All-fiber-optic sensor for liquid level measurement

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].