Sagnac interferometric optical system and fiber optic gyroscope

Abstract

To provide a Sagnac interference optical system having a small number of components and a structure for supplying light to each of a sensing coil and a buffering coil.SOLUTION: The Sagnac interferometric optical system 10 includes a 2x2 optical coupler 103. The 2x2 photocoupler 103 bifurcates the light, and supplies one light to the sensing coil 107 and the other light to the buffering coil 109.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a Sagnac interferometric optical system configured such that a phase difference between clockwise and counterclockwise light propagating through a sensing coil is generated by rotation, and more particularly to a structure that supplies light to each of a sensing coil and a buffering coil that helps detect abnormalities in the sensing coil. [Background technology]

[0002] The Sagnac interferometric optical system has a configuration in which a phase difference between clockwise and counterclockwise light propagating through a sensing coil, which is a coil of optical fiber, is generated by rotation. The sensing coil is wound around a bobbin. Patent Document 1 discloses a coil configuration in which a buffering coil, which is a coil of optical fiber, is wound around the bobbin to reduce the impact of thermal stress on the sensing coil, which is generated by the difference in thermal expansion coefficient between the sensing coil and the bobbin, and a sensing coil is further wound on the buffering coil. In Patent Document 1, the buffering coil is referred to as an "optical fiber constituting a buffer layer." Patent Document 1 further discloses that a strain measurement device or a Sagnac interferometer may be connected to the buffering coil. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2012-185046 Summary of the Invention [Problem to be solved by the invention]

[0004] According to Patent Document 1, a strain measurement device or a Sagnac interferometer is connected to the buffering coil, so that the strain measurement device or the Sagnac interferometer includes a light source that supplies light to the buffering coil, separate from the light source that supplies light to the sensing coil. Therefore, according to Patent Document 1, different light sources are required to supply light to the sensing coil and the buffering coil, respectively.

[0005] In view of the above prior art, the present invention discloses a Sagnac interferometric optical system that has fewer parts than the prior art and has a structure for supplying light to each of the sensing coil and the buffering coil, and a fiber optic gyroscope that includes this Sagnac interferometric optical system. [Means for solving the problem]

[0006] The technical matters described herein are not intended to explicitly or implicitly limit the invention described in the claims, nor to enable anyone other than those who benefit from the invention (e.g., the applicant and the right holder) to limit the invention described in the claims, but are provided simply to facilitate understanding of the gist of the invention. The outline of the invention from other perspectives can be understood, for example, from the claims at the time of filing of this patent application. The Sagnac interferometric optical system of the present disclosure includes a 2x2 optical coupler that splits light into two, providing one light to the sensing coil and the other light to the buffering coil. The other end of the buffering coil may be connected to a light sensor, or may not be connected to anything, in other words, may be a reflective end that reflects light. The fiber optic gyroscope of the present disclosure includes the Sagnac interferometric optical system of the present disclosure. [Effects of the Invention]

[0007] The Sagnac interferometric optical system disclosed herein has a reduced component count (i.e., the number of light sources) compared to the prior art, since a shared light source provides light to both the sensing coil and the buffering coil. [Brief explanation of the drawings]

[0008] [Figure 1] 1 shows the configuration of the optical fiber gyroscope of the first embodiment. [Figure 2] A bobbin configuration with a sensing coil and a buffering coil wound around it. [Figure 3] 1 shows the configuration of a fiber optic gyroscope according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The embodiments will be described with reference to the drawings. In order to clarify the gist of the embodiments, illustrations and descriptions of components that are actually necessary or may become necessary but are considered non-essential to the embodiments (such as a power supply, a phase modulator, and an intermediate amplifier) ​​will be omitted. In each drawing, to avoid complexity, illustrations of some components may be omitted, and further, reference numerals of some components may be omitted.

[0010] [First embodiment] The fiber optic gyroscope 1 of the first embodiment shown in FIG. 1 is a closed-loop fiber optic gyroscope and includes the Sagnac interferometer optical system 10 of the first embodiment, a signal processing system 20, and an optical sensor 301. The Sagnac interferometer optical system 10 utilizes the Sagnac effect, so that rotation generates a phase difference between clockwise and counterclockwise light propagating through an optical fiber coil (a sensing coil 107, described below). The signal processing system 20 includes an optical sensor 201 that converts light from the Sagnac interferometer optical system 10 into an electrical signal, and a signal processor 209 that determines physical quantities related to rotation (e.g., angle, angular velocity, and angular acceleration) from the electrical signal output by the optical sensor 201. Because the configuration and functions of the Sagnac interferometer optical system 10, excluding the features disclosed herein, are well known, only a general description of the configuration of the Sagnac interferometer optical system 10, excluding the features disclosed herein, will be provided. Furthermore, because the configuration and functions of the signal processor 209 are well known, detailed description thereof will be omitted.

[0011] The Sagnac interferometer optical system 10 includes a light source 101 , an optical coupler 103 , an optical element 105 , a sensing coil 107 , a buffering coil 109 , a bobbin 111 , and an optical sensor 201 .

[0012] The light source 101 is, for example, a superluminescent diode (SLD).

[0013] The optical element 105 is, for example, an optical crystal of lithium niobate (LiNbO3) in which a Y-shaped optical waveguide 105a is formed. For closed-loop processing, a phase modulator (not shown) is mounted on the optical element 105 to phase-modulate each of the clockwise and counterclockwise light based on the processing result of the signal processor 209.

[0014] The bobbin 111 around which the sensing coil 107 and the buffering coil 109 are wound may have a configuration disclosed in, for example, Patent Document 1 (see FIG. 2). An optical fiber 109a is wound in a quadrupole manner around an axis 111a of the aluminum bobbin 111, and the coil of the optical fiber 109a forms the buffering coil 109. Furthermore, on the bobbin 111, an optical fiber 107a is wound in a quadrupole manner on the buffering coil 109, and the coil of the optical fiber 107a forms the sensing coil 107. The optical fiber 107a of the sensing coil 107 and the optical fiber 109a of the buffering coil 109 may have the same structure, and both the optical fiber 107a and the optical fiber 109a are, for example, single-mode optical fibers. Although FIG. 2 illustrates the sensing coil 107 as having fewer turns than the buffering coil 109, in reality, the sensing coil 107 has far more turns than the buffering coil 109. In FIG. 1, the sensing coil 107 and the buffering coil 109 are depicted as intersecting, but the sensing coil 107 and the buffering coil 109 are not optically connected to each other.

[0015] The optical sensor 201 is a sensor that converts light into an electrical signal, and is, for example, a photodiode. The optical sensor 201 converts the intensity of the light that enters the optical sensor 201 into the intensity of a current.

[0016] The optical coupler 103 is, for example, a fused fiber coupler, a 2x2 optical coupler having a first end 103a, a second end 103b, a third end 103c, and a fourth end 103d for optical branching and optical coupling. The optical coupler 103 is optically connected to each of the light source 101, the sensing coil 107, the buffering coil 109, and the optical sensor 201. "Optical connection" means that an optical path exists between them, and does not exclude the existence of other components between them. The first end 103a of the optical coupler 103 is optically connected to the light source 101. Typically, the first end 103a of the optical coupler 103 and the light source 101 are connected to each other by an optical fiber 121, and therefore an optical path exists between the first end 103a of the optical coupler 103 and the light source 101. The second end 103b of the optical coupler 103 is optically connected to the sensing coil 107. In a closed-loop fiber optic gyroscope, typically, the second end 103b of the optical coupler 103 is connected to one end of the optical fiber 123, the other end of the optical fiber 123 is connected to a first end of the Y-shaped optical waveguide 105a of the optical element 105, and one end and the other end of the sensing coil 107 are connected to the second end and the third end of the Y-shaped optical waveguide 105a, respectively. Thus, an optical path exists between the second end 103b of the optical coupler 103 and the sensing coil 107. The third end 103c of the optical coupler 103 is optically connected to one end of the buffering coil 109. In the first embodiment, the third end 103c of the optical coupler 103 is directly connected to one end of the buffering coil 109. The fourth end 103d of the optical coupler 103 is optically connected to the optical sensor 201. Typically, the fourth end 103 d of the optical coupler 103 and the optical sensor 201 are connected to each other by an optical fiber 125 , so that an optical path exists between the fourth end 103 d of the optical coupler 103 and the optical sensor 201 .

[0017] In the first embodiment, the other end of the buffering coil 109 is directly connected to an optical sensor 301. The optical sensor 301 is a sensor that converts light from the other end of the buffering coil 109 into an electrical signal, and is, for example, a photodiode. The optical sensor 301 is, for example, a component of a strain measuring instrument (not shown in FIG. 1) or a Sagnac interferometer (not shown), as disclosed in Patent Document 1.

[0018] According to the configuration of the first embodiment, light emitted from the light source 101 passes through the optical fiber 121 and enters the optical coupler 103 from a first end 103a of the optical coupler 103. The optical coupler 103 splits the light supplied from the light source 101 into two beams, one beam directed to a second end 103b of the optical coupler 103 and the other beam directed to a third end 103c of the optical coupler 103.

[0019] The light emitted from the second end 103b of the optical coupler 103 passes through the optical fiber 123 and enters the optical element 105 from its first end. The Y-shaped optical waveguide 105a of the optical element 105 splits the light entering from the first end a of the optical element 105 into two beams with equal intensity, one beam traveling toward the second end of the optical element 105 and the other beam traveling toward the third end of the optical element 105. The light emitted from the second end of the optical element 105 circulates clockwise through the sensing coil 107 and enters the third end of the optical element 105 as clockwise light. The light emitted from the third end of the optical element 105 circulates counterclockwise through the sensing coil 107 and enters the second end of the optical element 105 as counterclockwise light. The counterclockwise light entering the second end of the optical element 105 and the clockwise light entering the third end of the optical element 105 are optically coupled to each other by the Y-shaped optical waveguide 105a of the optical element 105 and interfere with each other with equal intensity. The interference light exits the first end of the optical element 105, passes through the optical fiber 123, and enters the second end 103b of the optical coupler 103. The optical coupler 103 splits the interference light entering the second end 103b into two, one of which is directed to the fourth end 103d of the optical coupler 103. The interference light exiting the fourth end 103d of the optical coupler 103 enters the optical sensor 201. The electrical signal output by the optical sensor 201 enters the signal processor 209. The signal processor 209 determines a physical quantity related to rotation (e.g., angle, angular velocity, angular acceleration) based on the electrical signal output by the optical sensor 201.

[0020] The light coming from the light source 101 and exiting from the third end 103c of the optical coupler 103 enters the buffering coil 109. The light that has circulated through the buffering coil 109 enters the optical sensor 301. When the optical sensor 301 is a component of a strain measuring device (not shown in FIG. 1), an abnormality in the buffering coil 109 can be detected, and this abnormality in the buffering coil 109 can be regarded as an abnormality in the sensing coil 107. As can be seen from FIG. 2, since the curvature of the buffering coil 109 is greater than the curvature of the sensing coil 107, the risk of disconnection of the buffering coil 109 is greater than the risk of disconnection of the sensing coil 107. Therefore, a disconnection or damage of the buffering coil 109 can be used to determine a disconnection or damage of the sensing coil 107 or the risk thereof. For example, two threshold values σ1, σ2 (σ1 < σ2) are determined in advance. When σ1 < E ≤ σ2 holds for the intensity E of the electrical signal output by the optical sensor 301, the buffering coil 109 is damaged. Therefore, it is determined that the sensing coil 107 is damaged or there is a risk of damage. When E ≤ σ1, the buffering coil 109 is disconnected. Therefore, it may be determined that the sensing coil 107 is disconnected or there is a risk of disconnection.

[0021] As described above, since the common light source 101 supplies light to each of the sensing coil 107 and the buffering coil 109, a light source for supplying light only to the buffering coil 109 is not required. Therefore, in this regard, the number of components is smaller compared to the prior art.

[0022] [Second Embodiment] Here, differences between the first and second embodiments will be described, and for other technical matters, please refer to the description of the first embodiment. By this reference, the description of the first embodiment, excluding the differences, is expressly incorporated herein. In the fiber optic gyroscope 2 of the second embodiment shown in FIG. 3, the sensing coil 107 and the buffering coil 109 not only share the light source 101, but also the optical sensor 201. Therefore, in this respect, the number of parts is smaller than in the prior art.

[0023] Unlike the fiber optic gyroscope 1 of the first embodiment, the fiber optic gyroscope 2 does not include an optical sensor 301. The other end 109c of the buffering coil 109 is not connected to anything. Therefore, the other end 109c of the buffering coil 109 is a reflection end where Fresnel reflection occurs at the boundary surface between media with different refractive indices.

[0024] Light from the light source 101 and emitted from the third end 103c of the optical coupler 103 circulates through the buffering coil 109, reaches the other end 109c of the buffering coil 109, is reflected by the other end 109c of the buffering coil 109, circulates through the buffering coil 109 again, and travels toward the third end 103c of the optical coupler 103. The optical coupler 103 optically couples the interference light entering from its second end 103b and the reflected light entering from its third end 103c, and further splits the combined light of the interference light and the reflected light into two. One of the combined lights travels toward the fourth end 103d of the optical coupler 103. The combined light exiting the fourth end 103d of the optical coupler 103 enters the optical sensor 201. The electrical signal output by the optical sensor 201 enters the amplifier 202. The amplifier 202 may be a current-to-voltage converter. The interference light is modulated by a phase modulator (not shown) at a phase modulation frequency typically exceeding several tens of kilohertz. However, the reflected light is not modulated. Therefore, the AC component of the electrical signal corresponds to the interference light, and the DC component corresponds to the reflected light. Divider 203 divides the amplified electrical signal into two. One electrical signal from divider 203 passes through high-pass filter 204, and the AC component of the electrical signal is input to signal processor 209. Signal processor 209 determines a physical quantity related to rotation (e.g., angle, angular velocity, angular acceleration) based on the AC component of the electrical signal. The other electrical signal from divider 203 passes through low-pass filter 205, and the DC component of the electrical signal is input to distortion measuring instrument 206. Based on the DC component of the electrical signal, distortion measuring instrument 206 can detect an abnormality in buffering coil 109. As described above, an abnormality in buffering coil 109 can be considered an abnormality in sensing coil 107.

[0025] According to the second embodiment, it is positively desired that light is reflected at the end surface of the other end 109c of the buffering coil 109. Therefore, the end surface of the other end 109c of the buffering coil 109 is polished together with a ferrule (not shown) attached to the other end 109c by a polishing method that maximizes the amount of light reflected at the other end 109c of the buffering coil 109, in other words, the power P of the light coming from the light source 101. incident and the power P of light returning to the light source 101 due to internal reflection at the end surface. returnIt is preferable that the polishing be performed by a polishing method that minimizes the return loss RL (see equation (1)), which is the ratio of the return loss to the return loss. A metal film and / or a dielectric multilayer film may be formed on the end surface of the other end 109c of the buffering coil 109.

number

[0026] Since a portion of the combined light of the interference light and reflected light obtained by combining in the optical coupler 103 enters the optical sensor 201, it is desirable that the power of the interference light that enters the second end 103b of the optical coupler 103 from the sensing coil 107 and the power of the reflected light that enters the third end 103c of the optical coupler 103 from the buffering coil 109 after being combined at the coupling ratio of the optical coupler 103 are approximately the same.

[0027] Part of the signal processing system 20 is implemented as hardware or software. For example, the high-pass filter 204 and the low-pass filter 205 are typically implemented as hardware, but after an analog electrical signal is converted into a digital signal by an A / D converter, software filtering may be applied to the digital signal.

[0028] 1 and 3, which illustrate the embodiment, the optical sensor 201 is illustrated as being a component of both the Sagnac interferometer optical system 10 and the signal processing system 20. However, this is for the sake of convenience, and the optical sensor 201 may be understood as being a component of the Sagnac interferometer optical system 10 rather than the signal processing system 20, or alternatively, the optical sensor 201 may be understood as being a component of the signal processing system 20 rather than the Sagnac interferometer optical system 10.

[0029] Although the fiber optic gyroscopes 1 and 2 in the above-described embodiments are closed-loop fiber optic gyroscopes, the fiber optic gyroscope of the present disclosure may be an open-loop fiber optic gyroscope. Therefore, the Sagnac interferometer optical system of the present disclosure is not limited to a configuration used in a closed-loop fiber optic gyroscope, and may have a configuration used in an open-loop fiber optic gyroscope.

[0030] <Addendum> The technical features disclosed in the various embodiments and their modifications described above are not necessarily mutually exclusive, and technical features of one embodiment or its modifications may be applied to technical features of another embodiment or its modifications, provided that there is no contradiction from a technical viewpoint.

[0031] The claims set forth in the scope of claims as of the filing of this application do not necessarily exhaustively claim all inventions disclosed in this specification. In this regard, this should not be understood or construed as meaning that the applicant has pre-filing waived any right to a patent for any invention not claimed at the time of filing of this application. To the extent permitted by the laws, regulations, or treaties of any country or region where this application is filed, the applicant reserves the right to a patent for any invention not claimed in this application, the right to file a divisional application for such invention, the right to claim such invention by amendment, and any other rights, unless the applicant expressly and conclusively expresses a contrary intention.

[0032] While the present invention has been described with reference to exemplary embodiments, those skilled in the art will recognize that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope of the invention. Furthermore, many modifications can be made to adapt a particular system, device, or component thereof to the teachings of the present invention without departing from the essential scope of the invention. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.

[0033] Furthermore, the use of terms such as "first," "second," etc., when used in this specification and / or the appended claims, does not denote any order or importance, and terms such as "first," "second," etc., are used to distinguish between elements. The terms used herein are for the purpose of describing embodiments and are not intended to limit the invention in any way. The term "comprises" and its conjugations, when used in this specification and / or the appended claims, reveal the presence of referenced features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The term "and / or" includes any and all combinations of one or more of the associated listed elements, if any. In the claims and the specification, unless otherwise specified, the use of words such as "connected," "coupled," "joined," "connected," or synonyms thereof, and all word forms thereof, does not necessarily negate the presence of one or more intermediate elements between two elements, e.g., "connected" or "coupled" to each other or "connected" to each other. In the claims and the specification, the term "any," if any, should be understood as a term that has the same meaning as the universal symbol ∀, unless otherwise specified. For example, the phrase "for any X" has the same meaning as "for all X" or "for each X." A phrase such as "at least one of A, B, and C" (e.g., "at least one of A, B, and C," "at least one of A, B, or C," "at least one of A, B, and / or C"), if any, should be understood as a term that has the same meaning as the universal symbol ∀, unless otherwise specified. S This means that we arbitrarily select one element from the set P excluding the empty set φ. In this example, S={A,B,C},2 S={φ,{A},{B},{C},{A,B},{A,C},{B,C},{A,B,C}},P={{A},{B},{C},{A,B},{A,C},{B,C},{A,B,C}}, which means that one element (e.g., {A,C}) is arbitrarily selected from the set P.

[0034] Unless otherwise specified, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Furthermore, terms such as those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant art and this disclosure, and should not be interpreted ideally or excessively formally unless explicitly defined.

[0035] It will be understood that in describing the present invention, many techniques and steps are disclosed. Each of these has distinct advantages, and each can be used in combination with one or more, or in some cases all, of the other disclosed techniques. Therefore, to avoid cluttering, this specification will refrain from describing every possible combination of individual techniques or steps. Nevertheless, the specification and claims should be read with the understanding that such combinations are fully within the scope of the present invention and claims.

[0036] The corresponding structure, material, acts, and equivalents of all functional elements combined with means or steps in the following claims are intended to include the structure, material, or acts, if any, that perform the function in combination with other elements.

[0037] Although the present invention has been described above with reference to exemplary embodiments, it is not limited to these embodiments. Various modifications and variations are possible without departing from the spirit of the present invention. The selected and described embodiments are intended to illustrate the principles of the present invention and its practical application. The present invention may be used in various embodiments with various modifications and variations, which are determined according to the expected use. All such modifications and variations are intended to be included within the scope of the present invention, as defined by the appended claims, and are intended to be accorded the same protection when interpreted in accordance with the breadth that is fairly, legally, and equitably to be given. [Explanation of symbols]

[0038] 1. Fiber optic gyroscope 2. Fiber Optic Gyroscope 10 Sagnac Interferometric Optical System 20 Signal Processing System 101 Light source 103 Optical Coupler 103a 1st end 103b 2nd end 103c 3rd end 103d 4th end 105 Optical Elements 105a Y-shaped optical waveguide 107 Sensing coil 107a Optical Fiber 109 Buffering Coil 109a Optical Fiber 109c other end 111 Bobbin 111a axis 121 Optical Fiber 123 Optical Fiber 125 Optical Fiber 201 Optical Sensor 202 Amplifier 203 Distributor 204 High-pass filter 205 Low-pass filter 206 Strain Measuring Instrument 209 Signal Processor 301 Optical Sensor

Claims

1. A Sagnac interferometer optical system having a configuration in which a phase difference between clockwise light and counterclockwise light propagating through a sensing coil, which is a coil of optical fiber, is generated by rotation, a buffering coil, which is a coil of optical fiber having one end and the other end; a bobbin around which the buffering coil is wound; the sensing coil wound on the bobbin around the buffering coil; A light source and an optical coupler having a first end, a second end, a third end, and a fourth end; Light sensor and Including, the first end of the optical coupler is optically coupled to the light source; the second end of the optical coupler is optically connected to the sensing coil; the third end of the optical coupler is optically connected to the one end of the buffering coil; The fourth end of the optical coupler is optically connected to the optical sensor. Sagnac interferometric optical system.

2. 2. The Sagnac interferometric optical system of claim 1, further including an optical sensor different from the optical sensor, hereinafter referred to as an additional optical sensor; The other end of the buffering coil is connected to the additional light sensor. A Sagnac interferometric optical system.

3. 2. The Sagnac interferometric optical system of claim 1, The other end of the buffering coil is a reflective end that reflects light. A Sagnac interferometric optical system.

4. 4. The Sagnac interferometric optical system of claim 3, After being coupled at a coupling ratio of the optical coupler, the power of the light entering the second end of the optical coupler from the sensing coil and the power of the light entering the third end of the optical coupler from the buffering coil are approximately the same. A Sagnac interferometric optical system.

5. a Sagnac interferometric optical system having a configuration in which a phase difference between clockwise and counterclockwise light propagating through a sensing coil, which is a coil of optical fiber, is generated by rotation; a signal processing system including an optical sensor that converts light from the Sagnac interferometer optical system into an electrical signal, and a signal processor that determines a physical quantity related to the rotation from the electrical signal; A fiber optic gyroscope comprising: The Sagnac interferometric optical system a buffering coil, which is a coil of optical fiber having one end and the other end; a bobbin around which the buffering coil is wound; the sensing coil wound on the bobbin around the buffering coil; A light source and an optical coupler having a first end, a second end, a third end, and a fourth end; Including, the first end of the optical coupler is optically coupled to the light source; the second end of the optical coupler is optically connected to the sensing coil; the third end of the optical coupler is optically connected to the one end of the buffering coil; The fourth end of the optical coupler is optically coupled to the optical sensor included in the Sagnac interferometric optical system. Fiber optic gyroscope.

6. 6. The fiber optic gyroscope according to claim 5, The other end of the buffering coil is a reflective end that reflects light.

1. A fiber optic gyroscope comprising:

7. 7. The fiber optic gyroscope according to claim 6, The signal processor determines a physical quantity related to the rotation from an AC component of the electrical signal, and detects an abnormality in the buffering coil from a DC component of the electrical signal.

1. A fiber optic gyroscope comprising:

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