15 April 2003 Fiber-optic couplers as displacement sensors
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Abstract
We introduce the novel concept of using a fiber-optic coupler as a versatile displacement sensor. Comparatively long fiber-optic couplers, with a coupling region of approximately 10 mm, are manufactured using standard communication SM fiber and placed in a looped-back configuration. The result is a displacement sensor, which is robust and highly sensitive over a wide dynamic range. This displacement sensor resolves 1-2 μm over distances of 1-1.5 mm and is characterized by the essential absence of a 'spring constant' plaguing other strain gauge-type sensors. Consequently, it is possible to couple to extremely weak vibrations, such as the skin displacement affected by arterial heart beat pulsations. Used as a wrist-worn heartbeat monitor, the fidelity of the arterial pulse signal has been shown to be so high that it is possible to not only determine heartbeat and breathing rates, but to implement a new single-point blood pressure measurement scheme which does not squeeze the arm. In an application as a floor vibration sensor for the non-intrusive monitoring of independently living elderly, the sensor has been shown to resolve the distinct vibration spectra of different persons and different events.
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Martin C. Baruch, David W. Gerdt, Charles M. Adkins, "Fiber-optic couplers as displacement sensors", Proc. SPIE 4943, Fiber-based Component Fabrication, Testing, and Connectorization, (15 April 2003); doi: 10.1117/12.468566; https://doi.org/10.1117/12.468566
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