Lossy Mode Resonance Sensors in Uncoated Optical Fiber

This work demonstrates that the use of an unconventional optical fiber allows for generating lossy mode resonances (LMRs), without the need for an external high refractive index (RI) thin film. The basic idea consists of using a few centimeters of an optical fiber having a large core and cladding with higher RI, which is spliced between two multimode fibers. Here, the role of such kind of fiber is got by a commercially available double cladding fiber (DCF) having a W-type RI profile. The possibility to induce and tune the phenomenon is demonstrated, where the resonance wavelength of LMR peaks and mode order can be adjusted by varying the thickness of DCF outer cladding, e.g., through chemical etching. This novel sensing scheme becomes a valid alternative to thin-film coated optical fibers, where LMR-based sensors have been developed so far, due to advantages in terms of simplicity, cost, and stability. The response of fabricated LMR devices is characterized toward surrounding medium RI, demonstrating a sensitivity up to about 1700 nm/RIU in the RI range of 1.33-1.39, which makes this fiber sensor suitable for bio-chemical sensing applications. Low cross sensitivity to temperature is also found.

Automated summary

This study demonstrates the generation of lossy mode resonances (LMRs) using an unconventional optical fiber, eliminating the need for an external high refractive index thin film. A few centimeters of a commercially available double cladding fiber (DCF) with a W-type refractive index (RI) profile is spliced between two multimode fibers, allowing for the induction and tuning of LMR phenomenon. The LMR-based fiber sensor developed in this study offers advantages in terms of simplicity, cost, and stability compared to thin-film coated optical fibers. It exhibits a high sensitivity of up to 1700 nm/RIU in the RI range of 1.33-1.39, making it suitable for bio-chemical sensing applications, with low cross sensitivity to temperature.