Multimode exposed core fiber specklegram sensor

The inception of photonic crystal fibers (PCFs) allowed for unprecedented tailoring of waveguide properties for specialty sensing probes. Exposed core microstructured fibers (ECFs) represent a natural evolution of the PCF design for practical liquid and gas sensing. Until now, to the best of our knowledge, only single-mode or few-modes ECFs have been explored. In this Letter, we demonstrate a highly multimode ECF with a lateral access that extends throughout the whole length of the fiber. The ECF is operated as a fiber specklegram sensor for assessing properties of fluids and interrogated using a simple and low-cost setup. The probe exhibits a refractive index resolution and sensitivity of at least 4.6×10^-4 refractive index units (RIUs) and -10.97RIU^-1, respectively. A maximum temperature resolution up to 0.017°C with a -0.20^∘C^-1 temperature sensitivity over the 23°C-28°C range and a liquid level sensing resolution up to 0.12 mm with -0.015mm^-1 sensitivity over the 0.0-50.0 mm bathed the length range in water.