Insights into tunnelling rays: outperforming guided rays in fiber-optic sensing device

Area of Science:

• Optics and Photonics
• Fiber Optic Sensing Technology

Background:

• Evanescent-wave (EW) based fiber-optic sensors rely on light interaction with the surrounding medium.
• Understanding light propagation and energy transfer mechanisms is crucial for sensor efficiency.

Purpose of the Study:

• To investigate the role of total internal reflection (TIR) at fiber end-faces in enhancing EW power collection.
• To elucidate the mechanism behind the high efficiency of specific ray groups in EW fiber-optic sensors.

Main Methods:

• Analysis of tunneling rays and steep guided rays experiencing TIR at the air-clad fiber segment end-face.
• Experimental measurement of detected power variations with and without back reflection.
• Investigation of non-propagating ray excitation mechanisms.

Main Results:

• A specific group of tunneling rays and steep guided rays exhibit TIR, leading to nine times greater EW power collection efficiency.
• These TIR-capable rays originate from a wider launching ring, dominating the detected power.
• Eliminating back reflection caused a 91% drop in detected power, confirming the significance of end-face TIR.

Conclusions:

• The findings highlight the critical role of end-face TIR in maximizing EW power collection in fiber-optic sensors.
• Non-propagating ray excitation is identified as the mechanism responsible for high sensing efficiency.
• The results have significant implications for designing advanced EW-based fiber sensing devices for surface-event analysis.