A fiber-optic sensor designed to operate inside high-power electric plants is presented. The probe is based on a fiber-optic proximity sensor that detects the light intensity modulation induced by an elastic transducer. The nonlinear response of the optical head is exploited in an original manner to obtain the simultaneous and ndependent measurement of temperature and vibration at 100 Hz. The particular working principle provides an intrinsically lead-insensitive response.