Abstract: A method of calibrating bias drift with operating temperature over an operating temperature range for a vibrating structure gyroscope.

Abstract: An accelerometer having a plate-like proof mass (1), flexible mounting legs (2) each co-planar with the proof mass (1), a ring-like support (3), in which the proof mass (1) is moveably mounted, with each mounting leg (2) being connected at one end to the proof mass (1) and connected at another end to the support (3) and with the mounting legs (2) extending substantially perpendicularly to the sensing direction, a plurality of interdigitated capacitor fingers mounted, in a gaseous medium, in the ring-like support (3) for sensing linear movement of, and for providing gaseous medium squeeze damping for the proof mass (1) in the sensing direction, with the fingers, proof mass (1), mounting legs (2) and support (3) being co-planar and formed from a single plate of mono-crystalline silicon, which fingers comprise fixed first, second, third and fourth arrays (5, 6, 7, 8) of laterally spaced fingers extending substantially perpendicularly to the sensing direction and away from the support (3) towards to the proof mas

Abstract: The accelerometer is linear having a substantially planar plate-like proof mass (9) mounted by four or more flexible mounting legs (8) each co-planar with the proof mass (9) to a substantially planar plate-like support (10) fixedly mounted relative to the proof mass (9) and co-planar therewith. In this way the proof mass (9) is mounted for linear movement in a sensing direction in the plane containing the proof mass (9), mounting legs (8) and support (10) to sense acceleration change applied to the accelerometer. At least two spaced apart substantially planar capacitor plates (11) each co-planar with the proof mass, mounting legs and support, are provided for sensing linear movement of the proof mass (9) in the sensing direction C. The proof mass (9), mounting legs (8), support (10) and capacitor blades (11) are formed from a single sheet of silicon and the mounting legs (8) extend substantially perpendicularly to the sensing direction C.

Abstract: The accelerometer is linear having a substantially planar plate-like proof mass (9) mounted by four or more flexible mounting legs (8) each co-planar with the proof mass (9) to a substantially planar plate-like support (10) fixedly mounted relative to the proof mass (9) and co-planar therewith. In this way the proof mass (9) is mounted for linear movement in a sensing direction in the plane containing the proof mass (9), mounting legs (8) and support (10) to sense acceleration change applied to the accelerometer. At least two spaced apart substantially planar capacitor plates (11) each co-planar with the proof mass, mounting legs and support, are provided for sensing linear movement of the proof mass (9) in the sensing direction C. The proof mass (9), mounting legs (8), support (10) and capacitor blades (11) are formed from a single sheet of silicon and the mounting legs (8) extend substantially perpendicularly to the sensing direction C.

Abstract: An optical gyroscope includes an optical fibre ring or coil (2) around which light may propagate in clockwise and counter-clockwise directions, means (1, 3, 4, 5, 6) for inputting a beam of light in either direction into the coil (2), a phase modulator (7) for generating and applying a phase modulation at a modulation frequency between the clockwise and counter-clockwise beams, a detector (8) for detecting the combined clockwise and counter-clockwise beams and processing means for monitoring the intensity of the output of the detector means (8) at a plurality of integral multiples of the modulation frequency to determine the rate applied to the gyroscope.

Abstract: A fiber optic gyroscope sensing coil having two parts one wound clockwise and the other wound counter-clockwise from a central point on a spool towards ends thereof and back towards the center before crossing over each other and being wound out and back a plurality of times. Such an arrangement has the advantage of eliminating the temperature sensitivity of such coils and reducing microbending of the fibers thereby producing a more accurate coil for a fiber optic gyroscope. Preferably the outermost layer of fiber is a single layer.

Abstract: In a laser gyroscope, a non-reciprocal phase modulation is introduced between the clockwise (CW) and counterclockwise (CCW) beams at a modulation frequency (f). The CW and CCW beams are combined on a detector and the intensity of the output is observed at the fundamental frequency (f) and the higher harmonics (e.g. 2f, 4f). At each frequency, the detected signal is demodulated by mixing it with a reference signal at the same frequency and stepping the phase of the signal through successive increments of 90.degree., thereby to determine the in-phase and quadrature components for each frequency monitored.

Abstract: A ring resonator gyroscope has clockwise and counterclockwise light beams that are frequency shifted by an equal but opposite amount and then have their frequencies varied in antiphase relative to each other about a mean frequency (f.sub.o +f.sub.1 or f.sub.o -f.sub.1) so any backscatter signal is at the difference frequency and locking at zero rate thus is avoided.

Abstract: In a ring resonator gyro the CW and CCW beams are modulated to provide each with a spectrum including a carrier and an upper and a lower side band. The upper side band of one beam is kept at a resonance by a path length control loop 24 and the upper side band of the other beam is kept at a resonance by a rate control loop 40.

Abstract: A fiber resonator gyro in which the resonator loop includes a first length of fiber having opposed ends into which respective clockwise and counterclockwise beams are launched. A second length of fiber is connected by two coupler means to spaced portions of said first length to form the loop. The couplers are preferably four-way couplers which have ports for dumping resonant radiation.

Abstract: A fibre optic gyroscope including a fibre optic loop, a radiation source for generating a broadband signal, splitting means for splitting radiation from the source into two components and inserting them into the loop in clockwise (CW) and counter clockwise (CCW) directions, recombining means for recombining the components interferometrically to give an indication of rotation rate of the loop, characterized in that there is further provided amplification means for amplifying both components travelling within the loop.

Abstract: A ring resonator fibre optic gyro includes a single detector on which the clockwise and counter-clockwise beams interfere on leaving the ring. The output of the detector is used by a first and a second servo loop to compensate for optical path length changes and for rotation of the gyro respectively.

Abstract: The invention relates to detecting distortion in large engineering structures using one or more fibre optic cables bonded to or in the structure. An optical signal is transmitted along the cable and information is obtained from the received signal regarding the length and/or change in length of the cable.

Abstract: A sensor comprises a resonator loop formed of polarization-maintaining, high birefringent optical fibre. Changes in the optical path lengths of each of the "fast" and "slow" optical paths in the loop are measured and processed to determine the strain and temperature change experienced by said fibre loop.

Abstract: A cathode (12) for a glow discharge device and comprising a hollow body provided with an opening and having an internal working surface (18) which is substantially frusto-ellipsoidal. The cathode has particular application to a laser gyroscope.

Abstract: A ring resonator waveguide for a laser gyroscope comprises a ring of waveguide material (2) formed around the inside or outside surface of a hollow cylinder (3) or ellipsoid (4). Such a ring resonator waveguide is made by providing a hollow cylindrical substrate (1), depositing waveguide material (2) on the inside or outside surface of the hollow cylindrical substrate (1), heating the substrate (1) and blowing it to form a cylindrical or ellipsoidal (4) member, and cutting a circular section (5, 6) from the cylindrical member (3) or from a central portion of the ellipsoidal member (4).

Abstract: An alternative form of accelerometer is described herein in which an acceleration sensitive element (68, 69) is coupled to a deformable reflector (60) in a lasing cavity (58) to vary the radius of curvature of the reflector in response to experienced acceleration and hence to alter the beat frequency between two transverse lasing modes in the cavity to provide an output signal indicative of the acceleration.

Abstract: A ring laser gyroscope has a primary ring 13 including a gas discharge tube 4 enclosing an active lasing medium. The gyroscope has additionally a secondary, passive ring 14 optically coupled to the primary ring 13 by a partially transmissive mirror 8. A mirror 15 of the secondary ring 14 is adjustable, under the control of a feedback loop 19, to vary the optical path length of the secondary ring 14 so that the latter resonates at one of the longitudinal modes of the primary ring 13, thereby enhancing this mode and concentrating the output power of the gyroscope in one frequency, while suppressing other longitudinal modes of the primary ring.