Sagnac optical fiber vibration positioning structure based on dual-polarization structure

Abstract

The invention provides a Sagnac optical fiber vibration positioning structure based on a dual polarization structure. Comprising a broadband light source, a first polarization beam splitter, a first optical fiber coupler, a second optical fiber coupler, a first optical fiber delay ring, a second optical fiber delay ring, a third optical fiber coupler, a fourth optical fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing optical fiber, a first reflector, a second reflector, a first photoelectric detector and a second photoelectric detector. According to the positioning structure, X polarized light and Y polarized light sense the same vibration signal in the same vibration sensing optical fiber, two paths of independent interference signals with fixed time delay are formed, and the fixed time delay is related to the vibration position; by demodulating the phase information of the two paths of interference light intensities and performing cross-correlation time delay estimation, the specific position of the external vibration signal can be positioned. The problem that a traditional Sagnac interference type optical fiber vibration sensing system is complex in vibration positioning algorithm and limited by vibration frequency is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of vibration measurement, and in particular relates to a Sagnac interference type distributed optical fiber vibration positioning structure. Background Art

[0002] Distributed fiber optic vibration sensing systems have become a popular 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 precise positioning of the location 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 interference principle generally use the "zero frequency point" analysis method to locate the vibration position, and calculate the notch point frequency based on the Fourier transform of the vibration signal. However, the calculation process of this method is relatively complicated and requires that the notch point frequency must be included in the frequency range of the vibration signal. In addition, auxiliary positioning can also be performed by adding additional optical paths (such as Mach-Zehnder structure or Michelson structure), but this will increase the complexity and cost of the system and is not conducive to the large-scale application of the structure. Summary of the invention

[0004] In view of the technical problem that the Sagnac interferometric fiber optic vibration sensor is difficult to locate the vibration position, the present invention proposes a Sagnac interferometric fiber optic vibration positioning structure based on a dual polarization structure, which uses two independent interference phase signals to calculate the position where the vibration signal occurs.

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

[0006] As one aspect of the present invention, a Sagnac interferometric optical fiber vibration positioning structure based on a dual polarization structure is provided, comprising a light source, a first polarization beam splitter, a first optical fiber coupler, a second optical fiber coupler, a first optical fiber delay ring, a second optical fiber delay ring, a third optical fiber coupler, a fourth optical fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing optical 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 port and the c port of the first polarization beam splitter are respectively connected to the a port of the first fiber coupler and the a port of 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 optical fiber coupler and the second optical fiber coupler are connected to the b-ports of the third optical fiber coupler and the fourth optical fiber coupler through the first optical fiber delay ring and the second optical fiber delay ring respectively; the c-ports of the first optical fiber coupler and the second optical fiber coupler are connected to the c-ports of the third optical fiber coupler and the fourth optical fiber coupler respectively;

[0009] The a ports of the third optical fiber coupler and the fourth optical 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 ports of the second polarization beam splitter and the third polarization beam splitter are respectively connected to the two ends of the vibration sensing optical fiber.

[0010] Furthermore, the light source is a broadband light source, and the broadband light source outputs non-polarized incident light.

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

[0012] Furthermore, in addition to the single-mode optical fiber used by the light source, the first photodetector, and the second photodetector, the optical pigtails used by the first polarization beam splitter, the first optical fiber coupler, the second optical fiber coupler, the first optical fiber delay ring, the second optical fiber delay ring, the third optical fiber coupler, the fourth optical fiber coupler, the second polarization beam splitter, the third polarization beam splitter, the vibration sensing optical fiber, the first reflector, and the second reflector are all polarization-maintaining optical fibers.

[0013] Further, the X-polarized light incident on the a-port of the first polarization beam splitter is directly coupled to the first optical fiber coupler, and the Y-polarized light incident on the a-port of the first polarization beam splitter is cross-coupled to the second optical fiber coupler;

[0014] The X-polarized light is evenly divided into two light beams through the first optical fiber coupler, one light beam passes through the first optical fiber delay ring and the third optical fiber coupler to enter the second polarization beam splitter, and the other light beam directly enters the third optical fiber coupler to reach the second polarization beam splitter; the X-polarized light enters the vibration sensing optical fiber through the second polarization beam splitter to reach the a port of the third polarization beam splitter, is directly coupled to the second reflector, and is reflected back to the vibration sensing optical fiber. The X-polarized light returning to the second polarization beam splitter is directly coupled to the b port of the second polarization beam splitter, and is split again after passing through the third optical fiber coupler, one light beam passes through the first optical fiber delay ring and the first optical fiber coupler to reach the first photodetector, and the other light beam directly passes through the first optical fiber coupler to reach the first photodetector;

[0015] The Y polarized light is equally divided into two beams through the second optical fiber coupler, one beam passes through the second optical fiber delay ring and the fourth optical fiber coupler to enter the third polarization beam splitter, and the other beam directly passes through the fourth optical fiber coupler to reach the third polarization beam splitter; the Y polarized light enters the vibration sensing optical fiber through the third polarization beam splitter to reach the a port of the second polarization beam splitter, is cross-coupled to reach the first reflector, and is reflected back to the vibration sensing optical fiber. The Y polarized light returning to the third polarization beam splitter is cross-coupled to the c port of the third polarization beam splitter, and is split again after passing through the fourth optical fiber coupler, one beam passes through the second optical fiber delay ring and the second optical fiber coupler to reach the second photodetector, and the other beam directly passes through the second optical fiber coupler to reach the second photodetector.

[0016] Furthermore, the lengths of the first optical fiber delay loop and the second optical fiber delay loop may satisfy the following formula at different times:

[0017]

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

[0019] Furthermore, the vibration signal generation position obtained by using the Sagnac interferometric optical fiber vibration positioning structure is:

[0020]

[0021] Wherein, z is the distance from the position where the vibration signal occurs to the third polarization beam splitter, Δτ is the fixed delay obtained by cross-correlation calculation of the first voltage signal and the second voltage signal output by the first and second photodetectors; L1 and L2 are the lengths of the first fiber delay loop and the second fiber delay loop respectively, L3 is the length of the vibration sensing fiber, and L x is the length from the third polarization beam splitter to the second reflector, L y is the length from the second polarization beam splitter to the first reflector, n x 、n y are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, respectively.

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

[0023] The dual-polarization Sagnac fiber vibration structure designed in the present invention can obtain two independent interference phase signals. The location of the vibration signal can be quickly calculated through the cross-correlation delay algorithm. Compared with the traditional notch point frequency calculation method, it has 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) The vibration signal is sensed and located based on the same vibration sensing optical fiber, with high detection sensitivity and long sensing distance, which has great potential in long-distance vibration sensing applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The included drawings are used to provide a further understanding of the embodiments of the present invention, which constitute a part of the specification, are used to illustrate the embodiments of the present invention, and together with the text description, explain the principles of the present invention. Obviously, the drawings in the following description are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

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

[0028] Figure 2 Schematic diagram of the structure of the polarization beam splitter and the optical fiber coupler provided in the specific embodiment of the present invention, (a), (b), and (c) are schematic diagrams of the ports of the 1*2 polarization beam splitter, the 2*2 optical fiber coupler, and the 1*2 optical fiber coupler, respectively;

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

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

[0031] 1. Broad-spectrum light source, 2. First polarization beam splitter, 3. First optical fiber coupler, 4. Second optical fiber coupler, 5. First optical fiber delay loop, 6. Second optical fiber delay loop, 7. Third optical fiber coupler, 8. Fourth optical fiber coupler, 9. Second polarization beam splitter, 10. Third polarization beam splitter, 11. Vibration sensing optical fiber, 12. First reflector, 13. Second reflector, 14. First photodetector, 15. Second photodetector. DETAILED DESCRIPTION

[0032] Specific embodiments of the present invention are described in detail below. In the following description, for the purpose of explanation and not limitation, specific details are set forth to help fully understand the present invention. However, it will be apparent to those skilled in the art that the present invention may also be practiced in other embodiments that depart from these specific details.

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

[0034] As one aspect of the present invention, a Sagnac interferometric fiber optic vibration positioning structure based on a dual polarization structure is proposed, including a broadband light source, a first polarization beam splitter, a first fiber optic coupler, a second fiber optic coupler, a first fiber optic delay ring, a second fiber optic delay ring, a third fiber optic coupler, a fourth fiber optic 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 fiber coupler and the second fiber coupler are 2*2 fiber couplers, the third fiber coupler and the fourth fiber coupler are 1*2 fiber couplers, and the first polarization beam splitter, the second polarization beam splitter and the third polarization beam splitter are all 1*2 polarization beam splitters.

[0036] The connection relationship and working principle of each device are as follows:

[0037] The wide-spectrum light source is connected to the a-port of the first polarization beam splitter to output non-polarized incident light.

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

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

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

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

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

[0043] The Y polarized light is equally divided into two beams through the second fiber coupler, wherein the upper beam passes through the second fiber delay ring and enters the fourth fiber coupler and then enters the third polarization beam splitter, and the lower beam directly passes through the fourth fiber coupler and 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 optical 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 optical fiber.

[0045] The X-polarized light enters the vibration sensing optical fiber through the second polarization beam splitter and reaches the a port of the third polarization beam splitter, and then is directly coupled to the second reflector and returns to the vibration sensing optical fiber after reflection. The X-polarized light returning to the second polarization beam splitter is directly coupled to the b port of the second polarization beam splitter and is split again after passing through the third fiber coupler. The upper beam reaches the first photodetector via the first fiber delay ring and the first fiber coupler, and the lower beam reaches the first photodetector directly via the first fiber coupler.

[0046] The Y polarized light enters the vibration sensing optical fiber through the third polarization beam splitter and reaches the a port of the second polarization beam splitter, and then cross-couples to reach the first reflector, and returns to the vibration sensing optical fiber after reflection. The Y polarized light returning to the third polarization beam splitter is cross-coupled to the c port of the third polarization beam splitter, and is split again after passing through the fourth fiber coupler. The upper beam reaches the second photodetector via the second fiber delay ring and the second fiber coupler, and the lower beam directly reaches the second photodetector through the second fiber coupler.

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

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

[0049] As another aspect of the present invention, the technical solution of the present invention is described in detail in conjunction with a specific embodiment.

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

[0051] In this structure, except that the pigtails used by the broadband light source 1, the first photodetector 14 and the second photodetector 15 are single-mode optical fibers, other optical devices are designed with polarization-maintaining optical fibers, 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 the a port of the 1*2 polarization beam splitter can transmit X-polarized and Y-polarized light at the same time. The X-polarized light can be directly coupled to the b port via the a port, or in the reverse direction; the Y-polarized light can be cross-coupled to the c port via the a port, or in the reverse direction.

[0053] The port 2a 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 port 2b, and the Y-polarized light is cross-coupled to the port 2c.

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

[0055] The third optical fiber coupler 7 and the fourth optical fiber coupler 8 are 1*2 optical fiber couplers, and the splitting ratio is also 50:50. Figure 2 In (c), the single port of the 1*2 optical 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 optical fiber coupler 3 is connected to the first photodetector 14, and the 3b port on the same side thereof is connected to the 2b port of the first polarization beam splitter; the 3d port on the opposite side thereof is connected to one end of the first optical fiber delay loop 5, and the 3c port is connected to the 7c port of the third optical fiber coupler 7. The other end of the first optical fiber delay loop 5 is connected to the 7b port of the third optical fiber coupler 7.

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

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

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

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

[0061] The broadband light source 1 is a superluminescent diode light source, which emits non-polarized broadband light.

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

[0063] The X-polarized light is directly coupled to the first fiber coupler 3 through the first polarization beam splitter 2. The two beams after the splitting are transmitted through the first fiber delay ring 5 above and the optical path below to reach the third fiber coupler 7, and are directly coupled to the port 9a through the X-polarization port 9b of the second polarization beam splitter 9 to enter the vibration sensing fiber 11, and then directly coupled to the port 10b through the port 10a of the third polarization beam splitter 10 to reach the second reflector 13. The reflected X-polarized light returns to the vibration sensing fiber 11 again, reaches the third fiber coupler 7 through the second polarization beam splitter 9, and reaches the first fiber coupler 3 through the first fiber delay ring 5 above and the optical path below after the splitting, and finally reaches the first photodetector 14.

[0064] Similarly, the Y polarized light is cross-coupled to the second fiber coupler 4 through the first polarization beam splitter 2. The two beams after splitting are transmitted through the second fiber delay ring 6 above and the optical path below to reach the fourth fiber coupler 8, and are cross-coupled to port 9a through the Y polarization port 10c of the third polarization beam splitter 10 to enter the vibration sensing fiber 11, and then cross-coupled to port 9c through port 9a of the second polarization beam splitter 9 to reach the first reflector 12. The reflected Y polarized light returns to the vibration sensing fiber 11 again, reaches the fourth fiber coupler 8 through the third polarization beam splitter 10, and reaches the second fiber coupler 4 through the second fiber delay ring 6 above and the optical path below after splitting, 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 the Y-polarized light into a first voltage signal P x and the second voltage signal P y . Use the host computer to collect the first voltage signal P x and the second voltage signal P y , and demodulate the phase information therein, and perform time delay estimation on the two-phase signals, so as to determine the location where the external vibration signal to which the vibration sensing optical fiber 11 is sensitive occurs.

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

[0067] In the first voltage signal P x and the second voltage signal P y There are four optical signals with different transmission paths in the first optical fiber delay loop 5 and the second optical fiber delay loop 6. Since the optical fiber lengths of the first optical fiber delay loop 5 and the second optical fiber delay loop 6 are much longer than the coherence length of the broadband light source 1, the first voltage signal P x and the second voltage signal P y The optical power signals that can cause interference at can be simplified as

[0068]

[0069] in, and are the phase difference of the two lights interfering in the first photodetector 14 and the second photodetector 15, respectively, x0 ,φ y0 is the initial phase of the X-polarization and Y-polarization optical paths. Since the structure is relatively static, the initial phase also contains the respective Sagnac rotational speed phase shifts, P x0 is the power amplitude of the X-polarized light interference, P y0 is 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 transmission light in the vibration sensing optical fiber 11 is ω s is the frequency of the vibration signal, Phase amplitude, for different polarizations, the amplitude can be expressed as and n x and n y are the refractive indices of the slow axis and the fast axis of the polarization-maintaining optical fiber, respectively. The lengths of the first optical fiber delay ring 5 and the second optical fiber delay ring 6 are L1 and L2, the length of the vibration sensing optical 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 polarization beam splitter 9 and the first reflector 12 is L y , when the distance from the position where the vibration signal occurs to the third polarization beam splitter 10 is z, and Can be expressed as

[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) is the transmission time of X-polarized light from the vibration source to the second reflector, τ y (z) is the transmission time of Y polarized light from the vibration generating point to the first reflector, t1 is the transmission time of X polarized light through the first optical fiber delay loop, t2 is the transmission time of Y polarized light through the second optical fiber delay loop, is the phase amplitude of the vibration signal to the X-polarized light excitation, is the phase amplitude of the Y-polarized light excited by the vibration signal, ω s is the frequency of the vibration signal, L1 and L2 are the lengths of the first and second optical fiber delay loops, respectively, L3 is the length of the vibration sensing optical fiber, n x 、ny are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, respectively.

[0076] It should be noted that the first optical fiber delay loop 5 and the second optical fiber delay loop 6 cause a time delay between the X-polarized light and the Y-polarized light reaching the vibration sensing optical fiber 11, so that the phases caused by the vibration signal in the two paths of light are different. Theoretically, only when the external vibration frequency fs satisfies both (MHz), where m and n are integers, the method will fail. Therefore, as long as the lengths of L1 and L2 are reasonably controlled, the method will not be affected by vibration signals. Based on this, the lengths of the first optical fiber delay loop and the second optical fiber delay loop are different and satisfy the following formula:

[0077]

[0078] Wherein, L1 and L2 are the lengths of the first optical fiber delay loop and the second optical fiber delay loop respectively, and n x 、n y are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, ω s is the frequency of the vibration signal.

[0079] By demodulating the first voltage signal P x and the second voltage signal P y By using 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 device in the structure are determined, these two related signals P x , P y The time delay Δτ is only related to the vibration position z. After extracting the fixed time delay according to the cross-correlation algorithm, the position where the vibration occurs can be calculated. The vibration position z can be expressed as:

[0080]

[0081] Similar reference numerals and letters in the embodiments denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0082] It should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the technical product is usually placed when in use. It is only for the convenience of describing the present technology and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present technology. In addition, "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. Therefore, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In the description of the present invention, unless otherwise specified, the meaning of "multiple" is two or more.

[0083] In the description of this technology, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this technology can be understood according to 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 principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A Sagnac interferometric optical fiber vibration positioning structure based on a dual polarization structure, characterized in that: It includes a light source, a first polarization beam splitter, a first optical fiber coupler, a second optical fiber coupler, a first optical fiber delay ring, a second optical fiber delay ring, a third optical fiber coupler, a fourth optical fiber coupler, a second polarization beam splitter, a third polarization beam splitter, a vibration sensing optical 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 port and the c port of the first polarization beam splitter are respectively connected to the a port of the first fiber coupler and the a port of 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 optical fiber coupler and the second optical fiber coupler are connected to the b-ports of the third optical fiber coupler and the fourth optical fiber coupler through the first optical fiber delay ring and the second optical fiber delay ring respectively; the c-ports of the first optical fiber coupler and the second optical fiber coupler are connected to the c-ports of the third optical fiber coupler and the fourth optical fiber coupler respectively; The a ports of the third optical fiber coupler and the fourth optical 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 ports of the second polarization beam splitter and the third polarization beam splitter are respectively connected to the two ends of the vibration sensing optical fiber.

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

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

50.

4. The structure according to claim 1, characterized in that The pigtails used by the light source, the first photodetector, and the second photodetector are single-mode optical fibers, and the pigtails used by the first polarization beam splitter, the first optical fiber coupler, the second optical fiber coupler, the first optical fiber delay ring, the second optical fiber delay ring, the third optical fiber coupler, the fourth optical fiber coupler, the second polarization beam splitter, the third polarization beam splitter, the vibration sensing optical fiber, the first reflector, and the second reflector are all polarization-maintaining optical fibers.

5. The structure according to claim 1, characterized in that The X-polarized light incident on the port a of the first polarization beam splitter is directly coupled to the first optical fiber coupler, and the Y-polarized light incident on the port a of the first polarization beam splitter is cross-coupled to the second optical fiber coupler; The X-polarized light is evenly divided into two light beams through the first optical fiber coupler, one light beam passes through the first optical fiber delay ring and the third optical fiber coupler to enter the second polarization beam splitter, and the other light beam directly enters the third optical fiber coupler to reach the second polarization beam splitter; the X-polarized light enters the vibration sensing optical fiber through the second polarization beam splitter to reach the a port of the third polarization beam splitter, is directly coupled to the second reflector, and is reflected back to the vibration sensing optical fiber. The X-polarized light returning to the second polarization beam splitter is directly coupled to the b port of the second polarization beam splitter, and is split again after passing through the third optical fiber coupler, one light beam passes through the first optical fiber delay ring and the first optical fiber coupler to reach the first photodetector, and the other light beam directly passes through the first optical fiber coupler to reach the first photodetector; The Y polarized light is equally divided into two beams through the second optical fiber coupler, one beam passes through the second optical fiber delay ring and the fourth optical fiber coupler to enter the third polarization beam splitter, and the other beam directly passes through the fourth optical fiber coupler to reach the third polarization beam splitter; the Y polarized light enters the vibration sensing optical fiber through the third polarization beam splitter to reach the a port of the second polarization beam splitter, is cross-coupled to reach the first reflector, and is reflected back to the vibration sensing optical fiber. The Y polarized light returning to the third polarization beam splitter is cross-coupled to the c port of the third polarization beam splitter, and is split again after passing through the fourth optical fiber coupler, one beam passes through the second optical fiber delay ring and the second optical fiber coupler to reach the second photodetector, and the other beam directly passes through the second optical fiber coupler to reach the second photodetector.

6. The structure according to claim 1, characterized in that When the lengths of the first optical fiber delay loop and the second optical fiber delay loop are different, the following formula is satisfied: Where m and n are integers, L1 and L2 are the lengths of the first and second optical fiber delay loops, respectively. x 、n y are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, ω s is the frequency of the vibration signal.

7. The structure according to claim 1, characterized in that The vibration signal location obtained by using the Sagnac interferometric optical fiber vibration positioning structure is: Wherein, z is the distance from the position where the vibration signal occurs to the third polarization beam splitter, Δτ is the fixed delay obtained by cross-correlation calculation of the first voltage signal and the second voltage signal output by the first and second photodetectors; L1 and L2 are the lengths of the first fiber delay loop and the second fiber delay loop respectively, L3 is the length of the vibration sensing fiber, and L x is the length from the third polarization beam splitter to the second reflector, L y is the length from the second polarization beam splitter to the first reflector, n x 、n y are the refractive indices of the slow axis and fast axis of the polarization-maintaining fiber, respectively.

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