Many of the problems of flow, electical noise and nonlinearity experienced when using vortex flowmeters at low rate are overcome by using a fiber optic displacement sensor. Due to vibration in the sensory beam, the lift signal is modulated by varying the amount of coupling between two facing fiber ends. Modulation is proportional to the change in overlapping surface area of the two fibers. Use of large core fiber with low numerical aperture enhances sensitivity; A simple LED / PIN photodiode serves as the light emitter and detector which reduces the cost. Vortex shedding flowmeters can benefit from both smart electronic and optic technologies. The technologies are interconnected. Fiber optics has been able to improve range sensitivity operating temperature up to 500 degree remote mounting capabilities and protection against EMI / RFI effects. Smart electonics provide higher accuracy and flow totalization etc.
"Smart fiber optics flowmeter", Proc. SPIE 1230, International Conference on Optoelectronic Science and Engineering '90, 12305J (1 July 1990); doi: 10.1117/12.2294836; https://doi.org/10.1117/12.2294836