The use of the evanescent wave coupling between a critically cut optical fibre and a glass plate is described. An experimentally demonstrated configuration is used to illustrate the principle in an analogue force/pressure sensor addressed by light from a He-Ne laser, and application to a non-intensity dependent measurement scheme is shown.
K. T. V. Grattan,
A. W. Palmer,
D. P. S. Saini,
"Fibre-Optic Evanescent-Wave Coupling Force Transducer", Proc. SPIE 0586, Fiber Optic Sensors I, (7 August 1986); doi: 10.1117/12.951152; https://doi.org/10.1117/12.951152