Sensor device

A remote pressure sensor comprising a self-contained assembly, and including a generally cylindrical optical fibre ferrule formed from a borosilicate glass and on one end of which a single crystal silicon structure incorporating a pressure responsive diaphragm is mounted and secured thereto, the single crystal silicon structure defining an air-tight cavity between the diaphragm and the ferrule end, said cavity being evacuated so as to provide an absolute pressure reference and a single crystal silicon resonator element integral with and extending from the diaphragm into the cavity and responsive by variation of its resonant frequency to flexure of the diaphragm resulting from pressure applied thereto, the resonator element being disposed in register with and directly optically coupled to an optical fibre supported and permanently secured, in alignment with the resonator element, over a significant length adjacent its end in the ferrule whereby to provide means for maintaining the resonator element in a state of resonance at a resonant frequency, corresponding to the applied pressure, by an input optical signal, derived from feedback means and modulated with the resonant frequency, directed on to the resonator element via the fibre, said fibre further providing means for transmitting from the resonator element an output optical signal modulated with the resonator frequency corresponding to the applied pressure.