JPH0827194B2 - Fiber optic gyroscope - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to optical rotation sensors based on the Sagnac effect, such as fiber optic gyroscopes, and in particular, including relatively low cost components, thereby reducing system cost without degrading performance. Optical fiber gyroscope that minimizes

[0002]

BACKGROUND OF THE INVENTION Rotational measurements are of considerable importance in many areas from missile and aircraft guidance to spacecraft applications.

The rotary wheel or mechanical gyroscope system has been used for many years. Despite its widespread acceptance, this approach has some drawbacks known in the navigation guidance field. These include relatively short life due to continuous movement of component parts and high component cost.

Optics based on the Sagnac effect, such as ring laser gyroscopes, have replaced mechanical gyroscopes in many applications. Development of a small scattering mirror for generating laser light and a high-quality gas discharge tube
Facilitated the development of this technology. However, the ring laser gyroscope is apt to cause a frequency lock phenomenon that erases the rotation-induced frequency beat at a low rotation rate.

Fiber optic gyroscopes have emerged as an alternative to ring laser gyroscopes without the problem of frequency lock-in at low rotation rates. In addition, fiber optic gyroscopes offer the potential for cost savings. Therefore, this equipment may be suitable for large volume and low and medium precision navigation and guidance systems.

Fiber optic gyroscopes initially used weak birefringent fibers similar to those used in the fiber optic communications industry. A schematic diagram of a typical weak birefringent fiber optic gyroscope of the prior art is shown in FIG. Such a device comprises a laser diode light source 10 and two beam splitters 12 and 14 (or fiber directional couplers) for directing the light.
A photodetector 16, a multi-turn fiber coil 18 acting as a rotation sensing component, and a phase modulator 20 consisting of either a piezoelectric cylinder or a single groove LiNbO ₃ waveguide modulator.

One of the most well known problems of fiber optic gyroscopes made with weakly birefringent fibers and weakly birefringent optical components is the
It is a large polarization shift due to random and unpredictable changes in energy between two polarization states. This polarization instability, also known as polarization non-reciprocal (NR) polarization error, is briefly described below.

Ezekiel and Audi
rditty) ”“ Optical Fiber Rotation Sensor: Tutorial
Review, '' Proceedings of First International Confe
rence on Fiber Optic Rotation Sensors, Cambridge, M
As disclosed in A 1981), because of a small amount of phase shift Sagnac-induced in the optical fiber gyroscope, the spurious phase shift caused by parasitic effects a variety of different, larger orders than the phase shift Sagnac-induced The quantity may be easier. The only known way to cancel a large number of said spurious phase shifts is by using the so-called "reciprocity principle". By this principle, many of the parasitic unwanted phase shifts, regardless of their magnitude, will disappear, provided that the counter-propagating waves follow the same optical path in the sensing loop.

Single-mode optical fibers actually exhibit two orthogonal polarization modes. Even if it is always possible to emit light in only one polarization mode of a weakly birefringent single-mode fiber (a small lateral force on the fiber,
Many external sources of perturbing birefringence (such as fiber twist or flexure, magnetic fields or electric fields) will couple energy into the orthogonal modes. As a result, in the prior art fiber optic gyroscope of FIG. 1, two counter-propagating waves are "cross-coupled" with respect to orthogonal polarizations, with each portion of each wave traveling first in one polarization state. We cannot guarantee that we will follow the same optical path. Therefore, the principle of reciprocity prevents producing polarization non-reciprocity (PNR) polarization errors.

Due to the principle of reciprocity, introducing a perfect polarization filter (or polarizer) in front of the loop coupler (at point A in FIG. 1) will eliminate the PNR deflection error. However, in another type of all-weak birefringent fiber gyroscope, introducing a polarizer in front of the loop coupler would cause another problem known as "polarization fading". Polarization fading is found in weakly birefringent optical fiber systems that include polarizers. Since the polarization state (SOP) of light in a weakly birefringent single-mode fiber is perturbed (due to the external birefringent perturbation cause mentioned above, which results in a continuous change in energy between the two polarization modes), that state Occurs where the SOP is orthogonal to the propagation axis of the polarizer. The energy propagated in said state becomes zero. Therefore, large perturbations of energy (as large as 100 percent) occur repeatedly. Polarization fading is a feature of conventional fiber optic gyroscopes.
It has been mitigated by periodically manually adjusting the SOP using a fiber polarization controller that aligns the polarization axis with the SOP. Needless to say, such a make-up approach is unsuitable for the design of inexpensive, mass-producible devices.

In addition to polarization fading, weakly birefringent fiber optic gyroscopes using polarizers require unrealistically high performance polarizers to achieve satisfactory rotational sensitivity. It is estimated that, for example, a gyroscope consisting of weakly birefringent fibers and components requires a polarizer with an extinction ratio of about 120 dB to obtain navigation grade performance. Currently, the best known polarizers have an extinction ratio of about 90 dB. The extinction ratio of polarizers that can be mass-produced at low cost generally does not exceed 60 to 70 dB.

The problems of polarization fading and polarization non-reciprocal polarization errors have been greatly alleviated by the introduction of polarization maintaining (PM) fibers and low coherence or broadband light sources such as superluminescent diodes. For example, WKBurns, CLCh
en and RPMoeller, "Fiber-Optic Gyroscopes with Br
oadband Sources, " J. Lightwave Tech., Vol 1, No.98 , (19
See 83). PM fibers are characterized by the fact that the SOP of the light emitted in one of the fiber polarization modes is substantially constant over the long section of the fiber (hundreds of meters or kilometers), despite the presence of external birefringence perturbations. Designed to be maintained in a stable manner. Polarization fading fundamentally disappears when the SOP of light is always substantially aligned with the propagation axis of the polarizer. The PNR deflection error is greatly reduced because the low coherence of the light source, in conjunction with the strong birefringence of the PM fiber, greatly reduces the correlation between different parasitic cross-coupled and first-order waves.

The use of PM fibers and components has added substantial cost to both fiber and fiber component fabrication. PM fibers and PM couplers are much more costly to manufacture than their weakly birefringent counterparts, for example, as the manufacture of PM couplers requires costly alignment steps.

Further, if the average wavelength of the light source is not stable with respect to temperature change, a scale factor error may occur. The average wavelength has to be very stable with respect to the environment of the fiber optic gyroscope, but can be greatly influenced by eg the temperature dependence of the splitting ratio of the coupler. Prior designs have not addressed this problem traditionally for systems using PM or weakly birefringent components.

Another approach to reducing both polarization fading and PNR deflection error for weakly birefringent fiber sensing coils is described by Ulrich in "P.
olarization and Depolarization in the Fiber Optic
Gyroscope, " First International Conference on Fibe
r Optic Rotation Sensors, MA (1981). Ulrich discloses the principle of depolarization or "averaging" of polarized light. According to Ulrich, a stable polarization average is created if all SOPs likely to occur in the weakly birefringent fiber are present during the gyroscope detector's adjustment time. A practical way to obtain depolarization or polarization averaging is "The Temporal Coherence of Various S".
emiconductor Light Sources Used in Optical Fiber S
ensors. " Ibid on RE Epw
Orth) as described by the Lyot depolarizer associated with a broadband light source. Another reference for the Riot depolarizer is WK Burn.
s, "Degree of Polarization in the Lyot depolarizer
s, " J. Lightwave Tech. , Vol 1, p. 475 (1983), which reference is incorporated herein by reference. Gubbins handling equipment
U.S. Pat. No. 4,828,389, the concept of which is further described in "Multiplexed Approach for the Fiber Op
tic Gyro Inertial Measurement Unit, "SPIE Prceeding
s on Fiber Optic and Laser Sensors Vol 8, pgs. 93
Through 102 (1990), JL Paj (JL Pa
ge).

Depolarization gyroscopes are effective for low precision applications (minimum rotational sensitivity of 5 to 50 degrees / hour), but due to the limitations of today's polarizers and depolarizers, eg inertial navigation, Avionics attitude and heading reference,
Precision required for missile guidance applications (0.003
It is doubtful that a minimum rotational sensitivity of ~ 1.0 degree / hour) can be obtained.

[0017]

SUMMARY OF THE INVENTION The present invention comprises at least a light source, at least one photodetector, at least one fiber optic sensing coil, and at least one Y-shaped waveguide.
By overcoming an optical fiber gyroscope of the type including a multi-functional integrated optical chip, the above drawbacks of the prior art are overcome. The improvement of the device provided by the gyroscope of the present invention consists in the use of both weakly birefringent and polarization-maintaining (PM) components and in that the sensing coil consists of PM fibers.

The above and additional features and advantages of the present invention include:
It will become more apparent from the detailed description below. The above description is accompanied by a set of drawings. The numbers in the drawings correspond to the numbers in the written description and indicate the features of the invention. Like numbers refer to like features throughout both the drawings and the written description.

[0019]

FIG. 2 is a schematic diagram of a triaxial fiber optic gyroscope according to the present invention. The apparatus of FIG. 2 incorporates the teachings of the present invention into another conventional three-axis gyroscope system to provide performance comparable to systems formed solely of polarization-maintaining (PM) fibers and couplers at substantially lower cost. It can be seen from the description below that The savings are due to the selective incorporation of relatively inexpensive birefringent fibers and couplers into the system. It will be apparent from the following discussion that the teachings of the present invention are not limited to triaxial devices. Although a large number of components are inherently in a 3-axis system rather than a 1-axis system, and thus component cost may be significantly saved, the principles of the present invention are successful in systems using any number of gyroscopes. Can be applied. The gyroscope of FIG. 2 is divided at 19 into an area 20 made of weakly birefringent components and an area 22 made of the more costly PM components. The two areas are multifunction integrated optical chips (MIOCs) 30, 32 and 3
4 input pigtails each with multidirectional coupler 3
6, 38, and 40 at melt junctions 24, 26, and 28 (indicated by "x"). Coupler 3
6, 38 and 40 are conventional devices formed of a pair of fused weakly birefringent optical fibers, the chip 3
The input pigtails of 0, 32 and 34 consist of PM optical fibers.

MIOCs (or chips) 30, 32 and 34 are well known devices, each preferably of Li
It consists of a substrate made of a suitable electro-optical material such as NbO ₃ , which is pre-determined between a plurality of counter-reflecting propagating beams emanating from PM waveguide Y-shaped connections formed thereon. The resulting phase shift. The PM fiber optic output pigtails from MIOCs 30, 32 and 34 are connected to PM fiber optic sensing coils 42, 44 and 46 by a pair of splices 48, 50 and 52, respectively. In exchange, coils 42, 44 and 46 are
The IOCs 30, 32 and 34 may be pigtailed directly to eliminate the need for joints 48, 50 and 52, thereby further reducing system cost.

Returning to area 20, each of its optical paths is formed by a weakly birefringent fiber. The term "weak birefringence"
Is related to its relatively small anisotropy. That is, the transverse indices of refraction of the fibers are not significantly different. This is unlike PM fibers, which have significantly different indices of refraction (relative to the slow and fast axes). It is the above-mentioned property of PM fiber at the core of its ability to maintain the SOP of light.

Area 20 contains photodetectors 54, 56, 58 and 60, each having an associated pigtail of weak birefringent fiber connected to a weak birefringent coupler pigtail at the junction, the first of which. Of the three serve to measure the signal output of coils 42, 44 and 46.
The coils are preferably arranged to provide a rotational indication for one of the three orthogonal spatial axes. The fourth detector 60 acts as a monitor and provides a signal for measuring the output energy of the broadband depolarized fiber light source 62. (The detector 60 is, instead, 60
It may be positioned at one of the positions indicated by a, 60b and 60c. The detector 60 functions as part of a control system that regulates the output energy of the light source 62 by tuning the laser diode 64. The arrangement of the control system is well known and does not form part of the invention claimed herein, so the circuit is not shown in detail in FIG. (As shown, the laser diode 64 is placed in a reverse pumping state, which has the advantage of greatly reducing the likelihood of unabsorbed pump light propagation to the sensing coil of the gyroscope. Unintended light propagation can induce polarization and scale factor errors.)
The broadband fiber light source 62 preferably comprises an erbium-doped fiber connected at the junction 66 to the pigtail of a weakly birefringent wavelength division multiplexing (WDM) coupler 68. The end 63 of the fiber is made to avoid light being reflected back into the fiber. The coupler 68 is connected to the weakly birefringent coupler 72 at the joint 70. The pigtails of coupler 72 are connected to the pigtails of weakly birefringent directional couplers 78 and 80 at junctions 74 and 76, respectively. The junctions 82, 84 and 86 complete the optical path between the couplers 78 and 80 and the aforementioned couplers 36, 38 and 40. Couplers 72, 78 and 80 operate as energy splitting couplers. Such networks are
For example, a single coupler with a split ratio of 3: 1 or 4: 1 can be exchanged.

It is well recognized that broadband fiber sources, such as laser diode pumped erbium-doped weakly birefringent optical fibers, emit unpolarized light. An alternative embodiment of the present invention using a polarized light source is shown in FIG. In this figure, elements corresponding to those of the previous embodiment are indicated by corresponding numbers. As mentioned above, unlike the previous embodiment, the arrangement of FIG. 3 does not use a non-polarized light source. Rather, the gyroscope of FIG. 3 uses a polarized light source 88, such as a low coherence laser diode or superluminescent diode. Light source 88 has an associated PM pigtail that is connected to the weakly birefringent pigtail of coupler 72 at junction 90. Since no pumping diode is required, the overall system design is slightly rearranged with the elimination of WDM 68 in FIG.

The Riot depolarizers 120, 122 and 124 connect the joints 24, 26 and 28 to MIO, respectively.
It is incorporated into the PM fiber section that connects to C30, 32 and 34. The Riot depolarizer may be a stack of birefringent materials arranged to meet the phase retardation requirements for operation, or a PM of exactly 45 degrees.
Either of the fiber joints may be used. The operation of the Riot depolarizer is disclosed in the Barnes and Epworth articles cited above. Prior art attempts to incorporate PM and weakly birefringent components into an optical fiber triaxial system (eg US Pat. No. 4,828,389).
Unlike the present invention, where the Riot depolarizer is located outside the coil and is only used with a polarized light source,
It was necessary to place this depolarizer in the detection loop.

The inventor has shown that a system formed according to FIGS. 2 or 3 (or a similar single axis arrangement) can achieve comparable performance to a system using only relatively expensive PM fibers and couplers. discovered. This is due, in part, to the fact that using an area consisting of only weakly birefringent elements simplifies the analysis of the system and thus its design. The weakly birefringent zone 2 of the gyroscope system
0 can be treated as one polarization cross-coupling point for polarization error analysis. As a result, (1) the length of the fiber lead of the weakly birefringent component is not suitable for polarization non-reciprocal error cancellation, and (2) the conditions that can cause polarization non-reciprocal polarization error in the system are: Significantly reduced. This is due to the weakly birefringent and essentially different types of parasitic waves generated in PM fibers.
Whereas the parasitic wave causes polarization non-reciprocal error in both types of fibers and elements, the low degree of anisotropy of weakly birefringent fibers means that even if any cross-couplings are weakly birefringent optical paths. All cross-coupled energies, whether occurring along, will be coherent or correlative. Therefore, despite the discontinuity that may cause cross-coupling along the weak birefringent optical path, four or more different waves do not occur and the light propagates to the (weak birefringent) area 20. It will not be observed in any weakly birefringent optical fiber. This means that each cross-coupling from the fast axis to the slow axis or vice versa causes a parasitic wave that quickly becomes uncorrelated (or incoherent) with respect to the traveling wave.
Unlike the case of M fiber and element. Four different waves appear in each weakly birefringent optical path, which includes two orthogonally polarized waves A and B (which are uncorrelated A and B if the light source is not polarized) generated by the light source. . A
Waves orthogonally polarized with respect to and waves orthogonally polarized with respect to B result from cross-coupling along the weakly birefringent optical path. Each last named wave A ′ and B ′ is almost perfectly correlated with its corresponding generated wave (A or B).

Mathematically, the above condition, in which one has to deal analytically with only four waves per weak birefringent optical path, is the case where n is purely the cross-coupling in the PM optical path and the resulting parasitics. It can be contrasted with 2 ⁿ different (uncorrelated) waves generated in the PM optical path in the case of the number of wave progressions. The bond is (joint, pigtail, Y
Profile and / or LiNbO ₃ along the optical path, either discontinuous (due to the presence of shaped connections and couplers)
It can either be continuous (dispersed) due to the presence of irregularities in the crystal, further complicating the analysis results.

Therefore, in addition to reducing material costs, the elimination of some PM elements simplifies the analysis required for system design. Accordingly, the designer treats the weakly birefringent section 20 as a "bundle" for analysis and only considers the placement of the PM section 20 (fiber length,
Further economic savings are realized because the attention can be concentrated (with respect to device isolation etc.). Also, by using either a non-polarized light source or a polarized light source combined with a depolarizer, the problems associated with polarization fading are minimized in the present invention.

4 and 5 are schematic views of a single axis gyroscope according to the present invention. The gyroscope in Figure 4
A broadband light source such as an erbium-doped fiber 92 pumped by a laser diode 94 is used. As explained previously, such an arrangement is known to produce unpolarized light. On the other hand, in FIG. 3, the laser diode 96 emits polarized light. In general, the arrangements of Figures 4 and 5 correspond to the triaxial arrangements of Figures 2 and 3, respectively.

Returning to FIG. 4, the one-axis gyroscope is
Distinct "zones", ie a zone 98 to the left of 100 of weakly birefringent elements and 100 of PM elements.
Is divided into areas 102 to the right. As in the previous explanation, the optimum design is PM selection.
The invention simplifies as far as it can be done by focusing on the placement of the area 102. As mentioned above, area 98 is equal to one polarization cross-coupling point for polarization error analysis.

Conservation uses weakly birefringent couplers 104 and 106, which provides the ability of the coupler 104 to pump the doped fiber 92 into the pumping diode 94, which connects the photodiode 108 to the gyroscope system. , Area 98. All joints to the left of 100 interconnect weak birefringent fiber pigtails, and joint 110 connects the pigtails of weak birefringent coupler 106 to MIOC1.
Connect to 12 PM input pigtails. The output pigtail of chip 112 is connected to the PM fiber sensing coil by a pair of splices 116. As mentioned previously, this pair of joints is not needed if the coil is pigtailed directly to the tip 112.

The single-axis gyroscope of FIG. 4 incorporates the teachings and advantages of the present invention while at the same time providing essentially the same performance as a PM-only single-axis gyroscope. However, FIG.
System achieves substantial savings by replacing a pair of PM couplers with weakly birefringent couplers 104 and 106. While such cost savings are certainly less impressive than the cost savings realized in the 3-axis device according to the invention, the savings realized in terms of cheaper component costs and simplified overall design are:
It's not trivial.

The 1-axis gyroscope shown in FIG.
The single-axis gyroscope differs from the single-axis gyroscope of FIG. 4 in much the same way that the three-axis gyroscope of FIG. 2 differs. That is, the light source 96 emits polarized light, so that the Riot depolarizer 118 is required as in the triaxial version, which depolarizer 118 is located in the PM zone 102. As mentioned earlier, the polarization filtering of the light beam allows the beam to be detected by the beam to ensure that the beam modes propagating in a tie to a pair of teeth "experience" the same optical path (the principle of reciprocity). It must be done in a fiber optic gyroscope before entering the loop and after exiting the loop. In the present invention, the sensing coil 114 and the output pigtails of the MIOC are made of PM fiber. This is because PM in sensing coils such as those disclosed in the above-identified U.S. patents that use weakly birefringent sensing coils and in which a Riot depolarizer must be inserted. And unlike prior art attempts to incorporate weakly birefringent fibers. Rather, the inventor used only PM fiber for the rotation sensing portion of the gyroscope.

As previously mentioned, the present invention achieves a level of performance that is virtually indistinguishable from the fairly high cost systems formed solely of PM fibers and PM fiber couplers. Figure 6 shows a standard PM
FIG. 7 is a graph of deflection uncertainty data as a function of temperature for a 1-axis 0.8 micron gyroscope using a coupler, and FIG. 7 shows results obtained with a 1-axis gyroscope using a weakly birefringent coupler in accordance with the present invention. Is a graph of. A polarized light source (super light emitting diode) was used with the Riot depolarizer. A standard deviation of 0.61 degrees per hour was observed on the PM gyroscope and it was discovered that only a slightly larger variation of 1.07 degrees per hour was present in the output of the single axis gyroscope of the present invention.

8 and 9 (constant temperature) and FIGS. 10 and 1
1 (Temperature variable) 1 km using broadband (unpolarized) fiber light source and 3 weakly birefringent couplers
3 is a set of graphs showing gyroscope scale factor stability over time for a gyroscope. The scale factor stability data in FIG. 8 was taken while the coupler temperature was maintained approximately constant as shown in FIG. The data in FIG. 10 were taken during the cycling of the coupler temperature between 15 ° C. and 35 ° C. as shown in FIG. The large number of spikes in both Figures 8 and 10 is likely due to the closed loop electronics provided for the experimental measurements. A standard deviation of about 90 ppm is observed in the graphs of both FIG. 8 and FIG. The data in FIG. 10 is essentially indistinguishable from the data in FIG. 8 despite the coupler temperature profile.

Thus, as can be seen, the present invention is
Provide a fiber optic gyroscope with increased savings without degrading performance. By using the teachings of the present invention, one can obtain performance comparable to that obtained with a system using only PM fibers and couplers. In accordance with the present invention, using a broadband light source and utilizing analysis or modeling enabled by proper separation of PM and weakly birefringent components, polarization fading and polarization nonreciprocity (as well as scale factor error The problems associated with PNR) are minimized while the resulting device is reasonably more durable than the more costly prior art devices.

Although the present invention has been described in terms of its presently preferred embodiment, it is not limited thereto. For example, while illustrated with respect to 1-axis and 3-axis embodiments, the present invention can be extended to 4-axis, 6-axis and other multi-axis systems as based on the teachings provided herein. Will compete with those skilled in the art. Accordingly, the invention is limited only as defined by the appended claims,
Within its scope all equivalents are included.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a weakly birefringent fiber optic gyroscope according to the prior art.

FIG. 2 is a schematic view of a triaxial fiber optic gyroscope according to the present invention.

FIG. 3 is a schematic diagram of a triaxial fiber optic gyroscope according to an alternative embodiment of the present invention.

4 and 5 are schematic diagrams of alternative embodiments of a single axis fiber optic gyroscope according to the present invention.

6 and 7 are plots of deflection uncertainty data versus temperature for a 1-axis gyroscope according to the present invention from a PM configuration.

8 to 11 represent scale factor stability of the gyroscope (constant temperature (FIGS. 8 and 9) and variable temperature (FIGS. 10 and 11) over time for a gyroscope according to the present invention. It is two sets of graphs.

[Explanation of symbols]

 62 light source 60 photodetector 42, 44, 46 detection coil 30, 32, 34 optical chip 20 weak birefringent component 22 polarization maintaining (PM) component

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor George A. Pavlas United States, 91360 California, Thousand Oaks, Cole Kebleyco 3513 (56) Reference JP-A-3-255308 (JP, A) JP-A-5-21871 (JP, A) JP-A-3-505005 (JP, A) ) JP-A-2-136806 (JP, A) JP-A-62-223614 (JP, A)

Claims (25)

[Claims] 1. A light source and at least one photodetector,
An optical fiber gyroscope comprising at least one optical fiber sensing coil and at least one multifunction integrated optical chip including a Y-shaped connecting waveguide, wherein: a) the gyroscope has a weak birefringent component and a polarization maintaining (PM) ) Including both components, b) A fiber optic gyroscope, characterized in that the sensing coil consists of PM fiber. 2. The optical fiber gyroscope according to claim 1, further comprising at least one coupler composed of a weakly birefringent fiber. 3. The optical fiber gyroscope according to claim 2, wherein the input and output pigtails of the optical chip are made of PM fiber. 4. The fiber optic gyroscope of claim 3, wherein the light source emits unpolarized light. 5. The optical fiber gyroscope according to claim 4, wherein the light source further comprises: a) a weakly birefringent fiber made of a predetermined doped material; and b) the last designated fiber. A fiber optic gyroscope consisting of a laser diode arranged to be pumped, whereby unpolarized light is emitted from it. 6. The optical fiber gyroscope according to claim 5, wherein the predetermined doping property is erbium. 7. The optical fiber gyroscope according to claim 3, wherein the light source emits polarized light. 8. The fiber optic gyroscope according to claim 7, wherein the light source is a weak transient coherent laser diode. 9. The optical fiber gyroscope according to claim 7, wherein the light source is a super light emitting diode. 10. The optical fiber gyroscope according to claim 7, further comprising a Riot depolarizer. 11. The optical fiber gyroscope according to claim 10, wherein the Riot depolarizer is connected to an input pigtail of the optical chip. 12. The optical fiber gyroscope according to claim 3, further comprising: a) a first area having at least one optical path made of a weakly birefringent fiber and including the light source; and b) a PM fiber. A fiber optic gyroscope having at least one optical path and comprising a second zone containing at least one sensing coil. 13. The fiber optic gyroscope of claim 12, wherein the first and second sections are joined by a weak birefringence-PM fiber joint. 14. The fiber optic gyroscope of claim 13, wherein the second section further comprises: a) one MIOC, and b) the sensing coil connected to an output pigtail of the MIOC. Gyroscope. 15. The fiber optic gyroscope of claim 14, further comprising: a) the first section including seven weakly birefringent couplers and one unpolarized light source, and b) the second section. The optical fiber gyroscope, characterized in that the area of (3) includes three optical chips and three sensing coils arranged to measure rotation rates about three orthogonal axes. 16. The fiber optic gyroscope of claim 14, further comprising: a) the first section comprises five weakly birefringent couplers, and b) the second section comprises three orthogonal axes. A fiber optic gyroscope, characterized in that it comprises three optical chips and three sensing coils arranged to measure the rotation rate relative to. 17. The fiber optic gyroscope of claim 14, further comprising: a) the first section comprising six weakly birefringent couplers and one unpolarized light source, and b) the second section. Section comprises three optical chips and three sensing coils arranged to measure rotation rates about three orthogonal axes, and c) three Riot depolarizers in the second section. An optical fiber gyroscope, wherein each of said depolarizers is positioned between the input pigtail of said optical chip and a PM fiber portion. 18. The fiber optic gyroscope of claim 14, further comprising: a) the first section including two weakly birefringent couplers and one unpolarized light source; and b) the second section. The optical fiber gyroscope characterized in that the area of (1) includes one optical chip and one sensing coil arranged to measure the rotation rate. 19. The fiber optic gyroscope of claim 14, further comprising: a) the first section including one weakly birefringent coupler and one polarized light source; and b) the first section. The second section comprises one optical chip and one sensing coil arranged for measuring the rotation rate, and c) one Riot depolarizer is provided in said second section, An optical fiber gyroscope, wherein the optical fiber gyroscope is positioned between the input pigtail of the optical chip and the PM fiber portion. 20. The optical fiber gyroscope according to claim 13, wherein the second section further comprises: a) one optical chip; and b) an uninterrupted optical fiber including an output pigtail of the optical chip. A fiber optic gyroscope including a sensing coil. 21. The fiber optic gyroscope of claim 20, further comprising: a) the first zone comprises seven weakly birefringent couplers and one unpolarized light source, and b) the second. The optical fiber gyroscope, characterized in that the area of (3) includes three optical chips and three sensing coils arranged to measure rotation rates about three orthogonal axes. 22. The fiber optic gyroscope of claim 20, further comprising: a) the first section comprises five weakly birefringent couplers, and b) the second section comprises three orthogonal axes. A fiber optic gyroscope, characterized in that it comprises three optical chips and three sensing coils arranged to measure the rotation rate relative to. 23. The fiber optic gyroscope of claim 20, further comprising: a) the first section including six weakly birefringent couplers and one polarized light source; and b) the first section. The second zone comprises three optical chips and three sensing coils arranged to measure rotation rates about three orthogonal axes, and c) three Riot depolarizers in said second zone. The optical fiber gyroscope is provided in the optical fiber gyroscope, the depolarizer being positioned between the input pigtail and the PM fiber portion of the optical chip. 24. A fiber optic gyroscope according to claim 20, further comprising: a) the first section includes two weakly birefringent couplers and one unpolarized light source; and b) the second section. The optical fiber gyroscope characterized in that the area of (1) includes one optical chip and one sensing coil arranged to measure the rotation rate. 25. The fiber optic gyroscope of claim 20, further comprising: a) the first section including one weakly birefringent coupler and one polarized light source; and b) the first section. The second section comprises one optical chip and one sensing coil arranged for measuring the rotation rate, and c) one Riot depolarizer is provided in said second section, An optical fiber gyroscope, wherein the optical fiber gyroscope is positioned between the input pigtail of the optical chip and the PM fiber portion.