DE2934192A1 - INTERFEROMETER GYROSCOPE DEVICE - Google Patents

Description

-ν-

Aug 23, 1979 79-T-368O

ROCKWELL INTERNATIONAL CORPORATION, El Segundo, California 90245, V.St.A.

Interferometer gyroscope device

The invention relates to an interferometer gyroscope, and in particular to one at the phase detection between oppositely rotating light beams in a light path with a Another signal is combined to facilitate phase detection in between.

Laser gyroscopes are already known, and there are two types, the so-called beef laser gyroscope and that Ring interferometer gyroscope. These two types of gyroscopes are described in U.S. Patent 4,013,365.

In short, an interferometer gyroscope can point to which the present invention relates to be described by a structure shown in FIG. Operational the light coming from a laser light source is split and each part of the split beam becomes the Forced or restricted movement around a path or a path in the opposite direction of rotation. If the path is a

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Rotation is the apparent path length in a direction traversed by a portion of the ray longer than the true path length, whereas the apparent length of the path in the other direction is shorter than that true path length. This is the so-called Sagnac effect. The apparent change in path length has phase shifts in the light rays traversing the paths in each direction, compared to the state of the then prevailing would if the path were at rest. This phase difference can be measured and from this measurement the rotation of the path can be determined.

In the known devices, the light beam parts are rotated in opposite directions after passing through the light path combined after following the desired path. The combined waves are added to each other or from each other subtracts, which depends on the particular amount of phase shift experienced during the passage of the light path. The output variable is therefore only light with variable intensity, with the change in intensity indicates the speed or rate of rotation of the optical path. One recognizes "therefore that the known devices are singularly sensitive to light. So that means that when the light source, which is to be divided and in this The light to be introduced in the signal path is generated, the intensity changes, and the output variable in the same way its intensity will change, which can be interpreted as a rotation of the light path. Therefore need to make sure the gyroscope accuracy especially in inertial guidance application cases and the like special steps are provided to carefully adjust the intensity monitor the light source.

Brief description of the invention. The invention has set itself the goal of specifying an improved interferometer gyroscope, which is relatively insensitive to changes in the intensity of the light coming from the source. Further-

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the invention aims to provide an interferometer gyrsoscope, which has a reference signal source for comparison with that in an optical path in the opposite direction of rotation running light to determine the phase shift and the rotation rate or speed of the optical path. Furthermore, the invention provides an interferometer gyroscope of the type described, which is using integrated optical as well as integrated electronic circuit processes can be produced.

Further advantages, objectives and details of the invention emerge in particular from the claims and from the description of exemplary embodiments based on the drawing.

In general, the interferometer gyroscope according to the invention has a light source and an optical path that has a Zone circumscribes into which the first and second parts of the light are coupled to the path in opposite directions Directions to traverse. A reference light source is provided with which the light coupled into the optical path is combined after it has traversed the path to Generate phase differences between them for comparison to display the path rotation. Funding is also provided around the phase difference between the light after traversing the path in each direction, combined with the light of the Reference light source to be provided.

According to a further exemplary embodiment of the invention, the light coming from the signal source is divided and modulated at first and second frequencies to provide a signal source and a reference source. The signal source is shared and applied to an optical fiber in opposite directions of rotation. After the light has passed through the optical fiber, will it is compared to the light from the modulated reference source, and the phase difference therebetween is determined to determine the speed of rotation of the optical fiber around a sensitivity axis.

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In the drawing shows:

1 shows a schematic representation of a known ring laser interferometer gyroscope;

2 is a schematic representation of a laser interferometer gyroscope according to one aspect of the invention;

Fig. 3 is a schematic representation of a preferred embodiment of an inventive Ring laser interferometer gyroscope.

In the various figures there are light paths through dashed lines and electrical connections as well as mechanical ones Elements represented by solid lines.

Detailed description of preferred exemplary embodiments. Laser interferometer gyroscopes are already known and a typical example of this type is shown schematically in FIG. This well-known interferometer gyroscope 10 has three .. reflective surfaces 11, 12 and 13 supported by a common inertial frame (not shown). Light from a laser light source is used by everyone the reflective surfaces 11-13 in opposite directions of rotation reflected. This is achieved by the light from the laser source 16 striking a beam splitter 17 lets, which emits a first part of the light beam from the laser 16 in the direction indicated by arrow 18, while a second part is sent out in the direction of arrow 19. The light traveling in the direction of arrow 18 is from the surfaces 11, 12 and 13, in that order, reflected, in order then to be reflected again by the beam splitter 17 in order to be detected by a detector 22. The second part of the beam running in the direction of arrow 19 is successively the reflective surfaces 13,

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12 and 11 are reflected in order to then pass through the beam splitter 17 to run in the direction of the detector 22. The generated fringe shift is of a form in which the light intensity detected at the detector 22 changes according to the Changes the rate of angular rotation of the inertial frame supporting the reflective surfaces 11-13. The rotation of the inertial frame is indicated by the circular arrow 24. The interference pattern is determined by the apparent difference of the Path length generated by the counter-rotating light rays as a result of the angular rotation of the inertial frame will. The prior art interferometer gyroscope, however, suffers from the above-mentioned disadvantages that the present invention has should avoid.

According to one aspect of the invention, the interferometer gyroscope 30 shown in FIG. 2 is constructed similarly to the interferometer gyroscope 10 and has a light path or ring 34 which at three corners by reflective surfaces 31, 32 and 33 is defined, the latter being carried by an inertial frame (not shown). A beam splitter 35 is arranged on the vertical frame of the fourth corner of the light path to complete the ring for dividing the Light from a light source, such as laser source 36, the light is split into two beams, which are entered into the light path in counter-rotating directions, indicated by the arrows 38 and 39. The ring 34 is defined by reflective surfaces 31-33 and a beam splitter 35 forms an optical path that is a Encloses a zone that has a sensitivity axis (perpendicular to the plane of the paper) around which the optical path rotates, whose rotational speed or rate is to be measured.

Two beam splitters 42 and 43 are provided in the light path, to interrupt the oppositely rotating or circulating light within the light path, to the counter-rotating light Remove light after this has run its course

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Ring 34 has completed or substantially completed around. Thus, that portion of the light leaves from the signal source 36, which revolves in the direction of arrow 38, the beam splitter 35 to be transmitted by the beam splitter 42, whereupon Then the reflection takes place in turn from the reflective surfaces 31, 32 and 33 in order to hit the beam splitter 43, where the distance from the light path in Direction of arrow 45 takes place. In the same way, the part of the light that the beam splitter 35 in the direction of the Arrow 39 leaves, then reflected from the reflective surfaces 33, 32 and 31 to get out of the light path through the beam splitter 42 to be removed in the direction of arrow 46.

In addition to the light from the light source 36, an additional or reference light source 50 is provided in the interferometer gyroscope circuit 30. The light from the second light source 50 is split into two parts by a beam splitter 51, one of which becomes an ι. t_ray splitter 52 and the other is directed towards a beam splitter 53. The beam splitters 52 and 53 are arranged in the light paths in addition to receiving the split light beam from the source 50 in order to receive deflected light in front of the beam splitters 42 and 43, respectively. The result is therefore that the light removed from the ring in the opposite directions of rotation, which runs in the direction of arrows 46 and 45, is combined and compared with the reference rays from the light source 50. This comparison is made in each case by detecting the combination of the light removed from the ring and the reference beams on the corresponding photodiodes 56 and 57. Again, since the interference gyroscope generates light with a changed phase due to the angular rotation of the light path, after combination with the reference beam from the source 50 light with an intensity depending on the rotation rate the photodiodes 56 and 57 are detected. The output of the photodiodes 56 and 57 is then sent to amplifiers 59 and 60 as

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electrical signals are applied and the phase difference becomes determined by a phase detector 61. The output variable of the phase detector 61 therefore represents the phase difference of the light signals removed from the ring and therefore represents the angular rotation of the ring.

Since in fact the reference ray is constant and the light removed from the ring has the same phase shift in every direction, but with different directions or signs, experiences, represents the output quantity of the Phase detector 61 twice the phase difference, generated by the rate of rotation of the ring

In the embodiment shown in FIG. 2, the signal light source is 36 is referred to as a "signal" source and the reference light source is referred to as a "LO" or receive or Superposition oscillator called. This is to illustrate the analog nature of the interference gyroscope operation 30 for a heterodyne electronic processing plant. That is, the light from the signal source is "modulated" as it traverses the path around the ring and is then compared with a reference signal or Local oscillator signal "mixed" in a manner similar to heterodyne processing or heterodyne processing one electronic signal with another.

Since a comparison is made between the phase differences between light removed from each reverse rotation direction and the Reference shaft, is the interferometer gyroscope embodiment of FIG. 2 essentially as a function of the intensity. For example, if the intensity of the light from the signal source 36 decreases for some reason, the two outputs, each compared to a reference wave, produce one Phase difference that is essentially the same even though the source intensity has changed. Accordingly, the

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Operation of the device cannot be monitored as closely as the prior art and can therefore, inertial-type interferometer gyros can easily be provided. Since also two output signals are derived any ambiguity of a change in intensity at the output can be resolved to determine the direction of rotation of the device by generating square signals to determine what is known per se in the field of electronics and navigation is.

A preferred exemplary embodiment of a ring laser interferometer gyroscope according to the invention is shown in FIG. 3 and designated as a whole with 70. The embodiment of Fig. 3 is as an integrated electronic circuit and shown and described as an integrated optical arrangement, although the principles described are also included discrete components can be realized.

A laser light source 71 which is a helium neon gas laser or a distributed feedback gallium arsenide injection laser can be, generates an input beam incident on a first beam splitter. The one on the beam splitter 72 incident beam is split into two parts, one in the direction of arrow 74 and the other in the direction of arrow 75 is directed. The beam guided in the direction of arrow 74 hits an acousto-optic modulator 78, which is, for example, a surface elastic wave zinc oxide interdigital transducer can be. Those skilled in the art will recognize that other types of optical modulators can work equally can be used with advantage, for example an electro-optical modulator and the like.

The acousto-optic converter 78 receives a signal from the signal source 80 at, for example, the frequency W2 · Thus

the light output from the acousto-optic modulator 78 is a light beam with a frequency equal to the frequency w_ of the source 71 plus the frequency of the modulation frequency source w ~

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This signal is hereinafter referred to as the "signal frequency".

The light beam with the signal frequency from the akusLO-optical Modulator 78 is split into two beams by beam splitter 79, which are split by beam splitter 81 and 82 are placed in a light path 84 in opposite directions of rotation. The light path 84 in the illustrated embodiment is formed by an optical fiber. The optical fiber is of a commercially available type. Although a Multi-mode fiber can be used, but preferably the fiber should be a single-mode fiber for the Be operating with the greatest efficiency. The fiber can have multiple turns to define a path around which the applied signal can pass in opposite directions of rotation. As is the case with the well-known interferometer gyroscopes Increased the sensitivity of the gyroscope by increasing the number of turns of the fiber. For example, it was found that the optical fiber can have a number of turns, for a length of approximately one kilometer to take advantage of, being a satisfactory or two-dimensional Operation results.

The signal beam is taken out after passing through the light path 84 and applied to photodetectors such as Photodiodes 86 and 87 # routed along with a reference beam.

The above-mentioned reference beam is generated by the second part of the signal source, reflected from the beam splitter 72 along the path indicated by arrow 75. This beam is directed to a second acousto-optic modulator 88 of similar construction to the acousto-optic modulator 78, and it receives a signal from the signal generator 89 at a frequency of, for example, W ₁ . Thus, the output of the second acousto-optic modulator 88 is a light beam with the frequency w _o + w, .. This reference beam is split by a beam splitter 90 into two beams

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split each of them to a corresponding photodiode

86 and 87 is passed through beam splitters 92 and 93, respectively. In this way, the signal applied to the photodiode 86 is W ₀ + w ..- 0, and likewise it is to the photodiode

87 applied signal w _o + w .. + φ. The term "φ" represents the phase difference which the signal experiences as it traverses the optical fiber 84 as a result of the rotation of the optical fiber about its axis of sensitivity (an axis perpendicular to the plane of the paper in which the optical fiber is shown).

The output variables of the photodiodes 86 and 87 are applied to the amplifiers 85 and 96, respectively, and their output variables through a phase detector 97 can be compared to produce an output which is the phase difference, or as above mentioned, twice specifies the phase difference, namely as a result of the summation and subtraction, with this phase difference through the optical fiber.

As already mentioned above, the electronics of the signal generators 80 and 89, the amplifiers 95 and 96 and also the phase detector 97 as part of an integrated circuit which can conveniently be formed as part of the optical circuit described above can.

In addition, since the output of the interferometer gyrocope 70 When a voltage appears proportional to the phase difference between the two light beams, there are numerous methods for the electronic processing of the signal, which is read out as a function proportional to the developed phase can be. For example, a high frequency clock could be formed by the phase in a channel, wherein the counter reading is stopped by the phase in the other channel at a zero crossing point. The high frequency clock could then be counted by a simple counter, which would result in a value as an output variable that is the same is the time period representing the difference phase.

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In summary, the invention provides an interferometer gyroscope which has a light source, the Light is split and entered into a light path in opposite directions of rotation. After passing through the Path taken from the two opposite directions of rotation and the removed beams are combined with a reference signal. The phase difference between the two combined signals is determined so as to provide an indication of the rotation or indicate rotation of the optical path around which the light traveled. In one embodiment, these will be Signal and the reference signals are modulated with frequencies at which the difference between these frequencies is a Is frequency that is easily processable by the electronic circuit.

The documents submitted on the same day by the same applicant

Ifi ~ i. ■ rf ι /, /

te German patent application P (attorney's file number 79-T-3679) with the title "interferometer gyroscope" forms part of the present disclosure and is therefore attached to this application.

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Claims (14)

Claims 1. A interfero-meter gyroscope with a light source and an optical path that circumscribes an area and into which first and second parts of the light are coupled for traversing the path in two opposite directions, characterized by a reference light source with which the in the optical path coupled light is combined after it has traversed the path to produce phase differences therebetween for comparison to indicate the rotation of the path, and through Means for measuring the phase difference between the light after traversing the path in each direction, combined with the light of the reference light source. 2. Gyroscope according to claim 1, characterized in that the light path is an optical coil wound into a coil Having fiber. 3. Gyroscope according to claim 1 and / or 2, characterized in that the light source has a laser light source. 4. Gyroscope according to claim 1, characterized in that the means for detecting a pair of photodiodes each of which is arranged to receive the light after the path has been traversed in each direction, and to receive the light from the reference light source at the same time. 5. Gyroscope according to one or more of the preceding claims, in particular according to claim 4, characterized through a pair of amplifiers each connected to a corresponding one of the photodiodes to obtain an output representative of the intensity of the light received by the corresponding photodiode, and with a Phase detector to which the amplifier output variables are applied in order to generate an output variable which shows the phase 030013/0649 ORIGINAL INSPECTED difference of that received by each corresponding photodiode Light, whereby the rotation of the optical path can be determined. 6. Gyroscope, in particular according to one or more of the preceding claims, with an optical path, characterized by a laser light source having a first frequency, means for dividing the first laser light frequency into two Rays, Means for introducing the two beams in opposite directions into the optical path, thereby causing the rotation of the optical path a phase change between the rays circulating in opposite directions in the optical path generated. Means for removing the light from the optical path from each of the opposite directions to respective ones generate first and second signal beams after the light has substantially traversed the optical path, a laser light source at a second frequency, means for combining the laser light at the second frequency with the first and second signal beams for generation first and second combined beams, and means for comparing the intensity of the first and second combined beams, indicating the phase difference between the first and second signal beams. 7. Gyroscope according to claim 6, characterized in that the optical path has a plurality of turns of a having optical fiber. 8. Gyroscope according to claim 6, characterized in that the optical path reflecting a plurality of light Has elements arranged to define the optical path. 030013/0649 9. Gyroscope according to one or more of the preceding Claims, in particular according to Claim 8, characterized in that the plurality of light-reflecting elements are three such elements forming three sides of a rectangular optical path, and wherein the means have a beam splitter for introducing the two beams in opposite directions into the optical path, which is arranged at a fourth corner of the rectangular path to the laser light with the first frequency to receive and to do so in the optical path in opposite To introduce directions. 10. Gyroscope, in particular according to one or more of the preceding claims, characterized by an optical Fiber ring, a laser light source, means for splitting the laser light from the laser light source into first and second beams, means for modulating the first beam at a first frequency, and means for modulating the second beam with the first and second parts of the first modulation beam after the first and second parts die optical fiber traversed to produce a light of variable intensity, -which with a phase shift is related between the first and second parts to indicate rotation of the optical fiber about an axis of sensitivity. 11. Gyroscope according to one or more of the preceding Claims, in particular according to claim 10, characterized in that the means for modulating the first beam with a first frequency and the means for modulating the second beam at a second frequency are each an acousto-optical Have modulator, and an electrical signal source for operating the acousto-optic modulator. 030013/0649 12. Gyroscope according to one or more of the preceding claims, in particular according to claim 11 / characterized by means for determining the intensity of the combined first and second parts of the first modulated beam, combined with the second modulated beam to produce an indication of the intensity differences therebetween indicate the rotation of the optical fiber around the axis of sensitivity. 13. Gyroscope, particularly according to one or more of the preceding claims, characterized by an optical path with three light reflectors at three corners of the path, a first beam splitter forming an input element at a fourth corner of the optical path, a first laser signal source arranged to direct light onto a first beam splitter to do so in split two parts and enter them in the optical path in opposite directions of rotation, second and third beam splitters arranged in the optical Path for removing the counter-rotating light after this is substantially the length of the optical path has gone through first and second beam combiners each arranged to be out of the optical path of receives light distant from the second or third beam splitter, a fourth beam splitter, a second laser light source which is directed onto the fourth beam splitter and whose light is thereby divided into two parts is divided, of which one on the first beam combining device and the other on the second beam combining device is directed, whereby the light removed by the second and third beam splitters with the Light from the second laser light source is combined to produce first and second combined beams, each of which is one Has intensity which is at a frequency of the difference frequency between the first and second laser light sources varies and with a phase difference that 030013/0649 speed of the optical path is related, first and second light intensity detectors, arranged to receive the combined light from the first and second light combining device, respectively, first and second amplifiers »each having the first and second light intensity detectors for amplification of the detected signals is connected, and a phase detector connected to the outputs of the amplifiers to generate a signal which indicates the phase difference between the output variables of the two amplifiers, to thereby indicate the rate of rotation of the optical path. 14. Gyroscope, in particular according to one or more of the preceding claims, with a laser light source, characterized by having an optical integrated circuit a first beam splitter on the light from the laser light source hits to be split into two input beams, a first surface elastic wave interdigital transducer for adding a first frequency to a of the two input beams, a second beam splitter for splitting the output of the first transducer into two signal beams, an optical fiber connected to the optical integrated circuit and having two ends, each of which serves to receive a corresponding one of the two signal beams, the optical fiber enclosing an area whose Rotation about a sensitivity axis is to be determined, Means for directing the two signal beams into the two ends of the optical fiber, thereby creating each of the two signal beams a phase shift when passing through the optical fiber experiences when the optical fiber one Is subject to rotation around the sensitivity axis, 030013/0649 a second surface elastic wave interdigital transducer to add a second frequency to the other of the input beams, a third beam splitter for splitting the output of the second transducer into two reference beams, Beam combining means for combining or combining the signal beams after the signal beams have passed the optical Have traversed fiber, namely the combination with a corresponding one of the reference beams for generation of two combined signals, and further characterized by having an electrical integrated circuit Means for determining the two combined signals to generate two detected signals, Amplifier means for amplifying the two detected signals to generate two amplified signals, Means for receiving the two amplified signals to determine the relative phase difference therebetween for display the rotation of the optical fiber about the axis of symmetry or sensitivity, and first and second signal generators, the outputs of which supply the first and second frequencies, respectively added by the first and second surface elastic wave interdigital transducers. 030013/0649