An experimental realization of a simple all-fiber-optic sensor for liquid l
evel measurement is demonstrated. It is an intensity-modulated on-off switc
hing sensor whose operating principle is based on the frustrated-total-inte
rnal-reflection effect caused by the refractive-index change of the surroun
ding medium. The basic optical element in the scheme is a sensing single fi
ber which serves simultaneously to transmit both the forward laser emission
to the investigated medium and the useful signal backreflected from the fi
ber tip that is the sensing element. In order to achieve a maximum sensor s
ensitivity, we use a specially shaped fiber tip in two profile variants: an
gled and retroreflecting. The experimental investigations of the sensor pro
perties and the results obtained at the pure-water level measurement confir
m the sensor potential in liquid level determination with a high accuracy,
exceeding 10 mu m. [S0034-6748(99)01305-2].