In this paper, a highly-sensitive distributed shape sensor based on a multicore fiber (MCF) and phase-sensitive optical time-domain reflectometry (φ-OTDR) is proposed and experimentally demonstrated. The implemented system features a high strain sensitivity (down to ∼0.3 µɛ) over a 24 m-long MCF with a spatial resolution of 10 cm. The results demonstrate good repeatability of the relative fiber curvature and bend orientation measurements. Changes in the fiber shape are successfully retrieved, showing detectable displacements of the free moving fiber end as small as 50 µm over a 60 cm-long fiber. In addition, the proposed technique overcomes cross-sensitivity issues between strain and temperature. To the best of our knowledge, the results presented in this work provide the first demonstration of distributed shape sensing based on φ-OTDR using MCFs. This high-sensitivity technique proves to be a promising approach for a wide range of new applications such as dynamic, long distance and three-dimensional distributed shape sensing.

In this paper we present an all-fiber vector bend sensor by means of a self-fabricated micro-structured multicore optical fiber. The reported solution is based on differential intensity variations of the light transmitted along the cores whose changes are influenced by the bending angle and orientation. The unique asymmetric structure of the air-holes in the optical fiber provides each core with different confinement losses of the fundamental mode depending on the bending radius and orientation, making each of the cores bend-sensitive in a range of at least 80. It has been experimentally demonstrated that the reported sensor enables the bending angle and orientation to be detected in a full range of 360 without any dead-zones, and the possibility of end point detection with millimeter precision. Additionally, a reconstruction of the bending vector has been carried out theoretically, and a good match can be observed between the experimental and theoretical data.

In this paper, a long-distance distributed pressure sensing system based on a special fiber and using frequency-scanned phase-sensitive optical time-domain reflectometry is proposed. The fiber shows high pressure sensitivity (159 MHz/bar) and low loss (3 dB/km) owing to its simple structure made of two large air holes in the cladding. The pressure response of the two orthogonal polarization axes of the fiber is explored distinctively. Distributed pressure sensing over a long sensing range (720 m) and high spatial resolution (5 cm) is demonstrated, resulting in 14,400 resolved sensing points with uncertainty on pressure of 0.49 bar. Discrimination between the temperature/strain and pressure responses is demonstrated, taking advantage of the different pressure and temperature sensitivities of the two polarization axes. In addition, the temperature response of the fiber is studied and the simulation results show the possibility of scaling the temperature sensitivity by adjusting the size of the core. The sensing distance limit due to crosstalk between the polarization axes is also discussed.

Just like nanometer-scale conductive paths in an electronic chip at some point end up connected to macroscopic wires of the printed circuit board, photonic integrated circuits often need light in/out coupling from/to external devices, such as light sources or detectors. In the optical domain, these connections are challenging due to the scale mismatch and alignment precision required. At the same time, there is more than 24,500 μm² of space available on two cleaved single mode optical fiber tips. We demonstrate that this space can be used to fabricate compound photonic assembly – Photonic-chip-on-tip – directly integrated with the fibers. As an example, we present a simple setup consisting of in- and out-coupling prisms, tapered waveguide, and a whispering gallery micro-resonator, all made in a single process with two-photon laser photolithography. Temperature sensing is demonstrated as an example of application. This approach to photonic circuit design intrinsically addresses the problems of scale mismatch, fiber alignment, light coupling, and packaging.

Standard multimode optical fibers normally support transmission over some 100 modes. Large differences in the propagation constant and the spatial distribution of distinct modes degrade the performance of phase-sensitive optical time-domain reflectometry measurements. In this work, we present a new realization of a coherent time-domain interrogation technique using single-mode operation in multimode fibers. We demonstrate effectively distributed strain sensing on three different multimode optical fibers. Up to 4 km of multimode fiber has been correctly interrogated, featuring a spatial resolution of 20 cm.

A highly sensitive distributed pressure sensing system (< 20 hPa) based on phase sensitive optical time-domain reflectometry with side air holes fiber is proposed, reaching a sensing range of 1.05 km with a 5 cm spatial resolution.