CA2532247A1 - Differential fiber-optic frequency-modulated continuous-wave sagnac gyroscope - Google Patents
Differential fiber-optic frequency-modulated continuous-wave sagnac gyroscope Download PDFInfo
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- CA2532247A1 CA2532247A1 CA 2532247 CA2532247A CA2532247A1 CA 2532247 A1 CA2532247 A1 CA 2532247A1 CA 2532247 CA2532247 CA 2532247 CA 2532247 A CA2532247 A CA 2532247A CA 2532247 A1 CA2532247 A1 CA 2532247A1
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- 239000000835 fiber Substances 0.000 claims abstract description 51
- 239000013307 optical fiber Substances 0.000 claims abstract description 4
- 230000008878 coupling Effects 0.000 claims description 2
- 238000010168 coupling process Methods 0.000 claims description 2
- 238000005859 coupling reaction Methods 0.000 claims description 2
- 238000000926 separation method Methods 0.000 claims description 2
- 230000007274 generation of a signal involved in cell-cell signaling Effects 0.000 claims 2
- 239000004065 semiconductor Substances 0.000 claims 1
- 230000006641 stabilisation Effects 0.000 claims 1
- 238000011105 stabilization Methods 0.000 claims 1
- 230000007774 longterm Effects 0.000 abstract description 2
- 230000003287 optical effect Effects 0.000 description 8
- 230000010363 phase shift Effects 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 230000002452 interceptive effect Effects 0.000 description 1
- 230000001902 propagating effect Effects 0.000 description 1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/58—Turn-sensitive devices without moving masses
- G01C19/64—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
- G01C19/72—Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
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- Engineering & Computer Science (AREA)
- Optics & Photonics (AREA)
- Electromagnetism (AREA)
- Power Engineering (AREA)
- General Physics & Mathematics (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Gyroscopes (AREA)
Abstract
Disclosed is a differential fiber-optic frequency-modulated continuous-wave (FMCW) Sagnac gyroscope for measuring rotation velocity. The gyroscope comprises a frequency-modulated laser, two fiber-optic polarizers (P1 and P2), two Y-type single-mode fiber-optic couplers (FC1 and FC3), two X-type single-mode fiber-optic couplers (FC2 and FC4), a single-mode fiber coil and a photodiode.
The two output fibers of FC1 and FC3 are connected with the two input fibers of and FC4, the first output fibers of FC2 and FC4 are connected with the fiber coil, and the second output fibers of FC2 and FC4 are directly connected to each other to form an optical fiber shortcut, as shown in Fig. 1. The laser is driven by a gated modulation signal. The gyroscope uses the phase difference between the beat signal froin the fiber coil and the beat signal from fiber shortcut to measure the rotation velocity. The advantages of this gyroscope include high accuracy, long dynamic range, good long-term stability, compact size and light weight.
The two output fibers of FC1 and FC3 are connected with the two input fibers of and FC4, the first output fibers of FC2 and FC4 are connected with the fiber coil, and the second output fibers of FC2 and FC4 are directly connected to each other to form an optical fiber shortcut, as shown in Fig. 1. The laser is driven by a gated modulation signal. The gyroscope uses the phase difference between the beat signal froin the fiber coil and the beat signal from fiber shortcut to measure the rotation velocity. The advantages of this gyroscope include high accuracy, long dynamic range, good long-term stability, compact size and light weight.
Description
Specification This invention relates to a differential fiber-optic frequency-modulated continuous-wave (FMCW) Sagnac gyroscope used for measuring rotation velocity. Frequency-modulated continuous-wave interference, which was originally investigated in radar, has been recently introduced in optics. Optical FMCW interference naturally produces a dynamic signal, and thus to calibrate fractional phase, distinguish phase shift direction and count the number of full periods is much easier than with the classical homodyne interference. Comparing with the traditional interferometers, optical FMCW interferometers generally can offer a higher accuracy and longer dynamic range. The application of optical FMCW interference to rotation sensing can effectively solve the problems in the conventional fiber-optic Sagnac gyroscopes, such as zero-sensitivity point, inaccurate phase calibration, ambiguous shift direction determination and 7c-phase shift restriction.
For an optical FMCW Sagnac gyroscope, the basic requirement is that the gyroscope should be unbalanced so that the beat signal with an appropriate frequency can be obtained. However, the unbalanced interferometer structure may introduce a new problem: there will be a nonreciprocal phase drift in the gyroscope if the environmental parameters (such as temperature) change. This nonreciprocal phase drift will significantly affect the accuracy and long-term stability of the gyroscope.
The differential fiber-optic FMCW Sagnac gyroscope exposed in this patent consists of a single-mode frequency-modulated laser, two fiber-optic polarizers (Pi and P2), two Y-type single-mode fiber couplers (FC1 and FC3), two X-type single-mode fiber couplers (FC2 and FC4), a single-mode fiber coil and a photodiode, as shown in Fig. 1. The laser is driven by a gated modulation signal (e.g. a gated sawtooth-wave signal). The two output fibers of FCi and FC3 are connected with the two input fibers of FCz and FC4, to construct the basic structure of an unbalanced fiber-optic interferometer. The first output fibers of FC2 and FC4 are connected with the fiber coil, and second output fibers of FC2 and FC4 are directly connected to each other to form an optical fiber shortcut. The two fiber-optic polarizers and an in-line polarization controller (bend and twist of a portion of fiber coil) are used to ensure that the two counter propagating beams in the fiber coil travel in the same polarization mode, so that the contrast of the beat signal can be optimized.
This gyroscope actually is a time-division multiplexed fiber-optic FMCW
Sagnac gyroscope. A gated FMCW laser beam is first launched into FCi and split into two beams. When these beams pass through FC2 and FC4, they will split again.
Parts of the two beams traverse the fiber coil in opposite directions, and the remainders of the two beams take the shortcut. If the delay time introduced by the fiber coil is longer than the frequency modulation period T,,, but shorter than the separation of the gated wavelet (T,,,'-T,,,), the beat signal produced by the two counter-propagating beams in the fiber coil and the beat signal produced by the two counter-propagating beams in the shortcut will arrive on the photodetector at different time moments without overlapping, and therefore they can be separated by using an electric gate circuit, as shown in Fig. 2. Obviously, both beat signals contain the same nonreciprocal phase drift caused by the variation of the environmental conditions, but only the beat signal from the fiber coil contains the reciprocal Sagnac phase shift if the fiber coil is in rotation. Therefore, separating the two beat signals with an electronic gate circuit, finding the phase difference between them, the Sagnac phase shift caused by the rotation of the fiber coil can be determined.
For instance, if the frequency of the laser is modulated with a sawtooth waveform, the beat signal 11(t) from the fiber coil in a modulation period can be written as 1,(t)=1,o 1+ V,cos(21rAvc,NOPDt+ OPD+4 fl AO
where 110 and V1 are the average intensity and contrast of the beat signal from the fiber coil, Av is the optical frequency modulation excursion, ti,, is the modulation frequency, c is the speed of light in free space, A is the central optical wavelength in free space, and OPD is the initial optical path difference between the two interfering beams. The OPD is given by OPD= n,(112 +134 -114 -123).
where ne is the effective refractive index of the single-mode fiber, 112.134,114, and 123 are the lengths of the linking fibers from the FC1 to FC2, FC3 to FC4, FC1 to FC4, and FC2 to FC3, respectively. Properly choosing the lengths of the linking fibers, we can get any desired initial optical path difference.
Similarly, the beat signal 12(t) from the optical fiber shortcut in a modulation period can be written as r2zAvv OPD 2~r 1 I, (t) = 120 1 + V2 cosl\ c t + _ OPD) where 12o and V2 are the average intensity and contrast of the beat signal from the fiber shortcut. Obviously, the phase difference of the two beat signals A0 equals A¾ 4,RLfl C1,o Hence, the rotation angular velocity of the gyroscope can be determined by cl,o A
4zRL
Note that, because do is not relative to OPD, this gyroscope is free from the length variation of the linking fibers due to temperature change or strain.
For an optical FMCW Sagnac gyroscope, the basic requirement is that the gyroscope should be unbalanced so that the beat signal with an appropriate frequency can be obtained. However, the unbalanced interferometer structure may introduce a new problem: there will be a nonreciprocal phase drift in the gyroscope if the environmental parameters (such as temperature) change. This nonreciprocal phase drift will significantly affect the accuracy and long-term stability of the gyroscope.
The differential fiber-optic FMCW Sagnac gyroscope exposed in this patent consists of a single-mode frequency-modulated laser, two fiber-optic polarizers (Pi and P2), two Y-type single-mode fiber couplers (FC1 and FC3), two X-type single-mode fiber couplers (FC2 and FC4), a single-mode fiber coil and a photodiode, as shown in Fig. 1. The laser is driven by a gated modulation signal (e.g. a gated sawtooth-wave signal). The two output fibers of FCi and FC3 are connected with the two input fibers of FCz and FC4, to construct the basic structure of an unbalanced fiber-optic interferometer. The first output fibers of FC2 and FC4 are connected with the fiber coil, and second output fibers of FC2 and FC4 are directly connected to each other to form an optical fiber shortcut. The two fiber-optic polarizers and an in-line polarization controller (bend and twist of a portion of fiber coil) are used to ensure that the two counter propagating beams in the fiber coil travel in the same polarization mode, so that the contrast of the beat signal can be optimized.
This gyroscope actually is a time-division multiplexed fiber-optic FMCW
Sagnac gyroscope. A gated FMCW laser beam is first launched into FCi and split into two beams. When these beams pass through FC2 and FC4, they will split again.
Parts of the two beams traverse the fiber coil in opposite directions, and the remainders of the two beams take the shortcut. If the delay time introduced by the fiber coil is longer than the frequency modulation period T,,, but shorter than the separation of the gated wavelet (T,,,'-T,,,), the beat signal produced by the two counter-propagating beams in the fiber coil and the beat signal produced by the two counter-propagating beams in the shortcut will arrive on the photodetector at different time moments without overlapping, and therefore they can be separated by using an electric gate circuit, as shown in Fig. 2. Obviously, both beat signals contain the same nonreciprocal phase drift caused by the variation of the environmental conditions, but only the beat signal from the fiber coil contains the reciprocal Sagnac phase shift if the fiber coil is in rotation. Therefore, separating the two beat signals with an electronic gate circuit, finding the phase difference between them, the Sagnac phase shift caused by the rotation of the fiber coil can be determined.
For instance, if the frequency of the laser is modulated with a sawtooth waveform, the beat signal 11(t) from the fiber coil in a modulation period can be written as 1,(t)=1,o 1+ V,cos(21rAvc,NOPDt+ OPD+4 fl AO
where 110 and V1 are the average intensity and contrast of the beat signal from the fiber coil, Av is the optical frequency modulation excursion, ti,, is the modulation frequency, c is the speed of light in free space, A is the central optical wavelength in free space, and OPD is the initial optical path difference between the two interfering beams. The OPD is given by OPD= n,(112 +134 -114 -123).
where ne is the effective refractive index of the single-mode fiber, 112.134,114, and 123 are the lengths of the linking fibers from the FC1 to FC2, FC3 to FC4, FC1 to FC4, and FC2 to FC3, respectively. Properly choosing the lengths of the linking fibers, we can get any desired initial optical path difference.
Similarly, the beat signal 12(t) from the optical fiber shortcut in a modulation period can be written as r2zAvv OPD 2~r 1 I, (t) = 120 1 + V2 cosl\ c t + _ OPD) where 12o and V2 are the average intensity and contrast of the beat signal from the fiber shortcut. Obviously, the phase difference of the two beat signals A0 equals A¾ 4,RLfl C1,o Hence, the rotation angular velocity of the gyroscope can be determined by cl,o A
4zRL
Note that, because do is not relative to OPD, this gyroscope is free from the length variation of the linking fibers due to temperature change or strain.
The advantages of this gyroscope include no zero-sensitivity point, accurate phase calibration, easy shift-direction determination, no ir-phase shift restriction, no nonreciprocal phase drift, and free from the frequency drift of laser source, Moreover, since there is no bulk phase modulator or bulk frequency shifter in the system, the size and weight of the gyroscope is also reduced.
The coupling ratios of the fiber couplers are determined according to the light attenuation in the fiber coil in order that the intensities of the two pulsed beat signals can be almost equal. Moreover, the fiber-optic polarizers and fiber couplers in this gyroscope can also be replaced by integrated-optic polarizers and integrated-optic couplers.
The coupling ratios of the fiber couplers are determined according to the light attenuation in the fiber coil in order that the intensities of the two pulsed beat signals can be almost equal. Moreover, the fiber-optic polarizers and fiber couplers in this gyroscope can also be replaced by integrated-optic polarizers and integrated-optic couplers.
Claims (12)
1. A differential fiber-optic FMCW Sagnac gyroscope for measuring rotation velocity, comprising a single-mode frequency-modulated laser, two fiber-optic polarizers (P1 and P2), two Y-type single-mode fiber couplers (FC1 and FC3), two X-type single-mode fiber couplers (FC2 and FC4), a single-mode fiber coil and a photodiode; wherein the two output fibers of FC1 and FC3 are connected with the two input fibers of FC2 and FC4, the first output fibers of FC2 and are connected with the fiber coil, and second output fibers of FC2 and FC4 are directly connected to each other as an optical fiber shortcut;
2. A gyroscope as defined in claim 1, wherein said laser is driven by a gated modulation signal, the frequency modulation period T m of said gated modulation signal is shorter than the delay time introduced by said fiber coil, and the separation of said gated wavelet (T m'-T m) is longer than the delay time introduced by said fiber coil; wherein the beat signal produced by the two counter-propagating beams in said fiber coil and the beat signal produced by the two counter-propagating beams in said fiber shortcut are detected by said photodetector and separated by using an electric gate circuit, and the phase difference between these two beat signals is measured to determine the rotation velocity;
3. A gyroscope as defined in claim 1 or claim 2, wherein said single-mode frequency-modulated laser can be at least a single-mode semiconductor laser;
4. A gyroscope as defined in claim 1 or claim 2 or claim 3, wherein said single-mode frequency-modulated laser includes coupling lenses, a temperature control system or frequency stabilization system, and a current driving circuit;
5. A gyroscope as defined in claim 1 or claim 2 or claim 3, wherein said gated modulation signal can be at least a gated sawtooth-wave signal, a gated triangular-wave signal, a gated sinusoidal-wave signal, or a gated rectangular-wave signal;
6. A gyroscope as defined in claim 1 or claim 2, wherein said fiber-optic polarizers and fiber-optic couplers can be integrated-optic polarizers and integrated-optic couplers;
7. A gyroscope as defined in claim 1 or claim 2, wherein said photodetector can be at least a p-i-n photodiode or avalanche photodiode;
8. A gyroscope as defined in claim 1 or claim 2, including a signal generation and processing electric circuit or a microcomputer-controlled digital signal generation and processing system;
9. A gyroscope as defined in claim 1 or claim 2, wherein the rotation velocity is determined by comparing the phase difference between said two beat signals;
10. A gyroscope as defined in claim 1 or claim 2, wherein the rotation velocity is determined by comparing the phase difference between the beat signal from the said fiber coil and a standard reference signal of the same frequency;
11. A gyroscope as defined in claim 1 or claim 2 or claim 9 or claim 10, wherein the phase difference of said two signals can be measured at least by comparing the phase difference of their most intensive harmonics, or by comparing the relative intensity of said two signals at a certain time moment in a modulation period;
12. A gyroscope as defined in claim 1 or claim 2, wherein said fiber couplers and said fiber coil can be single-mode polarization-maintaining fiber couplers and single-mode birefringent fiber coil.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2532247 CA2532247A1 (en) | 2006-01-05 | 2006-01-05 | Differential fiber-optic frequency-modulated continuous-wave sagnac gyroscope |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2532247 CA2532247A1 (en) | 2006-01-05 | 2006-01-05 | Differential fiber-optic frequency-modulated continuous-wave sagnac gyroscope |
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| Publication Number | Publication Date |
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| CA2532247A1 true CA2532247A1 (en) | 2007-07-05 |
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| CA 2532247 Abandoned CA2532247A1 (en) | 2006-01-05 | 2006-01-05 | Differential fiber-optic frequency-modulated continuous-wave sagnac gyroscope |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009065086A3 (en) * | 2007-11-15 | 2009-07-02 | Univ Leland Stanford Junior | Low-noise fiber-optic sensor utilizing a laser source |
| US8223340B2 (en) | 2007-11-15 | 2012-07-17 | The Board Of Trustees Of The Leland Stanford Junior University | Laser-driven optical gyroscope having a non-negligible source coherence length |
| CN115950459A (en) * | 2023-02-27 | 2023-04-11 | 安徽大学 | Data processing method and device of optical fiber interferometer |
-
2006
- 2006-01-05 CA CA 2532247 patent/CA2532247A1/en not_active Abandoned
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2009065086A3 (en) * | 2007-11-15 | 2009-07-02 | Univ Leland Stanford Junior | Low-noise fiber-optic sensor utilizing a laser source |
| US7911619B2 (en) | 2007-11-15 | 2011-03-22 | The Board Of Trustees Of The Leland Stanford Junior University | Low-noise fiber optic sensor utilizing a laser source |
| US8223340B2 (en) | 2007-11-15 | 2012-07-17 | The Board Of Trustees Of The Leland Stanford Junior University | Laser-driven optical gyroscope having a non-negligible source coherence length |
| US8289521B2 (en) | 2007-11-15 | 2012-10-16 | The Board Of Trustees Of The Leland Stanford Junior University | Low-noise fiber-optic sensor utilizing a laser source |
| US8437005B2 (en) | 2007-11-15 | 2013-05-07 | The Board Of Trustees Of The Leland Stanford Junior University | Optical sensor having a non-negligible source coherence length |
| US8681339B2 (en) | 2007-11-15 | 2014-03-25 | The Board Of Trustees Of The Leland Stanford Junior University | Optical sensor having a non-negligible source coherence length |
| CN115950459A (en) * | 2023-02-27 | 2023-04-11 | 安徽大学 | Data processing method and device of optical fiber interferometer |
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