A sagnac fiber vibration positioning structure based on a dual-polarization structure

Abstract

The application provides a Sagnac fiber vibration positioning structure based on a double-polarization structure, which comprises a wide-spectrum light source, a first polarization beam splitter, a first fiber coupler, a second fiber coupler, a first fiber delay ring, a second fiber delay ring, a third fiber coupler, a fourth fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing fiber, a first reflector, a second reflector, a first photodetector and a second photodetector.In the positioning structure, X and Y polarized lights in the same vibration sensing fiber can sense the same vibration signal, and two independent interference signals with a fixed time delay are formed, the fixed time delay is related to the vibration position; through demodulating the phase information of the two interference light intensities and performing cross-correlation time delay estimation, the specific position of the external vibration signal can be positioned.The application solves the problems that the vibration positioning algorithm of the traditional Sagnac type interference fiber vibration sensing system is complex and is restricted by the vibration frequency.

Description

Technical Field

[0001] This invention belongs to the field of vibration measurement technology, specifically relating to a Sagnac interferometric distributed optical fiber vibration positioning structure. Background Technology

[0002] Distributed fiber optic vibration sensing systems have become a hot development direction in the current security technology field due to their strong environmental adaptability, excellent long-distance real-time positioning and monitoring capabilities, and extremely low power consumption. Among them, the accurate positioning of vibration events has always been a research hotspot for long-distance distributed fiber optic vibration sensing systems.

[0003] Sagnac-type fiber optic vibration sensors based on the interferometric principle typically use a "zero-frequency" analysis method to locate vibration positions. The notch frequency is calculated based on the Fourier transform of the vibration signal. However, this method is relatively complex and requires the notch frequency to be within the frequency range of the vibration signal. Alternatively, additional optical paths (such as Mach-Zehnder or Michelson structures) can be added for auxiliary positioning, but this increases system complexity and cost, hindering the widespread application of this structure. Summary of the Invention

[0004] To address the technical problem of Sagnac interferometric fiber optic vibration sensors having difficulty locating vibration positions, this invention proposes a Sagnac interferometric fiber optic vibration positioning structure based on a dual polarization structure. It uses two independent interference phase signals to calculate the location where the vibration signal occurs.

[0005] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0006] As one aspect of the present invention, a Sagnac interferometric fiber vibration positioning structure based on a dual polarization structure is provided, comprising a light source, a first polarization beam splitter, a first fiber coupler, a second fiber coupler, a first fiber delay loop, a second fiber delay loop, a third fiber coupler, a fourth fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing fiber, a first reflector, a second reflector, a first photodetector, and a second photodetector.

[0007] The a port of the first polarization beam splitter is connected to the light source, and the b and c ports of the first polarization beam splitter are respectively connected to the a port of the first fiber coupler and the second fiber coupler; the b ports of the first fiber coupler and the second fiber coupler are respectively connected to the first photodetector and the second photodetector.

[0008] The d ports of the first fiber optic coupler and the second fiber optic coupler are respectively connected to the b ports of the third fiber optic coupler and the fourth fiber optic coupler through the first fiber optic delay loop and the second fiber optic delay loop; the c ports of the first fiber optic coupler and the second fiber optic coupler are respectively connected to the c ports of the third fiber optic coupler and the fourth fiber optic coupler.

[0009] The a port of the third fiber coupler and the fourth fiber coupler are respectively connected to the b port of the second polarization beam splitter and the c port of the third polarization beam splitter; the c port of the second polarization beam splitter is connected to the first reflector, and the b port of the third polarization beam splitter is connected to the second reflector; the a port of the second polarization beam splitter and the third polarization beam splitter are respectively connected to the two ends of the vibration sensing fiber.

[0010] Furthermore, the light source is a broadband light source, and the broadband light source outputs unpolarized incident light.

[0011] Furthermore, the splitting ratios of the first fiber optic coupler, the second fiber optic coupler, the third fiber optic coupler, and the fourth fiber optic coupler are all 50:50.

[0012] Furthermore, in addition to the single-mode fiber used in the light source, the first photodetector, and the second photodetector, the polarization-maintaining fiber used in the first polarization beam splitter, the first fiber coupler, the second fiber coupler, the first fiber delay loop, the second fiber delay loop, the third fiber coupler, the fourth fiber coupler, the second polarization beam splitter, the third polarization beam splitter, the vibration sensing fiber, the first reflector, and the second reflector is polarization-maintaining fiber.

[0013] Furthermore, the X-polarized light incident at port a of the first polarization beam splitter is directly coupled to the first fiber coupler, and the Y-polarized light incident at port a of the first polarization beam splitter is cross-coupled to the second fiber coupler.

[0014] X-polarized light is split into two beams by the first fiber coupler. One beam passes through the first fiber delay loop and the third fiber coupler to enter the second polarization beam splitter, while the other beam directly enters the third fiber coupler to reach the second polarization beam splitter. The X-polarized light then enters the vibration sensing fiber through the second polarization beam splitter and reaches port a of the third polarization beam splitter. It is then directly coupled to the second reflector, reflected back to the vibration sensing fiber, and returns to the second polarization beam splitter. The X-polarized light is then directly coupled to port b of the second polarization beam splitter, and after passing through the third fiber coupler, it is split again. One beam passes through the first fiber delay loop and the first fiber coupler to reach the first photodetector, while the other beam directly passes through the first fiber coupler to reach the first photodetector.

[0015] The Y-polarized light is split into two beams by the second fiber coupler. One beam passes through the second fiber delay loop and the fourth fiber coupler to enter the third polarization beam splitter, while the other beam passes directly through the fourth fiber coupler to reach the third polarization beam splitter. The Y-polarized light then enters the vibration sensing fiber through the third polarization beam splitter and reaches port a of the second polarization beam splitter. It is cross-coupled to the first reflector, reflected back to the vibration sensing fiber, and returns to the third polarization beam splitter. The Y-polarized light is cross-coupled to port c of the third polarization beam splitter, and after passing through the fourth fiber coupler, it is split again. One beam passes through the second fiber delay loop and the second fiber coupler to reach the second photodetector, while the other beam passes directly through the second fiber coupler to reach the second photodetector.

[0016] Furthermore, the lengths of the first fiber delay loop and the second fiber delay loop do not simultaneously satisfy the following formula:

[0017]

[0018] Where m and n are integers, L1 and L2 are the lengths of the first and second fiber delay loops, respectively, and n x n y ω represents the refractive index of the slow axis and fast axis of the polarization-maintaining fiber, respectively. s The frequency of the vibration signal.

[0019] Furthermore, the location of the vibration signal obtained using the Sagnac interferometric fiber optic vibration positioning structure is as follows:

[0020]

[0021] Where z is the distance from the location where the vibration signal occurs to the third polarization beam splitter, Δτ is the fixed time delay obtained by cross-correlation calculation of the first and second voltage signals output by the first and second photodetectors; L1 and L2 are the lengths of the first and second fiber delay loops, respectively, and L3 is the length of the vibration sensing fiber. x L is the length between the third polarizing beam splitter and the second mirror. y n is the length between the second polarizing beam splitter and the first reflecting mirror. x n y These are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, respectively.

[0022] The beneficial effects of this invention compared to the prior art are as follows:

[0023] The dual-polarization Sagnac fiber vibration structure designed in this invention can generate two independent interference phase signals. The location of the vibration signal can be quickly calculated using a cross-correlation time-delay algorithm. Compared to traditional notch point frequency calculation methods, this invention offers the following advantages:

[0024] (1) The algorithm for locating the vibration position is simpler and more direct, and is not limited by the frequency of the vibration signal;

[0025] (2) Based on the same vibration sensing fiber, vibration signals are sensed and located. The detection sensitivity is high and the sensing distance is long, which has great potential in long-distance vibration sensing applications. Attached Figure Description

[0026] The accompanying drawings, which form part of this specification, are provided to further illustrate embodiments of the invention and, together with the textual description, explain the principles of the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0027] Figure 1 A schematic diagram of the dual-polarization structure of the Sagnac fiber vibration positioning structure provided in a specific embodiment of the present invention;

[0028] Figure 2 The following are schematic diagrams of the polarization beam splitter and fiber coupler provided in specific embodiments of the present invention. (a), (b), and (c) are port schematic diagrams of the 1*2 polarization beam splitter, the 2*2 fiber coupler, and the 1*2 fiber coupler, respectively.

[0029] Figure 3 The diagram shows the equivalent transmission optical paths of X-polarized light and Y-polarized light in a specific embodiment of the present invention; (a) and (b) are the equivalent transmission optical paths of X-polarized light and Y-polarized light, respectively.

[0030] The above figures include the following reference numerals:

[0031] 1. Broadband light source; 2. First polarization beam splitter; 3. First fiber coupler; 4. Second fiber coupler; 5. First fiber delay loop; 6. Second fiber delay loop; 7. Third fiber coupler; 8. Fourth fiber coupler; 9. Second polarization beam splitter; 10. Third polarization beam splitter; 11. Vibration sensing fiber; 12. First reflector; 13. Second reflector; 14. First photodetector; 15. Second photodetector. Detailed Implementation

[0032] Specific embodiments of the present invention will now be described in detail. In the following description, specific details are set forth for purposes of explanation and not limitation, in order to aid in a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced in other embodiments departing from these specific details.

[0033] It should be noted that, in order to avoid obscuring the invention with unnecessary details, only the device structure and / or processing steps closely related to the solution of the invention are shown in the accompanying drawings, while other details that are not closely related to the invention are omitted.

[0034] As one aspect of the present invention, a Sagnac interferometric fiber vibration positioning structure based on a dual polarization structure is proposed, comprising a broadband light source, a first polarization beam splitter, a first fiber coupler, a second fiber coupler, a first fiber delay loop, a second fiber delay loop, a third fiber coupler, a fourth fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing fiber, a first reflector, a second reflector, a first photodetector, and a second photodetector.

[0035] The first and second fiber optic couplers are 2x2 fiber optic couplers, while the third and fourth fiber optic couplers are 1x2 fiber optic couplers. The first, second, and third polarization beamsplitters are all 1x2 polarization beamsplitters.

[0036] The connection relationships and working principles of each component are as follows:

[0037] A broadband light source is connected to port a of the first polarization beam splitter to output unpolarized incident light.

[0038] Ports b and c of the first polarization beam splitter are connected to the first fiber coupler and the second fiber coupler, respectively. X-polarized light incident through port a is directly coupled to the first fiber coupler via the first polarization beam splitter, while Y-polarized light is cross-coupled to the second fiber coupler.

[0039] The two ports on one side of the first fiber coupler are connected to the b port of the first polarization beam splitter and the first photodetector, respectively. Similarly, the two ports on the same side of the second fiber coupler are connected to the c port of the first polarization beam splitter and the second photodetector, respectively.

[0040] The two ports on the other side of the first fiber coupler are respectively connected to one end of the first fiber delay ring and one end of the dual port of the third fiber coupler, wherein the other port of the first fiber delay ring is connected to the other end of the dual port of the third fiber coupler; similarly, the two ports on the other side of the second fiber coupler are respectively connected to one end of the second fiber delay ring and one end of the dual port of the fourth fiber coupler, wherein the other port of the second fiber delay ring is connected to the other end of the dual port of the fourth fiber coupler.

[0041] The single port of the third fiber coupler is connected to the b port of the second polarization beam splitter, and the single port of the fourth fiber coupler is connected to the c port of the third polarization beam splitter.

[0042] X-polarized light is split into two beams by the first fiber coupler. The upper beam passes through the first fiber delay loop, enters the third fiber coupler, and then enters the second polarization beam splitter. The lower beam directly enters the third fiber coupler and then reaches the second polarization beam splitter.

[0043] Y-polarized light is split into two beams by the second fiber coupler. The upper beam passes through the second fiber delay loop, enters the fourth fiber coupler, and then enters the third polarization beam splitter. The lower beam passes directly through the fourth fiber coupler and then reaches the third polarization beam splitter.

[0044] The c port of the second polarization beam splitter is connected to the first reflector, and the a port is connected to one end of the vibration sensing fiber; the b port of the third polarization beam splitter is connected to the second reflector, and the a port is connected to the other end of the vibration sensing fiber.

[0045] After entering the vibration sensing fiber through the second polarization beam splitter, the X-polarized light reaches port a of the third polarization beam splitter. It is then directly coupled to the second reflector, reflected, and returns to the vibration sensing fiber. The X-polarized light returning to the second polarization beam splitter is directly coupled to port b of the second polarization beam splitter. After passing through the third fiber coupler, it is split again. The upper beam reaches the first photodetector through the first fiber delay loop and the first fiber coupler, while the lower beam directly reaches the first photodetector through the first fiber coupler.

[0046] Y-polarized light enters the vibration sensing fiber through the third polarization beam splitter and reaches port a of the second polarization beam splitter. It then cross-couples to the first reflector, is reflected, and returns to the vibration sensing fiber. The Y-polarized light returning to the third polarization beam splitter cross-couples to port c of the third polarization beam splitter. After passing through the fourth fiber coupler, it is split again. The upper beam reaches the second photodetector via the second fiber delay loop and the second fiber coupler, while the lower beam directly reaches the second photodetector via the second fiber coupler.

[0047] A first photodetector is used to convert the X-polarized light signal into a first voltage signal P. x The second detector is used to convert the Y-polarized light signal into a second voltage signal P. y .

[0048] By demodulating the first voltage signal P x Second voltage signal P y From the phase signal, two signal subsets with time delays related to the vibration location can be obtained. After extracting the fixed time delay using the cross-correlation algorithm, the location where the vibration occurs can be calculated.

[0049] As another aspect of the present invention, the technical solution of the present invention will be described in detail with reference to a specific embodiment.

[0050] like Figure 1 As shown, this embodiment presents a Sagnac-type fiber optic vibration positioning structure based on the polarization multiplexing principle. This embodiment includes a broadband light source 1, a first polarization beam splitter 2, a first fiber coupler 3, a second fiber coupler 4, a first fiber delay loop 5, a second fiber delay loop 6, a third fiber coupler 7, a fourth fiber coupler 8, a second polarization beam splitter 9, a third polarization beam splitter 10, a vibration sensing fiber 11, a first reflector 12, a second reflector 13, a first photodetector 14, and a second photodetector 15.

[0051] In this structure, except for the broadband light source 1, the first photodetector 14, and the second photodetector 15 which use single-mode fiber pigtails, all other optical devices adopt polarization-maintaining fiber design, which will not be described in detail below.

[0052] The first polarization beam splitter 2, the second polarization beam splitter 9, and the third polarization beam splitter 10 are all 1*2 polarization beam splitters. Figure 2 (a) defines that port a of the 1*2 polarization beam splitter can transmit X-polarized and Y-polarized light simultaneously. X-polarized light can be directly coupled to port b via port a, or vice versa; Y-polarized light can be cross-coupled to port c via port a, or vice versa.

[0053] The 2a port of the first polarization beam splitter 2 is connected to the broadband light source 1. The X-polarized light in the incident light is directly coupled to the 2b port, and the Y-polarized light is cross-coupled to the 2c port.

[0054] The first fiber coupler 3 and the second fiber coupler 4 are 2*2 fiber couplers, both with a splitting ratio of 50:50. Figure 2 (b) The 2*2 fiber optic coupler has four ports: a, b, c, and d.

[0055] The third fiber coupler 7 and the fourth fiber coupler 8 are both 1*2 fiber couplers with a splitting ratio of 50:50. Figure 2 (c) The single port of the 1*2 fiber coupler is port a, and the dual ports on the other side are port b and port c.

[0056] The 3a port of the first fiber coupler 3 is connected to the first photodetector 14, and its 3b port on the same side is connected to the 2b port of the first polarization beam splitter; its 3d port on the opposite side is connected to one end of the first fiber delay ring 5, and its 3c port is connected to the 7c port of the third fiber coupler 7. The other end of the first fiber delay ring 5 is connected to the 7b port of the third fiber coupler 7.

[0057] Port 4a of the second fiber coupler 4 is connected to port 2c of the first polarization beam splitter, and port 4b on the same side is connected to the second photodetector 15; port 4d on the opposite side is connected to one end of the second fiber delay ring 6, and port 4c is connected to port 8c of the fourth fiber coupler 8. The other end of the second fiber delay ring 6 is connected to port 8b of the fourth fiber coupler 8.

[0058] The 9b port of the second polarization beam splitter 9 is connected to the 7a port of the third fiber coupler 7, and the 9c port of the second polarization beam splitter 9 is connected to the first reflector 12.

[0059] The 10c port of the third polarization beam splitter 10 is connected to the 8a port of the fourth fiber coupler 8, and the 10b port of the third polarization beam splitter 10 is connected to the second reflector 13.

[0060] One end of the vibration sensing fiber 11 is connected to port 9a of the second polarization beam splitter 9, and the other end is connected to port 10a of the third polarization beam splitter 10.

[0061] Broadband light source 1 is a superluminescent diode light source that emits unpolarized broadband light.

[0062] like Figure 3 As shown, it gives the following: Figure 1 The equivalent transmission optical paths of X-polarized light and Y-polarized light in the structure are described in detail below:

[0063] X-polarized light is directly coupled to the first fiber coupler 3 via the first polarization beam splitter 2. The two beams after splitting are transmitted to the third fiber coupler 7 via the upper first fiber delay loop 5 and the lower optical path, respectively. They then pass through the X-polarization port 9b of the second polarization beam splitter 9 and are directly coupled to port 9a to enter the vibration sensing fiber 11. After that, they pass through port 10a of the third polarization beam splitter 10 and are directly coupled to port 10b to reach the second reflector 13. The reflected X-polarized light returns to the vibration sensing fiber 11, passes through the second polarization beam splitter 9 to reach the third fiber coupler 7, and after splitting, are transmitted to the first fiber coupler 3 via the upper first fiber delay loop 5 and the lower optical path, respectively, and finally reach the first photodetector 14.

[0064] Similarly, the Y-polarized light is cross-coupled to the second fiber coupler 4 via the first polarization beam splitter 2. After splitting, the two beams are transmitted to the fourth fiber coupler 8 via the upper second fiber delay loop 6 and the lower optical path, respectively. They then cross-couple to port 9a via the Y-polarization port 10c of the third polarization beam splitter 10 and enter the vibration sensing fiber 11. After that, they cross-couple to port 9c via port 9a of the second polarization beam splitter 9 and reach the first reflector 12. The reflected Y-polarized light returns to the vibration sensing fiber 11, passes through the third polarization beam splitter 10 to the fourth fiber coupler 8, and after splitting, is transmitted to the second fiber coupler 4 via the upper second fiber delay loop 6 and the lower optical path, respectively, and finally reaches the second photodetector 15.

[0065] The first photodetector 14 and the second photodetector 15 convert the optical power of the received X-polarized light and Y-polarized light, respectively, into a first voltage signal P. x Second voltage signal P y The first voltage signal P is acquired using a host computer. x Second voltage signal P y The phase information is demodulated, and the time delay of the two phase signals is estimated to determine the location of the external vibration signal that the vibration sensing fiber 11 is sensitive to.

[0066] This embodiment also provides a Sagnac interferometric fiber vibration localization method based on a dual polarization structure, the principle of which is as follows:

[0067] First voltage signal P x Second voltage signal P y There are four different optical signals with different transmission paths. Since the fiber lengths of the first fiber delay loop 5 and the second fiber delay loop 6 are much greater than the coherence length of the broadband light source 1, the first voltage signal P... x Second voltage signal P y The optical power signals that can interfere at a certain point can be simplified as follows:

[0068]

[0069] in, and The phase difference φ represents the two beams that interfere in the first photodetector 14 and the second photodetector 15, respectively. x0 φ y0 The initial phase of the two optical paths, X-polarization and Y-polarization, is given by P. Since the structure is relatively stationary, this initial phase also includes the Sagnac rotation phase shift for each path. x0 P represents the power amplitude of the interference of X-polarized light. y0 ω represents the power amplitude of the interference of Y-polarized light, and ω is the angular frequency of the transmitted light.

[0070] Assuming that when an external vibration signal is generated, the phase excitation applied to the transmitted light in the vibration sensing fiber 11 is as follows: ω s The frequency of the vibration signal, The phase amplitude, for different polarized light, can be expressed as follows: and n x and n y The refractive indices of the slow and fast axes of the polarization-maintaining fiber are L1 and L2, respectively; the lengths of the first fiber delay ring 5 and the second fiber delay ring 6 are L1 and L2, respectively; the length of the vibration sensing fiber 11 is L3; and the length between the third polarization beam splitter 10 and the second reflector 13 is L. x The length between the second polarizing beam splitter 9 and the first reflecting mirror 12 is L. y When the distance from the location where the vibration signal occurs to the third polarization beam splitter 10 is z, and They can be represented as follows:

[0071]

[0072] t 1,2 =2n x,y L 1,2 / c…………………………(5)

[0073] τ x (z)=n x (L x +z) / c……………………(6)

[0074] τ y (z)=n y (L3+L y -z) / c……………………(7)

[0075] Where c is the speed of light, τ x (z) represents the propagation time of X-polarized light from the vibration point to the second reflecting mirror, τ y (z) represents the propagation time of the Y-polarized light from the vibration point to the first reflecting mirror, t1 represents the propagation time of the X-polarized light through the first fiber delay loop, and t2 represents the propagation time of the Y-polarized light through the second fiber delay loop. The phase amplitude of the vibration signal excited by the X-polarized light. ω represents the phase amplitude generated by the vibration signal on the Y-polarized light. s Let L1 be the frequency of the vibration signal, L2 be the lengths of the first and second fiber delay loops, respectively, and L3 be the length of the vibration sensing fiber. x ny These are the refractive indices of the slow and fast axes of the polarization-maintaining fiber, respectively.

[0076] It should be noted that the first fiber delay loop 5 and the second fiber delay loop 6 introduce a time delay between the X-polarized and Y-polarized light arriving at the vibration sensing fiber 11, thus causing the vibration signal to exhibit different phases in these two light paths. Theoretically, only when the external vibration frequency fs simultaneously satisfies... (MHz), where m and n are integers, this method will fail. Therefore, as long as the lengths of L1 and L2 are properly controlled, this method is unaffected by vibration signals. Based on this, the lengths of the first fiber delay loop and the second fiber delay loop do not simultaneously satisfy the following formula:

[0077]

[0078] Where L1 and L2 are the lengths of the first and second fiber delay loops, respectively, and n x n y ω represents the refractive index of the slow axis and fast axis of the polarization-maintaining fiber, respectively. s The frequency of the vibration signal.

[0079] By demodulating the first voltage signal P x Second voltage signal P y From the phase signal in the structure, two signal subsets with time delays related to the vibration position can be obtained. It can be seen from formulas (3) and (4) that when the length, vibration frequency, and vibration position of each component in the structure are determined, these two related signals P... x P y The time delay Δτ depends only on the vibration position z. After extracting this fixed time delay using the cross-correlation algorithm, the location of the vibration can be calculated. This vibration position z can be expressed as:

[0080]

[0081] Similar reference numerals and letters in the embodiments indicate similar items in the following figures. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0082] It should be noted that the terms "upper," "lower," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the technical product is in use. They are used only for the convenience of describing the technology and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the technology. Furthermore, "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. Therefore, the terms "first," "second," and "third," etc., are used only for distinguishing descriptions and should not be construed as indicating or implying relative importance. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0083] In the description of this technology, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this technology based on the specific circumstances.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Sagnac interferometric fiber optic vibration positioning structure based on a dual polarization structure, characterized in that, It includes a light source, a first polarization beam splitter, a first fiber coupler, a second fiber coupler, a first fiber delay loop, a second fiber delay loop, a third fiber coupler, a fourth fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing fiber, a first reflector, a second reflector, a first photodetector, and a second photodetector. The a port of the first polarization beam splitter is connected to the light source, and the b and c ports of the first polarization beam splitter are respectively connected to the a port of the first fiber coupler and the second fiber coupler; the b ports of the first fiber coupler and the second fiber coupler are respectively connected to the first photodetector and the second photodetector. The d ports of the first fiber optic coupler and the second fiber optic coupler are respectively connected to the b ports of the third fiber optic coupler and the fourth fiber optic coupler through the first fiber optic delay loop and the second fiber optic delay loop; the c ports of the first fiber optic coupler and the second fiber optic coupler are respectively connected to the c ports of the third fiber optic coupler and the fourth fiber optic coupler. The a-ports of the third and fourth fiber couplers are respectively connected to the b-port of the second polarization beamsplitter and the c-port of the third polarization beamsplitter; the c-port of the second polarization beamsplitter is connected to the first reflector, and the b-port of the third polarization beamsplitter is connected to the second reflector; the a-ports of the second and third polarization beamsplitters are respectively connected to the two ends of the vibration sensing fiber. The X-polarized light incident at port a of the first polarization beam splitter is directly coupled to the first fiber coupler, and the Y-polarized light incident at port a of the first polarization beam splitter is cross-coupled to the second fiber coupler.

2. The structure according to claim 1, characterized in that, The light source is a broadband light source, and the broadband light source outputs unpolarized incident light.

3. The structure according to claim 1, characterized in that, The splitting ratios of the first fiber optic coupler, the second fiber optic coupler, the third fiber optic coupler, and the fourth fiber optic coupler are all 50:

50.

4. The structure according to claim 1, characterized in that, Except for the single-mode fiber used in the light source, the first photodetector, and the second photodetector, the polarization-maintaining fiber used in the first polarization beam splitter, the first fiber coupler, the second fiber coupler, the first fiber delay loop, the second fiber delay loop, the third fiber coupler, the fourth fiber coupler, the second polarization beam splitter, the third polarization beam splitter, the vibration sensing fiber, the first reflector, and the second reflector.

5. The structure according to claim 1, characterized in that, X-polarized light is split into two beams by the first fiber coupler. One beam passes through the first fiber delay loop and the third fiber coupler to enter the second polarization beam splitter, while the other beam directly enters the third fiber coupler to reach the second polarization beam splitter. The X-polarized light then enters the vibration sensing fiber through the second polarization beam splitter and reaches port a of the third polarization beam splitter. It is then directly coupled to the second reflector, reflected back to the vibration sensing fiber, and returns to the second polarization beam splitter. The X-polarized light is then directly coupled to port b of the second polarization beam splitter, and after passing through the third fiber coupler, it is split again. One beam passes through the first fiber delay loop and the first fiber coupler to reach the first photodetector, while the other beam directly passes through the first fiber coupler to reach the first photodetector. The Y-polarized light is split into two beams by the second fiber coupler. One beam passes through the second fiber delay loop and the fourth fiber coupler to enter the third polarization beam splitter, while the other beam passes directly through the fourth fiber coupler to reach the third polarization beam splitter. The Y-polarized light then enters the vibration sensing fiber through the third polarization beam splitter and reaches port a of the second polarization beam splitter. It is cross-coupled to the first reflector, reflected back to the vibration sensing fiber, and returns to the third polarization beam splitter. The Y-polarized light is cross-coupled to port c of the third polarization beam splitter, and after passing through the fourth fiber coupler, it is split again. One beam passes through the second fiber delay loop and the second fiber coupler to reach the second photodetector, while the other beam passes directly through the second fiber coupler to reach the second photodetector.

6. The structure according to claim 1, characterized in that, The following formula applies when the lengths of the first fiber delay loop and the second fiber delay loop are not simultaneously: , Where m and n are integers, , These are the lengths of the first fiber delay ring and the second fiber delay ring, respectively. , These are the refractive indices of the slow and fast axes of the polarization-maintaining fiber, respectively. The frequency of the vibration signal.

7. The structure according to claim 1, characterized in that, The location of the vibration signal obtained using the Sagnac interferometric fiber optic vibration positioning structure is as follows: ,in, The distance from the location where the vibration signal occurs to the third polarization beam splitter. The fixed time delay is obtained by cross-correlation calculation of the first voltage signal and the second voltage signal output by the first and second photodetectors; , These are the lengths of the first fiber delay ring and the second fiber delay ring, respectively. The length of the vibration sensing fiber. The length between the third polarizing beam splitter and the second reflecting mirror. The length between the second polarizing beam splitter and the first reflecting mirror. , These are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, respectively.

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