Fibre=optic hydrophone especially for measuring sound pressure of ultrasonic signals

The fibre-optic hydrophone with its smooth or modified end surface of a monomode or multi-mode light wave conductor is coated using one or more hard dielectric optical layers deposited by sputter, is immersed in a liquid. The alteration of the complex coefficients of the layer or layer system is measured as a result of the pressure reaction. The alteration of the amplitude or the phase of a light field, coupled in the light wave conductor, and reflected at the end surface, is detected with a suitable optical system. Especially for shock wave tests, only one layer of a material with high optical refractive index e.g. Nb2O5 is coated.