Exposed-core fiber multimode interference sensor

In this manuscript, we report on, to the best of our knowledge, the first experimental realization of a multimode interference device based on self-image phenomenon accomplished by using a microstructured-cladding exposed-core fiber set in a singlemode-multimode-singlemode (SMS) configuration. Its application as a refractive index sensor is also demonstrated. The specialty multimode fiber studied herein exhibits a holey microstructure that surrounds and defines the fiber core. The latter, in turn, interfaces the external fiber environment thanks to lateral access along the entire fiber length. To explore the device's sensing capabilities, numerical simulations have been carried out, and the system sensitivity and spectral characteristics were evaluated. The experimental results demonstrate a refractive index sensitivity of 890 nm/RIU in the refractive index range from 1.41 to 1.43 with a detection limit of 2.7 × 10−3 RIU. This novel SMS configuration has the potential to extend the capabilities of current multimode interference-based sensors by providing an additional path to the realization of refractive index monitoring in liquid samples