2021/01/07 by Ubaid Ullah, Ullah, Ubaid, M. Imran Cheema +1
Engineering · #Advanced Fiber Optic Sensors #Photonic and Optical Devices #Optical Coherence Tomography Applications
paper · pdf · doi:10.48550/arxiv.2101.02493
Liquid phase sensing applications at 1550~nm are highly desirable due to\nwidely available off-the-shelf components. Generally, liquids at 1550~nm induce\na high absorption loss that limits the overall sensor's sensitivity and\ndetection limit. One solution is to use an active fiber loop in conjunction\nwith cavity ring down spectroscopy to overcome these absorption losses.\nHowever, the amplifier inside the fiber loop suffers from inherent gain\nfluctuations that limit the sensing system's overall performance. Here, we\nprovide a novel sensor using the wavelength-scanned phase shift-cavity ring\ndown spectroscopy (PS-CRDS) in conjunction with a linear active fiber cavity\nthat potentially offers a more sensitive solution than traditional fiber loop\nsensors. We use a tapered fiber as a sensing head inside the active cavity\nbuilt from fiber Bragg gratings. We derive a theoretical phase shift expression\nfor our system and simulate it using the finite element method to determine\noptimum tapered fiber diameter for glucose sensing in DI water. Compared to a\nnon-amplified system, we find that our amplified system can increase the\nsensitivity by fourteen times via the amplifier gain tuning. We also conduct\nexperimental measurements using 0-15.5~mM glucose solutions and find them in\nexcellent agreement with our theoretical predictions. Experimentally we obtain\nthe sensor's sensitivity of 0.768~o/mM (1164~o/RIU) and detection limit\nof 0.75~mM ( 4.5~\×~10-4~RIU) without any temperature stabilization\nin the system. We anticipate that the present work will find a wide range of\nsensing applications in fiber cavities, ring resonators, and other microcavity\nstructures.\n