Generation of lossy mode resonance in uncoated double cladding fiber

This work reports as a novelty the excitation of lossy mode resonance (LMR) phenomena in uncoated double cladding fiber (DCF), without the need of an external high refractive index thin film. The configuration chosen for this purpose is a DCF having W-type refractive index (RI) profile spliced between multimode fibers. Here, the outer cladding of the DCF acts as a high RI overlay permitting the generation of LMR. The tuning of the phenomenon is performed by changing the thickness of the outer cladding, e.g., through chemical etching. Resulting LMR device was characterized towards surrounding refractive index demonstrating a sensitivity around 300 nm/RIU in the range of 1.33-1.39, which makes this fiber sensor suitable for bio-chemical sensing applications. Such device exhibits advantages in terms of simplicity and cost with respect to traditional LMR devices.