Lossy Mode Resonance Sensors Based on Unconventional Optical Fiber with High Refractive Index Cladding

The fabrication and characterization of a fiber optic sensor based on the phenomenon of lossy mode resonance (LMR) is shown in this work. This kind of sensors typically involve the presence of an optical fiber, e.g., cladding removed multi-mode, tapered or polished, along with the deposition of nanosized material with high refractive index (HRI) and small absorption losses. Here we demonstrate that such phenomena can be induced without the use of an external coating onto the fiber if a specialty optical fiber is used instead. Such fiber has a cladding with refractive index higher than core (high index cladding, HIC), permitting the generation of lossy modes. As the number, mode order and wavelength of LMR attenuation bands is generally dependent on the thickness of HRI layer, here the phenomenon is tuned by modifying the thickness of the HIC fiber through chemical etching. The device exhibits simplicity and cheapness, moreover a maximum surrounding refractive index (SRI) sensitivity of 1700 nm/RIU around water refractive index is achieved, making it suitable for biological and chemical sensing applications.