Leland Stanford Junior University

Honeywell G.m.b.h.

Other

Ralph A Bergh

Herbert J Shaw

Herve C Lefevre

Glen Aaron Sanders

Randy P Goettsche

Lee Kevin Strandjord

Bogdan Szafraniec

Michel J Digonnet

Wayne V Sorin

James N Blake

Rudolf C Dankwort

Ren-Young Liu

Brian Culshaw

Brian H Kolner

C Chapin Cutler

Rudy Dankwort

George A Kotler

A method and system for transmitting source light to a plurality of Sagnac interferometers includes a first directional coupler that splits the source light into a second light beam and a third light beam. The second light beam supplies light to a first Sagnac interferometer and the second light beam supplies light to a second directional coupler, and the first directional coupler also delivers light returning from the first Sagnac interferometer to a first detector that is used to indicate rotation of the first Sagnac interferometer. The second directional coupler splits the third light beam into a fourth light beam and a fifth light beam, and the fourth light beam supplies light to a second Sagnac interferometer. The second directional coupler delivers light returning from the second Sagnac interferometer to a second detector, and the second detector provides a signal indicative of rotation of the second Sagnac interferometer.

Method and apparatus for multiplexing multiple Sagnac interferometers with single input for source light

An interferometer employed, in part, as a Sagnac interferometer or fiber optic gyro (FOG) includes a light source that provides a source light wave that is split into first and second light waves that are directed to traverse a defined optical loop path in opposite directions. The defined optical loop path in accordance with the present invention is provided by multiple waveguides wound into a coil such that the opposite traveling first and second light waves serially travel through all of the waveguides in opposite directions around the optical loop path.

Interferometer employing a multi-waveguide optical loop path and fiber optic rotation rate sensor employing same

An occasional calibration waveform is used to, first, make an interferometer sensitive to small changes in Sagnac phase difference due to rotating the gyroscope (this is commonly referred to as biasing the interferometer); second, supply a feedback phase difference to keep the interferometer sensitive to small changes in rotation rate; and third, supply the calibration modulation necessary to keep the digital electronics calibrated with respect to the Sagnac phase difference being measured.

Occasional calibration phase-difference modulation for sagnac interferometer

An interferometer employed, in part, as a Sagnac interferometer or fiber optic gyro (FOG) includes a light source () that provides a source light wave that is split into first and second light waves that are directed to traverse a defined optical loop path () in opposite directions. The defined optical loop path () in accordance with the present invention is provided by multiple waveguides wound into a coil such that the opposite traveling first and second light waves serially travel through all of the waveguides in opposite directions around the optical loop path.

Disclosed is a method and apparatus for modulating the phase difference between a pair of optical waves that exit a Sagnac interferometer, and, more particularly, one that is commonly employed as a fiber gyro, and includes a detector responsive to phase difference between the pair of waves that exit the interferometer, and a phase modulator that forms part of two control loops that are instrumental in deriving an accurate measurement of rotation rate. As disclosed herein, phase modulation applied equally to the pair of waves as they counter-propagate through the phase modulator induces modulation of the phase-difference between the two waves as they exit the interferometer. This phase difference modulation includes (i) a bias phase-difference modulation component having a selected frequency, amplitude, and waveform, (ii) a rotation-rate feedback phase-difference component that is equal in magnitude to, and opposite in sign of, the Sagnac phase difference, so that the sum thereof is controlled to be substantially zero, and (iii) a calibration feedback phase-difference modulation component that is characterized by a predetermined phase difference magnitude having substantially alternating positive and negative sign values.

Signal processing for a Sagnac interferometer

An interferometric fiber optic gyroscope having compensation electronics to virtually eliminate rotation rate sensing errors caused by Kerr effect in the IFOG due to differing intensities of the counter-propagating beams relative to each other. Compensation accounts for varying intensities of the beams due to all or some changes of: the light beam splitter ratio relative to temperature; fiber coil loss due to temperature and longevity; and the intensity of the light source because of age.

Kerr effect compensator for a fiber optic gyroscope

A deadband error reducer for a fiber optic gyroscope, which is an offset modulation signal that averages the deadband producing error over the range of the feedback modulation signal provided to the phase modulator. Although the offset modulation signal may be introduced at any of several points in the feedback loop, the offset modulation must approximate a critical amplitude at the phase modulator. If the offset modulation is a signal having segments that are linear with time, the critical amplitude of this signal will be 2.pi..

Fiber optic gyroscope with deadband error reduction

An apparatus for eliminating or reducing vibration-induced errors due to vibration rectification by applying a variable weighting function at the demodulator or analog-to-digital converter by changing the size of the demodulator reference signal or the converter gain, respectively. The changing is performed within the frequency spectrum of the vibration. Sampling of the detector output may be utilized and the samples are accumulated and processed to remove the variations due to vibration, and the rotation rate is recovered by digital demodulation.

Vibration rectification error reducer for fiber optic gyroscope

A gyroscope having three fiber optic loops for sensing rates of rotation in three axes orthogonal to one another. The gyroscope has one or two detectors and one source that is shared among the three fiber optic sensing loop subsystems with a special multi-coupler configuration. Also, portions of the rotation rate signal processing electronics, whether an open or closed loop configuration, are shared among the three sensing loops. The gyroscope may be a single mode optical fiber depolarized configuration or a polarization maintaining optical fiber configuration.

Three-axis fiber optic gyroscope having a single source and

A backscatter or secondary wave error reducer for an interferometric fiber optic gyroscope having at least one phase modulator for receiving a square wave bias phase modulation signal and a sine wave carrier suppression modulation signal. The amplitude of the carrier suppression modulation signal is sufficient to greatly reduce the interference between two sets of backscattered or secondary waves of light originating in the Sagnac loop of the gyroscope. Reduction or elimination of the interference of the two sets of secondary waves reduces or eliminates the secondary wave induced rotation rate sensing error. The frequency of the carrier suppression signal is near or equal to an even harmonic of the proper frequency of the Sagnac loop to reduce the sinusoidal or periodic rotation rate sensing error caused by the carrier suppression modulation signal.

Backscatter error reducer for interferometric fiber optic gyroscope

A fiber optic gyroscope having at least one forty-five degree splice connected to a polarization maintaining sensing coil. The splice is an alignment of forty-five or so degrees between a major axis of a state of polarization of light or an axis of birefringence at a port of a splitter/combiner, which may be an IOC or a coupler, and an axis of birefringence at an end of a fiber of a fiber optic coil loop. The gyroscope is rendered significantly more insensitive to ambient magnetic fields which cause non-rotation errors in the gyroscope's indication of rotation of its sensing loop or coil. The polarization amplitude errors of the present depolarized gyroscope are no greater than those of a similar but non-depolarized gyroscope. The present gyroscope may use an integrated optic circuit or an optical fiber coupler for splitting the light into two beams that counterpropagate in the sensing coil, for combining the beams when they exit the sensing coil. Two forty-five degree splices are placed at each end of the coil thereby resulting in depolarized light beams in the coil. The gyroscope may be either an open loop or a closed loop configuration.

Magnetically insensitive fiber optic rotation sensor

In a optical fiber coil arrangement for use in rotation sensors, for example, axial and/or radial errors can be reduced or substantially eliminated by employing trimming lengths of the first and second ends of the optical fiber used to wind the coil. The first and second ends are spatially separated from one another so as to reduce such errors. The trimming lengths may be in the form of trimming turns. To eliminate axial errors, the first end is formed into a first number of trimming turns and the second end is formed into a second number of trimming turns so that the first and second number of trimming turns are spatially offset from each other in an axial direction. To eliminate radial errors, the first end is formed into a first number of trimming turns and the second end is formed into a second number of trimming turns so that the first and second number of trimming turns are spatially offset from each other in a radial direction. Radial and axial compensation may be combined.

Trimming of fiber optic winding and method of achieving same

Apparatus and method for trimming of fiber optic winding

In a optical fiber coil arrangement for use in rotation sensors, for example, errors resulting from axial and/or radial time varying temperature gradients can be minimized or substantially eliminated by employing reverse quadrupoles for the sensor coil. One of the quadrupoles is wound in a + - - + winding configuration. However, the next adjacent quadrupole is wound in a - + + - winding configuration. This reverse quadrupole arrangement substantially eliminates radial time varying temperature gradient dependent errors and reduces axial time varying temperature gradient dependent errors. The axial time varying temperature gradient dependent errors can be substantially eliminated by winding a reverse octupole arrangement. Accordingly, a reverse octupole arrangement is wound with a + - - + - + + - - + + - + - - + winding configuration. Alternatively, the axial time varying temperature gradient dependent errors can be substantially eliminated by providing extra lengths of the '+' and '-' ends which are axially displaced so as to substantially eliminate this axial time varying temperature gradient dependent error.

Optical fiber sensor coil using reverse quadrupoles and method of

A fiber optic rotation sensor comprises a fiber optic interferometer loop formed from a highly birefringent optical fiber, and a short coherence length source for introducing light into the inteferometer loop to provide a pair of waves which counter-propogate therethrough. A detector is included to detect the phase difference between the waves after they have traversed the loop to provide an indication of the loop rotation rate, in accordance with the Sagnac effect. Phase errors are reduced by selecting the coherence length of the source and the birefringence of the fiber, so that the loop is comprised of plural fiber coherence lengths. The term 'fiber coherence length' should be distinguished from source coherence length. Fiber coherence length is the length of fiber required for the optical path length difference between the two polarization modes of a single mode fiber to equal one coherence length of the light source. In addition, phase errors are reduced by providing a birefringent waveguide between the source and the loop such that light propagates from the source to the loop in an optical path having a path length difference which is at least equal to a coherence length of the source. Phase errors are further reduced by positioning the detector to intercept the optical output signal from the loop such that light wave components in orthogonal modes are spatially averaged.

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Palo Alto, CA, United States of America

Ralph A Bergh