A distributed optical fiber temperature sensor

Abstract

This invention relates to a distributed fiber optic temperature sensor, comprising: an intensity-encoded light source unit that outputs a probe light signal according to a modulation code; an optical wavelength division multiplexer (WDM) serving as a light guiding unit, including a probe light input end, a sensing fiber input / output end, a Stokes light output end, and an anti-Stokes light output end, wherein the probe light input end is connected to the output of the intensity-encoded light source unit, the sensing fiber input / output end is connected to a sensing fiber, and the Stokes light output end and the anti-Stokes light output end are connected to a photodetector unit; a sensing fiber; a photodetector unit; a signal acquisition unit, the input of which is connected to the output of the photodetector unit for digital signal acquisition; and a signal processing unit, the input of which is connected to the output of the signal acquisition unit for executing a signal demodulation algorithm according to the modulation code to obtain the distributed temperature sensing result. Compared with the prior art, this invention has advantages such as high temperature measurement accuracy and high speed.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to a distributed fiber optic temperature sensor. Background Technology

[0002] Distributed fiber optic temperature sensors are a new type of sensor that has seen rapid development in recent years. They offer advantages such as resistance to electromagnetic interference, high sensitivity, small size, low cost, and long sensing distance, making them particularly suitable for measurement scenarios with large measurement ranges, difficult access, and harsh environments, such as coal mines, natural gas pipelines, and oil pipelines. Distributed fiber optic temperature sensors use light as the carrier, with the optical fiber serving as both the transmission medium and the sensing element. The fiber is laid in the temperature field to be measured, and any point along the entire fiber can be used to sense the temperature, thus enabling distributed temperature measurement.

[0003] Distributed fiber optic temperature sensors are based on the Raman scattering effect. Existing technologies typically employ a pulsed light source to inject pulsed probe light into the sensing fiber. This pulsed probe light, within the sensing fiber, excites backscattered Raman light, the intensity of which is related to the fiber temperature. Further, as the pulsed probe light propagates forward through the sensing fiber, it excites backscattered Raman light at various locations from the near end to the far end of the fiber, in chronological order. Upon returning to the near end of the fiber, the backscattered light is received by a photodetector, which measures its intensity. Because the time it takes for the probe light pulse to propagate to different points in the sensing fiber varies, and the time it takes for the backscattered Raman light to return to the near end also differs, the light intensity signals captured by the photodetector at different times correspond to the light intensities of the backscattered Raman light at each point in the fiber. Finally, based on the physical mechanism of the Raman scattering effect and the relevant physical constants of the fiber material, the temperature at each point in the fiber is calculated from the light intensity, thus achieving distributed temperature sensing.

[0004] The temperature measurement accuracy, speed, and distance of a Raman scattering-based distributed fiber optic temperature sensor are all determined by the signal-to-noise ratio (SNR) of the sensing system. Since the spontaneous Raman scattering effect of optical fiber materials is extremely weak, multimode fiber, which typically exhibits a relatively strong backscattered Raman signal, is usually used as the sensing fiber. In contrast, if single-mode fiber, with its even weaker backscattered Raman signal, is chosen, the system's SNR will further decrease, significantly reducing its temperature measurement accuracy, real-time performance, and maximum measurement distance, thus failing to meet the temperature measurement requirements of some applications. Considering that existing infrastructure such as oil and gas pipelines, submarine cables, and communication systems extensively utilize or reserve single-mode fiber optic cables primarily for communication, introducing a distributed fiber optic temperature sensor could both meet application needs and fully utilize existing infrastructure, but it would require further improvement in the SNR of the distributed fiber optic temperature sensing system.

[0005] Increasing the peak power of a pulsed light source is one way to enhance the signal-to-noise ratio (SNR) of a distributed fiber optic temperature sensing system. However, the effective peak power of a pulsed light source has an upper limit, namely the stimulated Raman scattering threshold. Once the peak power of the pulsed laser exceeds this limit, the system's SNR cannot be further improved. The peak power of existing commercially available pulsed light sources has reached or is close to this limit. On the other hand, introducing coding techniques is another effective means to enhance the system's SNR. In coding techniques, the SNR gain is positively correlated with the coding order N. For distributed fiber optic temperature sensing technology, simplex coding is commonly used to improve the system's SNR. However, simplex coding is based on N×N dimensional matrix operations, and the computing and storage resources required for decoding are proportional to the square of N. Once the coding order N is too large, the computational cost required for the decoding process will increase dramatically or even become impossible. Therefore, in practical systems based on simplex coding, the coding order N generally does not exceed several hundred, which limits the SNR gain that simplex coding technology can bring, and thus limits the improvement it can bring to the system in terms of temperature measurement accuracy, temperature measurement speed, and temperature measurement distance. Summary of the Invention

[0006] The purpose of this invention is to provide a distributed fiber optic temperature sensor to improve the system signal-to-noise ratio, thereby improving temperature measurement accuracy, measurement speed, and measurement distance.

[0007] The objective of this invention can be achieved through the following technical solutions:

[0008] A distributed fiber optic temperature sensor, comprising:

[0009] An intensity-encoded light source unit, which outputs a probe light signal according to a modulation code pattern;

[0010] An optical wavelength division multiplexer is used as a light guiding unit. The optical wavelength division multiplexer includes a probe light input end, a sensing fiber input and output end, a Stokes light output end, and an anti-Stokes light output end. The probe light input end is connected to the output of an intensity encoding light source unit. The sensing fiber input and output end is connected to a sensing fiber. The Stokes light output end and the anti-Stokes light output end are connected to a photoelectric detection unit.

[0011] Sensing fiber optics;

[0012] Photoelectric detection unit;

[0013] A signal acquisition unit, the input of which is connected to the output of the photoelectric detection unit, performs digital signal acquisition on it;

[0014] The signal processing unit has its input connected to the output of the signal acquisition unit. It executes a signal demodulation algorithm according to the modulation code to obtain the distributed temperature sensing results.

[0015] The modulation code is a binary pseudo-random sequence.

[0016] The intensity-encoded light source unit includes a continuous laser, an intensity modulator, and a modulation code electrical signal generator;

[0017] The output of the continuous laser is connected to the optical input terminal of the optical intensity modulator.

[0018] The output of the modulation code electrical signal generator is connected to the electrical input terminal of the optical intensity modulator;

[0019] The light output terminal of the light intensity modulator outputs a probe light signal.

[0020] The intensity encoding light source unit includes a laser diode, a laser diode driving circuit, and a modulation code electrical signal generator;

[0021] The electrical output terminal of the modulation code electrical signal generator is connected to the electrical input terminal of the laser diode driving circuit;

[0022] The electrical output terminal of the laser diode driving circuit is connected to the electrical input terminal of the laser diode;

[0023] The laser diode outputs a detection light signal from its optical output terminal.

[0024] The modulation code electrical signal generator outputs a voltage signal according to the modulation code.

[0025] The sensing fiber is a single-mode fiber or a multimode fiber.

[0026] The photoelectric detection unit includes a first photodetector and a second photodetector, wherein...

[0027] The input terminal of the first photodetector is connected to the Stokes output terminal of the optical wavelength division multiplexer;

[0028] The input terminal of the second photodetector is connected to the anti-Stokes output terminal of the optical wavelength division multiplexer.

[0029] The signal acquisition unit includes a first analog-to-digital conversion channel and a second analog-to-digital conversion channel, wherein...

[0030] The first analog-to-digital conversion channel is connected to the output terminal of the first photodetector to obtain the first digital signal;

[0031] The second analog-to-digital conversion channel is connected to the output of the second photodetector to obtain the second digital signal.

[0032] The signal processing unit performs a signal demodulation algorithm on the first digital signal and the second digital signal according to the modulation code to obtain the distributed temperature sensing result.

[0033] The signal demodulation algorithm includes the following steps:

[0034] S1: Perform multiple averaging denoising operations on the first digital signal to obtain the third digital signal; perform multiple averaging denoising operations on the second digital signal to obtain the fourth digital signal;

[0035] S2: Perform a cross-correlation decoding calculation based on the third digital signal and the modulation code to obtain the fifth digital signal; perform a cross-correlation decoding calculation based on the fourth digital signal and the modulation code to obtain the sixth digital signal;

[0036] S3: Substitute the fifth and sixth digital signals into the Raman scattering temperature equation to obtain the distributed temperature sensing results.

[0037] Compared with the prior art, the present invention has the following beneficial effects:

[0038] This invention employs a modulation code based on a binary pseudo-random sequence, with an encoding order of N. The digital signal generated in a single detection cycle is a one-dimensional vector, and the required computer storage resources are proportional to N raised to the power of one. Regarding computational resources, since the digital signal generated in a single detection cycle is a one-dimensional vector, multiple sets of digital signals generated in multiple detection cycles can be averaged first, followed by a circular convolution calculation, significantly reducing the algorithm's computational resource requirements. Furthermore, a fast algorithm based on the Fast Fourier Transform exists for the circular convolution function, further reducing the demodulation algorithm's computational resource requirements. According to background technology, existing Simplex coding techniques often choose a relatively small encoding order N, typically not exceeding several hundred, resulting in limited signal-to-noise ratio (SNR) gain. In contrast, the modulation code and demodulation algorithm based on a binary pseudo-random sequence in this invention significantly reduce the demand for both computational and storage resources. This allows the system to achieve encoding orders of several thousand or even tens of thousands of N, thereby improving the SNR gain brought by the coding technology and ultimately enhancing the system's temperature measurement accuracy, speed, and distance. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the distributed optical fiber temperature sensor of the present invention;

[0040] Figure 2 This is a schematic diagram of an externally modulated intensity-encoded light source unit according to an embodiment of the present invention;

[0041] Figure 3 This is a schematic diagram of an internal modulation intensity-encoded light source unit according to an embodiment of the present invention;

[0042] Figure 4 This is a flowchart of the signal demodulation algorithm of the present invention;

[0043] Figure 5 This is a schematic diagram of the actual results of a distributed optical fiber temperature sensor according to an embodiment of the present invention. Detailed Implementation

[0044] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0045] This embodiment provides a distributed fiber optic temperature sensor, such as... Figure 1 As shown, it includes:

[0046] (1) Intensity-encoded light source unit 11

[0047] The intensity-encoded light source unit 11 outputs a probe light signal according to the modulation code. In this embodiment, the modulation code is a binary pseudo-random sequence.

[0048] The intensity encoding light source unit 11 can be selected as either an external modulation type structure or an internal modulation type structure.

[0049] The structure of the externally modulated intensity-encoded light source unit is as follows: Figure 2 As shown, it includes a continuous laser 111, an optical intensity modulator 112, and a modulation code electrical signal generator 113;

[0050] The output of the continuous laser 111 is connected to the optical input of the optical intensity modulator 112;

[0051] The output of the modulation code electrical signal generator 113 is connected to the electrical input terminal of the optical intensity modulator 112;

[0052] The light output terminal of the light intensity modulator 112 outputs a probe light signal.

[0053] In this embodiment, the continuous laser 111 outputs a center wavelength of 1550nm and an output constant power P. cw =65mW continuous laser.

[0054] In this embodiment, the light intensity modulator 112 is an acousto-optic modulator. Its optical input terminal is connected to the output terminal of the continuous laser 111, and its insertion loss is 2.2 dB. The turn-on voltage of the electrical control terminal of the acousto-optic modulator is V. on =4V, when the instantaneous voltage applied to the electrical control terminal reaches V on When the voltage is 0V, the acousto-optic modulator is fully turned on; when the instantaneous voltage applied to it is 0V, the modulator is completely turned off.

[0055] The modulation code electrical signal generator 113 generates a voltage signal based on a binary pseudo-random sequence. In this embodiment, the M-sequence {M} generated by a 13-stage linear feedback shift register is selected. k As a binary pseudo-random sequence, the corresponding encoding order N = 2. 13 -1 = 8191. Sequence {M} k}satisfy:

[0056] M k =1 or -1, k = 0, 1, ..., N-1,

[0057] And its autocorrelation sequence {X k}satisfy:

[0058]

[0059] Where XCORR(·,·) represents the cyclic cross-correlation operation in the discrete domain.

[0060] The rectangular chip function u(t) is redefined as follows:

[0061]

[0062] Where τ c This represents the chip period, which is τ in this embodiment. c =40ns.

[0063] Based on the binary pseudo-random sequence {M k Given the chip function u(t), construct the modulation code function c based on the binary pseudo-random sequence according to the following formula. M (t):

[0064]

[0065] Where T c =Nτ c =327.64μs represents the coding period.

[0066] The voltage signal V generated by the modulation code electrical signal generator 113 EM (t) is:

[0067] V EM (t)=V on c M (t)

[0068] V EM (t) is continuously output to the electrical input of the acousto-optic modulator with a period of T. The acousto-optic intensity modulator outputs a probe light signal modulated by a binary pseudo-random code intensity, with a power P. inc (t) is

[0069]

[0070] Where IL is the modulator insertion loss.

[0071] In another embodiment, the intensity-encoded light source unit 11 can also be implemented based on an internally modulated intensity-encoded light source unit, with the structure as follows: Figure 3 As shown, it includes a laser diode 115, a laser diode driving circuit 114, and a modulation code electrical signal generator 113.

[0072] The electrical output terminal of the modulation code electrical signal generator 113 is connected to the electrical input terminal of the laser diode driving circuit 114;

[0073] The electrical output terminal of the laser diode driver circuit 114 is connected to the electrical input terminal of the laser diode 115;

[0074] The laser diode 115 outputs a detection light signal from its optical output terminal.

[0075] Among them, the modulation code electrical signal generator 113 is based on the modulation code function c M (t), generating an internally modulated electrical signal V based on a binary pseudo-random code. IM (t), this signal controls the laser diode driving circuit 114 to generate a corresponding driving current signal I. LD (t) drives the laser diode 115, causing the laser diode 115 to directly output a probe light signal P modulated by the intensity of a binary pseudo-random code. inc (t), achieving the same effect as the aforementioned external modulation structure.

[0076] Whether it is an externally modulated intensity-encoded light source unit or an internally modulated intensity-encoded light source unit, the modulation code electrical signal generator 113 outputs a voltage signal according to the modulation code.

[0077] (2) Optical wavelength division multiplexer 12

[0078] The optical wavelength division multiplexer 12 is used as a light guiding unit, including a probe light input end, a sensing fiber input and output end, a Stokes light output end and an anti-Stokes light output end. The probe light input end is connected to the output of the intensity encoding light source unit 11, the sensing fiber input and output end is connected to the sensing fiber 13, and the Stokes light output end and the anti-Stokes light output end are connected to the photoelectric detection unit 14.

[0079] After the probe optical signal enters the light guiding unit (i.e., the optical wavelength division multiplexer 12), it is directly guided into the sensing optical fiber 13. For any position on the sensing optical fiber at a distance l from the starting end, the instantaneous power P of the forward probe optical signal at that moment is determined according to the current instantaneous power P. incThe temperature (t) of the optical fiber at that location, T(l), excites a corresponding backscattering Raman signal. The backscattering signal consists of Stokes light with a center wavelength of 1660 nm and anti-Stokes light with a center wavelength of 1450 nm. Taking the starting end of the sensing fiber as a reference point, the Stokes light power P at any given time... s (t) and anti-Stokes power P as (t) can be characterized as:

[0080]

[0081] Where c0 is the speed of light in vacuum, n is the refractive index of the optical fiber, and α i To detect the loss coefficient of light in an optical fiber, α s Let α be the loss coefficient of Stokes light in the optical fiber. as The loss factor of anti-Stokes light in optical fiber. This is the linear convolution operator. R s (l) represents the back Raman-Stokes scattering coefficient at position l in the sensing fiber, R as (l) represents the back-scattering Raman anti-Stokes light coefficient at position l in the sensing fiber, and the two satisfy the Raman scattering temperature equation:

[0082]

[0083] Where, ν s ν is the Stokes frequency. as ν0 is the anti-Stokes frequency, h is Planck's constant, ν0 is the Raman frequency shift of the fiber material, and k is the anti-Stokes frequency. B is the Boltzmann constant. T(l) is the actual temperature at position l in the optical fiber to be solved, i.e., the temperature distribution on the sensing optical fiber.

[0084] In this embodiment, a single-mode fiber wavelength division multiplexer (WDM) is selected. The 1450nm fiber port of the single-mode fiber WDM is used as the Stokes light output terminal to output the Stokes light signal P back-Raman scattered in the sensing fiber. s (t) Derivation; The 1660nm fiber port of the single-mode fiber wavelength division multiplexer is used as the anti-Stokes light output terminal to output the anti-Stokes light signal P back-scattered by the sensing fiber in the sensing fiber. as (t) Export.

[0085] (3) Sensor fiber 13

[0086] The sensing fiber 13 can be selected as a single-mode fiber or a multimode fiber. In this embodiment, a single-mode fiber is selected.

[0087] (4) Photoelectric detection unit 14

[0088] The photoelectric detection unit 14 includes a first photodetector 141 and a second photodetector 142, wherein,

[0089] The input terminal of the first photodetector 141 is connected to the Stokes output terminal of the optical wavelength division multiplexer 12;

[0090] The input terminal of the second photodetector 142 is connected to the anti-Stokes output terminal of the optical wavelength division multiplexer 12.

[0091] In this embodiment, the first photodetector 141 is an avalanche photodetector, which converts the Stokes light signal P... s (t) is converted into an analog voltage signal U s (t). The second photodetector 142 is an avalanche photodetector, which transmits the anti-Stokes light signal P. as (t) is converted into an analog voltage signal U as (t).

[0092] (5) Signal acquisition unit 15

[0093] The signal acquisition unit 15 includes a first analog-to-digital conversion channel 151 and a second analog-to-digital conversion channel 152, wherein...

[0094] The first analog-to-digital conversion channel 151 is connected to the output terminal of the first photodetector 141 to obtain the first digital signal;

[0095] The second analog-to-digital conversion channel 152 is connected to the output terminal of the second photodetector 142 to obtain the second digital signal.

[0096] The analog-to-digital conversion channel includes a pre-amplifier circuit and an analog-to-digital converter. In this embodiment, the analog-to-digital converter has a sampling rate of 250 MSps and a resolution of 14 bits. The first analog-to-digital conversion channel 151 converts the analog voltage signal U... s (t) is converted into a digital signal V s (t). The second analog-to-digital conversion channel 152 converts the analog voltage signal U... as (t) is converted into a digital signal V as (t). During continuous system operation, the signal acquisition unit 15 continuously transmits signals at T. c The period is T, and the duration is T. c digital signal V s (t) and V as (t).

[0097] (6) Signal processing unit 16

[0098] The input of the signal processing unit 16 is connected to the output of the signal acquisition unit 15, and it continuously acquires digital signal V from the signal acquisition unit 15. s(t) and digital signal V as (t), and execute the signal demodulation algorithm according to the modulation code to obtain the distributed temperature sensing results.

[0099] In this embodiment, the signal demodulation algorithm sequentially includes multiple averaging steps, decoding operation steps, and temperature calculation steps, as shown in the flowchart below. Figure 4 As shown, specifically, it includes the following steps:

[0100] S1: For digital signal V s (t) Perform multiple averaging denoising operations to obtain the digital signal V. s ave (t); for digital signal V as k(t) is subjected to multiple averaging denoising operations to obtain the digital signal V. as ave (t):

[0101] In this embodiment, the average time T is set. ave If the time is 10 seconds, then a total of K = T can be obtained. ave / T c =30521 V s (t) and V as (t). For ease of description, let's consider K such V... s (t) is denoted as {V s k (t)}, K V as (t) is denoted as {V as k (t)}, where k = 1, 2, ..., K.

[0102] The signal V obtained after multiple averaging and denoising of the digital signal s ave (t) and V as ave (t) is as follows:

[0103]

[0104] Its duration is T c .

[0105] S2: Based on digital signal V s ave (t) is cross-correlation decoded with the modulation code to obtain the digital signal D. s (t); based on V as ave (t) is cross-correlation decoded with the modulation code to obtain the digital signal D. as (t).

[0106] Specifically, first define the function c.D (t) is as follows:

[0107] c D (t)=2c M (t)-1

[0108] Then for V respectively s ave (t) and V as ave (t) Perform cross-correlation to obtain the decoding result D. s (t) and D as (t) is:

[0109]

[0110] Here, xcorr(·,·) represents the cyclic cross-correlation operation in a continuous field.

[0111] S3: D s (t) and D as Substituting (t) into the Raman scattering temperature equation, we obtain the distributed temperature sensing results.

[0112] Specifically, first, substitute the relationship between the time variable t and the space variable l into D. s (t) and D as (t), and calculate the ratio r(l) between the two:

[0113]

[0114] Where n is the refractive index of the optical fiber and c0 is the speed of light in a vacuum.

[0115] When the temperature of the sensing fiber is constant at a known temperature T0, the measured r(l) is recorded and denoted as r0(l). This process only needs to be performed once during system calibration.

[0116] During system operation, substituting the real-time measured r(l), and the T0 and r0(l) during system calibration into the Raman scattering temperature equation, we have:

[0117]

[0118] Where Planck's constant h, the Raman frequency shift ν0 of the optical fiber material, and Boltzmann's constant k are all represented. B The physical constants can be obtained from a table.

[0119] Finally, using the Raman scattering temperature equation, the temperature distribution on the optical fiber can be solved as follows:

[0120]

[0121] Figure 5The temperature measurement accuracy curve of the distributed optical fiber temperature sensor in this embodiment is given. As can be seen from the figure, when the system uses 25km single-mode sensing fiber, the end temperature measurement accuracy reaches 2 degrees Celsius.

[0122] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A distributed optical fiber temperature sensor, characterized in that, include: An intensity-coded light source unit outputs a probe light signal according to a modulation code pattern, wherein the modulation code pattern is a binary pseudo-random sequence and the digital signal generated in a single detection cycle is a one-dimensional vector. An optical wavelength division multiplexer is used as a light guiding unit. The optical wavelength division multiplexer includes a probe light input end, a sensing fiber input and output end, a Stokes light output end, and an anti-Stokes light output end. The probe light input end is connected to the output of an intensity encoding light source unit. The sensing fiber input and output end is connected to a sensing fiber. The Stokes light output end and the anti-Stokes light output end are connected to a photoelectric detection unit. Sensing fiber optics; Photoelectric detection unit; A signal acquisition unit, the input of which is connected to the output of the photoelectric detection unit, performs digital signal acquisition on it; The signal processing unit has its input connected to the output of the signal acquisition unit. It executes a signal demodulation algorithm according to the modulation code to obtain the distributed temperature sensing results.

2. The distributed optical fiber temperature sensor according to claim 1, characterized in that, The intensity coding light source unit includes a continuous laser, an intensity modulator, and a modulation code electrical signal generator; The output of the continuous laser is connected to the optical input terminal of the optical intensity modulator. The output of the modulation code electrical signal generator is connected to the electrical input terminal of the optical intensity modulator; The light output terminal of the light intensity modulator outputs a probe light signal.

3. A distributed optical fiber temperature sensor according to claim 1, characterized in that, The intensity encoding light source unit includes a laser diode, a laser diode driving circuit, and a modulation code electrical signal generator; The electrical output terminal of the modulation code electrical signal generator is connected to the electrical input terminal of the laser diode driving circuit; The electrical output terminal of the laser diode driving circuit is connected to the electrical input terminal of the laser diode; The laser diode outputs a detection light signal from its optical output terminal.

4. A distributed optical fiber temperature sensor according to claim 2 or 3, characterized in that, The modulation code electrical signal generator outputs a voltage signal according to the modulation code.

5. A distributed optical fiber temperature sensor according to claim 1, characterized in that, The sensing fiber is a single-mode fiber or a multimode fiber.

6. A distributed optical fiber temperature sensor according to claim 1, characterized in that, The photoelectric detection unit includes a first photodetector and a second photodetector, wherein... The input terminal of the first photodetector is connected to the Stokes output terminal of the optical wavelength division multiplexer; The input terminal of the second photodetector is connected to the anti-Stokes output terminal of the optical wavelength division multiplexer.

7. A distributed optical fiber temperature sensor according to claim 6, characterized in that, The signal acquisition unit includes a first analog-to-digital conversion channel and a second analog-to-digital conversion channel, wherein... The first analog-to-digital conversion channel is connected to the output terminal of the first photodetector to obtain the first digital signal; The second analog-to-digital conversion channel is connected to the output of the second photodetector to obtain the second digital signal.

8. A distributed optical fiber temperature sensor according to claim 7, characterized in that, The signal processing unit performs a signal demodulation algorithm on the first digital signal and the second digital signal according to the modulation code to obtain the distributed temperature sensing result.

9. A distributed optical fiber temperature sensor according to claim 8, characterized in that, The signal demodulation algorithm includes the following steps: S1: Perform multiple averaging denoising operations on the first digital signal to obtain the third digital signal; perform multiple averaging denoising operations on the second digital signal to obtain the fourth digital signal; S2: Perform a cross-correlation decoding calculation based on the third digital signal and the modulation code to obtain the fifth digital signal; perform a cross-correlation decoding calculation based on the fourth digital signal and the modulation code to obtain the sixth digital signal; S3: Substitute the fifth and sixth digital signals into the Raman scattering temperature equation to obtain the distributed temperature sensing results.

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