Low-cost frequency domain incoherent distributed optical fiber temperature sensing system and application thereof

Abstract

The application discloses a low-cost frequency domain incoherent distributed optical fiber temperature sensing system and application thereof, which comprises a first laser light source, a second laser light source, an optical switch, a modulator, a signal generator, an optical coupler, a reference section optical fiber, an optical fiber connecting port, a temperature sensing optical fiber, an optical filter, a detector and a signal analysis unit, the optical switch is connected with the optical source, the optical switch is connected with the modulator, the modulator is connected with the optical coupler, the optical coupler is connected with the reference section optical fiber, the reference section optical fiber is connected with the temperature sensing optical fiber through the optical fiber connecting port, the optical coupler is connected with the optical filter through an optical fiber, the optical filter is connected with the detector, the signal generator is electrically connected with the modulator and the signal analysis unit respectively, and the detector is electrically connected with the signal analysis unit. The application can effectively reduce the system cost under the premise of guaranteeing the measurement accuracy.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a low-cost frequency-domain incoherent distributed fiber optic temperature sensing system and its applications. Background Technology

[0002] Distributed fiber optic temperature sensing systems can acquire temperature information along several kilometers of optical cable at once, making them an effective sensing tool. With the widespread application of distributed fiber optic temperature sensing systems in fields such as cables, fire protection, and geophysical exploration, users are placing more stringent demands on their performance, such as superior long-term stability and lower system costs.

[0003] US10082429B2 employs a combination of a laser and a broadband SLED light source to compensate for system instability, but this increases system cost and limits the application of fiber optic temperature sensing. EP0692705A1 proposes a detection scheme based on frequency-domain incoherent technology, allowing the use of relatively inexpensive low-power laser light sources. However, it still requires two detection combinations at the signal receiving end to detect S-rays and AS-rays respectively. Each combination includes one optical filter and one detector. S-rays refer to Stokes scattering, and AS-rays refer to anti-Stokes scattering. The hardware cost is relatively high, especially since the detector typically requires a high-performance, high-cost avalanche photodiode. In summary, existing technologies cannot satisfactorily reduce the cost of distributed fiber optic temperature sensing systems. Summary of the Invention

[0004] To address the shortcomings of the existing technologies, this invention provides a low-cost frequency-domain incoherent distributed fiber optic temperature sensing system and its application, which can not only effectively reduce system costs but also ensure measurement accuracy.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] A low-cost frequency-domain incoherent distributed fiber optic temperature sensing system is disclosed. The system includes a first laser source, a second laser source, an optical switch, a modulator, a signal generator, an optical coupler, a reference fiber, an optical fiber connection port, a temperature-sensing fiber, an optical filter, a detector, and a signal analysis unit. Both the first and second laser sources are connected to the optical switch. The optical switch is connected to the modulator. The optical coupler includes a receiving port, an output port, and a receive / output port. The modulator is connected to the receiving port of the optical coupler. The receive / output port of the optical coupler is connected to the reference fiber. The reference fiber and the temperature-sensing fiber are connected via the optical fiber connection port. The output port of the optical coupler is connected to the optical filter. The optical filter is connected to the detector.

[0007] The signal generator is electrically connected to the modulator and the signal analysis unit, respectively, and the detector is electrically connected to the signal analysis unit;

[0008] The first laser source is used to generate the S-light required for sensing; the second laser source is used to generate the AS-light required for sensing; the optical switch is used to select the input light source; the modulator is used to receive the input light transmitted from the optical switch and modulate it to generate the probe light; the optical coupler is used to receive the probe light transmitted from the modulator and couple it to the reference fiber, and receive the scattered light returned from the reference fiber and transmit it to the optical filter; the optical filter is used to receive the scattered light transmitted from the optical coupler and separate the Raman scattered signal light from it, and then transmit the Raman scattered signal light to the detector; the detector is used to receive the Raman scattered signal light transmitted from the optical filter and convert it into a Raman scattered electrical signal and transmit it to the signal analysis unit.

[0009] The signal generator is used to generate modulated electrical signals and transmit them to the modulator and the signal analysis unit respectively; the signal analysis unit is used to receive the modulated electrical signals transmitted from the signal generator and the Raman scattering electrical signals transmitted from the detector, and to analyze and calculate the temperature and Raman scattering electrical signal intensity at each location of the temperature-sensing fiber using a frequency domain incoherent method.

[0010] Furthermore, the reference fiber itself has a constant temperature, and its temperature measurement results can be used to calibrate the temperature measurement results of the temperature-sensing fiber.

[0011] Furthermore, the temperature-sensing optical fiber is made of the same material as the reference section optical fiber.

[0012] Furthermore, the first laser source, the second laser source, the optical switch, the modulator, the signal generator, the optical coupler, the reference fiber, the optical filter, the detector, and the signal analysis unit are located inside the demodulation device of the sensing system, the optical fiber connection port is located on the demodulation device of the sensing system, and the temperature-sensing fiber is located outside the demodulation device of the sensing system.

[0013] Furthermore, both the first laser source and the second laser source are continuous light lasers.

[0014] Furthermore, the detector is an avalanche photodiode.

[0015] Furthermore, the S-light spectral range generated by the first laser source in the temperature-sensing fiber and the reference fiber, and the AS-light spectral range generated by the second laser source in the temperature-sensing fiber and the reference fiber, overlap or substantially overlap.

[0016] Furthermore, the passband of the optical filter includes the S-spectrum generated by the first laser source in the temperature-sensing fiber and the reference fiber, which overlap or substantially overlap, and the AS-spectrum generated by the second laser source in the temperature-sensing fiber and the reference fiber.

[0017] This invention also provides an application of a low-cost frequency-domain incoherent distributed fiber optic temperature sensing system. This system enables distributed temperature sensing and eliminates the influence of power fluctuations in the first and second laser sources. The process includes the following steps:

[0018] Step S1, Selecting the input light source: Switch the optical switch, select the first laser light source as the input light source and output it to the reference fiber and the temperature sensing fiber. Set the output power of the optical switch to I1, where I1 is an unknown quantity. At this time, the optical filter outputs S-light to the detector.

[0019] Step S2, Obtaining S-optical Power: Adjust the modulation signal of the signal generator. At this time, the signal analysis unit reads and processes the Raman scattering signal output by the detector to obtain the S-optical power I at each point along the reference fiber segment. S,ref And the S-optical power I at each point along the temperature-sensing fiber S,sig .

[0020] Step S3, switch the input light source: switch the optical switch, select the second laser light source as the input light source and output it to the reference fiber and the temperature sensing fiber, and set the output power of the optical switch at this time to I2, where I2 is an unknown quantity. At this time, the optical filter outputs AS light to the detector.

[0021] Step S4, Obtain AS optical power: Adjust the modulation electrical signal of the signal generator. At this time, the signal analysis unit reads and processes the Raman scattering electrical signal output by the detector to obtain the AS optical power I at each point along the reference fiber segment. AS,ref And the AS optical power I at each point along the temperature-sensing fiber AS,sig .

[0022] Step S5, calculate the temperature at each point on the temperature-sensing fiber: calculate the ratio. and According to the physical principles of Raman scattering, the two ratios mentioned above can be expressed as follows: and According to R ref B, T ref Find Substitute again Calculate the temperature measurement value T at various points on the temperature-sensing fiber that is unaffected by fluctuations in laser source power. sig (d);

[0023] Among them, R refR represents the power ratio of the AS and S beams at various points along the reference fiber optic segment. sig T represents the power ratio of the AS and S beams at various points along the temperature-sensing fiber; ref The known temperature of the reference fiber segment; T sig (d) represents the temperature at each point on the temperature-sensing fiber; d is the length of the temperature-sensing fiber measured from the fiber connection port; B is a known fixed constant related to the fiber characteristics.

[0024] Furthermore, in steps S2 and S4, the method by which the signal analysis unit reads and processes the Raman scattering electrical signal output by the detector is to measure the Raman scattering power at each position of the reference fiber and the temperature sensing fiber using frequency domain incoherent temperature sensing technology.

[0025] According to the above technical solution, the present invention has the following advantages: 1. It increases the number of cheaper lasers and reduces the number of more expensive optical filters and detectors, thereby reducing the overall cost of the distributed fiber optic temperature measurement system; 2. By using a reference fiber and signal processing method, it offsets the negative impact of power fluctuations between the two light sources in the system during multiple measurements, ensuring that the system's measurement accuracy is not compromised. Attached Figure Description

[0026] Figure 1 This is a structural diagram of a low-cost frequency-domain incoherent distributed optical fiber temperature sensing system according to the present invention.

[0027] Figure 2 This is a schematic diagram of the spectra of the probe light and Raman scattering signal light of a low-cost frequency-domain incoherent distributed optical fiber temperature sensing system according to the present invention.

[0028] Figure 3 This is a flowchart illustrating the operation of a low-cost frequency-domain incoherent distributed optical fiber temperature sensing system according to the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples, so as to make a clearer understanding of its structural type and usage, but this should not be used to limit the scope of protection of the present invention patent.

[0030] like Figure 1As shown in the figure, solid connecting lines represent optical fiber or optical waveguide connections, and solid arrows represent the direction of light propagation; dashed connecting lines represent electrical signal waveguide connections, and dashed arrows represent the direction of electrical signal propagation. A low-cost frequency-domain incoherent distributed optical fiber temperature sensing system is disclosed. This system includes a first laser source 101, a second laser source 102, an optical switch 103, a modulator 104, a signal generator 105, an optical coupler 106, a reference fiber 107, an optical fiber connection port 108, a temperature-sensing fiber 109, an optical filter 110, a detector 111, and a signal analysis unit 112. Both the first laser source 101 and the second laser source 102 are connected to the optical switch 103 via optical fibers. The optical switch 103 is connected to the modulator 104... The optical coupler 106, which is connected via optical fibers, includes a receiving port, an output port, and a receiving / output port. The modulator 104 is connected to the receiving port of the optical coupler 106 via an optical fiber. The receiving / output port of the optical coupler 106 is connected to a reference fiber 107. The reference fiber 107 is connected to a temperature-sensing fiber 109 via an optical fiber connection port 108. The output port of the optical coupler 106 is connected to an optical filter 110 via an optical fiber. The optical filter 110 is connected to a detector 111 via an optical fiber.

[0031] The signal generator 105 is electrically connected to the modulator 104 and the signal analysis unit 112 respectively, and the detector 111 is electrically connected to the signal analysis unit 112.

[0032] The first laser source 101 is used to generate S-light required for sensing; the second laser source 102 is used to generate AS-light required for sensing; the optical switch 103 is used to select the input light source; the modulator 104 is used to receive the input light transmitted from the optical switch 103 and apply modulation at a specific frequency to generate probe light; the optical coupler 106 is used to receive the probe light transmitted from the modulator 104 and couple it to the reference fiber 107, and receive the scattered light returned from the reference fiber 107 and transmit it to the optical filter 110; the optical filter 110 is used to receive the scattered light transmitted from the optical coupler 106 and separate the Raman scattered signal light from it, and then transmit the Raman scattered signal light to the detector 111; the detector 111 is used to receive the Raman scattered signal light transmitted from the optical filter 110, sense the relatively weak Raman scattered signal light and convert it into a Raman scattered electrical signal and transmit it to the signal analysis unit 112.

[0033] The signal generator 105 is used to generate modulated electrical signals and transmit them to the modulator 104 and the signal analysis unit 112 respectively; the signal analysis unit 112 is used to receive the modulated electrical signals transmitted by the signal generator 105 and the Raman scattering electrical signals transmitted by the detector 111, and to analyze and calculate the temperature and Raman scattering electrical signal intensity at each position of the temperature-sensing fiber 109 using a frequency domain incoherent method.

[0034] Furthermore, the reference fiber 107 has a constant temperature, and its temperature measurement results can be used to calibrate the temperature measurement results of the temperature-sensing fiber 109.

[0035] Furthermore, the temperature-sensing fiber 109 and the reference fiber 107 are made of the same material, and when the probe light is transmitted in the temperature-sensing fiber 109 and the reference fiber 107, it generates backscattered light.

[0036] Furthermore, the first laser source 101, the second laser source 102, the optical switch 103, the modulator 104, the signal generator 105, the optical coupler 106, the reference fiber 107, the optical filter 110, the detector 111, and the signal analysis unit 112 are located inside the sensor system demodulation device, the optical fiber connection port 108 is located on the sensor system demodulation device, and the temperature-sensing optical fiber 109 is located outside the sensor system demodulation device.

[0037] Furthermore, both the first laser source 101 and the second laser source 102 are continuous light lasers.

[0038] Furthermore, the detector 111 is an avalanche photodiode.

[0039] Furthermore, the passband of the optical filter 110 includes the S-light spectrum generated by the first laser source 101 in the temperature-sensing fiber 109 and the reference fiber 107, and the AS-light spectrum generated by the second laser source 102 in the temperature-sensing fiber 109 and the reference fiber 107.

[0040] Distributed fiber optic temperature sensing requires the separate acquisition of S-beams and AS-beams in the fiber. Existing frequency-domain incoherent distributed fiber optic temperature sensing systems use a single light source, requiring two filters at the receiver to separate the S-beams and AS-beams, and then two photodetectors for reception, resulting in high costs. This embodiment adds a lower-cost laser light source and an optical switch 103, requiring only one optical filter 110 and one detector 111 at the receiver, reducing the number of more expensive photodetectors and lowering the overall system cost. The relationship between the two light sources is as follows: Figure 2As shown, the first spectral line 201 is the spectral line of the first laser source 101; the second spectral line 202 is the spectral line of the second laser source 102; the first laser source 101 generates a first AS light 203 and a first S light 204 through the reference fiber 107 and the temperature-sensing fiber 109; the second laser source 102 generates a second AS light 205 and a second S light 206 through the reference fiber 107 and the temperature-sensing fiber 109; the spectral ranges of the first S light 204 and the second AS light 205 are close to or overlap, both located in the passband 207 of the optical filter 110. Therefore, only a single optical filter 110 and a single detector 111 are needed to obtain the first S light 204 and the second AS light 205 for subsequent temperature calculations.

[0041] like Figure 3 As shown, the present invention also provides an application of a low-cost frequency-domain incoherent distributed fiber optic temperature sensing system. This system enables distributed temperature sensing and eliminates the influence of power fluctuations in the first laser source 101 and the second laser source 102. The process includes the following steps:

[0042] Step S1, Select input light source: Switch optical switch 103, select the first laser light source 101 as the input light source and output it to the reference fiber 107 and the temperature sensing fiber 109. Set the output power of optical switch 103 at this time to I1, where I1 is an unknown quantity. At this time, optical filter 110 outputs S light to detector 111.

[0043] Step S2, Obtaining S-optical Power: Adjust the modulation electrical signal of the signal generator 105. At this time, the signal analysis unit 112 reads and processes the Raman scattering electrical signal output by the detector 111 to obtain the S-optical power I at each point along the reference fiber 107. S,ref And the S-optical power I at each point along the temperature-sensing fiber 109 S,sig .

[0044] Step S3, switch the input light source: switch the optical switch 103, select the second laser light source 102 as the input light source and output it to the reference section fiber 107 and the temperature sensing fiber 109, and set the output power of the optical switch 103 at this time to I2, where I2 is an unknown quantity. At this time, the optical filter 110 outputs AS light to the detector 111.

[0045] Step S4, Obtain AS optical power: Adjust the modulation electrical signal of the signal generator 105. At this time, the signal analysis unit 112 reads and processes the Raman scattering electrical signal output by the detector 111 to obtain the AS optical power I at each point along the reference fiber 107. AS,ref And the AS optical power I at each point along the temperature-sensing fiber 109 AS,sig .

[0046] Step S5, calculate the temperature at each point on the temperature-sensing fiber 109: calculate the ratio. and According to the physical principles of Raman scattering, the two ratios mentioned above can be expressed as follows: and According to R ref B, T ref Find Substitute again The temperature measurements T at various points on the temperature-sensing fiber 109, unaffected by fluctuations in laser source power, were calculated. sig (d);

[0047] Among them, R ref The power ratio of AS light to S light at various points along the reference fiber optic cable 107; R sig T represents the power ratio of the AS and S beams at various points along the temperature-sensing fiber 109; ref The known temperature of the reference fiber optic section 107; T sig (d) represents the temperature at each point on the temperature-sensing fiber 109; d is the length of the temperature-sensing fiber 109 measured from the fiber connection port 108; B is a known fixed constant related to the fiber characteristics. This step utilizes the signal from the reference fiber 107 to protect the temperature calculation results from the negative impact of changes in the power I1 of the first laser source 101 and the power I2 of the second laser source 102 between multiple measurements, ensuring the accuracy and long-term reliability of the system.

[0048] Furthermore, in steps S2 and S4, the method by which the signal analysis unit 112 reads and processes the Raman scattering electrical signal output by the detector 111 is to measure the Raman scattering light power at each position of the reference fiber 107 and the temperature sensing fiber 109 using frequency domain incoherent temperature sensing technology. This processing method is a conventional method, as mentioned in patent EP0692705A1, and is common knowledge in the field, so it will not be elaborated here.

[0049] Undoubtedly, the present invention may have other similar structural compositions and uses besides the embodiments described above. In summary, the present invention also includes other modifications and substitutions that will be obvious to those skilled in the art.

Claims

1. A low-cost frequency domain non-coherent distributed optical fiber temperature sensing system, characterized in that, The system comprises a first laser light source (101), a second laser light source (102), an optical switch (103), a modulator (104), a signal generator (105), an optical coupler (106), a reference section optical fiber (107), an optical fiber connection port (108), a temperature sensing optical fiber (109), an optical filter (110), a detector (111) and a signal analysis unit (112), the first laser light source (101) and the second laser light source (102) are connected with the optical switch (103), the optical switch (103) is connected with the modulator (104), the optical coupler (106) comprises a receiving port, an output port and a receiving / output port, the modulator (104) is connected with the receiving port of the optical coupler (106), the receiving / output port of the optical coupler (106) is connected with the reference section optical fiber (107), the reference section optical fiber (107) is connected with the temperature sensing optical fiber (109) through the optical fiber connection port (108), the output port of the optical coupler (106) is connected with the optical filter (110), and the optical filter (110) is connected with the detector (111); The signal generator (105) is electrically connected with the modulator (104) and the signal analysis unit (112), and the detector (111) is electrically connected with the signal analysis unit (112); The first laser light source (101) is used for generating Stokes scattering light required for sensing, the second laser light source (102) is used for generating anti-Stokes scattering light required for sensing, the optical switch (103) is used for selecting an input light source, the modulator (104) is used for receiving input light transmitted to the modulator (104) from the optical switch (103) and modulating the input light to generate detection light, the optical coupler (106) is used for receiving detection light transmitted to the optical coupler (106) from the modulator (104) and coupling the detection light to the reference section optical fiber (107), and receiving scattering light returned from the reference section optical fiber (107) and the temperature sensing optical fiber (109) and transmitting the scattering light to the optical filter (110), the optical filter (110) is used for receiving scattering light transmitted to the optical filter (110) from the optical coupler (106), separating Raman scattering signal light from the scattering light, and then transmitting the Raman scattering signal light to the detector (111), and the detector (111) is used for receiving Raman scattering signal light transmitted to the detector (111) from the optical filter (110) and converting the Raman scattering signal light into a Raman scattering electrical signal and transmitting the Raman scattering electrical signal to the signal analysis unit (112). The signal generator (105) is used for generating a modulation electrical signal and transmitting the modulation electrical signal to the modulator (104) and the signal analysis unit (112), and the signal analysis unit (112) is used for receiving the modulation electrical signal transmitted to the signal analysis unit (112) from the signal generator (105) and the Raman scattering electrical signal transmitted to the signal analysis unit (112) from the detector (111), and analyzing and calculating the temperature and the Raman scattering electrical signal intensity at each position of the temperature sensing optical fiber (109) by a frequency domain incoherent method.

2. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 1, wherein, The reference section optical fiber (107) has a constant temperature and is used as a control group of the temperature sensing optical fiber (109).

3. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 1 or 2, characterized in that, The temperature sensing optical fiber (109) has the same material as the reference section optical fiber (107).

4. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 1, wherein, The first laser light source (101), the second laser light source (102), the optical switch (103), the modulator (104), the signal generator (105), the optical coupler (106), the reference section optical fiber (107), the optical filter (110), the detector (111) and the signal analysis unit (112) are arranged inside the sensing system demodulation device, the optical fiber connection port (108) is arranged on the sensing system demodulation device, and the temperature sensing optical fiber (109) is arranged outside the sensing system demodulation device.

5. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 1, wherein, The first laser light source (101) and the second laser light source (102) are both continuous light lasers.

6. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 1, wherein, The detector (111) is an avalanche photodiode.

7. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 1, wherein, The first laser light source (101) generates Stokes scattered light in the temperature sensing optical fiber (109) and the reference section optical fiber (107), and the second laser light source (102) generates anti-Stokes scattered light in the temperature sensing optical fiber (109) and the reference section optical fiber (107).

8. The low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 7, wherein, The passband of the optical filter (110) includes the Stokes scattered light generated by the first laser light source (101) in the temperature sensing optical fiber (109) and the reference section optical fiber (107) and the anti-Stokes scattered light generated by the second laser light source (102) in the temperature sensing optical fiber (109) and the reference section optical fiber (107).

9. Application of a low-cost frequency domain non-coherent distributed optical fiber temperature sensing system, characterized in that, The low-cost frequency-domain incoherent distributed optical fiber temperature sensing system according to any one of claims 1-4 comprises the following steps: Step S1, selecting an input light source: switching the optical switch (103), selecting the first laser light source (101) as an input light source output to the reference section optical fiber (107) and the temperature sensing optical fiber (109), and setting the output power of the optical switch (103) at this time as an unknown quantity I1, at this time the optical filter (110) outputs Stokes scattered light to the detector (111); Step S2, obtaining the stokes scattering light power: adjusting the modulated electric signal of the signal generator (105), at this time the signal analysis unit (112) reads the Raman scattering electric signal output by the detector (111) and processes it, obtaining the stokes scattering light power I S,ref of the reference section optical fiber (107) at each point along the line S,sig ; Step S3, switching the input light source: switching the optical switch (103), selecting the second laser light source (102) as an input light source output to the reference section optical fiber (107) and the temperature sensing optical fiber (109), and setting the output power of the optical switch (103) at this time as an unknown quantity I2, at this time the optical filter (110) outputs anti-Stokes scattered light to the detector (111); Step S4, obtaining anti-Stokes scattering light power: adjusting the modulated electric signal of the signal generator (105), at this time the signal analysis unit (112) reads the Raman scattering electric signal output by the detector (111) and processes it to obtain the anti-Stokes scattering light power I AS,ref of the reference section optical fiber (107) at each point along the line AS,sig ; Step S5, calculating the temperature of each point of the temperature sensing fiber (109): calculating the ratio and According to the physical principle of Raman scattering, the above two ratios can be expressed as and Through R ref and R sig Eliminate I1 and I2, and finally calculate the temperature T of each point of the temperature sensing fiber (109) which is not affected by the power fluctuation of the laser light source sig (d); where R ref is the ratio of the power of anti-Stokes to Stokes scattered light along the reference segment fiber (107) at a point along the line; R sig is the ratio of the power of anti-Stokes to Stokes scattered light along the temperature sensing fiber (109) at a point along the line; T ref is the known temperature of the reference segment fiber (107); T sig (d) is the temperature of the temperature sensing fiber (109) at a point along the fiber; d is the length of the temperature sensing fiber (109) from the fiber connection port (108); and B is a fixed constant known to be related to the characteristics of the fiber.

10. The use of a low-cost frequency domain non-coherent distributed optical fiber temperature sensing system according to claim 9, characterized in that, In the step S2 and the step S4, the method for the signal analysis unit (112) to read and process the Raman scattered electrical signal output by the detector (111) is to measure the Raman scattered light power of each position of the reference section optical fiber (107) and the temperature sensing optical fiber (109) by using the frequency-domain incoherent temperature sensing technology.

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