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US 4,299,490 AGranted
Phase nulling optical gyro
AssigneeMcDonnell Douglas Corporation
InventorsRichard F. Cahill, Eric Udd
Life of this patent
Estimating the term…
Abstract
A beam of light is split and introduced into different ends of a light path whose rotation is to be sensed. At least one frequency shifter is placed in the light path to affect the frequency difference of the two beams so as to introduce or adjust a nonreciprocal phase shift. The beams are then mixed back together and the resultant beam is detected and analyzed by suitable circuitry to provide an output indicative of rotation of the light path.
Claims74
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light;
- means for detecting said fourth beam of light and producing therefrom an output indicative of phase shift induced by the rotation about said predetermined axis;
- and
- means for compensating said output of said means for detecting to restore said output of said means for detecting to the phase relationship without rotation by producing an output indicative of the degree of phase compensation and applying said output indicative of the degree of phase compensation to said means capable of varying nonreciprocal phase shift, said output indicative of the degree of phase compensation also indicating rotation.
4 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including:
- at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light;
- and
- a second frequency shifter, said first frequency shifter being positioned between said means for splitting and recombining and said first fiber end, and said second frequency shifter being positioned between said means for splitting and recombining and said second fiber end;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis.
8 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis including:
- a detector positioned to intercept said fourth beam of light, said detector including means to produce an electrical detector output signal indicative of the intensity of said fourth beam of light;
- and
- electrical circuitry connected to receive said electrical detector output signal and to produce therefrom said output indicative of the rotation about said predetermined axis, wherein said output indicative of the rotation about said predetermined axis is an electrical signal which is fed to said first light beam frequency shifter, said electrical circuitry including:
- a synchronous demodulator which rectifies and low pass filters said electrical detector output signal and produces a demodulator signal output;
- an integrator which receives said demodulator signal output and produces therefrom a rotation rate output signal proportional to rotation rate about said predetermined axis;
- and
- a controllable oscillator to which is fed said rotation rate output signal which controls the frequency of the output thereof which is said output indicative of the rotation about said predetermined axis.
13 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams including a optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends, at least one of said ends of said optical fiber including a ferrule to which said optical fiber end is attached, said ferrule having an end surface thereon at a non-right angle to said optical fiber therein, and means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis.
3 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light;
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis including:
- a detector positioned to intercept said fourth beam of light, said detector including means to produce an electrical detector output signal indicative of the intensity of said fourth beam of light;
- and
- electrical circuitry connected to receive said electrical detector output signal and to produce therefrom said output indicative of the rotation about said predetermined axis;
- a light source output detector which produces an electrical signal in accordance with the light impinging thereon;
- a light source monitor beam splitter positioned to intercept and split a portion of said first beam of light onto said light source output detector;
- a connection to feed said electrical signal from said light source output detector to said electrical circuitry where it is used to adjust said electrical detector output signal of said detector positioned to intercept said fourth beams of light for variations in output of said light source;
- a frequency monitor beam splitter positioned to intercept and split a portion of said first beam of light into a frequency monitoring beam;
- a wide band pass, low finesse etalon positioned in said frequency monitoring beam;
- and
- a frequency monitor beam detector positioned to detect said frequency monitoring beam after it has passed through said wide band pass, low finesse etalon to produce an electrical output which varies with the frequency of said first beam whereby the frequency of said light source can be monitored.
15 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light;
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis including:
- a detector positioned to intercept said fourth beam of light, said detector including means to produce an electrical detector output signal indicative of the intensity of said fourth beam of light;
- and
- electrical circuitry connected to receive said electrical detector output signal and to produce therefrom said output indicative of the rotation about said predetermined axis;
- a light source output detector which produces an electrical signal in accordance with the light impinging thereon;
- a light source monitor beam splitter positioned to intercept and split a portion of said first beam of light onto said light source output detector;
- a connection to feed said electrical signal from said light source output detector to said electrical circuitry where it is used to adjust said electrical detector output signal of said detector positioned to intercept said fourth beam of light for variations in output of said light source;
- a frequency monitor beam splitter positioned to intercept and split a portion of said first beam of light into a frequency monitoring beam;
- an interference filter positioned in said frequency monitoring beam;
- and
- a frequency monitor beam detector positioned to detect said frequency monitoring beam after it has past through said interference filter, said frequency monitor beam detector producing an electrical output which varies with the frequency of said first beam whereby the frequency of said light source can be monitored.
15 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light;
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis including:
- a detector positioned to intercept said fourth beam of light, said detector including means to produce an electrical detector output signal indicative of the intensity of said forth beam of light;
- and
- electrical circuitry connected to receive said electrical detector output signal and to produce therefrom said output indicative of the rotation about said predetermined axis;
- a light source output detector which produces an electrical signal in accordance with the light impinging thereon;
- a light source monitor beam splitter positioned to intercept and split a portion of said first beam of light onto said light source output detector;
- a connection to feed said electrical signal from said light source output detector to said electrical circuitry where it is used to adjust said electrical detector output signal of said detector positioned to intercept said fourth beam of light for variations in output of said light source;
- a frequency monitor beam splitter positioned to intercept and split a portion of said first beam of light into a frequency monitoring beam;
- an optical grating positioned to reflect said frequency monitoring beam at an angle which is dependent upon the frequency of said first beam of light;
- and
- a frequency monitor, beam position sensitive, detector positioned to detect the position of said frequency monitoring beam after it has been reflected by said optical grating, said frequency monitor beam position sensitive detector producing an electrical output which varies with the frequency of said first beam wherey the frequency of said light source can be monitored.
15 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light said second beam of light having a polarization in a first predetermined direction;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light;
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis;
- a polarizing beam splitter positioned and oriented in said second beam of light so that said second beam of light can pass out thereof in a first predetermined direction, said light beam frequency shifter being positioned in said second beam of light after said second beam of light has passed out of said polarizing beam splitter in said first predetermined direction, said second beam passed out of said polarizing beam splitter having zero-order and first-order portions, the zero-order and first-order portions of said second beam of light thereafter going in different directions;
- a quarter-wave plate positioned in said second beam of light after said second beam of light has passed through said light beam frequency shifter and oriented 45.degree. from said first predetermined direction of polarization to convert the polarization of said second beam of light to circular polarization;
- means to change the wavefront radius of curvature of said second beam of light once it has passed through said quarter-wave plate;
- and
- means to reflect said first-order portion of said second beam of light back through said quarter-wave plate, said frequency shifter, and said polarizing beam splitter whereby the effect of beam deflection of said frequency shifter is suppressed.
10 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams including an optical fiber;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including piezoelectric means connected to apply force to said optical fiber and means to introduce a phase dither in said second and third beams of light;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis.
3 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including means to introduce a phase dither in said second and third beams of light which include an optical fiber through which said second and third beams of light pass and means to apply force to said optical fiber;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis.
3 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including piezoelectric means connected to apply force to said optical fiber;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis.
6 more elements
An optical device for determining rotation including:
- a light source which produces a first beam of light;
- means for splitting said first beam of light into at least second and third beams of light and recombining said second and third beams into a fourth beam of light;
- means for directing said second and third beams of light in opposite directions along a path about a predetermined axis about which the rotation is to be measured to establish a counterpropagating light path for said second and third beams, including:
- an optical fiber wound in a coil about said predetermined axis about which the rotation is to be measured, said optical fiber having first and second ends;
- and
- means for applying said second and third beams of light to said first and second fiber ends respectively;
- means capable of varying nonreciprocal phase shift between said second and third beams of light positioned in said second and third beams of light including at least a first light beam frequency shifter positioned in said counterpropagating light path to introduce and vary nonreciprocal phase shift in said second and third beams of light wherein said first light beam frequency shifter includes an optical fiber positioned in said counterpropagating light path and a piezoelectric element connected to apply force thereto to induce nonreciprocal phase shift in light in said counterpropagating light paths;
- and
- means for detecting said fourth beam of light and producing therefrom an output indicative of the rotation about said predetermined axis.
6 more elements
Dependencies are inferred from the claim text.