able to resolve both the curvature radius and angle.

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