Abstract: An optical displacement sensor comprises first and second optical fibers which transmit light to and receive light reflected from first and second fixed reflectors. A third optical fiber transmits light to and receives light reflected from a moving reflector on the end of a core which moves in response to the displacement to be measured. The intensities of the light reflected to the fibers allows the displacement to be determined with immunity from variations such as in transmissivity and refractive index of a medium between the fibers and the reflectors.

Abstract: An optical displacement sensor suitable for use in drowned environments where the refractive index of a medium in the optical path may vary, comprises a light source emitting first to fourth wavelengths. The first and second wavelengths are within the infrared region of the spectrum, whereas the third and fourth wavelengths are in the visible region of the spectrum. A zone plate focuses the first and second wavelengths to respective positions substantially at the extremes of movement of a reflective element whose position is to be measured. The zone plate also focuses the third and fourth wavelengths to respective positions. A cold mirror is interposed between the zone plate and the reflective element and is arranged to transmit the first and second wavelengths and to reflect the third and fourth wavelengths. The ratio of the intensities of the light reflected from the cold mirror gives information about the refractive index of the medium in the optical path.

Abstract: An optically driven microresonator sensor comprising a sensor member having a vibratory bridge onto which a light beam is directed at a non-zero angle relative to a normal to said bridge, the light beam causing the bridge to oscillate at its resonant frequency, in use, in the direction of said normal, between a first position, where most of the incident light is reflected by the bridge to a light intensity measuring system, and a second position, where most of the incident light is not intercepted by said bridge, so that the reflected incident light sensed by said light intensity measuring system is reduced, the resonant frequency of oscillation of the bridge thus determined from said system, being dependent upon the nature of an applied force, such as stress, exerted on the sensor member.