|Title:||Vital signs monitoring based on Few-mode fiber sensors|
|Subject:||Hong Kong Polytechnic University -- Dissertations|
Optical fiber detectors
|Department:||Faculty of Engineering|
|Pages:||51 pages : color illustrations|
|Abstract:||In the context of technological development, recent medical institutions require more medical equipment to monitor the patient's vital signs in real time, with breathing and heartbeat being the two most important indicators. This paper discussed in detail and put forward a feasible sensing scheme for vital signs monitoring. Few-mode fibers (FMF) are adapted to build a kind of fibbed-based interferometer. There are two types of the few-mode fibers are studied, Dual-mode fiber (DMF) and Four-mode fiber respectively. DMF support LP₀₁ and LP₁₁. Also, Four-mode fiber support four modes, LP₀₁, LP₁₁, LP₂₁, LP₀₂. To excite the mode other than LP₀₁ in the fiber, a kind of structure adopt with three segments of the optical fibers, SMF (Single-mode fiber)-FMF-SMF. A core-offset distance existence between lead-in SMF and FMF. In this sensing structure, the cores of SMF and FMF are horizontally unaligned and this called core-offset. High-order mode and fundamental mode propagate simultaneously in FMF and produce inter-mode interference. Finally, the interference beam coupled to lead-out SMF. We have numerically optimized the core-offset distance for the two-mode and four-mode core-offset, and the optimized parameters can lead to a desired experimental result. The extinction ratio of the four-mode fiber reached 10 dB. Both of DMF and Four-mode fiber can accurately measure the signals of respiration and heartbeat. All the preliminary steps in the experiment are repeatable, and the fabrication of such fiber-based interferometers is not complicated. From the above viewpoint, this kind of sensor based on the few-mode optical fiber could be worked as a valuable medical sensor in the future.|
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