Brillouin temperature sensing system based on multi-core optical fiber, analysis method, medium, equipment and product

Abstract

The invention discloses a Brillouin temperature sensing system based on a multi-core optical fiber, an analysis method, a medium, equipment and a product, and relates to the field of optical fiber sensing. The system comprises a laser unit, a signal amplification unit, a carrier suppression modulation unit, a signal source, a first beam splitter, a second beam splitter, a third beam splitter, first to Nth circulators, first to Nth couplers, first to Nth signal processing units, a multi-core fan-in and fan-out coupler, a multi-core optical fiber and a signal acquisition and processing device. The temperature analysis method comprises the following steps: processing N paths of signals acquired by a signal acquisition and processing device to obtain a Brillouin gain spectrum of N fiber cores, and determining a Brillouin frequency shift of each fiber core; and carrying out weighted average on the Brillouin frequency shifts of the N fiber cores, and obtaining the temperature according to the Brillouin frequency shifts after average processing. According to the invention, the detection precision of the temperature sensing system can be improved.

Description

Technical Field

[0001] This invention relates to the field of fiber optic sensing technology, and in particular to Brillouin temperature sensing systems, analysis methods, media, devices and products based on multi-core optical fibers. Background Technology

[0002] Distributed fiber optic sensing technology is a technology developed based on optical time-domain reflectometry (OTDR). Using optical fibers as a carrier, it utilizes the scattering or nonlinear effects of light waves within the fiber to accurately sense changes in physical parameters such as temperature, strain, bending, and vibration along the fiber. Brillouin optical time-domain reflectometry (BDR) is an advanced distributed fiber optic sensing technology capable of long-distance, high-density, real-time sensing and monitoring. This technology is based on the principle of spontaneous Brillouin scattering, measuring the Brillouin frequency shift of backscattered light generated by the interaction of laser pulses with thermally excited phonons in the fiber to achieve temperature detection. The Brillouin frequency shift is the core detection parameter of the Brillouin ODR system, and its changes are closely related to environmental factors such as temperature and strain. Brillouin ODR has unique advantages in resisting electromagnetic interference and long-distance transmission, making it particularly suitable for monitoring large infrastructure such as power transmission lines, underground pipelines, and internal structural deformation. However, many factors need to be considered in practical Brillouin ODR sensing. For example, the selection of the sensing fiber, the influence of system noise, external environmental interference, and the width of the probe pulse all affect the sensing linearity and accuracy. Therefore, improving the linearity and measurement accuracy of the Brillouin frequency shift response has become a popular research topic. Summary of the Invention

[0003] The purpose of this invention is to address the noise and interference problems in distributed optical fiber sensing by proposing a Brillouin temperature sensing system based on multi-core optical fiber. The system comprises: a laser unit, a signal amplification unit, a carrier suppression modulation unit, a signal source, a first beam splitter, a second beam splitter, a third beam splitter, first to Nth circulators, first to Nth couplers, first to Nth signal processing units, a multi-core fan-in / fan-out coupler, a multi-core optical fiber, and a signal acquisition and processing device; N is the number of cores in the multi-core optical fiber.

[0004] The laser unit emits a laser beam, which is split into a probe beam and a local oscillator beam by a first beam splitter. The probe beam is amplified by a signal amplification unit. The amplified probe beam is split into N paths by a second beam splitter. The N probe beams pass through the first ports of the first to Nth circulators respectively. The light output from the second ports of the first to Nth circulators passes through a multi-core fan-in fan-out coupler and is fanned into a multi-core optical fiber. The Brillouin backscattered light carrying temperature information generated by the multi-core optical fiber is fanned out by the multi-core fan-in fan-out coupler to the second ports of the first to Nth circulators. The signal generated by the signal source and the local oscillator light are modulated in the carrier suppression modulation unit to obtain the modulated signal. The modulated signal is divided into N paths by the third beam splitter. The N modulated signals are coupled to the third port output signals of the first to Nth circulators through the first to Nth couplers respectively. The outputs of the first to Nth couplers are respectively processed by the first to Nth signal processing units and acquired by the signal acquisition and processing device.

[0005] Furthermore, the signal amplification unit includes a semiconductor optical amplifier and an erbium-doped fiber amplifier. The probe light first passes through the semiconductor optical amplifier and then is amplified by the erbium-doped fiber amplifier.

[0006] Furthermore, the signal source is a microwave source, which generates a radio frequency sweep signal.

[0007] Furthermore, the carrier suppression modulation unit includes a Mach-Zehnder modulator, a polarization scrambler, and a bias control board. The Mach-Zehnder modulator performs carrier suppression modulation on the signal generated by the signal source and the local oscillator light, and the bias control board performs bias control. Finally, the polarization scrambler outputs the modulated signal.

[0008] Furthermore, each signal processing unit includes a balanced detector, an electrical amplifier, and a bandpass filter. The outputs of the first to Nth couplers are sequentially passed through the balanced detector, electrical amplifier, and bandpass filter of the first to Nth signal processing units before being output.

[0009] This invention also proposes a Brillouin temperature sensing and analysis method based on multi-core optical fiber, which, based on the above-mentioned system implementation, includes the following steps: The N signals acquired by the signal acquisition and processing device are processed to obtain the Brillouin gain spectrum of N fiber cores, and the Brillouin frequency shift of each fiber core is determined. The temperature is obtained based on the weighted average Brillouin frequency shift. The Brillouin shift after weighted averaging is:

[0010] in, The Brillouin frequency shift of fiber core i at water bath temperature T; The Brillouin frequency shift of the system after data weighted averaging at a water bath temperature T; The weighting of fiber core i; Define the basic weight formula for each fiber core:

[0011] in, This represents the basic weight of fiber core i. Let i be the sum of squares of the frequency errors of fiber core i. , The measurement frequency at temperature T. The fitted frequency at temperature T; Calculate the sum of squared frequency errors for each fiber core, select fiber cores whose sum of squared frequency errors is lower than a set threshold, calculate the base weight of the selected fiber cores, and then use an inverse proportional allocation to obtain the weight of the selected fiber cores.

[0012] The present invention also proposes a computer-readable storage medium storing a computer program, characterized in that: when the computer program is executed by a processor, it implements the above-described method.

[0013] The present invention also proposes an electronic device, characterized in that it includes a processor and a memory, the processor being interconnected with the memory, wherein the memory is used to store a computer program, the computer program including computer-readable instructions, and the processor is configured to invoke the computer-readable instructions to execute the above-described method.

[0014] The present invention also proposes a computer program product, including a computer program / instruction, characterized in that the computer program / instruction implements the above-described method when executed by a processor.

[0015] The beneficial effects of the technical solution provided by this invention are: This invention utilizes a multi-core fiber to fan out Brillouin backscattered light carrying temperature information into N single-core fibers via a multi-core fan-in / fan-out coupler. Simultaneously, it acquires Brillouin backscattered signals from N independent spatial channels (each fiber core has an independent sensing path). Through the multi-core fan-in / fan-out coupler, the N scattered light signals are physically separated into N independent single-mode fibers, achieving spatial parallelism and channel separation, thus suppressing system errors introduced by crosstalk. Each channel can have an independent and identical detection link, allowing the system to simultaneously and in real-time acquire N complete distributed temperature profiles. The N Brillouin backscattered lights carrying temperature information are combined with N modulation signals, and the combined light is input to a balancer for beat frequency detection. A highly coherent intrinsic reference light is provided for each separated signal light, and heterodyne beat frequency detection is performed in the balanced detector to suppress intrinsic laser noise and environmental interference. Each beat frequency signal can operate independently, facilitating the identification of intrinsic Brillouin frequency shift differences caused by manufacturing variations in different fiber cores, thereby providing a more reliable temperature detection solution. Attached Figure Description

[0016] Figure 1 This is a block diagram of a Brillouin temperature sensing system based on multi-core optical fiber, according to an example of the present invention. Figure 2 This is a block diagram of a Brillouin temperature sensing system based on multi-core optical fiber, which is another embodiment of the present invention. Figure 3 This is a Brillouin gain spectrum signal acquired at room temperature; Figure 4 It is the Brillouin frequency shift of a seven-core optical fiber heated at different water bath temperatures, where (a)~(g) represent core 1~core 7; Figure 5 These are the temperature-frequency shift measurement curves and fitting curves of a seven-core optical fiber after Lorentz fitting, where (a) to (g) represent core 1 to core 7. Figure 6 The graphs are temperature-frequency shift curves of the system after weighted averaging, where (a) is the result after averaging of fiber cores 1, 4, 5, and 6, and (b) is the result after averaging of fiber cores 2, 3, and 7. Figure 7 This is a block diagram of an electronic device according to an exemplary embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0018] A block diagram of a Brillouin temperature sensing system based on multi-core optical fiber, according to an example of the present invention, is shown below. Figure 1 Specifically, it includes: The system comprises a laser unit, a signal amplification unit, a carrier suppression modulation unit, a signal source, a first beam splitter, a second beam splitter, a third beam splitter, first to Nth circulators, first to Nth couplers, first to Nth signal processing units, multi-core fan-in / fan-out couplers, multi-core optical fibers, and signal acquisition and processing devices. N is the number of cores in the multi-core optical fiber. Optical signals are transmitted between the various devices via single-core optical fibers.

[0019] Multi-core optical fibers integrate multiple independent cores within a single optical fiber, with 7 cores being one of the most common configurations. This allows for the simultaneous transmission of 7 independent signals, significantly increasing transmission capacity. Using multi-core fan-in / fan-out couplers, signals from multiple single-core fibers can be fanned into the individual cores of the multi-core fiber, and the signals from the multi-core fiber can be fanned out (split) into the individual single-core fibers with low loss and low crosstalk. The multi-core optical fiber of this invention is a homogeneous seven-core low-loss optical fiber with a core spacing of 41.5 mm. Cladding diameter 150 Coating diameter 245 It can provide seven data transmission channels for the system, with inter-channel crosstalk less than -48dB / km. The multi-core fan-in / fan-out coupler used in this invention is a seven-core fiber fan-in / fan-out coupler, with a single coupler insertion loss of less than 1dB, reducing the loss of Brillouin signals during transmission. It is also compatible with optical devices in various single-mode optical fibers.

[0020] A circulator can guide optical signals in one direction: light enters from the first port and exits from the second port; light enters from the second port and exits from the third port. However, light cannot return from the second port to the first port, nor can it return from the third port to the second port.

[0021] The optical path of this invention embodiment is as follows: This invention selects a narrow-line polarization-maintaining laser as the light source to stably output continuous light with a linewidth of 1 kHz and an emission wavelength of 1550.12 nm. The laser unit emits laser light, which is split into probe light and local oscillator light by a first beam splitter. The probe light is amplified by a signal amplification unit, and the amplified probe light is split into N paths by a second beam splitter. The N probe lights pass through the first ports of the first to Nth circulators, respectively. The light output from the second ports of the first to Nth circulators is fanned into a multi-core optical fiber by a multi-core fan-in fan-out coupler. The Brillouin backscattered light carrying temperature information generated by the multi-core optical fiber is fanned out by the multi-core fan-in fan-out coupler to the second ports of the first to Nth circulators.

[0022] In the carrier suppression modulation unit, the signal generated by the signal source and the local oscillator light are modulated to obtain a modulated signal. The modulated signal is split into N paths by a third beam splitter. The N modulated signals are then combined with the output signals from the third ports of the first to Nth circulators via first to Nth couplers, respectively. The outputs of the first to Nth couplers are then processed by first to Nth signal processing units and acquired by the signal acquisition and processing device. The coupler combines the modulated signal with the Brillouin backscattered light output from the third port of the circulator. A block diagram of a Brillouin temperature sensing system based on multi-core optical fiber, as described in another embodiment of the present invention, is shown below. Figure 2 ,exist Figure 1 Based on this, the signal amplification unit includes a semiconductor optical amplifier and an erbium-doped fiber amplifier. The probe light first passes through the semiconductor optical amplifier to modulate the continuous light into pulse light, and then the erbium-doped fiber amplifier amplifies the modulated pulse light to increase the peak power of the pulse light.

[0023] The signal source is a microwave source, which generates a radio frequency sweep signal. The radio frequency sweep signal is a high-frequency electrical signal that scans continuously and linearly within a range over time. Its instantaneous frequency... Where K is the frequency modulation slope, t is the initial frequency, and t is time.

[0024] The carrier suppression modulation unit includes a Mach-Zehnder modulator, a polarization scrambler, and a bias control board. In fiber optic communication and optical sensing, the performance of the modulator is affected by the polarization state of the input light. The polarization scrambler can eliminate or randomize the polarization state of the optical signal, improving the signal-to-noise ratio of the Brillouin backscattered signal. To address the issue of bias point drift in the Mach-Zehnder modulator, a bias control board is used for bias control (see the paper: Mach-Zehnder Modulator Bias Control Technology Based on the Swing Method). Carrier suppression modulation is performed on the signal generated by the signal source and the local oscillator light within the Mach-Zehnder modulator, and the bias is controlled by the bias control board. Finally, the polarization scrambler outputs the modulated signal. The radio frequency sweep signal serves as the modulation signal, and its frequency variation is loaded onto the optical carrier. The local oscillator light serves as the optical carrier signal, acting as the carrier signal for the radio frequency sweep signal. Through modulation, a laser with a linearly scanning frequency is generated, whose frequency variation is completely synchronized with the input radio frequency sweep signal, serving as the subsequent probe light.

[0025] Each signal processing unit includes a balanced detector, an electrical amplifier, and a bandpass filter. The outputs of the first to Nth couplers sequentially pass through the balanced detectors, electrical amplifiers, and bandpass filters of the first to Nth signal processing units before being output. The combined light in the couplers interferes with the balanced detector, generating a beat frequency signal. Beat frequency refers to the periodic variation in amplitude of the synthesized signal when two signals with similar frequencies are superimposed. This phenomenon is called a "beat," and the number of beats occurring per unit time is called the beat frequency. The frequency of the beat frequency is equal to the difference between the frequencies of the two signals.

[0026] In this embodiment of the invention, a seven-core optical fiber is placed in a water bath for water heating. Water bath heating ensures that the optical fiber experiences consistent temperature changes in all directions. The microwave frequency sweep starts at 10.4 GHz, with a frequency interval of 2 MHz, acquiring 101 frequency points, and the sweep range is 10.4 GHz to 10.6 GHz.

[0027] Figure 3 In this example, the Brillouin gain spectrum of fiber core 1 obtained by the above system at room temperature has a center frequency of approximately 10.5 GHz and a system signal-to-noise ratio of approximately 11.4 dB.

[0028] During the heating process, the water bath temperature is gradually increased from 25℃ to 75℃ in increments of 5℃, while the remaining sections of the optical fiber are kept at the same ambient temperature (25℃-30℃). Figure 4This example illustrates the Brillouin frequency shift of a seven-core optical fiber after mean filtering under different water bath temperatures. After a 50°C temperature increase, the frequency shifts of each fiber core were 48MHz, 45MHz, 47MHz, 46MHz, 54MHz, 46MHz, and 43MHz, respectively. Fiber core 7 exhibited the smallest frequency shift, while fiber core 5 showed the largest. Under the same temperature change, the center frequency shifts produced by each fiber core differed.

[0029] Figure 5 The figures show the temperature-frequency shift measurement curves and fitting curves of the seven-core optical fiber after Lorentz fitting in this example. The data clearly show that the Brillouin frequency shift of all seven fiber cores gradually increases with increasing temperature; however, there are significant differences in the linearity of the response among different fiber cores. Fiber cores 1, 4, and 6 exhibit obvious nonlinear characteristics during heating: the Brillouin frequency shift of fiber core 1 deviates significantly from the linear fitting curve in the temperature range of 20℃-35℃; fiber core 4 also shows a similar deviation in the 20℃-35℃ range; while the deviation of fiber core 6 appears earlier, already evident during the temperature increase from 10℃-20℃.

[0030] This invention also proposes a Brillouin temperature sensing and analysis method based on multi-core optical fiber. Based on the aforementioned system implementation, a weighted average of seven channel sensing data is used to improve the temperature measurement accuracy and system linearity of the Brillouin optical time-domain reflectometer system. The method includes the following steps: The N signals acquired by the signal acquisition and processing device are processed to obtain the Brillouin gain spectrum of N fiber cores and determine the Brillouin frequency shift of each fiber core; the Brillouin frequency shift of the fiber cores is weighted and averaged, and the temperature is obtained based on the weighted average Brillouin frequency shift.

[0031] The formula for the weighted average is:

[0032] in, The Brillouin frequency shift of fiber core i at water bath temperature T; The Brillouin frequency shift of the system after data weighted averaging at a water bath temperature T; The weighting is the weight of fiber core i.

[0033] Define the basic weight formula for each fiber core:

[0034] in, This represents the basic weight of fiber core i. Let i be the sum of squares of the frequency errors of fiber core i. , The measurement frequency at temperature T. denoted as the fitted frequency at temperature T.

[0035] In this embodiment of the invention, based on the differences in fiber core linearity, the fiber cores are divided into two groups for processing. The sum of squared frequency errors for each fiber core is calculated and used as the fiber core linearity index. Multiple fiber cores with a sum of squared frequency errors exceeding a set threshold are designated as a control group, while fiber cores below the threshold are designated as the actual calculation group. This invention found that the linearity of fiber cores 1, 4, 5, and 6 is significantly worse than that of other fiber cores. Therefore, they are used as a control group and subjected to inverse proportional allocation. The inverse proportional allocation process is as follows: First, the basic weights of fiber cores 1, 4, 5, and 6 are calculated according to the fiber core basic weight formula. , , and :

[0036] The allocation is performed inversely based on the base weights, calculated using the following formula:

[0037] In this invention example, the following calculations were performed: =0.19; =0.20; =0.36; =0.25. For fiber cores 2, 3, and 7, these three fiber cores have similar linearity, and are used as the actual calculation group for inverse proportional allocation to obtain the weights: =0.57, =0.197, =0.233.

[0038] Figure 6 This is a temperature-frequency shift curve of the Brillouin optical time-domain reflectometer system after weighted averaging in this example. Figure 6 The figures show the temperature-frequency shift curves of the system after weighted averaging, where (a) is the result after averaging the data from fibers 1, 4, 5, and 6, and (b) is the result after averaging the data from fibers 2, 3, and 7. After weighted averaging the data from fibers 1, 4, 5, and 6 using the formula above, the system's temperature measurement error was reduced to 0.287℃, lower than the error when these fibers were used individually. After weighted averaging the data from fibers 2, 3, and 7, the error was further reduced to 0.134℃, a result superior to the performance of any single fiber.

[0039] This invention uses fiber core linearity (with the sum of squared frequency errors of the fiber core as a linearity indicator) and sets a threshold for the sum of squared frequency errors. It then performs a weighted average of the Brillouin frequency shifts of fiber cores below the threshold, and obtains the temperature from the weighted averaged Brillouin frequency shifts. To verify the effectiveness of the weighted averaging method, a weighted average was also performed on the Brillouin frequency shifts of fiber cores above the threshold; both sets of temperature measurement errors showed a reduction. This example demonstrates how the above method effectively reduces the temperature measurement error of the Brillouin optical time-domain reflectometer system and improves the system linearity.

[0040] In one exemplary embodiment, a computer-readable storage medium is included, which stores a computer program that, when executed by a processor, implements the method described above.

[0041] Please see Figure 7 In one exemplary embodiment, the device further includes an electronic device including at least one processor, at least one memory, and at least one communication bus.

[0042] The memory stores a computer program, which includes computer-readable instructions. The processor calls the computer-readable instructions stored in the memory through a communication bus to execute the above method.

[0043] In one exemplary embodiment, a computer program product is proposed, including a computer program / instructions that, when executed by a processor, implement the method described above.

[0044] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A Brillouin temperature sensing system based on multi-core optical fiber, characterized in that, The system includes: a laser unit, a signal amplification unit, a carrier suppression modulation unit, a signal source, a first beam splitter, a second beam splitter, a third beam splitter, first to Nth circulators, first to Nth couplers, first to Nth signal processing units, a multi-core fan-in fan-out coupler, a multi-core optical fiber, and a signal acquisition and processing device; N is the number of cores in the multi-core optical fiber. The laser unit emits a laser beam, which is split into a probe beam and a local oscillator beam by a first beam splitter. The probe beam is amplified by a signal amplification unit. The amplified probe beam is split into N paths by a second beam splitter. The N probe beams pass through the first ports of the first to Nth circulators respectively. The light output from the second ports of the first to Nth circulators passes through a multi-core fan-in fan-out coupler and is fanned into a multi-core optical fiber. The Brillouin backscattered light carrying temperature information generated by the multi-core optical fiber is fanned out by the multi-core fan-in fan-out coupler to the second ports of the first to Nth circulators. The signal generated by the signal source and the local oscillator light are modulated in the carrier suppression modulation unit to obtain the modulated signal. The modulated signal is divided into N paths by the third beam splitter. The N modulated signals are coupled to the third port output signals of the first to Nth circulators through the first to Nth couplers respectively. The outputs of the first to Nth couplers are respectively processed by the first to Nth signal processing units and acquired by the signal acquisition and processing device.

2. The Brillouin temperature sensing system based on multi-core optical fiber according to claim 1, characterized in that, The signal amplification unit includes a semiconductor optical amplifier and an erbium-doped fiber amplifier. The probe light first passes through the semiconductor optical amplifier and then is amplified by the erbium-doped fiber amplifier.

3. The Brillouin temperature sensing system based on multi-core optical fiber according to claim 1, characterized in that, The signal source is a microwave source, which generates a radio frequency sweep signal.

4. The Brillouin temperature sensing system based on multi-core optical fiber according to claim 1, characterized in that, The carrier suppression modulation unit includes a Mach-Zehnder modulator, a polarization scrambler, and a bias control board. The Mach-Zehnder modulator performs carrier suppression modulation on the signal generated by the signal source and the local oscillator light, and the bias control board performs bias control. Finally, the polarization scrambler outputs the modulated signal.

5. The Brillouin temperature sensing system based on multi-core optical fiber according to claim 1, characterized in that, Each signal processing unit includes a balanced detector, an electrical amplifier, and a bandpass filter. The outputs of the first to Nth couplers are sequentially processed by the balanced detector, electrical amplifier, and bandpass filter of the first to Nth signal processing units before being output.

6. A Brillouin temperature sensing and analysis method based on multi-core optical fiber, characterized in that, The system implementation based on any one of claims 1-5 includes the following steps: The N signals acquired by the signal acquisition and processing device are processed to obtain the Brillouin gain spectrum of N fiber cores, and the Brillouin frequency shift of each fiber core is determined. The temperature is obtained based on the weighted average Brillouin frequency shift. The Brillouin shift after weighted averaging is: in, The Brillouin frequency shift of fiber core i at water bath temperature T; The Brillouin frequency shift of the system after data weighted averaging at a water bath temperature T; The weighting of fiber core i; Define the basic weight formula for each fiber core: in, This represents the basic weight of fiber core i. Let i be the sum of squares of the frequency errors of fiber core i. , The measurement frequency at temperature T. The fitted frequency at temperature T; Calculate the sum of squared frequency errors for each fiber core, select fiber cores whose sum of squared frequency errors is lower than a set threshold, calculate the base weight of the selected fiber cores, and then use an inverse proportional allocation to obtain the weight of the selected fiber cores.

7. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, it implements the method as described in claim 6.

8. An electronic device, characterized in that, The system includes a processor and a memory interconnected thereto, wherein the memory is used to store a computer program, the computer program including computer-readable instructions, and the processor is configured to invoke the computer-readable instructions to perform the method as described in claim 6.

9. A computer program product, comprising a computer program / instructions, characterized in that, When the computer program / instructions are executed by the processor, they implement the method of claim 6.

Images