JPH06221858A - Optical fiber gyro - Google Patents

Optical fiber gyro

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Publication number
JPH06221858A
JPH06221858A JP1286593A JP1286593A JPH06221858A JP H06221858 A JPH06221858 A JP H06221858A JP 1286593 A JP1286593 A JP 1286593A JP 1286593 A JP1286593 A JP 1286593A JP H06221858 A JPH06221858 A JP H06221858A
Authority
JP
Japan
Prior art keywords
optical fiber
circular polarization
polarization mode
optical
ring resonator
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
JP1286593A
Other languages
Japanese (ja)
Inventor
Kazuo Hotate
Ryozo Yamauchi
和夫 保立
良三 山内
Original Assignee
Fujikura Ltd
Kazuo Hotate
和夫 保立
株式会社フジクラ
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fujikura Ltd, Kazuo Hotate, 和夫 保立, 株式会社フジクラ filed Critical Fujikura Ltd
Priority to JP1286593A priority Critical patent/JPH06221858A/en
Publication of JPH06221858A publication Critical patent/JPH06221858A/en
Granted legal-status Critical Current

Links

Abstract

(57) [Summary] [Structure] A light source, an optical coupler for branching the light emitted from the light source, an optical ring resonator 2 constituted by an optical fiber, and the branched light propagating clockwise to the optical ring resonator 2. Resonance comprising an optical directional coupler 3 that is incident as light and counterclockwise propagating light, respectively, and a photodetector that detects the resonance frequencies of the clockwise propagating light and the counterclockwise propagating light in the optical ring resonator 2. In the optical fiber gyro of the method, the optical ring resonator 2 is configured by using a circular polarization maintaining optical fiber that propagates while maintaining two circular polarization modes of a right-hand circular polarization mode and a left-hand circular polarization mode. In the middle of the optical ring resonator 2, there is provided a polarization mode conversion means 1 for converting the right-hand circular polarization mode to the left-hand circular polarization mode and the left-hand circular polarization mode to the right-hand circular polarization mode. . [Effect] A resonance type optical fiber gyro capable of preventing polarization fluctuation induced noise can be obtained by using an ordinary single mode optical fiber.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber gyro for detecting the rotational angular velocity of a moving body such as an aircraft, a rocket, a ship or an automobile, and more particularly to a resonance type optical fiber gyro.

[0002]

2. Description of the Related Art In an optical fiber gyro, a phase difference between two lights propagating in opposite directions, that is, a light propagating in a clockwise direction and a light propagating in a counterclockwise direction is propagated in a circular optical path formed of optical fibers. This utilizes the Sagnac effect in which the phase difference with the light changes in proportion to the rotational angular velocity received by the optical path due to the movement of the moving body. Then, the resonance type optical fiber gyro forms an optical ring resonator by forming an optical fiber in a ring shape, and determines the rotational angular velocity of the rotational motion that the optical ring resonator receives by the movement of the moving body.
This is to be understood as a change in resonance frequency caused by the Sagnac effect.

FIG. 2A is a schematic diagram showing an example of a conventional resonance type optical fiber gyro. The light emitted from the light source 11 is split into two lights by the optical coupler 12 and is incident on the optical ring resonator 15 as clockwise propagating light and counterclockwise propagating light via the optical couplers 13 and 14, respectively. The light intensity of each propagating light is measured by the photodetectors 16, 16.
FIG. 2B is an explanatory diagram of resonance peaks obtained by the optical ring resonator. In FIG. 2B, the vertical axis represents the light intensity, and the horizontal axis represents the phase rotation ωτ when the light propagates through the optical ring resonator once. Here, ω is the frequency of the propagating light, τ is the time required for the light to go around the optical ring resonator once, and changes linearly with the rotational angular velocity Ω received by the optical ring resonator due to the Sagnac effect. Is. The resonance peak is obtained when the phase rotation of the propagating light is an integral multiple of 2π.

In such a resonance type optical fiber gyro, in order to cancel the influence of temperature and mechanical fluctuations of the optical ring resonator length, clockwise propagating light and counterclockwise propagating in the resonator face each other. Circularly propagating light is used. That is, one of these two propagating lights is used to monitor and compensate for a change in the optical resonance frequency caused by a temperature or mechanical fluctuation of the optical ring resonator length, and the other light is used to perform optical resonance due to the Sagnac effect. By measuring the frequency change, it is possible to eliminate the effect of cavity length variation.

However, even if the optical resonance frequency change due to the Sagnac effect is measured in one of the two propagating lights propagating in the optical ring resonator, the propagating light actually has two unique polarization states. Consists of. Here, the eigenpolarization state changes as light propagates through the resonator, but it has the special property of returning to the original polarization state when the resonator makes one round. Is. The unique polarization states independently form resonance characteristics. The two eigenpolarization states change due to the birefringence exhibited by the optical fiber forming the optical ring resonator. Therefore, when the optical ring resonator is formed by using a single-mode optical fiber, the birefringence changes due to temperature fluctuations, etc., so that the eigenpolarization state also changes and stable resonance characteristics are obtained. There is an inconvenience that it does not exist.

Therefore, in order to eliminate this inconvenience, if the optical ring resonator is constructed by using a polarization maintaining optical fiber,
Since the polarization-maintaining optical fiber originally has a large linear birefringence, it is unlikely to be affected by the additional change in birefringence, and the above inconvenience can be eliminated. When an ideal optical ring resonator with no polarization mode coupling is constructed with a polarization maintaining optical fiber, two linear polarization modes are in a unique polarization state, and resonance characteristics are formed independently of each other. Therefore, it is considered that the influence of the other polarization mode can be removed by exciting only one linear polarization mode and detecting the resonance peak.

However, in reality, an extremely slight coupling between the two polarized waves occurs at the connecting portion for forming the optical coupler and the ring. Therefore, the eigenpolarization state is no longer linearly polarized, and it is not possible to excite only one of them completely selectively, so that in addition to the main resonance peak, there is an unnecessary resonance peak. Become. Furthermore, if the resonator length changes due to temperature fluctuations or the like, the unnecessary resonance peak and the main resonance peak easily cross each other. This causes a problem of causing a large drift, which is fatal for a high-precision gyro.

In order to solve the problem of the measurement accuracy deterioration due to the coupling between the two linear polarization modes, the birefringent main axis of the polarization maintaining optical fiber is twisted by 90 degrees in the optical ring resonator. It is carried out to provide a part connected by. According to this method, the two linear polarization modes are switched at the site where the birefringent principal axes are twisted by 90 degrees and connected. As a result, the phase difference between the two eigenpolarization states becomes smaller, and the difference is fixed at π,
The two peaks are located at the center of the other resonance peak periods, and it is possible to prevent these resonance peaks from crossing. As described above, a resonance type optical fiber gyro has been developed which can solve the problem of noise due to polarization fluctuation by using a polarization maintaining optical fiber.

[0009]

However, in the case of producing a resonance type optical fiber gyro using the polarization maintaining optical fiber as described above, not only the optical fiber constituting the optical ring resonator but also the optical fiber There is also a problem that optical components such as an optical coupler necessary for constructing a gyro must be manufactured by using a polarization maintaining optical fiber. At the present time, the polarization-maintaining optical fiber and each polarization component are expensive, so that they cannot be used in inexpensive low- and medium-precision gyros for navigation systems such as passenger cars. It was

The present invention has been made in view of the above circumstances, and provides a resonance type optical fiber gyro which can be manufactured at low cost and which can solve the problem of noise due to polarization fluctuation. The purpose is.

[0011]

An optical fiber gyroscope according to the present invention comprises a light source, an optical ring resonator formed of an optical fiber, and a light beam emitted from the light source. The optical ring resonator is provided with means for respectively entering clockwise propagating light and counterclockwise propagating light into the resonator, and photodetectors for respectively detecting the resonance frequencies of the clockwise propagating light and the counterclockwise propagating light in the optical ring resonator. In a resonance type optical fiber gyro, the optical ring resonator is configured by using a circular polarization maintaining optical fiber that propagates while holding two circular polarization modes of a right-handed circular polarization mode and a left-handed circular polarization mode. A polarization mode for converting the right-hand circular polarization mode to the left-hand circular polarization mode and the left-hand circular polarization mode to the right-hand circular polarization mode in the middle of the optical ring resonator. That the conversion means are thus provided it was solutions of the problems.

[0012]

The present invention will be described in detail below. The optical fiber gyro of the present invention is greatly different from the conventional one in that the optical ring resonator is configured by using a circular polarization maintaining optical fiber, and the polarization mode conversion means is provided in the middle of the optical ring resonator. That is the point. FIG. 1A is a partial configuration diagram showing a main part of an optical fiber gyro of the present invention. In the figure, reference numeral 1 is a polarization mode conversion means, 2 is an optical ring resonator, and 3 is an optical directional coupler.

The optical ring resonator 2 is constructed by using a circular polarization maintaining optical fiber which propagates while maintaining two circular polarization modes of a right-hand circular polarization mode and a left-hand circular polarization mode. As such a circular polarization maintaining optical fiber, a twisted fiber obtained by continuously twisting a single mode optical fiber is used. This twisted fiber can be manufactured by a method of drawing while rotating the preform during drawing, or by heating and twisting the optical fiber after drawing, but the method of twisting during drawing is simple in terms of manufacturing process. Therefore, it is preferably used in that twist can be surely formed.

The optical ring resonator 2 can be constructed using, for example, a circular polarization maintaining optical fiber having a total length of about 10 m, which is twisted 100 turns per 1 m. Here, in the twisted optical fiber, the optical rotation angle φ when the optical fiber is twisted by η (turn / m) is φ = αη (α is the optical activity of quartz glass and α≈0.0
7 ), The propagation constant difference δβ between the left and right circularly polarized waves of the twisted optical fiber is given by δβ = 2φ, and the beat length Λc is Λc = 2π / δβ. Since η = 100 now,
The beat length of this circular polarization maintaining optical fiber is Λc = 7 cm.

The polarization mode conversion means 1 converts the right-hand circular polarization mode to the left-hand circular polarization mode and the left-hand circular polarization mode to the right-hand circular polarization mode, and has an arbitrary configuration. be able to. A known one can be used as the polarization mode conversion means 1, and in this embodiment, a single mode optical fiber is used as a loop with a small radius. Here, the radius and the number of turns of the loop are appropriately set so that the polarization mode of the propagating light can be converted into a desired state. It is preferable to use a carbon-coated optical fiber as the optical fiber forming the polarization mode conversion means 1 because the reliability is improved. Alternatively, even when a normal single mode optical fiber is used, reliability can be improved by expanding the radius of the loop and increasing the number of turns. Alternatively, a normal half-wave plate can be used as the polarization mode conversion means. When an optical fiber is used as the polarization mode conversion means 1, the optical fiber gyro can be configured to use only the optical fiber, so that the reliability of the gyro can be improved and the size can be reduced, which is more preferable. As the polarization mode conversion means 1, for example, a single mode optical fiber loop having a radius of 1.5 cm, a number of turns of 2 and a total length of about 20 cm can be used.

The optical directional coupler 3 makes the clockwise propagating light and the counterclockwise propagating light enter the optical ring resonator 2 and branches the light from the resonator 2 in order to detect the resonance characteristic of the propagating light. The optical ring resonator 2 is provided at an appropriate position. As the optical directional coupler 3, an optical fiber type optical branching coupler configured by using a single mode optical fiber can be preferably used.

In the optical fiber gyro of the present invention, in addition to the above-mentioned structure, optical components necessary for angular velocity detection such as a light source and a photodetector are used, and temperature drift, Rayleigh scattering induced noise, and optical Kerr effect induced noise are also used. It is configured by suitably using known means for reducing various noises such as.

When the angular velocity is detected using the optical fiber gyro of the present invention, a relatively high coherent light source is used, and the spectral line width is about the resonance peak width of the resonator or less. Can be preferably used. The light source can be appropriately selected so as to obtain the required accuracy according to the purpose of use of the optical fiber gyro. For example, for inertial navigation of an aircraft, which requires a resolution capable of detecting the revolution of the earth, a light source having a spectral line width of about 100 kHz or less is required. It is also possible to use a light source having a spectral line width of several MHz for a low-precision, inexpensive gyro. First, the oscillation light from the light source is branched, the branched light is propagated through the optical ring resonator 2 in the clockwise direction and the counterclockwise direction, and the respective resonance frequencies of the clockwise propagation light and the counterclockwise propagation light are measured. . Then, the rotational angular velocity of the rotational motion given to the optical ring resonator 2 can be obtained from the change in the resonance frequency by a known method.

In the optical fiber gyro having the structure as shown in FIG. 1A, assuming that the length of the single mode optical fiber constituting the polarization mode conversion means 1 is L 1 , the transmission in the polarization mode conversion means 1 The matrix F 1 is represented by the following formula (I). Further, assuming that the length of the twisted fiber constituting the optical ring resonator 2 is L 2 and the optical rotation angle per fiber unit length is φ, the transfer matrix F 2 in this optical ring resonator 2 is expressed by the following formula (II). To be done. Therefore, the transfer matrix F of the entire optical ring resonator is expressed by the following formula (III). Here, the total length of the optical fiber that constitutes the entire optical ring resonator,
That is, L 1 + L 2 is L. Further, β is a propagation constant of the optical fiber, and here, the polarization mode conversion means 1 and the optical ring resonator 2 are assumed to be configured by a single mode optical fiber having a similar propagation constant β.

[0020]

[Equation 1]

The two eigenvalues of the equation (III) give the phase rotations of the two eigenpolarization states of the optical ring resonator 2. That is, the position of each resonance peak is given, and its two eigenvalues λ 1 ,
λ 2 is given by the following equations (IV) and (V), respectively.

[0022]

[Equation 2]

From the above equations (IV) and (V), it is recognized that the eigenvalues of the two eigenpolarization states are deviated from each other by π. This means that, as shown in FIG. 1B, the resonance peak corresponding to the first eigenpolarization state (indicated by a solid line in the figure) and the resonance peak corresponding to the second eigenpolarization state (in the figure). , Indicated by dotted lines) are located in the center of the resonance peak periods of each other. Therefore, 2
It is recognized that two resonance peaks can be prevented from crossing.

[0024]

As described above, the optical fiber gyroscope of the present invention splits the light radiated from the light source, the optical ring resonator constituted by the optical fiber, and the light source, and outputs the branched light to the above-mentioned light. Means for injecting clockwise propagating light and counterclockwise propagating light into the ring resonator, respectively, and a photodetector for detecting the resonance frequency of the clockwise propagating light and counterclockwise propagating light in the optical ring resonator, respectively. In the resonance type optical fiber gyro, the optical ring resonator uses a circular polarization maintaining optical fiber that propagates while holding two circular polarization modes of a right-hand circular polarization mode and a left-hand circular polarization mode. Polarizations configured to convert the right-hand circular polarization mode to the left-hand circular polarization mode and the left-hand circular polarization mode to the right-hand circular polarization mode in the middle of the optical ring resonator. Over de conversion means in which is provided.

Therefore, it is possible to obtain a resonance type optical fiber gyro which can prevent polarization fluctuation induced noise by using a normal single mode optical fiber. Therefore, it is possible to provide an inexpensive and high-performance resonant optical fiber gyro, and it is possible to improve the versatility of the optical fiber gyro.

[Brief description of drawings]

FIG. 1 (a) in an optical fiber gyro of the present invention
It is the partial block diagram which shows a principal part, and (b) explanatory drawing of a resonance peak.

2A is a partial configuration diagram showing a main part of a conventional resonance-type optical fiber gyro, and FIG. 2B is an explanatory diagram of a resonance peak.

[Explanation of symbols]

1 ... Polarization mode conversion means, 2 ... Optical ring resonator, 3 ... Optical directional coupler

Claims (5)

[Claims]
1. A light source, an optical ring resonator constituted by an optical fiber, and a light emitted from the light source are branched,
Means for injecting the branched light into the optical ring resonator as clockwise propagating light and counterclockwise propagating light, respectively, and detecting the resonance frequencies of the clockwise propagating light and the counterclockwise propagating light in the optical ring resonator, respectively. In a resonance-type optical fiber gyroscope including a photodetector, the optical ring resonator propagates while holding two circular polarization modes of a right-handed circular polarization mode and a left-handed circular polarization mode. A holding optical fiber is used, and in the middle of the optical ring resonator, the right-hand circular polarization mode is a left-hand circular polarization mode, and the left-hand circular polarization mode is a right-hand circular polarization mode, respectively. An optical fiber gyro, characterized in that polarization mode conversion means for conversion is provided.
2. The optical fiber gyro according to claim 1, wherein the circular polarization maintaining optical fiber is a twisted optical fiber.
3. The optical fiber gyro according to claim 1, wherein the polarization mode conversion means is composed of a loop of a single mode optical fiber.
4. The optical fiber gyro according to claim 3, wherein the single mode optical fiber constituting the polarization mode conversion means is a carbon coated optical fiber.
5. The optical fiber gyro according to claim 1, wherein the polarization mode conversion means is a half-wave plate.
JP1286593A 1993-01-28 1993-01-28 Optical fiber gyro Granted JPH06221858A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP1286593A JPH06221858A (en) 1993-01-28 1993-01-28 Optical fiber gyro

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
JP1286593A JPH06221858A (en) 1993-01-28 1993-01-28 Optical fiber gyro

Publications (1)

Publication Number Publication Date
JPH06221858A true JPH06221858A (en) 1994-08-12

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Family Applications (1)

Application Number Title Priority Date Filing Date
JP1286593A Granted JPH06221858A (en) 1993-01-28 1993-01-28 Optical fiber gyro

Country Status (1)

Country Link
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Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002054930A (en) * 2000-08-10 2002-02-20 Tokyo Aircraft Instrument Co Ltd Method of reducing polarizatin variation induction drift in resonant optical fiber gyro and device applying the same
JP2007127650A (en) * 2005-11-02 2007-05-24 Honeywell Internatl Inc Transmission mode rfog, and method of detecting rotation with rfog
US7701983B2 (en) 2005-03-03 2010-04-20 Nec Corporation Tunable resonator, tunable light source using the same, and method for tuning wavelength of multiple resonator
CN102353374A (en) * 2011-10-09 2012-02-15 浙江大学 Fiber-optic gyroscope signal processing device and method thereof

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2002054930A (en) * 2000-08-10 2002-02-20 Tokyo Aircraft Instrument Co Ltd Method of reducing polarizatin variation induction drift in resonant optical fiber gyro and device applying the same
US7701983B2 (en) 2005-03-03 2010-04-20 Nec Corporation Tunable resonator, tunable light source using the same, and method for tuning wavelength of multiple resonator
JP2007127650A (en) * 2005-11-02 2007-05-24 Honeywell Internatl Inc Transmission mode rfog, and method of detecting rotation with rfog
CN102353374A (en) * 2011-10-09 2012-02-15 浙江大学 Fiber-optic gyroscope signal processing device and method thereof

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