Vibration sensing device based on Sagnac interferometer

Abstract

The utility model discloses a vibration sensing device based on a Sagnac interferometer, and the device comprises a wide line width light source module which comprises an amplified spontaneous emission light source and a circulator, and the output end of the amplified spontaneous emission light source is connected to the input end of the circulator; a linear type Sagnac module; the multiplexing sensing module comprises x first dense wavelength division multiplexers and x fiber mirrors, and each dense wavelength division multiplexer corresponds to one fiber mirror; and a coupler demodulation module. The linear Sagnac module comprises a first coupler, a depolarizer and a second coupler which are connected in sequence, the output end of the circulator is connected to one input end of the first coupler, two of the output ends of the first coupler are connected to the input end of the second coupler, and the output end of the second coupler is connected to the output end of the circulator. The depolarizer is arranged on one optical path where the first coupler and the second coupler are connected, and the output end of the second coupler is connected to the first dense wavelength division multiplexer of the multiplexing sensing module.

Description

Technical Field

[0001] The utility model relates to the field of optical fiber sensing, in particular to a vibration sensing device based on a Sagnac interferometer. Background Art

[0002] Fiber optic sensing systems have been widely used in many practical occasions and scientific research fields, such as environmental monitoring, resource exploration, biomedicine, aerospace, etc., due to their unique advantages such as strong anti-electromagnetic interference ability, no electricity at the detection end, and resistance to harsh environments. The optical fiber used in the interferometric fiber optic vibration sensor has the functions of transmitting signals and sensing external signals. When the sensing unit of the system is loaded with a vibration signal, the phase of the light wave transmitted in the optical fiber will change accordingly, so the relevant information of the vibration signal can be obtained by detecting the returned phase change. There are several main types of phase-modulated fiber optic vibration systems: Mach-Zehnder type, Michelson type, Sagnac type and Fabry-Perot type, and their structural composition is relatively flexible and diverse.

[0003] The distributed fiber optic vibration sensing system based on the linear Sagnac interference principle can accurately restore regional intrusion events by detecting the optical phase changes caused by vibration and sound signals. It has the advantages of high frequency response, no phase fading, low laser line width requirements, and simple signal demodulation. However, it is commonly used to use wavelength division multiplexing technology at the front end of the linear Sagnac interferometer, which will require a large number of couplers, which will easily lead to increased costs. In addition, a distributed fiber optic vibration sensor disclosed in application number 201110008557.6 uses a Faraday rotator to compensate for the polarization fading problem. However, according to actual tests, in this optical path configuration, due to the temperature change of the environment in which the optical path is located, the Faraday rotator cannot improve the polarization fading, and there is still a problem of polarization crosstalk between the two light beams.

[0004] Therefore, there is room for further improvement. Utility Model Content

[0005] The technical problem to be solved by the utility model is to provide a vibration sensing device based on Sagnac interferometer in view of the deficiencies in the above-mentioned prior art, thereby avoiding the polarization crosstalk problem of the interferometer and realizing multi-channel, high-precision and high-resolution real-time strain sensing at a lower device cost.

[0006] The technical solution adopted by the utility model to solve the above technical problems is: a vibration sensing device based on Sagnac interferometer, comprising:

[0007] A wide linewidth light source module comprises an amplified spontaneous radiation light source and a circulator, wherein the output end of the amplified spontaneous radiation light source is connected to the input end of the circulator;

[0008] Linear Sagnac modules;

[0009] A multiplexing sensing module, comprising x first dense wavelength division multiplexers and x optical fiber mirrors, each dense wavelength division multiplexer corresponding to one optical fiber mirror; and

[0010] Coupler demodulation module; characterized in that:

[0011] The linear Sagnac module comprises a first coupler, a depolarizer and a second coupler connected in sequence, the output end of the circulator is connected to one of the input ends of the first coupler, two of the output ends of the first coupler are respectively connected to the input end of the second coupler, the depolarizer is arranged on one of the optical paths connecting the first coupler and the second coupler, and the output end of the second coupler is connected to a first dense wavelength division multiplexer of the multiplexing sensor module;

[0012] The coupler demodulation module includes y second dense wavelength division multiplexers and ny photodetectors, each second dense wavelength division multiplexer corresponds to n photodetectors, and the second second dense wavelength division multiplexers are also connected to the input end of the first coupler and the circulator respectively.

[0013] The linear Sagnac interferometer is used, and its balanced interferometer structure ensures that white light interference can be easily realized (reducing the requirements of other interferometers on the width of the interference light, and avoiding the trouble caused by the precise optical path length matching required by other interferometers due to the limited interference distance of the light source). At the same time, the incident light and the return light of the linear Sagnac interferometer sensing fiber share the same optical path, and a single sensing fiber is more conducive to practical applications. A depolarizer is introduced to ensure that at least one of the two interfering light beams has polarization components in two mutually perpendicular directions, thereby avoiding the polarization of the two light beams being completely perpendicular to each other and thus no interference occurs, ensuring that the polarization directions of the two subsequent interfering light beams are the same, and solving the polarization crosstalk problem in the linear Sagnac interferometer; the wavelength division multiplexing and de-wavelength division multiplexing introduced by the linear Sagnac at the sensor end and the photoelectric detection end can ensure the consistency of each channel by using a common interference optical path; the back-end wavelength division multiplexing technology route is adopted, and all sensors share a set of interferometer main optical paths, which effectively reduces the number of couplers and depolarizers, and further reduces costs.

[0014] Preferably, a delay line is provided on one of the optical paths connecting the first coupler and the second coupler. The delay line can make the two light beams returning after the vibration signal modulates the light beam and interfere with each other have different phases and a fixed phase difference, thereby satisfying the conditions for generating interference phenomenon.

[0015] Preferably, according to one aspect of the utility model, the first coupler is a 3×3 coupler, the second coupler is a 2×1 coupler, y=3, two second dense wavelength division multiplexers are connected to the input end of the first coupler, and another second dense wavelength division multiplexer is connected to the circulator.

[0016] Preferably, according to another aspect of the utility model, the first coupler is a 2×1 coupler, the second coupler is a 2×1 coupler, y=2, one second dense wavelength division multiplexer is connected to the input end of the first coupler, and the other second dense wavelength division multiplexer is connected to the circulator.

[0017] Preferably, in order to facilitate demodulation of the signal detected by the photodetector, the coupler demodulation module further includes an analog-to-digital converter and a personal computer, the photodetector is electrically connected to the analog-to-digital converter, and the analog-to-digital converter is electrically connected to the personal computer.

[0018] Preferably, the wavelength of the laser emitted by the amplified spontaneous emission light source is in the range of 1528-1563 nm.

[0019] Preferably, the first dense wavelength division multiplexer and the second dense wavelength division multiplexer use a designated frequency greater than 100 GHZ, and the bandwidth of the divided channels is less than 1.6 nm.

[0020] Preferably, in order to ensure that the depolarizer can depolarize, the depolarizer is composed of a length L d With 2L d The birefringent crystals are connected along the main axis at 45°, wherein Δn is the birefringence difference, Δλ is the bandwidth of the first dense wavelength division multiplexer and the second dense wavelength division multiplexer, and the following conditions are satisfied:

[0021] Compared with the prior art, the utility model has the following advantages: using a linear Sagnac interferometer, its balanced interferometer structure ensures that white light interference can be easily realized (reducing the requirements of other interferometers on the width of the interference light, and avoiding the trouble caused by the precise optical path length matching required by other interferometers due to the limited interference distance of the light source), and at the same time, the incident light and the return light of the linear Sagnac interferometer sensing fiber share the same optical path, and a single sensing optical fiber is more conducive to practical applications. A depolarizer is introduced to ensure that at least one of the two interfering light beams has polarization components in two mutually perpendicular directions, thereby avoiding the polarization of the two light beams being completely perpendicular to each other so that no interference occurs, ensuring that the polarization directions of the two subsequent interfering light beams are the same, and solving the polarization crosstalk problem in the linear Sagnac interferometer; the wavelength division multiplexing and de-wavelength division multiplexing introduced at the sensor end and the photoelectric detection end of the linear Sagnac can ensure the consistency of each channel by using a common interference optical path; adopting the back-end wavelength division multiplexing technology route, all sensors share a set of interferometer main optical paths, effectively reducing the number of couplers and depolarizers, and further reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a principle block diagram of the vibration sensor structure of the first embodiment of the utility model;

[0023] Figure 2 Vibration sensing data of an outfield experiment of the vibration sensing scheme of the embodiment of the utility model;

[0024] Figure 3 This is a principle block diagram of the vibration sensor structure of the second embodiment of the utility model. DETAILED DESCRIPTION

[0025] Embodiments of the present utility model are described in detail below, and examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions.

[0026] In the description of the present utility model, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate the orientation or position relationship based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present utility model 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. Since the embodiments disclosed in the present utility model can be set in different directions, these terms indicating directions are only for illustration and should not be regarded as limitations. For example, "up" and "down" are not necessarily limited to directions opposite to or consistent with the direction of gravity. In addition, the features defined as "first" and "second" may explicitly or implicitly include one or more of such features.

[0027] Embodiment 1

[0028] See also Figure 1 , a vibration sensing device based on Sagnac interferometer, including a wide line width light source module, a linear Sagnac module, a multiplexing sensing module and a coupler demodulation module. The following connections are all connected by optical fiber except for the analog-to-digital converter 11 and the personal computer 12, and the connection between the analog-to-digital converter 11 and the personal computer 12 is an electrical connection.

[0029] The wide linewidth light source module includes an amplified spontaneous emission light source (ASE) 1 and a circulator (CIR) 2. The output end of the amplified spontaneous emission light source 1 is connected to the input end of the circulator (CIR) 2, and the output end of the circulator 2 is connected to the linear Sagnac module. The wavelength range of the laser emitted by the amplified spontaneous emission light source 1 is in the range of 1528 to 1563 nm. The circulator 2 has three ports, which are respectively marked as port 1, port 2 and port 3. When incident, the light beam enters port 1 and exits port 2. When the light beam is reflected back, it enters port 2 and exits port 3.

[0030] The linear Sagnac module includes a first coupler 3, a depolarizer (LYOT type) 4, a delay line 5 and a second coupler 6 connected in sequence, wherein the first coupler 3 is a 3×3 coupler and the second coupler 6 is a 2×1 coupler. The output end of the circulator 2 is connected to the input end of the first coupler 3, and the output end of the second coupler 6 is connected to the multiplexed sensing module.

[0031] The output end of the first coupler 3 has three ports, one of which is not connected to the optical path, and the remaining two ports are respectively connected to the input end of the second coupler 6. The above-mentioned depolarizer 4 and delay line 5 are arranged on one of the optical paths connected to the first coupler 3 and the second coupler 6. The depolarizer 4 and the delay line 5 can be arranged in the same optical path or in different optical paths. The function of the depolarizer 4 is to ensure that at least one of the two interfering light beams has polarization components in two directions perpendicular to each other, so as to avoid that the polarizations of the two light beams are completely perpendicular to each other so that no interference occurs, and to ensure that the polarization directions of the two subsequent interfering light beams are the same. The function of the delay line 5 is to make the two light beams that return to interfere after the vibration signal modulates the light beam have different phases and a fixed phase difference, so as to meet the conditions for generating interference.

[0032] The multiplexed sensing module comprises x first dense wavelength division multiplexers 7 and x optical fiber mirrors 8, each dense wavelength division multiplexer corresponds to one optical fiber mirror. In this embodiment, x=3.

[0033] The coupler demodulation module includes y second dense wavelength division multiplexers 9, ny photodetectors 10, an analog-to-digital converter 11 and a personal computer 12. Each second dense wavelength division multiplexer 9 corresponds to n photodetectors 10, which are shown in the figure as PD1-1, PD1-2...PD1-n, PD2-1, PD2-2...PD2-n and PD3-1, PD3-2...PD3-n. In this embodiment, y=3. Two of the second dense wavelength division multiplexers 9 are connected to the input end of the first coupler 3, and the other second dense wavelength division multiplexer 3 is connected to the circulator 3. The photodetector 10 is electrically connected to the input end of the analog-to-digital converter 11, and the output end of the analog-to-digital converter 11 is electrically connected to the personal computer 12.

[0034] The first dense wavelength division multiplexer 7 and the second dense wavelength division multiplexer 9 preferably use a specified frequency greater than 100 GHZ, preferably 200 GHZ, and the bandwidth of the separated channels is less than 1.6 nm. The bandwidth selection must meet the requirement of separating x wavelength channels within the laser wavelength range emitted by the amplified spontaneous emission light source 1 used. The length of the polarization-maintaining fiber of the depolarizer 4 is selected to meet the requirement of depolarizing the wavelength channel laser separated by the first dense wavelength division multiplexer 7 and the second dense wavelength division multiplexer 9. Specifically, the depolarizer 4 is composed of a length of L d With 2L d The birefringent crystal is connected to the main axis at 45° (welded or spatially butted), wherein Δn is the birefringence difference, Δλ is the bandwidth of the first dense wavelength division multiplexer 7 and the second dense wavelength division multiplexer 9, and satisfies:

[0035]

[0036] The optical path of the above device is as follows: the amplified spontaneous radiation light source 1 emits a broad-spectrum laser to the circulator 2, and the laser enters the first coupler 3 after passing through the circulator 2. The two light beams output from the two ports at the output end of the first coupler 3 pass through the second coupler 6, and then enter the first dense wavelength division multiplexer 7, thereby dividing the original broad-spectrum light into multiple narrow-linewidth laser beams, and each beam is then injected into the corresponding fiber optic mirror 8 as a sensing arm, thereby realizing multi-channel simultaneous sensing without crosstalk. After these narrow linewidth light beams are incident on the fiber optic mirror 8, they are reflected and then pass through the corresponding first dense wavelength division multiplexer 7 and then pass through the second coupler 6 to be divided into two light beams. However, if the light beams pass through the same optical path as when they are incident, due to the delay line 5, the optical path difference of the two light beams used for interference will be too large and they cannot interfere. Therefore, only when the two light beams pass through an optical path different from that when they are incident and the optical paths are equal, can interference occur; then the two light beams pass through the first coupler 3 and are divided into three paths, two of which are respectively incident on a second dense wavelength division multiplexer 9, and the other is incident on another second dense wavelength division multiplexer 9 through the circulator 2, and then the second dense wavelength division multiplexer 9 divides the three light beams into multiple narrow linewidth light beams with the same wavelength range as the sensor arm; then the narrow linewidth light beams are incident on the photodetector 10, then connected to the analog-to-digital converter 11, and finally connected to the personal computer 12, and demodulated using the 3×3 coupler demodulation method in the personal computer 12 to complete the vibration sensing function.

[0037] This multi-channel high-precision vibration sensing device based on a linear Sagnac interferometer utilizes a dense wavelength division multiplexer to achieve high-precision and high-resolution real-time measurement of multi-channel optical fiber vibration signals, avoids mutual crosstalk between signals, and has strong reusability.

[0038] The principle of the above 3×3 coupler demodulation method is:

[0039] Assuming the coupler is completely symmetrical, the three output signals are expressed as follows:

[0040]

[0041] Adding I1, I2, and I3 gives the following result:

[0042]

[0043] I1, I2, and I3 are then added to -M to remove the influence of the DC factor, and a, b, and c are obtained:

[0044]

[0045] By performing the same differentiation on a, b, and c obtained in the above formula, we can obtain d, e, and f:

[0046]

[0047] From the above, we can get:

[0048]

[0049] Adding the above three formulas together we get:

[0050]

[0051] In a real environment, the polarization state and intensity changes of the light source signal will cause I0 to change, so the influence of I0 can be eliminated by squaring and then dividing, as shown below:

[0052]

[0053] Finally, integrate R to get the output:

[0054]

[0055] Realize the demodulation process of obtaining phase from light intensity.

[0056] See also Figure 2 , shows the vibration signal waveforms returned by the three-way multiplexed sensor channels using the above-mentioned vibration sensing device. The signals detected by each channel are clean and have no crosstalk, and can be detected simultaneously, thereby verifying the feasibility of the device.

[0057] Embodiment 2

[0058] See also Figure 3 In this embodiment, the difference from the above-mentioned embodiment 1 is that the first coupler 3 is a 2×1 coupler. At this time, the depolarizer 4 and the delay line 5 are arranged in the same optical path, y=2, so that after the interference light returns to the photodetector 10, the vibration signal waveform can be obtained without demodulation.

Claims

1. A vibration sensing device based on a Sagnac interferometer, comprising: A wide linewidth light source module comprises an amplified spontaneous radiation light source (1) and a circulator (2), wherein the output end of the amplified spontaneous radiation light source (1) is connected to the input end of the circulator (2); Linear Sagnac modules; A multiplexing sensing module, comprising x first dense wavelength division multiplexers (7) and x optical fiber mirrors (8), each dense wavelength division multiplexer corresponding to one optical fiber mirror (8); and Coupler demodulation module; characterized in that: The linear Sagnac module comprises a first coupler (3), a depolarizer (4) and a second coupler (6) connected in sequence, the output end of the circulator (2) is connected to one of the input ends of the first coupler (3), two of the output ends of the first coupler (3) are respectively connected to the input end of the second coupler (6), the depolarizer (4) is arranged on one of the optical paths connecting the first coupler (3) and the second coupler (6), and the output end of the second coupler (6) is connected to a first dense wavelength division multiplexer (7) of the multiplexing sensor module; The coupler demodulation module comprises y second dense wavelength division multiplexers (9) and ny photodetectors (10), each second dense wavelength division multiplexer (9) corresponds to n photodetectors (10), and the second second dense wavelength division multiplexers (9) are also respectively connected to the input end of the first coupler (3) and the circulator (2).

2. The vibration sensing device based on Sagnac interferometer according to claim 1, characterized in that: A delay line (5) is provided on one of the optical paths connecting the first coupler (3) and the second coupler (6).

3. The vibration sensing device based on Sagnac interferometer according to claim 1, characterized in that: The first coupler (3) is a 3×3 coupler, the second coupler (6) is a 2×1 coupler, y=3, two second dense wavelength division multiplexers (9) are connected to the input end of the first coupler (3), and another second dense wavelength division multiplexer (9) is connected to the circulator (2).

4. The vibration sensing device based on Sagnac interferometer according to claim 1, characterized in that: The first coupler (3) is a 2×1 coupler, the second coupler (6) is a 2×1 coupler, y=2, one second dense wavelength division multiplexer (9) is connected to the input end of the first coupler (3), and the other second dense wavelength division multiplexer (9) is connected to the circulator (2).

5. The vibration sensing device based on Sagnac interferometer according to claim 1, characterized in that: The coupler demodulation module further comprises an analog-to-digital converter (11) and a personal computer (12), the photodetector (10) is electrically connected to the analog-to-digital converter (11), and the analog-to-digital converter (11) is electrically connected to the personal computer (12).

6. The vibration sensing device based on Sagnac interferometer according to any one of claims 1 to 5, characterized in that: The wavelength of the laser emitted by the amplified spontaneous emission light source (1) is in the range of 1528-1563 nm.

7. The vibration sensing device based on Sagnac interferometer according to any one of claims 1 to 5, characterized in that: The first dense wavelength division multiplexer (7) and the second dense wavelength division multiplexer (9) both use a specified frequency greater than 100 GHZ and the bandwidth of the divided channels is less than 1.6 nm.

8. The vibration sensing device based on Sagnac interferometer according to any one of claims 1 to 5, characterized in that: The depolarizer (4) The lengths are L d With 2L d The birefringent crystals are connected along the main axis at 45°, wherein Δn is the birefringence difference, Δλ is the bandwidth of the first dense wavelength division multiplexer (7) and the second dense wavelength division multiplexer (9), and the following conditions are satisfied:

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