Abstract: An optical sensor uses a torsion-mounted thin silicon paddle (1) with magnetically soft material on its back. A light beam falls on the front face and part of the beam is reflected to a photo-diode (4) whose output drives a current in a magnetizing coil (5). The magnetic field thus produced rotates the paddle out of the beam, which cuts off the light to the photo-diode. Thus the paddle oscillates with an amplitude which depends on the strain due to the torsion mounting. This modulates the light beam, and if they have different resonances several such sensors can share the same beam with a common read-out.

Abstract: In a fiber optic interferometric magnetic sensor or magnetic gradient detector a magnetic bias field is applied to a magnetically sensitized portion of an optical fiber by means which are driven by optical power whereby a completely passive sensor head arrangement may be achieved. In a magnetic gradient detector optical power from a high power laser (34) may be supplied via an optical fiber (35) to illuminate a solar cell 27 to whose electrical output terminals solenoids (25,26) are connected. A portion of a respective optical fiber (21, 22) which is magnetically sensitized, by for example bonding to a strip of magnetostrictive material (23, 24), is disposed inside each solenoid (25, 26).

Abstract: Amorphous metallic material in ribbon form is employed to provide hermeticity of cable elements, particularly optical fibres. The metallic glass CuZr has a low permeability for hydrogen, particularly when erbium is included. Thus sealing optical fibres (1) in amorphous metal tubes (3) will prevent increase in attenuation of such fibres when used in submarine cables by preventing contact with hydrogen generated in such cables during use thereof.

Abstract: A magnetic field sensor is comprised by a length of magnetically sensitized single mode optical fibre wound in substantially random directions on a sphere of non-magnetic material, so that an omnidirectional response is obtained. Specific directionality can be obtained by application of a dc bias field in the desired direction. All three perpendicular components can be measured by applying three perpendicular ac fields at different frequencies. The sensor is intended for use in all fibre Mach-Zehnder interferometer types of magnetometer or magnetic gradient detector, examples of which are described.

Abstract: An alternating magnetic excitation field is generated in the flux concentrators (11,12) of a Hall effect device, including a Hall element (13), by passing an a.c. current through a coil (14). This alternating field serves to drive the flux concentrators into and out of saturation. In the presence of a d.c. magnetic field and when a Hall current is applied to the Hall element, a second harmonic component is generated in the output voltage of the Hall element (13); the amplitude of the second harmonic component providing a measure of the d.c. magnetic field. In an alternative arrangement (FIG. 4) the flux concentrator means is in loop form rather than in a flat configuration as in FIG. 3.

Abstract: Certain materials (e.g. polymers, glasses) exhibit the photo-elastic effect, whereby when they are subject to stress become birefringent, which influences a light beam passing through the glass. This beam, e.g. from a laser is collimated and circularly polarized as it approaches the glass and is again polarized as it leaves the glass. This stress is applied, according to this invention, by magnetostrictive strips on the glass which are influenced, by the magnetic field to be measured or the AC bias field. A miniaturized arrangement using this principle is described.

Abstract: Two portions (B,C) of one arm of an optical fibre Mach-Zehnder interferometer are magnetically sensitized and each has applied thereto an a.c. bias fields at a respective different frequency (w.sub.1, w.sub.2). One portion (A) of the other arm of the interferometer is magnetically sensitized and has two a.c. bias fields applied thereto, each at one of the different frequencies (w.sub.1,w.sub.2). The fields for portion A and C are aligned with a first direction (x) whereas those for A and B are parallel, A and B being separated in a second direction (y). The detected output of the interferometer at frequency w.sub.1 is related to the magnetic gradient in the y direction, whereas the detected output at frequency w.sub.2 is related to the magnetic gradient in the x direction. Thus using two bias frequencies allows one interferometer to be used to detect two gradients (FIG. 8).

Abstract: An optical fibre Fabry-Perot etalon can be used as a sensor if the parameter being monitored is allowed to influence the etalon's length, e.g. by pressure, temperature, magneto-strictive effects, piezo-electric effects, acoustically, etc. However, with single-mode fibre and only one set of peaks in the transmission function the device is direction insensitive so that the sign of the parameter being monitored cannot be detected.In the present arrangement the etalon is driven in such a way as to support two different path-length distinct transmission modes, e.g. by the use as a light source of a laser emitting light at 1.3 micrometers wavelength. Two sequences of peaks are then produced in the transmission function which are peaks of different sizes, so that the transmission function is asymmetrical. The peaks are separated at the detection circuitry by discriminations followed by pulse counting means so that the arrangement becomes sign responsive.

Abstract: An arrangement for the remote actuation of a controlled device, e.g. a hydraulic valve, in situations with stringent safety requirements, uses optical power. The optical power, e.g. from a high-power laser, is conveyed via an optical fibre (1) to the controlled device. Here it falls on a heat-absorbent surface (2), as a result of which a volatile fluid (e.g. freon) is evaporated. This via a bellows (4) drives an output rod (5), which operates the controlled device.Alternatives include a bimetallic strip, a thermostat-type capsule, and a memory metal strip, as the heat responsive device.