On: Underground fiber optics spy on humans moving above

[dustfinger]

The paper I linked was also from March 1991. I imagine that the technology has changed since then. Here is another article on fiber optic microphones designed for operation in harsh environments [1]. It is from 1999.

[1] https://ui.adsabs.harvard.edu/abs/1999SPIE.3852..106K/abstra...

[seizethegdgap → dustfinger]

The abstract on that paper makes it seem like the study pertains to medical equipment, not telecommunications.