Signal receiving apparatus, signal transmitting apparatus, and optical fiber sensing apparatus

Abstract

The present application relates to the technical field of optical fiber sensing. Provided are a signal receiving apparatus, a signal transmitting apparatus and an optical fiber sensing apparatus, which are used for ameliorating the problem of requirements for an existing optical fiber sensing apparatus being relatively high when same detects Rayleigh scattering and Brillouin scattering at the same time, etc. The signal receiving apparatus comprises a coherent receiver, a radio frequency analog-to-digital conversion unit and a frequency band calculation unit, wherein the coherent receiver is configured to obtain four electrical signals with orthogonal phases on the basis of local oscillator light and signal light; the radio frequency analog-to-digital conversion unit converts the four electrical signals to obtain two digital signals in a first polarization state and two digital signals in a second polarization state; and the frequency band calculation unit is configured to perform calculation on the basis of the two digital signals in the first polarization state of the signal light and the two digital signals in the second polarization state of the signal light, so as to obtain the frequency spectrum of the signal light, the frequency spectrum comprising a φQTDR signal located at a positive frequency and a BOTDR signal located at a negative frequency.

Description

Signal receiving device, transmitting device and optical fiber sensing device

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office on October 27, 2023, with application number 202311426488.X and application name “Signal receiving device, transmitting device and optical fiber sensing device”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of distributed optical fiber sensing technology, and in particular to a signal receiving device, a transmitting device, and an optical fiber sensing device. Background Art

[0003] When an optical fiber is affected by the external environment (such as temperature, stress, and vibration), parameters such as the intensity, phase, and frequency of the light transmitted through it will change accordingly. By detecting these parameters of the transmitted light, the corresponding physical quantities can be obtained. This technology is called fiber optic sensing. Distributed fiber optic sensing uses the optical fiber itself as a sensor. By measuring the intensity, phase, or frequency shift of scattered light at each point along the fiber, it can obtain information such as temperature, stress, and vibration along the fiber path, enabling the monitoring of these physical quantities.

[0004] The combination of phase-sensitive optical time-domain reflectometry and Brillouin optical time-domain reflectometry is a form of multi-parameter sensing. It realizes the sensing of vibration, temperature, and stress by simultaneously detecting Rayleigh scattering and Brillouin scattering. However, when detecting both at the same time, its detection performance places high demands on the bandwidth of the receiver.

[0005] Summary of the Invention

[0006] The present application provides a signal receiving device, a transmitting device, and an optical fiber sensing device, as well as a signal processing method applied to the optical fiber sensing device, to improve the current optical fiber sensing device's high equipment requirements when simultaneously detecting Rayleigh scattering and Brillouin scattering.

[0007] In a first aspect, a signal receiving device is provided, including a coherent receiver, a radio frequency analog-to-digital conversion unit and a frequency band calculation unit; the coherent receiver is used to obtain four orthogonal electrical signals based on local oscillator light and signal light generated in the optical fiber under test, the four orthogonal electrical signals including two orthogonal electrical signals in a first polarization state and two orthogonal electrical signals in a second polarization state, where the two electrical signals are orthogonal means that the frequencies of the two electrical signals are the same and the phase difference is π / 2, that is, the phases are orthogonal, and the same is true for the orthogonal signals mentioned later, which will not be repeated here; the radio frequency analog-to-digital conversion unit is used to convert the four electrical signals into two digital signals in a first polarization state and two digital signals in a second polarization state; the frequency band calculation unit is used to calculate the spectrum of the signal light based on the two digital signals in the first polarization state and the two digital signals in the second polarization state, the spectrum including a first detection signal at a positive frequency and a second detection signal at a negative frequency.

[0008] The signal receiving device provided in the embodiment of the present application uses a coherent receiver to receive signal light, and obtains two orthogonal electrical signals X of the first polarization state of the signal light according to the signal light and the local oscillator light. I 、X Q and two orthogonal electrical signals Y of the second polarization state I 、Y Q After the RF analog-to-digital conversion unit converts the four-way orthogonal electrical signals into digital signals, the frequency band calculation unit calculates the X I 、X Q 、Y I 、Y Q After the frequency band calculation of the four-way digital signal, the frequency spectrum of the first detection signal at the positive frequency and the second detection signal at the negative frequency can be obtained. For example, the first detection signal can be a φOTDR signal, and the second detection signal can be a BOTDR signal. On this basis, by adjusting the frequency of the detection light, the frequency of the first detection signal at the positive frequency can be located near the center sampling frequency (positive frequency) of the analog-to-digital converter, and the frequency of the second detection signal at the negative frequency can be distributed near the center sampling frequency (negative frequency) of the analog-to-digital converter. In this way, the first detection signal can be sampled at the positive frequency and the second detection signal can be sampled at the negative frequency by the same ADC, so as to take advantage of the advantages of the φOTDR signal. A set of transceiver devices can simultaneously receive BOTDR signals and φOTDR signals to realize monitoring of multiple parameters such as vibration, temperature and strain. Compared with traditional fiber optic sensing devices, the solution provided in the embodiment of the present application can reduce the requirements for the frequency coverage range of coherent receivers and ADCs in the signal receiving device. For example, traditional fiber optic sensing devices sample the first detection signal and the second detection signal at the positive frequency, and the frequency coverage range requirements are high; the solution provided in the present application samples the first detection signal at the positive frequency and the second detection signal at the negative frequency, and the frequency coverage range requirements of the coherent receiver and ADC in the signal receiving device can be reduced by half.

[0009] In one possible implementation, the coherent receiver includes four output terminals, the RF analog-to-digital conversion unit includes four RF analog-to-digital converters, the four RF analog-to-digital converters are connected to the four output terminals of the coherent receiver in a one-to-one correspondence, and the RF analog-to-digital converter includes a digitally controlled oscillator, a first mixer, a first filter and a first analog-to-digital converter; the output terminal of the digitally controlled oscillator is connected to the first input terminal of the first mixer, and the second input terminal of the first mixer is connected to the output terminal of the coherent receiver; the output terminal of the first mixer is connected to the input terminal of the first filter, the output terminal of the first filter is connected to the input terminal of the first analog-to-digital converter, and the output terminal of the first analog-to-digital converter is connected to the frequency band calculation unit; the digitally controlled oscillator is used to generate a RF signal of a first frequency, and the first mixer is used to mix an electrical signal with a RF signal of the first frequency; the first filter is used to filter out high-frequency components in the mixed signal to convert the electrical signal to baseband; the first analog-to-digital converter is used to convert the electrical signal converted to baseband into a digital signal, wherein the center sampling frequency of the first analog-to-digital converter is the first frequency. By downconverting the RF signal to near baseband for sampling, the performance requirements of the analog-to-digital converter can be relaxed.

[0010] In one possible implementation, the RF analog-to-digital converter also includes a 90° phase shifter, a second mixer, a second filter and a second analog-to-digital converter; the output end of the digitally controlled oscillator is also connected to the input end of the 90° phase shifter, the output end of the 90° phase shifter is connected to the first input end of the second mixer, the second input end of the second mixer is connected to the output end of the coherent receiver, the output end of the second mixer is connected to the input end of the second filter, the output end of the second filter is connected to the input end of the second analog-to-digital converter, and the output end of the second analog-to-digital converter is connected to the frequency band calculation unit; the digitally controlled oscillator is used to generate a radio frequency signal of a first frequency, the 90° phase shifter is used to shift the phase of the radio frequency signal by 90°, the mixer is used to mix an electrical signal output by the coherent receiver with the phase-shifted radio frequency signal, the second filter is used to filter out high-frequency components in the mixed signal to convert the electrical signal to baseband; the second analog-to-digital converter is used to convert the electrical signal converted to baseband into a digital signal, wherein the center sampling frequency of the second analog-to-digital converter is the first frequency. Each analog signal output by the coherent receiver is collected by two ADCs, which respectively collect the in-phase (I) and quadrature (Q) signals. Compared with using only one ADC to collect the I signal, using two ADCs to collect the I and Q signals separately doubles the frequency range of the signal that can be collected, reducing the sampling bandwidth requirements of the ADC.

[0011] In a possible implementation, for example, the first detection signal is a phase-sensitive optical time domain reflectometer φOTDR signal, and the second detection signal is a Brillouin optical time domain reflectometer BOTDR signal.

[0012] In one possible implementation, the first detection signal and the second detection signal are detection signals generated by scattering the same probe light pulse, or the first detection signal and the second detection signal are detection signals generated by different probe light pulses. If the first detection signal and the second detection signal are detection signals generated by scattering the same probe light pulse, then the frequency difference between the two is approximately the Brillouin frequency shift (vB). If the same type of ADC is used to sample the first detection signal and the second detection signal respectively, the center sampling frequency of the ADC needs to be near vB in order to sample the second detection signal and the first detection signal near the negative frequency (-vB) and the positive frequency (vB), respectively. The range of the ADC sampling frequency that can be adjusted is limited. However, when the first detection signal and the second detection signal are detection signals generated by scattering different probe light pulses, for example, the first detection signal is generated by the first probe light pulse and the second detection signal is generated by the second probe light pulse, then the frequency difference between the first detection signal and the second detection signal is not limited. The frequency distribution of the first detection signal and the second detection signal can be adjusted by adjusting the frequencies of the first probe light pulse and the second probe light pulse, so that the sampling frequency of the ADC can be flexibly adjusted.

[0013] In a possible implementation, the signal receiving device further includes a signal quality calculation unit, which is configured to determine the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal.

[0014] In a second aspect, a signal transmitting device is provided, which includes a laser, a coupler, a first RF transmitting unit, an orthogonal modulator and an optical fiber circulator; the laser is used to emit an optical signal, and the optical signal emitted by the laser is coupled into two paths by the coupler, one of which is transmitted to the orthogonal modulator as a detection light, and the other is transmitted to a coherent receiver as a local oscillator light; the first RF transmitting unit is used to generate a first RF signal and a second RF signal with a second frequency and orthogonal to each other; the orthogonal modulator is used to modulate the orthogonal first RF signal and the second RF signal onto a detection light of a first polarization state to obtain a detection light pulse signal; the optical fiber circulator is used to connect to the optical fiber under test, the optical fiber circulator is used to input the detection light pulse signal into the optical fiber under test, and the optical fiber circulator is also used to output the signal light generated in the optical fiber under test.

[0015] In one possible implementation, the signal transmitting device also includes a second transmitting unit; the second RF transmitting unit is used to generate a third RF signal and a fourth RF signal having a third frequency and being orthogonal; the detection light output by the orthogonal modulator has two polarization states, and the orthogonal modulator is further used to modulate the orthogonal third RF signal and the fourth RF signal onto the detection light of the second polarization state.

[0016] The solution provided in the embodiment of the present application can modulate radio frequency signals of different frequencies onto the two polarization states of the detection light respectively. The two polarization states do not affect each other, and the first detection signal generated by the pulse of the first polarization state and the second detection signal generated by the pulse of the second polarization state can be collected. In this way, the frequency distribution range of the first detection signal and the second detection signal can be flexibly adjusted by adjusting the second frequency and the third frequency respectively. Flexible adjustment of the frequencies of the first detection signal and the second detection signal can adapt to the working frequency bands of different signal receiving devices.

[0017] In one possible implementation, the first RF transmitting unit is further configured to adjust the magnitude of the second frequency. By adjusting the magnitude of the second frequency, the frequency distribution of the first detection signal and the second detection signal can be adjusted, and the first detection signal and the second detection signal can be adjusted to be near the sampling center frequency of the analog-to-digital converter. This allows the first detection signal to be sampled at the positive frequency and the second detection signal to be sampled at the negative frequency simultaneously, thereby reducing the requirements for the ADC sampling bandwidth.

[0018] In a possible implementation, the second RF transmitting unit is further configured to adjust the magnitude of the third frequency and the time delay between the signal generated by the second RF transmitting unit and the signal generated by the first RF transmitting unit.

[0019] In a third aspect, a fiber optic sensing device is provided, which includes: a laser, a coupler, a first radio frequency transmitting unit, an orthogonal modulator, an optical fiber circulator, a coherent receiver, an radio frequency analog-to-digital conversion unit, and a frequency band calculation unit; the optical signal emitted by the laser is coupled into two paths by the coupler, one of which is transmitted to the orthogonal modulator as a detection light, and the other is transmitted to the coherent receiver as a local oscillator light; the first radio frequency transmitting unit is used to generate a first radio frequency signal and a second radio frequency signal that are orthogonal to each other at a second frequency; the orthogonal modulator is used to modulate the orthogonal first radio frequency signal and the second radio frequency signal onto the detection light of the first polarization state to obtain a detection light pulse signal; the optical fiber circulator is used to connect to the optical fiber to be measured, the optical fiber circulator is used to input the detection light pulse signal into the optical fiber to be measured, and the optical fiber circulator is also used to The signal light generated in the optical fiber under test is output to a coherent receiver; the coherent receiver is used to obtain four orthogonal electrical signals based on the local oscillator light and the signal light generated in the optical fiber under test, and the four orthogonal electrical signals include two orthogonal electrical signals in a first polarization state and two orthogonal electrical signals in a second polarization state; the radio frequency analog-to-digital conversion unit is used to convert the four electrical signals into two digital signals in a first polarization state and two digital signals in a second polarization state; the frequency band calculation unit is used to calculate the spectrum of the signal light based on the two digital signals in the first polarization state and the two digital signals in the second polarization state, and the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency.

[0020] The optical fiber sensing device provided in the embodiment of the present application uses a coherent receiver to receive the signal light, and obtains two orthogonal electrical signals X of the first polarization state of the signal light according to the signal light and the local oscillation light. I 、X Q and two orthogonal electrical signals Y of the second polarization state I 、Y Q After the RF analog-to-digital conversion unit converts the four-way orthogonal electrical signals into digital signals, the frequency band calculation unit calculates the X I 、X Q 、Y I 、Y Q After performing frequency band calculation on the four digital signals, the spectra of the first detection signal at the positive frequency and the second detection signal at the negative frequency can be obtained. For example, the first detection signal can be a φOTDR signal, and the second detection signal can be a BOTDR signal. On this basis, by adjusting the frequency of the probe light, the frequency of the positive-frequency first detection signal can be located near the center sampling frequency (positive frequency) of the analog-to-digital converter, and the frequency of the negative-frequency second detection signal can be distributed near the center sampling frequency (negative frequency) of the analog-to-digital converter. In this way, the first detection signal and the second detection signal can be sampled at the negative frequency and the positive frequency respectively by the same type of ADC. In this way, a set of transceivers can simultaneously receive BOTDR signals and φOTDR signals, realizing multiple parameter monitoring such as vibration, temperature, and strain. Compared with traditional optical fiber sensing devices, the solution provided in the embodiment of the present application can reduce the requirements for the frequency coverage range of the coherent receiver and ADC in the signal receiving device. For example, traditional optical fiber sensing devices sample the first detection signal and the second detection signal at the positive frequency, and the frequency coverage range requirements are high. The solution provided in the present application samples the first detection signal at the positive frequency and the second detection signal at the negative frequency, and the frequency coverage range requirements of the coherent receiver and ADC in the signal receiving device can be reduced by half.

[0021] In one possible implementation, the coherent receiver includes four output terminals, the RF analog-to-digital conversion unit includes four RF analog-to-digital converters, the four RF analog-to-digital converters are connected to the four output terminals of the coherent receiver in a one-to-one correspondence, and the RF analog-to-digital converter includes a digitally controlled oscillator, a first mixer, a first filter and a first analog-to-digital converter; the output terminal of the digitally controlled oscillator is connected to the first input terminal of the first mixer, and the second input terminal of the first mixer is connected to the output terminal of the coherent receiver; the output terminal of the first mixer is connected to the input terminal of the first filter, the output terminal of the first filter is connected to the input terminal of the first analog-to-digital converter, and the output terminal of the first analog-to-digital converter is connected to the frequency band calculation unit; the digitally controlled oscillator is used to generate a RF signal of a first frequency, and the first mixer is used to mix an electrical signal with a RF signal of the first frequency; the first filter is used to filter out high-frequency components in the mixed signal to convert the electrical signal to baseband; the first analog-to-digital converter is used to convert the electrical signal converted to baseband into a digital signal, wherein the center sampling frequency of the first analog-to-digital converter is the first frequency.

[0022] In one possible implementation, the RF analog-to-digital converter also includes a 90° phase shifter, a second mixer, a second filter, and a second analog-to-digital converter; the output end of the digitally controlled oscillator is also connected to the input end of the 90° phase shifter, the output end of the 90° phase shifter is connected to the first input end of the second mixer, the second input end of the second mixer is connected to the output end of the coherent receiver, the output end of the second mixer is connected to the input end of the second filter, the output end of the second filter is connected to the input end of the second analog-to-digital converter, and the output end of the second analog-to-digital converter is connected to the frequency band calculation unit; the digitally controlled oscillator is used to generate a radio frequency signal of a first frequency, the 90° phase shifter is used to shift the phase of the radio frequency signal by 90°, the second mixer is used to mix an electrical signal output by the coherent receiver with the phase-shifted radio frequency signal, the second filter is used to filter out high-frequency components in the mixed signal to convert the electrical signal to baseband; the second analog-to-digital converter is used to convert the electrical signal converted to baseband into a digital signal, wherein the center sampling frequency of the second analog-to-digital converter is the first frequency.

[0023] In a possible implementation, for example, the first detection signal is a phase-sensitive optical time domain reflectometer φOTDR signal, and the second detection signal is a Brillouin optical time domain reflectometer BOTDR signal.

[0024] In a possible implementation, the first detection signal and the second detection signal are detection signals generated by pulse scattering of a first polarization state of the detection light.

[0025] In one possible implementation, the signal transmitting device also includes a second transmitting unit; the second RF transmitting unit is used to generate a third RF signal and a fourth RF signal with a third frequency and orthogonal to each other; the orthogonal modulator is also used to modulate the orthogonal third RF signal and the fourth RF signal onto the detection light of the second polarization state; the frequency band calculation unit is used to calculate the spectrum of the signal light based on the two digital signals of the first polarization state and the two digital signals of the second polarization state, and the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency; wherein the first detection signal and the second detection signal are detection signals generated by pulse scattering of the first polarization state of the detection light, and the second detection signal is a detection signal generated by pulse scattering of the second polarization state of the detection light.

[0026] In the optical fiber sensing device provided in the embodiment of the present application, the signal transmitting device modulates radio frequency signals of different frequencies onto two polarization states of the detection light respectively, and the two polarization states do not affect each other. The signal receiving device can collect a first detection signal generated by a pulse of the first polarization state and a second detection signal generated by a pulse of the second polarization state. In this way, the frequency distribution ranges of the first detection signal and the second detection signal can be flexibly adjusted by adjusting the second frequency and the third frequency respectively. Flexible adjustment of the first detection signal and the second detection signal can adapt to the working frequency bands of different signal receiving devices.

[0027] In one possible implementation, when the frequency range of the first detection signal does not match the first frequency range, or when the frequency range of the second detection signal does not match the second frequency range, the first RF transmitting unit is used to adjust the second frequency, and / or the RF analog-to-digital converter is used to adjust the first frequency.

[0028] In a possible implementation, the first RF transmitting unit is further configured to adjust the second frequency when an absolute value of a frequency range of the first detection signal intersects an absolute value of a frequency range of the second detection signal.

[0029] In one possible implementation, the first detection signal is a phase-sensitive optical time domain reflectometer φOTDR signal, the second detection signal is a Brillouin optical time domain reflectometer BOTDR signal, and the optical fiber sensing device also includes a signal quality calculation unit, which is used to determine the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal.

[0030] In one possible implementation, the second RF transmitting unit is further used to adjust the size of the third frequency and the time delay between the signal transmitted by the second RF transmitting unit and the signal transmitted by the first RF transmitting unit according to the fitting accuracy of the BOTDR signal and / or the phase noise of the φOTDR signal.

[0031] In a fourth aspect, a signal processing method is provided, which is applied to the optical fiber sensing device provided by any implementation of the third aspect, and the method includes: an optical signal emitted by a laser; a coupler couples the optical signal emitted by the laser into two paths, one of which is transmitted to an orthogonal modulator as a detection light, and the other is transmitted to a coherent receiver as a local oscillator light; a first radio frequency transmitting unit generates a first radio frequency signal and a second radio frequency signal having a second frequency and being orthogonal; the orthogonal modulator modulates the orthogonal first radio frequency signal and the second radio frequency signal onto a detection light of a first polarization state to obtain a detection light pulse signal; and a fiber circulator inputs the detection light pulse signal into the optical fiber under test. And the signal light generated in the optical fiber under test is output to a coherent receiver; the coherent receiver obtains four phase-orthogonal electrical signals according to the local oscillator light and the signal light, and the four orthogonal electrical signals include two phase-orthogonal electrical signals in a first polarization state and two phase-orthogonal electrical signals in a second polarization state; the radio frequency analog-to-digital conversion unit converts the four electrical signals to obtain two digital signals in a first polarization state and two digital signals in a second polarization state; the frequency band calculation unit calculates the spectrum of the signal light according to the two digital signals in the first polarization state and the two digital signals in the second polarization state, and the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency.

[0032] In one possible implementation, the method further includes: when the frequency range of the first detection signal does not match the first frequency range, or when the frequency range of the second detection signal does not match the second frequency range, the first RF transmitting unit is used to adjust the second frequency, and / or the RF analog-to-digital converter is used to adjust the first frequency.

[0033] In a possible implementation, the method further includes: when an absolute value of the frequency range of the first detection signal intersects an absolute value of the frequency range of the second detection signal, the first RF transmitting unit adjusts the second frequency.

[0034] In one possible implementation, the method further includes: the second RF transmitting unit adjusting the magnitude of the third frequency and the time delay between the signal transmitted by the second RF transmitting unit and the signal transmitted by the first RF transmitting unit according to the fitting accuracy of the BOTDR signal and / or the phase noise of the φOTDR signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic diagram of several light scatterings provided in an embodiment of the present application;

[0036] FIG2 is a schematic diagram of Rayleigh scattering provided in an embodiment of the present application;

[0037] FIG3 is a schematic diagram of a distributed optical fiber sensing technology provided in an embodiment of the present application;

[0038] FIG4 is a schematic diagram of a fiber optic sensing device for multi-yield detection provided by an embodiment of the present application;

[0039] FIG5 is a schematic diagram of the frequency difference between Rayleigh scattered light and Brillouin scattered light provided in an embodiment of the present application;

[0040] FIG6 is a schematic diagram of an optical fiber sensing device provided in an embodiment of the present application;

[0041] FIG7 is a schematic diagram of a first polarization state of the probe light provided in an embodiment of the present application;

[0042] FIG8 is a schematic diagram of a spectrum of signal light provided in an embodiment of the present application;

[0043] FIG9 is a comparison diagram of two ADC acquisition frequency bands provided in an embodiment of the present application;

[0044] FIG10 is a schematic diagram of another optical fiber sensing device provided in an embodiment of the present application;

[0045] FIG11 is a schematic diagram of double-sideband modulation;

[0046] FIG12 is a schematic diagram of single sideband modulation;

[0047] FIG13 is a schematic diagram of a detection signal and its mirror image signal;

[0048] FIG14 is a schematic diagram of a coherent receiver provided in an embodiment of the present application;

[0049] FIG15 is a schematic diagram of a radio frequency analog-to-digital converter provided in an embodiment of the present application;

[0050] FIG16 is a comparison diagram of the sampling ranges of two analog-to-digital converters provided in an embodiment of the present application;

[0051] FIG17 is a schematic diagram of a radio frequency analog-to-digital converter provided in an embodiment of the present application;

[0052] FIG18 is a schematic diagram of a signal quality curve of a detection signal provided in an embodiment of the present application;

[0053] FIG19 is a sampling diagram of another analog-to-digital converter provided in an embodiment of the present application;

[0054] FIG20 is a schematic diagram of another optical fiber sensing device provided in an embodiment of the present application;

[0055] FIG21 is a schematic diagram of a first polarization state and a second polarization state of a probe light provided in an embodiment of the present application;

[0056] FIG22 is a schematic diagram of a spectrum of signal light provided in an embodiment of the present application;

[0057] FIG23 is a schematic diagram of a signal quality curve of another detection signal provided in an embodiment of the present application;

[0058] FIG24 is a schematic diagram of another optical fiber sensing device provided in an embodiment of the present application;

[0059] Figure 25 is a flowchart of the signal processing method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0060] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. In the present application, "at least one" refers to one or more, and "more" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can represent: the existence of A alone, the existence of A and B at the same time, and the existence of B alone, where A and B can be singular or plural. "At least one of the following items (individuals)" or similar expressions refers to any combination of these items, including any combination of single items (individuals) or plural items (individuals). For example, at least one of a, b or c can represent: a, b, c, a and b, a and c, b and c or a, b and c, where a, b and c can be single or multiple.

[0061] The embodiments of this application use terms such as "first" and "second" to distinguish objects with similar names, functions, or effects. Those skilled in the art will understand that terms such as "first" and "second" do not limit the quantity or order of execution. The term "coupled" is used to indicate an electrical connection, including direct connection via wires or connectors or indirect connection via other devices. Therefore, "coupling" should be considered a broadly defined electronic communication connection.

[0062] It should be noted that, in this application, words such as "exemplary" or "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described in this application as "exemplary" or "for example" should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "for example" is intended to present the relevant concepts in a concrete manner.

[0063] When light propagates through an optical fiber, the inhomogeneity or nonlinearity of the fiber's refractive index can cause some of the incident light to deviate from its original propagation direction and propagate in random directions. This phenomenon is called light scattering. A small portion of this randomly scattered light travels in the opposite direction of the incident direction, known as backscattered light.

[0064] There are three main types of backscattered light in optical fibers: Rayleigh scattering, Brillouin scattering, and Raman scattering, each with its own distinct scattering mechanisms. Raman and Brillouin scattering shift the optical frequency and are therefore known as inelastic scattering; Rayleigh scattering, which does not shift the optical frequency, is known as elastic scattering.

[0065] Raman scattering and Brillouin scattering are caused by the interaction of light with optical phonons and acoustic phonons, respectively, causing the light to shift in frequency upward or downward. As shown in Figure 1, under the action of optical phonons in the optical fiber, the light frequency produces a frequency shift of about 13 THz, resulting in Raman scattered light; while under the action of acoustic phonons, the light frequency produces a frequency shift of about 11 GHz, resulting in Brillouin scattered light. The light that moves in the direction of decreasing frequency is called Stokes light, and the light that moves in the direction of increasing frequency is called anti-Stokes light. Various distributed optical fiber sensing systems, such as Raman optical time-domain reflectometry (ROTDR) and Brillouin optical time-domain analysis (BOTDA), are based on these two inelastic scattering mechanisms to achieve sensing.

[0066] Rayleigh scattering is primarily caused by the inhomogeneity of the medium within the optical fiber. As shown in Figure 2, during optical fiber manufacturing, factors such as the production process inevitably introduce random refractive index fluctuations, represented by the black dots in Figure 2. When the probe light propagates through the fiber, these refractive index fluctuations generate scattered light that propagates randomly in various directions. A small portion of this scattered light propagates backward, meeting the propagation conditions of single-mode fiber and returning from the scattering location to the probe light input port. This backward Rayleigh scattered light forms the foundation of distributed fiber optic sensing based on Rayleigh scattering.

[0067] Distributed fiber optic sensing technology is a new type of sensing technology that uses light as a carrier and utilizes changes in the phase and intensity of light to sense external measured parameters (temperature, strain, pressure, etc.). Fiber optic sensing technology uses optical fiber as a sensing and transmission element, so it is simpler in structure and more convenient to use than traditional electromechanical sensors. Optical fiber is inexpensive, has a wide working bandwidth range, and low loss, and can achieve long-distance and large-scale sensing. Optical fiber is resistant to pressure and tension, and can be used in small and narrow areas, as well as in dangerous areas such as flammable and explosive areas. Using light as a sensing signal is not easily susceptible to electromagnetic interference and can be used in areas with strong electromagnetic fields. Distributed fiber optic sensing technology has obvious advantages and is widely used in power, petrochemical, transportation, civil engineering, aerospace and other fields.

[0068] The basic principle of distributed fiber-optic sensing technology is shown in Figure 3. A laser generates light, which is modulated into light pulses by a modulator and then injected into the fiber under test via a fiber circulator. The backscattered light generated in the fiber propagates backward and is detected by a photodetector to obtain intensity information. Backscattered light includes Rayleigh scattering and Brillouin scattering. Due to fiber loss, the intensity of the backscattered light decays exponentially along the fiber. The speed of this exponential decay can be used to measure the degree of fiber loss. A sudden increase in the local signal indicates a high reflection point, while a sudden increase in attenuation indicates a loss point or discontinuity. Optical time-domain reflectometry (OTDR) instruments based on this principle are widely used in fields such as communications to monitor the status of fiber links.

[0069] Common optical time-domain reflectometers include phase-sensitive OTDR (ΦOTDR) and Brillouin optical time-domain reflectometry (BOTDR). ΦOTDR utilizes the interference effect between backward Rayleigh scattered light and is an interferometric scattering fiber optic sensing technology with numerous advantages, including high sensitivity, long measurement distance, and a simple and easy-to-implement structure. Because Rayleigh scattered light has greater power than Brillouin scattered light and Raman scattered light, it reduces the average signal processing time and enables vibration measurement. Therefore, simply detecting changes in the Rayleigh scattered light in the fiber can detect the fiber's vibration.

[0070] BOTDR utilizes the Brillouin scattering of optical fiber. In ordinary single-mode quartz optical fiber, the core material has thermo-optic effect and elasto-optic effect. These two effects affect the speed of sound in the optical fiber material, and the change in sound speed will cause the change of Brillouin scattered light. Therefore, the change of Brillouin scattered light is related to the temperature and strain of the optical fiber. Therefore, as long as the change of Brillouin scattered light in the optical fiber is detected, the temperature or stress distribution of each point on the optical fiber can be detected.

[0071] The combination of φOTDR and BOTDR is a form of multi-parameter sensing. By simultaneously monitoring Rayleigh and Brillouin scattering signals, it enables simultaneous sensing of vibration, temperature, and stress. Brillouin scattering and Rayleigh scattering are characterized by a large frequency separation of approximately 11 GHz, a wide distribution range (hundreds of MHz to GHz), and relatively weak scattering coefficients (Rayleigh and Brillouin scattering coefficients of -81 dB / ns and -93 dB / ns, respectively). Simultaneous detection of both signals places high demands on receiver bandwidth and system spurious and harmonic interference. Simultaneous sampling and spectrum analysis of both Rayleigh and Brillouin scattering signals places very high demands on the performance and operating frequency range of the sampling and spectrum analysis equipment, leading to sampling difficulties, low sampling accuracy, and high equipment costs.

[0072] FIG4 shows a fiber optic sensing device for multi-parameter detection. Laser light emitted by a laser is split into two paths via a first fiber optic coupler. One path is modulated into optical pulses by an optical pulse modulator, and the other path is connected to a second fiber optic coupler. The optical pulses are connected to the first port of a fiber optic circulator, which outputs the optical pulses at the second port. The optical pulses are then injected into the optical fiber under test via an optical interface. Backscattered light from the optical pulses in the optical fiber under test enters the second port of the fiber optic circulator via the optical interface, and then enters the second fiber optic coupler via the third port of the fiber optic circulator. The second fiber optic coupler causes the injected laser light and the backscattered light to coherently generate envelope information, which is then output to a balanced photodetector. The balanced photodetector converts the envelope information into an RF signal, which is amplified by a low-noise amplifier and then connected to a power divider. Because the first filter corresponds to the Rayleigh scattering signal band (i.e., the 200MHz carrier band), and the second filter corresponds to the Brillouin scattering signal band (i.e., the 10.8GHz carrier band), the power divider splits the incoming RF signal into two paths. One path is filtered by the first filter to produce a Rayleigh scattering signal, which is connected to the first channel of the data acquisition and processing module. The other path is filtered by the second filter to produce a Brillouin scattering signal, which is connected to the signal input of the mixer. The local oscillator signal output by the frequency synthesizer is connected to the local oscillator input of the mixer. The mixer mixes the Brillouin scattering signal and the local oscillator signal to produce a baseband signal, which is filtered by a low-pass filter and connected to the second channel of the data acquisition and processing module.

[0073] The data acquisition and processing module extracts the time domain power information of the Rayleigh scattering signal collected by the first channel to obtain the attenuation information of the optical fiber under test. When the data acquisition and processing module extracts the vibration frequency of each position point from the data collected by the first channel, for example, it first saves 200 pieces of data about each position along the optical fiber and the scattering power, and then performs fast Fourier transform on the 200 power values ​​corresponding to each position along the optical fiber to obtain the vibration information of each position along the optical fiber under test.

[0074] The data acquisition and processing module extracts the time domain, frequency domain and power information of the Brillouin signal corresponding to the frequency synthesizer sweep frequency point, and simultaneously fits the Brillouin frequency points corresponding to each position of the measured optical fiber to obtain the center frequency of the Brillouin spectrum, which is then subtracted from the center frequency of the Brillouin spectrum used as a reference, ultimately reflecting the temperature and strain information of the measured optical fiber.

[0075] The solution shown in Figure 4 utilizes a wide-bandwidth balanced receiver to receive signals and separates the φOTDR signal from the BOTDR signal through a first filter and a second filter. The BOTDR signal is mixed and filtered using a separate RF source (frequency synthesizer) and mixer, then transferred to baseband. Multiple ADCs are then used to acquire both the φOTDR and BOTDR signals, enabling simultaneous detection of Brillouin and Rayleigh scattering signals. Signal multiplexing, sensing, and demodulation enable monitoring of multiple parameters of the fiber under test, including vibration, temperature, and strain.

[0076] However, the above scheme still has some disadvantages. In conjunction with Figure 1, since the frequency of Rayleigh scattered light is the same as the frequency of the detection light, the frequency of Brillouin scattered light usually increases or decreases vB based on the frequency of the detection light. vB is the Brillouin frequency shift. Depending on the fiber material or type, the Brillouin frequency shift is approximately between 8GHz and 12GHz, for example, vB≈11GHz. In a single test scenario, the Brillouin frequency shift is a fixed value. On this basis, in conjunction with Figure 5, the frequency of Rayleigh scattered light (f A ) and the frequency of Brillouin scattered light (f B ) There is a frequency difference of about 11 GHz in the spectrum. Therefore, for the solution shown in Figure 4, the frequency synthesizer, receiver, mixer, filter, etc. must be able to cover a frequency range greater than 11 GHz to achieve complete sampling of the φOTDR signal and the BOTDR signal, which places high performance requirements on the equipment. In addition, the above solution cannot flexibly control the receiving frequency of the φOTDR signal and the BOTDR signal. In actual engineering applications, the detection performance has high requirements on indicators such as the spurious-free dynamic range and total harmonic distortion of the transceiver system.

[0077] In order to improve the above problems, an embodiment of the present application provides a multi-parameter optical fiber sensing device, which can reduce the requirements for the frequency range covered by the equipment while realizing the monitoring of multiple parameters such as vibration, temperature and strain.

[0078] For example, refer to Figure 6, which shows a schematic structural diagram of a fiber optic sensing device provided in an embodiment of the present application. The fiber optic sensing device provided in an embodiment of the present application includes a signal transmitting device and a signal receiving device, wherein the signal transmitting device includes a laser 201, a coupler 202, an orthogonal modulator 203, an optical fiber circulator 204 and a first radio frequency transmitting unit 210. The signal receiving device includes a coherent receiver 205, a radio frequency analog-to-digital conversion unit 206, a frequency band calculation unit 207 and a signal quality calculation unit 208. The signal transmitting device is used to transmit a detection light pulse, which generates scattering in the optical fiber under test to obtain signal light, and the signal receiving device is used to receive the signal light and process it.

[0079] Exemplarily, the laser 201 is used to generate an optical signal, and the first RF transmitting unit 210 is used to generate a first RF signal and a second RF signal having a second frequency (f2) and being orthogonal, that is, the first RF signal and the second RF signal have the same frequency and a phase difference of 90°. The optical signal generated by the laser 201 is coupled into two paths by the coupler 202, one of which is transmitted to the orthogonal modulator 203 as a probe light, and the other is transmitted to the coherent receiver 205 as a local oscillator light. The orthogonal modulator 203 is used to modulate the first RF signal and the second RF signal onto the probe light, as shown in FIG7 , to obtain a probe light pulse signal with a period of T. The fiber optic circulator 204 is used to input the probe light pulse signal into the optical fiber under test. The probe light will be scattered in the optical fiber under test to obtain signal light. The fiber optic circulator 204 is also used to output the signal light generated in the optical fiber under test to the coherent receiver 205. The coherent receiver 205 is used to obtain two simulated orthogonal electrical signals (denoted as X) of the first polarization state of the signal light based on the local oscillator light and the signal light. I and X Q ) and the two simulated orthogonal electrical signals of the second polarization state of the signal light (denoted as Y I and Y Q ), and the above four signals (X I 、X Q 、Y I 、Y Q) is output to the RF analog-to-digital conversion unit 206, the RF analog-to-digital conversion unit 206 is used to convert the analog signal output by the coherent receiver 205 into a digital signal, and send the converted digital signal to the frequency band calculation unit 207, the frequency band calculation unit 207 is used to perform frequency band calculation on the digital signal output by the RF analog-to-digital converter 206 to obtain a spectrum, as shown in Figure 8, the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency, and the frequency difference between the first detection signal and the second detection signal is vB, where vB refers to the Brillouin frequency shift.

[0080] The optical fiber sensing device provided in the embodiment of the present application includes a signal transmitting device and a signal receiving device. The signal transmitting device uses an orthogonal modulator 203 to modulate two orthogonal radio frequency signals onto optical signals to form a detection light pulse, and uses an optical fiber circulator 204 to input the detection light pulse signal into the optical fiber under test. The detection light pulse generates Rayleigh scattering and Brillouin scattering in the optical fiber under test, and the generated backscattered light is output as signal light to the signal receiving device through the optical fiber circulator 204.

[0081] The signal receiving device uses the coherent receiver 205 to analyze the received signal light. The coherent receiver 205 obtains two analog electrical signals (X I and X Q ) and two analog electrical signals of the second polarization state of the signal light (Y I and Y Q ), the RF analog-to-digital conversion unit 206 performs analog-to-digital conversion to obtain two digital electrical signals (X I 、X Q ) and two digital signals (Y I 、Y Q ), where each polarization state includes an in-phase (I) signal and a quadrature (Q) signal, so for the first polarization state I signal (i.e. X I ) and Q-path signal (ie X Q ) Perform Fourier transform on the complex plane, take the modulus and then square the obtained spectrum, which includes the first detection signal at the positive frequency and the second detection signal at the negative frequency, for example, the first detection signal is a φOTDR signal and the second detection signal is a BOTDR signal, or the first detection signal is a BOTDR signal and the second detection signal is a φOTDR signal; for the I-path signal of the second polarization state (i.e., Y I ) and Q-path signal (ie Y Q ) Perform Fourier transform on the complex plane, take the modulus and then square it to get the spectrum. Since the polarization states of the signal light and the detection light rotate in the optical fiber, when calculating the frequency band of the first polarization state and the second polarization state of the signal light, the YI and Y Q The spectrum obtained by frequency band calculation is the same as that of X I and X Q The spectra obtained by frequency band calculation are the same. Here, the same spectrum means that the frequency distribution is the same, but the amplitudes of the various frequency components may be different.

[0082] On this basis, the signal transmitting device adjusts the second frequency (f2), which is the frequency of the first radio frequency signal and the second radio frequency signal transmitted by the first radio frequency transmitting unit, so that the frequency distribution of the first detection signal and the second detection signal is in the analog to digital converter (analog to digital Near the center sampling frequency of a converter (ADC) (denoted as the first frequency (f1) in the embodiment of the present application), the first detection signal and the second detection signal can be sampled at the negative frequency and the positive frequency respectively by the same type of ADC. In this way, a set of transceivers can simultaneously receive the BOTDR signal and the φOTDR signal, thereby realizing the monitoring of multiple parameters such as vibration, temperature, and strain. On the other hand, using the same type of ADC to sample the first detection signal at the positive frequency and the second detection signal at the negative frequency can reduce the frequency coverage requirement of the ADC, as shown in Figure 9a. In the scheme shown in Figure 4, the balanced optical detector, low-noise amplifier, etc. need to cover a frequency range of 11 GHz. As shown in Figure 9b, in the optical fiber sensing device provided by the present application, the signal receiving device can sample at both the positive and negative frequencies. This reduces the frequency coverage requirement of the signal receiving device by half, to 5.5 GHz. On the other hand, sampling the first detection signal at the positive frequency and the second detection signal at the negative frequency can reduce the spectral crosstalk and harmonic crosstalk between the BOTDR signal and the φOTDR signal, thereby improving the detection accuracy of the system.

[0083] 1 , the frequency of the Rayleigh scattered light generated by the Rayleigh scattering of the probe light in the optical fiber is the same as the frequency of the probe light. However, when Brillouin scattering occurs, it may be scattered toward a high frequency or a low frequency. If the Brillouin frequency shift vB is approximately 11 GHz, that is, if f is the frequency of the probe light, then the frequency of the generated Brillouin scattered light may be f±11 GHz. Therefore, the first detection signal at the positive frequency may be a BOTDR signal, and the second detection signal at the negative frequency may be a φOTDR signal; alternatively, the first detection signal at the positive frequency may be a φOTDR signal, and the second detection signal at the negative frequency may be a BOTDR signal. However, since the intensity of the Brillouin scattered light signal scattered toward a low frequency is greater than the intensity of the Brillouin scattered light signal scattered toward a high frequency, in the embodiment of the present application, the Brillouin scattered light is scattered toward a low frequency as an example, that is, the frequency of the Brillouin scattered light signal is f-vB.

[0084] In the optical fiber sensing device provided in the embodiment of the present application, the signal receiving device can sample the first detection signal at a positive frequency and sample the second detection signal at a negative frequency, for example, sampling the φOTDR signal at a positive frequency and sampling the BOTDR signal at a negative frequency. Since the frequency difference between the φOTDR signal and the BOTDR signal is the Brillouin frequency shift, for example, 11 GHz, if the same type of ADC is used to sample the first detection signal and the second detection signal at a negative frequency and a positive frequency respectively, the center sampling frequency of the ADC should be around 5.5 GHz. For example, if the frequency of the φOTDR signal is about 6 GHz and the frequency of the BOTDR signal is about -4 GHz, then an ADC with a center sampling frequency of about 5 GHz (-5 GHz) can be selected. Since the frequency of the φOTDR signal (6 GHz) is close to 5 GHz and the frequency of the BOTDR signal (-4 GHz) is close to -5 GHz, the ADC can sample the φOTDR signal at a positive frequency and also sample the BOTDR signal at a negative frequency.

[0085] Setting the φOTDR signal to sample at the positive frequency and the BOTDR signal to sample at the negative frequency can reduce the crosstalk between the φOTDR signal and the BOTDR signal. However, due to the imperfections of the coherent receiver, a small amount of the negative frequency signal may leak to the positive frequency to form an image, and a small amount of the positive frequency signal may leak to the negative frequency to form an image. Therefore, in order to avoid the φOTDR signal being crosstalked by the image signal of the BOTDR signal, or to avoid the BOTDR signal being crosstalked by the φOTDR signal, the absolute values ​​of the frequencies of the φOTDR signal and the BOTDR signal are similar but different, or the absolute values ​​of the frequency ranges of the two signals do not overlap, for example, the frequency of the image signal of the φOTDR signal is different from the frequency of the BOTDR signal, or the frequency of the image signal of the BOTDR signal is different from the frequency of the φOTDR signal.

[0086] For example, the frequency of the φOTDR signal is about 6 GHz, the frequency of the BOTDR signal is about -4 GHz, the frequency of the mirror signal of the BOTDR signal is about +4 GHz, and the frequency of the mirror signal of the φOTDR signal is about 6 GHz. In this way, the frequency of the φOTDR signal and the frequency of the mirror signal of the BOTDR signal are staggered, and the frequency of the BOTDR signal and the frequency of the mirror signal of the φOTDR signal are staggered, which can reduce crosstalk between them.

[0087] For example, in a possible implementation, referring to FIG10 , the first RF transmitting unit 210 includes a first baseband RF unit 211, a first pulse generating unit 212, and a first up-converting unit 213. The first baseband RF unit 211 is configured to generate two orthogonal baseband FM signals, such as an orthogonal first baseband FM signal and a second baseband FM signal, wherein the first baseband FM signal can be represented as x i, the second baseband FM signal can be expressed as x q For example, x i =cos(2πΔf1t),x q =sin(2πΔf1t).

[0088] The first baseband RF unit 211 transmits the generated first baseband FM signal and the second baseband FM signal to the first pulse generating unit 212. The first pulse generating unit 212 generates a first baseband FM signal with a pulse width of τ based on the first baseband FM signal. The first pulse generating unit 212 generates a second baseband FM signal with a pulse width of τ based on the second baseband FM signal. The first baseband FM signal can be expressed as x pi , the second baseband pulse frequency modulation signal can be expressed as x pq For example,

[0089] The first up-conversion unit 213 is used to generate an orthogonal first radio frequency signal and a second radio frequency signal according to the first baseband pulse frequency modulation signal and the second baseband pulse frequency modulation signal, wherein the first radio frequency signal can be expressed as s xi , the second RF signal can be expressed as s xq , exemplary, s xi =x pi cos(2πf IF1 t)-x pq sin(2πf IF1 t), s xq =x pi sin(2πf IF1 t)+x pq cos(2πf IF1 t). The frequencies of the first RF signal and the second RF signal are f1, f1=f IF1 +Δf1. By adjusting Δf1 and f IF1 , the frequencies of the first RF signal and the second RF signal can be adjusted. In a possible implementation, if the frequency of the baseband signal generated by the first baseband RF unit 211 is not adjustable, then Δf1 in the above example can be zero.

[0090] The orthogonal modulator 203 can modulate the orthogonal first RF signal and the second RF signal generated by the first RF transmitting unit 210 onto the detection light generated by the laser 201 to form single sideband modulation, thereby avoiding the generation of double sideband signals.

[0091] A traditional modulator can only modulate the intensity or phase of a signal. If only the intensity or phase of a signal is modulated, a double-sideband signal will often be generated, as shown in FIG11 . That is, while a signal with a frequency of +ω is generated, a signal with a frequency of -ω will also be generated. If double-sideband modulation is used, strong interference will occur between the BOTDR signal and the φOTDR signal. For example, in the embodiment of the present application, the frequency of the BOTDR signal is at a negative frequency, and the frequency of the φOTDR signal is at a positive frequency. If only the intensity or phase of the signal is modulated, and double-sideband modulation is used, then for the positive-frequency φOTDR signal, a negative-frequency φOTDR signal will also be generated. The intensity of the negative-frequency φOTDR signal is similar to that of the positive-frequency φOTDR signal, and the negative-frequency φOTDR signal will cause strong interference to the BOTDR signal at the negative frequency.

[0092] In the optical fiber sensing device provided in the embodiment of the present application, the signal transmitting device uses an orthogonal modulator to modulate the intensity and phase at the same time, and can modulate the signal onto a single sideband. Referring to Figure 12, only the positive frequency signal is modulated, and the negative frequency has no signal and will not cause interference. However, as mentioned in the above example, due to the imperfections of the coherent receiver, etc., a small part of the negative frequency signal may leak to the positive frequency to form an image, and a small part of the positive frequency signal may leak to the negative frequency to form an image. Referring to Figure 13, the intensity of the image signal is much smaller than the signal intensity generated by the double-sideband modulation at the negative frequency. In this way, the orthogonal modulator 203 can be used to convert the crosstalk of the φOTDR signal to the BOTDR signal into the crosstalk of the image component of the φOTDR signal to the BOTDR signal, and the crosstalk of the BOTDR signal to the φOTDR signal into the crosstalk of the image component of the BOTDR signal to the φOTDR signal, thereby greatly reducing the size of the crosstalk and improving the system performance.

[0093] The orthogonal modulator 203 modulates the orthogonal first RF signal and the second RF signal into the probe light (for example, in this case, the probe light is single-polarized light) to form a probe light pulse signal. The probe light pulse signal is injected into the optical fiber under test through the optical fiber circulator 204, and the backscattered light (signal light) generated by the probe light pulse in the optical fiber under test can be output to the coherent receiver 205 through the optical fiber circulator 204.

[0094] In one possible implementation, the fiber circulator 204 includes a first end, a second end, and a third end. The first end of the fiber circulator 204 is connected to the output end of the orthogonal modulator 203, the second end of the fiber circulator 204 is connected to the optical fiber under test, and the third end of the fiber circulator 204 is connected to the input end of the coherent receiver 205.

[0095] The coherent receiver 205 is an optoelectronic hybrid device that receives signal light and local oscillator light, and after polarization diversity and optical orthogonal mixing, performs optoelectronic conversion to output electrical signals in two orthogonal polarization states. In each polarization state, two electrical signal outputs that are orthogonal in phase are obtained. For example, in an embodiment of the present application, the coherent receiver 205 is used to receive signal light with Brillouin scattered light and Rayleigh scattered light, as well as to receive local oscillator light, and obtain two orthogonal electrical signals of the first polarization state of the signal light and two orthogonal electrical signals of the second polarization state of the signal light based on the signal light and the local oscillator light. Since the frequency of the signal light is relatively high, it is necessary to beat the received signal light with the local oscillator light before performing the conversion.

[0096] 14 , in a possible implementation, the two orthogonal electrical signals of the first polarization state output by the coherent receiver 205 are respectively denoted as X I and X Q , the two orthogonal electrical signals of the second polarization state are respectively recorded as Y I and Y Q The coherent receiver 205 can receive and decompose the signal light of any polarization state into the orthogonal first polarization state and second polarization state, and output four signals: X I 、X Q 、Y I and Y Q .

[0097] The RF analog-to-digital conversion unit 206 is used to convert the four signals output by the coherent receiver 205: X I 、X Q 、Y I and Y Q Perform analog-to-digital conversion and convert it into a digital signal. The coherent receiver 205 includes four output terminals, and the corresponding RF analog-to-digital conversion unit 206 includes four RF analog-to-digital converters. The four RF analog-to-digital converters are connected to the four output terminals of the coherent receiver 205 in a one-to-one correspondence. In the embodiment of the present application, one of the RF analog-to-digital converters is used as an example, for example, to convert X I For example, in one possible implementation, as shown in FIG15 a, the RF analog-to-digital converter 206 includes a digitally controlled oscillator (NCO) 2061, a mixer 2062, a first filter 2063, and a first analog-to-digital converter (ADC) 2064. The output of the NCO 2061 is connected to the first input of the first mixer 2062, and the second input of the first mixer 2062 is connected to the output of the coherent receiver 205 (for example, the coherent receiver 205 outputs X).I The output end of the first mixer 2062 is connected to the input end of the first filter 2063, the output end of the first filter 2063 is connected to the input end of the first ADC 2064, and the output end of the first ADC 2064 is connected to the frequency band calculation unit 207. The NCO 2061 is used to generate a radio frequency signal with a first frequency (f1), wherein the first mixer 2062 is used to convert X I The analog signal is mixed with a radio frequency signal having a first frequency (f1). The mixed signal is filtered by a first filter 2063 and transmitted to a first ADC 2064 for sampling, thereby converting the analog signal into a digital signal. The first frequency (f1) is the center sampling frequency of the first ADC 2064.

[0098] For example, since the ADC samples near the baseband, it is necessary to convert X I The analog signal is down-converted to baseband, and then the ADC samples and converts the down-converted signal to baseband. I The analog signal frequency is fs, then mixing fs with f1 can obtain two frequency components, fs+f1 and fs-f1. The first filter 2063 can be a low-pass filter. The low-pass filter can filter out the high-frequency component (i.e., fs+f1) in the signal and only retain the low-frequency component (i.e., fs-f1) in the signal. By adjusting the size of f1, X I The analog signal is down-converted to baseband, for example, f1 is close to fs or f1 is equal to fs. In this way, the ADC can sample near f1. Assuming the sampling bandwidth is ω, the first ADC 2064 can sample signals in the frequency range from f1 to f1+ω.

[0099] In the above example, one ADC is used to I When sampling analog signals, as shown in Figure 16 (a), only positive frequency signals (i.e., f1 to f1+ω) can be sampled, and negative frequency signals (f1-ω to f1) cannot be sampled. In order to increase the bandwidth, negative frequency signals can be sampled at the same time, as shown in Figure 15 (b), two ADCs can also be used to sample X. I The analog signals are sampled, one of which is mixed by the first mixer 2062, filtered by the first filter 2063, and sampled by the first ADC 2064 as in the above example as the in-phase signal, which is recorded as X I i, the other path is phase-shifted by 90° and then sampled as the orthogonal path signal, denoted as X I q. Digital signal X of the quadrature path I q and the digital signal X in the same phase I i together as X I digital signal.

[0100] The RF analog-to-digital converter 206 further includes a 90° phase shifter 2065, a second mixer 2066, a second filter 2067, and a second ADC 2068. The output of the NCO 2061 is further connected to the input of the 90° phase shifter 2065, the output of the 90° phase shifter 2065 is connected to the first input of the second mixer 2066, and the second input of the second mixer 2066 is connected to the output of the coherent receiver 207 (e.g., the output of the coherent receiver 205 is X). I The output end of the second mixer 2066 is connected to the input end of the second filter 2067, the output end of the second filter 2067 is connected to the input end of the second analog-to-digital converter 2068, and the output end of the second analog-to-digital converter 2068 is connected to the frequency band calculation unit 207; the 90° phase shifter 2065 is used to shift the phase of the RF signal generated by the NCO 2061 by 90°, the second mixer 2066 is used to mix the electrical signal output by the coherent receiver 205 with the phase-shifted RF signal, the second filter 2067 is used to filter out high-frequency components in the mixed signal to convert the electrical signal to baseband; the second analog-to-digital converter 2068 is used to convert the electrical signal converted to baseband into a digital signal, wherein the center sampling frequency of the second analog-to-digital converter 2068 is the first frequency. I The analog signal and the RF signal after 90° phase shift are sampled to obtain the orthogonal signal, which is recorded as X I q. In this way, X is obtained by sampling with two ADCs. I i signal and X I After receiving the q signal, the two signals are combined into one to obtain X I i+jX I q, so that we can get the complete X I The digital signal of the X I i signal and X I The q signal is a digital signal, so the operation of combining the two signals into one can be calculated in the frequency band calculation unit.

[0101] Setting two ADCs to sample positive and negative frequency signals respectively can double the ADC sampling bandwidth. As shown in Figure 16b, the original bandwidth is ω when sampling only the positive frequency. When setting two ADCs to sample both positive and negative frequencies, the sampling frequency range covers f1-ω to f1+ω, and the bandwidth is 2ω. The sampling bandwidth is doubled, which can improve the accuracy of the system.

[0102] The above is based on X I The coherent receiver 205 outputs four polarization signals X I 、X Q 、Y Iand Y Q Therefore, the RF analog-to-digital conversion unit 206 needs to sample and convert the above four signals. Referring to Figure 17, it is equivalent to setting up four RF analog-to-digital converters 206_A, 206_B, 206_C and 206_D. This embodiment of the present application will not be described in detail.

[0103] The RF analog-to-digital conversion unit 206 converts X I 、X Q 、Y I and Y Q The four analog signals are converted into digital signals, and the four digital signals are output to the frequency band calculation unit 207. The frequency band calculation unit 207 performs frequency band calculation based on the four digital signals to obtain a spectrum. The spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency. The frequency band calculation unit 207 is used to determine whether the frequency range of the first detection signal and the frequency range of the second detection signal meet expectations.

[0104] For example, the frequency band calculation unit 207 calculates the orthogonal X I Road signal and X Q The signal is transformed into a Fourier transform in the complex plane, modulo and squared, which is recorded as |f(X I +jX Q )| 2 , for the orthogonal Y I Road signal and Y Q The signal is transformed into a Fourier transform in the complex plane, and then squared after taking the modulus, which is recorded as |f(Y I +jY Q )| 2 , and then sum the two to get the spectrum: |f(X I +jX Q )| 2 +|f(Y I +jY Q )| 2

[0105] In the above formula, f(x) represents the Fourier transform of x. I +jX Q After Fourier transform, the amplitude value of each frequency component can be obtained, and the power of each frequency component can be obtained by taking the modulus and squaring it. The sum of the power of the first polarization state and the second polarization state of the signal light is a constant value. Therefore, here we sum the square of the modulus of the two orthogonal signals of the first polarization state after Fourier transform in the complex plane and the square of the modulus of the two orthogonal signals of the second polarization state after Fourier transform in the complex plane. In addition, since X I Signal and X Q are two orthogonal signals on the first polarization state of the signal light, Y I Signal and Y Qare two orthogonal signals on the second polarization state of the signal light, so for X I +jX Q and Y I +jY Q The frequency distributions obtained after Fourier transform are the same, the only difference is that the intensity of each frequency component may be different. Here, Fourier transform is performed on the signals of the two polarization states, and then the power is obtained by taking the square of the modulus, which is equivalent to averaging the signals of the two polarization states. This averaging can overcome the interference between the polarization states, make the signal more stable, and improve the accuracy of the system.

[0106] The frequency band calculation unit 207 performs frequency band calculation based on the four digital signals to obtain a spectrum, where the spectrum includes the frequency distribution of the first detection signal at the positive frequency and the second detection signal at the negative frequency. The frequency band calculation unit 207 is used to determine whether the frequency range of the first detection signal and the frequency range of the second detection signal match a preset frequency range. For example, taking the first detection signal as a φOTDR signal and the second detection signal as a BOTDR signal as an example, the frequency bandwidth of the first frequency range of the φOTDR signal is approximately ±10 MHz, and the frequency bandwidth of the second frequency range of the BOTDR signal is approximately ±150 MHz. The frequency band calculation unit 207 determines whether the frequency range of the φOTDR signal matches the first frequency range, that is, determines whether the frequency range of the φOTDR signal matches the first frequency range. Whether the frequency range of the DR signal is within the first frequency range; the frequency band calculation unit 207 determines whether the frequency range of the BOTDR signal matches the second frequency range, that is, determines whether the frequency range of the BOTDR signal is within the second frequency range. If the frequency range of the first detection signal does not match the first frequency range or the frequency range of the second detection signal does not match the second frequency range, the second frequency (f2) of the first RF signal and the second RF signal generated by the first RF transmitting unit 210 can be adjusted in the signal transmitting device, or the central sampling frequency first frequency (f1) of the ADC in the RF analog-to-digital conversion unit 206 can be fine-tuned to ensure that the φOTDR signal and the BOTDR signal are both within the ADC acquisition frequency band.

[0107] Exemplarily, the signal receiving device also includes a signal quality calculation unit 208, which is used to judge the quality of the BOTDR signal and the φOTDR signal. In one possible implementation, the signal quality can be judged by some indicators such as the fitting accuracy of the BOTDR signal, the phase noise of the φOTDR signal, and other indicators.

[0108] Exemplarily, when the optical fiber sensing device is initialized, the first RF transmitting unit 210 can scan the second frequency (f2), that is, adjust the size of the second frequency (f2), and the signal quality calculation unit 208 is used to judge the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal under different sizes of the second frequency, and then the first RF transmitting unit 210 adjusts the second frequency according to the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal until the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal meet the requirements, and the frequency at this time is used as the target frequency. In the subsequent operation of the optical fiber sensing device, the first RF transmitting unit 210 of the signal transmitting device transmits the first RF signal and the second RF signal of the target frequency to improve the signal quality obtained by the signal receiving device.

[0109] For example, Figure 18 shows the relationship between frequency f2, obtained by sweeping frequency f2, and the BOTDR and φOTDR signal qualities. For example, Indicator 1 represents the BOTDR signal fitting accuracy, and Indicator 2 represents the OTDR signal phase noise. An f2 range can be selected based on the threshold value of Indicator 1, and an f2 range can be selected based on the threshold value of Indicator 2. The intersection of these two ranges is the selectable operating range. When f2 is set to a frequency within this operating range, both Indicators 1 and 2 meet the requirements.

[0110] In some other possible implementations, the width or period of the light pulse can be adjusted accordingly in the same way. After determining the optimal parameters, the optical fiber sensing device can operate based on the above parameters and realize simultaneous detection of vibration, temperature, and stress under the optimal state.

[0111] In some possible implementations, the fiber under test may be composed of multiple fiber types fused together, and the stress on the fiber may be significant, causing the BOTDR signal spectrum obtained by the signal receiving device to exceed the ADC's acquisition frequency range. In this case, multiple tests can be performed to detect the complete BOTDR signal, achieving ultra-wide-range detection.

[0112] For example, assuming the ADC's acquisition frequency range is 200 MHz, while the BOTDR signal's frequency range may exceed 300 MHz, as shown in Figure 19, when the ADC's center sampling frequency is f1 (or -f1), only the φOTDR signal and a portion of the BOTDR signal can be acquired, but the complete BOTDR signal cannot be captured. Therefore, by adjusting the ADC's center sampling frequency and performing multiple sampling, the BOTDR signals can be spliced ​​together to form a complete BOTDR signal. For example, if the ADC's center sampling frequency is adjusted from f1 (-f1) to f1' (or -f1'), the two adjustments of the ADC's center sampling frequency should ensure that the ADC's acquisition frequency ranges overlap before and after the adjustments. This allows for the acquisition of a portion of the same signal during the two samplings. Using the common portion of the BOTDR signal from the two samplings as an anchor point, the two BOTDR signals can be spliced ​​together to form a complete BOTDR signal, enabling detection over a very wide range.

[0113] The frequency band calculation unit 207, signal quality calculation unit 208, etc. can be implemented by hardware circuits, such as integrated circuits for implementing the above functions, or the frequency band calculation unit 207, signal quality calculation unit 208, etc. can be integrated into a computer and implement the above functions through software algorithms.

[0114] In the above example, the signal transmitting device adjusts the first and second RF signals to a polarization state of the probe light to form a probe light pulse signal. Using only a single pulse for multi-parameter detection significantly limits the flexibility of the frequency band control of the scattered signal, which is strongly correlated with the Brillouin scattering frequency of the optical fiber. The optical fiber sensing device as a whole may operate in a frequency band with a poor signal-to-noise ratio, affecting the system's measurement accuracy. On this basis, the present embodiment also provides another implementation method, using multiple pulses for multi-parameter detection.

[0115] For example, FIG20 shows a schematic diagram of another fiber optic sensing device provided in an embodiment of the present application, including a signal transmitting device and a signal receiving device. The signal transmitting device includes a laser 301, a coupler 302, a first RF transmitting unit 310, a second RF transmitting unit 320, a dual-bias quadrature modulator 303, and a fiber circulator 304. The signal receiving device includes a coherent receiver 305, a RF analog-to-digital conversion unit 306, a frequency band calculation unit 307, and a signal quality calculation unit 308. Compared with the fiber optic sensing device shown in FIG6, the signal transmitting device of the fiber optic sensing device shown in FIG20 also includes a second RF transmitting unit 320. The remaining structure is basically the same as the fiber optic sensing device shown in FIG6, and the embodiment of the present application only provides a brief description. The second RF transmitting unit 320 is used to generate a third RF signal and a fourth RF signal with a third frequency (f3) and orthogonal to each other. In the embodiment of the present application, the detection light output by the orthogonal modulator may include a first polarization state and a second polarization state. The first RF signal and the second RF signal may be modulated to the first polarization state of the detection light, and the third RF signal and the fourth RF signal may be modulated to the second polarization state of the detection light. The first polarization state and the second polarization state here are two orthogonal polarization states. Therefore, the orthogonal modulator in the embodiment of the present application is a dual-polarization orthogonal modulator 303.

[0116] Exemplarily, the second RF transmitting unit 320 includes a second baseband RF unit 321, a second pulse generating unit 322, and a second up-converting unit 323. The second baseband RF unit 321 is used to generate two orthogonal baseband FM signals, such as an orthogonal third baseband FM signal and a fourth baseband FM signal, wherein the third baseband FM signal can be expressed as y i , the fourth baseband FM signal can be expressed as y q . For example, y i =cos(2πΔf3t),y q =sin(2πΔf3t).

[0117] The second baseband RF unit 321 transmits the generated third baseband FM signal and fourth baseband FM signal to the second pulse generating unit 322. The second pulse generating unit 322 generates a third baseband pulse FM signal with a pulse width of τ according to the third baseband FM signal. The second pulse generating unit 322 generates a fourth baseband pulse FM signal with a pulse width of τ according to the fourth baseband FM signal. The third baseband pulse FM signal can be expressed as y pi , the fourth baseband pulse frequency modulation signal can be expressed as y pq For example,

[0118] The second up-conversion unit 323 is used to generate an orthogonal third radio frequency signal and a fourth radio frequency signal according to the third baseband pulse frequency modulation signal and the fourth baseband pulse frequency modulation signal, wherein the third radio frequency signal can be expressed as s yi , the fourth RF signal can be expressed as s yq , exemplary, s yi =y pi cos(2πf IF3 t)-y pq sin(2πf IF3 t), s yq =y pi sin(2πf IF3 t)+y pq cos(2πf IF3 t). The frequencies of the third RF signal and the fourth RF signal are f3, f3=f IF3 +Δf3. By adjusting Δf3 and f IF3 , the frequency f3 of the third RF signal and the fourth RF signal can be adjusted. In a possible implementation, if the frequency of the baseband signal generated by the second baseband RF unit 321 is not adjustable, then Δf3 in the above example can be zero.

[0119] As shown in FIG21 , the dual-bias quadrature modulator 303 can modulate the orthogonal first and second RF signals onto the probe light of the first polarization state, and modulate the orthogonal third and fourth RF signals onto the probe light of the second polarization state to form a probe light pulse signal. Therefore, the embodiment of the present application uses a dual-bias quadrature modulator for modulation. The pulse period of the probe light pulse is T, and the pulse width is τ. In one possible implementation, the pulse period T can range from 0 to 2000 microseconds, and the pulse width τ can be less than 1000 nanoseconds, for example, τ can be 100 nanoseconds. The time delay between the signal emitted by the first RF transmitting unit 310 and the signal emitted by the second RF transmitting unit 320 is t12, that is, the time delay between the pulse in the first polarization state and the pulse in the second polarization state is t12, t12 < T, for example, T can be 500 microseconds, and t12 is 499 microseconds.

[0120] For ease of explanation, the pulse formed by modulating the first and second RF signals with a frequency of f2 onto the probe light of the first polarization state is denoted as p1, and the pulse formed by modulating the third and fourth RF signals with a frequency of f3 onto the probe light of the second polarization state is denoted as p2. Since both p1 and p2 generate backscattered light, the signals received by the coherent receiver 305 include the φOTDR signal and BOTDR signal generated by the p1 pulse, as well as the φOTDR signal and BOTDR signal generated by the p2 pulse. To improve signal quality, the φOTDR signal and BOTDR signal can be sampled in different polarization states. For example, the φOTDR signal generated by the p1 pulse in the first polarization state can be sampled, and the BOTDR signal generated by the p2 pulse in the second polarization state can be sampled. This can improve the linearity of the system. Since the two polarization states are independent of each other, the frequencies of f2 and f3 can be flexibly adjusted to improve system performance.

[0121] For example, in the optical fiber sensing device shown in FIG6 , φOTDR signals and BOTDR signals are generated only by single-polarization pulses. The frequency difference between the φOTDR signal and the BOTDR signal is the Brillouin frequency shift vB, which is approximately 11 GHz. If the same type of ADC is used to sample the BOTDR signal at a negative frequency and the φOTDR signal at a positive frequency, the center sampling frequency of the ADC needs to be around 5.5 GHz. If the performance of the ADC near 5.5 GHz is poor, resulting in poor signal quality, the overall detection performance of the optical fiber sensing device will also be affected.

[0122] However, in the solution provided in the embodiment of the present application, the φOTDR signal generated by the p1 pulse is sampled, and the BOTDR signal generated by the p2 pulse is sampled. For example, the frequency of the φOTDR signal generated by the p1 pulse is f2, and the frequency of the BOTDR signal generated by the p2 pulse is approximately f3-vB. By adjusting f2 and f3, the ADC can sample the φOTDR signal and the BOTDR signal at any center sampling frequency (i.e., the first frequency f1). Referring to FIG. 22 , the X output by the coherent receiver 305 is I 、X Q 、Y I and Y Q The four signals are converted into digital signals by the radio frequency analog-to-digital conversion unit 306 and then the frequency band calculation unit 307 performs frequency band calculation to restore the spectrum.

[0123] Exemplarily, the frequency band calculation unit 307 performs frequency band calculation based on the four digital signals to obtain a spectrum, where the spectrum includes the frequency distribution of the first detection signal at the positive frequency and the second detection signal at the negative frequency. The frequency band calculation unit 307 is also used to determine whether the frequency range of the first detection signal and the frequency range of the second detection signal meet expectations.

[0124] For example, assuming the first detection signal is a φOTDR signal and the second detection signal is a BOTDR signal, the frequency band calculation unit 307 can calculate the frequency bands to obtain a φOTDR signal with a frequency of f2 and a BOTDR signal with a frequency of approximately f3-vB. However, the φOTDR signal generated by pulse p2 (i.e., the φOTDR signal with a frequency of f3) may be outside the ADC's acquisition frequency band and will not be sampled. The frequency width of the φOTDR signal is approximately ±10 MHz, and the frequency width of the BOTDR signal is approximately ±150 MHz. The frequency band calculation unit 307 determines whether the frequency range of the φOTDR signal is within the ±10 MHz range, and whether the frequency range of the BOTDR signal is within the ±150 MHz range. If not, the frequency band calculation unit 307 can adjust the second frequency (f2) of the first and second RF signals generated by the first RF transmitting unit 310, and the third frequency (f3) of the third and fourth RF signals generated by the second RF transmitting unit 320. Alternatively, the center sampling frequency f1 of the ADC in the RF analog-to-digital converter can be fine-tuned to ensure that both the φOTDR signal and the BOTDR signal are within the ADC's acquisition frequency band.

[0125] In the embodiment of the present application, the RF analog-to-digital converter samples the φOTDR signal generated by the p1 pulse of the first polarization state and the BOTDR signal generated by the p2 pulse of the second polarization state, and samples the φOTDR signal and the BOTDR signal in different polarization states, which can improve the linearity of the system. Moreover, since the two polarization states are independent of each other, the second frequency and the third frequency can be flexibly adjusted to change the frequency distribution of the φOTDR signal and the BOTDR signal. For example, in the aforementioned example, the φOTDR signal and the BOTDR signal are generated by the same (polarization state) detection light pulse. In order to be able to use the same type of ADC to sample the BOTDR signal at a negative frequency and the φOTDR signal at a positive frequency, due to the frequency difference between the φOTDR signal and the BOTDR signal The Brillouin frequency shift vB requires that the center sampling frequency of the ADC be set near vB / 2. In the embodiment of the present application, the φOTDR signal generated by the p1 pulse is sampled, and the BOTDR signal generated by the p2 pulse is sampled. For example, the φOTDR signal generated by the p1 pulse is f2, and the BOTDR signal frequency generated by the p2 pulse is approximately f3-vB. The frequency difference between the φOTDR signal and the BOTDR signal is f2-f3+vB. Therefore, by adjusting the second frequency and the third frequency, the limitation of the center sampling frequency f1 of the ADC in the RF analog-to-digital converter (for example, in the aforementioned embodiment, it is limited to around 5.5GHz by f1) can be cancelled. The center sampling frequency f1 of the ADC can also be adjusted as needed, which can improve the performance of the system. For example, if the sampling performance of the ADC near 5.5GHz is poor, the ADC can be operated at a center sampling frequency of around 10GHz, and then by adjusting f2 and f3, the φOTDR signal and the BOTDR signal are both within the acquisition frequency band of the ADC.

[0126] In some possible implementations, to ensure that the first detection signal can be sampled at a positive frequency and the second detection signal can be sampled at a negative frequency, the frequency f2 of the first and second RF signals can range from vB to 0, and the frequency f3 of the third and fourth RF signals can range from 0 to vB. For example, f2 can be 4.7 GHz and f3 can be 6.0 GHz. However, to enable sampling of the φOTDR signal and the BOTDR signal using the same type of ADC, the absolute values ​​of the frequencies of the φOTDR signal and the BOTDR signal must be similar, but not identical.

[0127] Exemplarily, the optical fiber sensing device also includes a signal quality calculation unit 308, which is used to judge the quality of the BOTDR signal and the φOTDR signal. In one possible implementation, the signal quality can be judged by some indicators. For example, the above indicators may include the fitting accuracy of the BOTDR signal, the phase noise of the φOTDR signal, etc.

[0128] Exemplarily, when the optical fiber sensing device is initialized, the second RF transmitting unit 320 can scan the frequency f3 and the time delay t12, and the signal quality calculation unit 308 is used to judge the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal under different sizes of the third frequency (f3) and the time delay t12. In this way, the second RF transmitting unit 320 can select a suitable third frequency (f3) and time delay t12 according to the fitting accuracy of the BOTDR signal and the phase noise of the φOTDR signal. During the subsequent operation of the optical fiber sensing device, the third frequency (f3) and time delay t12 of the RF signal emitted by the second RF transmitting unit 320 are adjusted to improve the signal quality.

[0129] For example, FIG23 shows a schematic diagram of the relationship between f3 or t12, obtained by sweeping f3 and t12 by the second RF transmitting unit 320, and the quality of the BOTDR signal and the φOTDR signal. For example, indicator 1 represents the fitting accuracy of the BOTDR signal, and indicator 2 represents the phase noise of the OTDR signal. A range of f3 or t12 can be selected based on the threshold value of indicator 1, and a range of f3 and t12 can be selected based on the threshold value of indicator 2. The intersection of these two ranges is the optional operating range. When f3 or t12 is set within this operating range, both indicators 1 and 2 meet the requirements, improving the quality of the BOTDR signal and the φOTDR signal. The optical fiber sensing device can achieve simultaneous vibration, temperature, and stress detection under optimal conditions.

[0130] In the above example, a dual-polarization quadrature modulator is used to modulate the orthogonal first RF signal and the second RF signal onto the detection light of the first polarization state, and the third RF signal and the fourth RF signal are modulated onto the detection light of the second polarization state for detection. In some other possible implementations, different RF pulses can also be modulated onto the detection light of the same polarization state.

[0131] For example, referring to FIG24 , an embodiment of the present application provides another optical fiber sensing device, including a signal transmitting device and a signal receiving device. The signal transmitting device includes a laser 401, a coupler 402, a first RF transmitting unit 410, a second RF transmitting unit 420, an orthogonal modulator 403, a signal synthesizer 409, and an optical fiber circulator 404. The signal receiving device includes a coherent receiver 405, an RF analog-to-digital conversion unit 406, a frequency band calculation unit 407, and a signal quality calculation unit 408. Compared with the optical fiber sensing device shown in FIG20 , the signal transmitting device of the optical fiber sensing device provided in the embodiment of the present application does not need to use a dual-bias orthogonal modulator for modulation, but instead uses an orthogonal modulator for modulation. However, a signal synthesizer 409 is added. The signal synthesizer 409 can combine the two orthogonal signals generated by the first RF transmitting unit and the two orthogonal signals generated by the second RF transmitting unit. The combined RF signal is then modulated onto the detection light of the same polarization state using the orthogonal modulator 403, thereby achieving a similar effect of modulation to dual polarization states.

[0132] The optical fiber sensing device provided in the embodiment of the present application uses a coherent receiver to receive signal light including a φOTDR signal and a BOTDR signal. The coherent receiver obtains two analog electrical signals (X and B) of the first polarization state of the signal light according to the local oscillator light and the signal light. I and X Q ) and two analog electrical signals of the second polarization state of the signal light (Y I and Y Q ), the RF analog-to-digital converter performs down-conversion and analog-to-digital conversion to output two digital electrical signals (X I 、X Q ) and two digital signals (Y I 、Y Q), where each polarization state includes an in-phase (I) signal and a quadrature (Q) signal, and a spectrum obtained by performing Fourier transform on the complex plane of the I signal and the Q signal of each polarization state and then squaring the spectrum after modulo taking includes a first detection signal at a positive frequency and a second detection signal at a negative frequency, for example, the first detection signal is a φOTDR signal and the second detection signal is a BOTDR signal, or the first detection signal is a BOTDR signal and the second detection signal is a φOTDR signal, on this basis, by adjusting the second frequency (f2) of the first radio frequency signal and the second radio frequency signal in the signal transmitting device, or adjusting the third The third frequency (f3) of the radio frequency signal and the fourth radio frequency signal makes the frequency distribution of the first detection signal and the second detection signal near the center sampling frequency of the ADC (i.e., the first frequency (f1)). The first detection signal and the second detection signal can be sampled at the negative frequency and the positive frequency respectively through the same type of ADC. In this way, a set of transceiver devices can be used to receive BOTDR signals and φOTDR signals to realize multiple parameter monitoring such as vibration, temperature and strain. On the other hand, by using the same type of ADC to sample the first detection signal at the positive frequency and the second detection signal at the negative frequency respectively, the coverage frequency range requirements for the coherent receiver, ADC, etc. of the signal receiving device can be reduced.

[0133] This fiber optic sensing device can be applied in a wide range of scenarios, including buried fiber optic intrusion alarms, underground well monitoring, bridge health monitoring, urban pipeline corridor monitoring, oil and gas leak detection, and cable icing detection. In these scenarios, the simultaneous detection of multiple parameters such as vibration, temperature, and stress can effectively improve the fiber optic sensing system's applicability, detection accuracy, and positioning precision.

[0134] For example, in buried pipeline intrusion alarm scenarios, the location accuracy of intrusion alarms can be biased due to temperature differences of over 30 degrees Celsius across the pipeline's location. This device can simultaneously detect vibration and temperature to compensate for positioning errors caused by temperature differences. In oil and gas leak and pipeline corridor monitoring scenarios, the leakage of liquefied gas or gas transport can cause temperature fluctuations near the leak point, simultaneously introducing acoustic parameters such as orifice noise and negative pressure waves. Simultaneous temperature and vibration detection can effectively improve the sensitivity of pipeline leak detection. In bridge health monitoring and cable icing monitoring, static stress on bridges and cables can be measured to determine their health. Low-frequency vibration detection can also be used to detect wind dance and bridge resonance. In underground exploration scenarios, distributed detection of underground vibration waves generated by active excitation sources can extract compositional and structural information at different depths. Temperature detection can also provide formation temperature profiles, providing guidance for underground mining operations.

[0135] In conjunction with FIG25 , FIG25 shows a workflow diagram of a signal processing method for an application and optical fiber sensing device provided in an embodiment of the present application, including:

[0136] S601: The laser emits an optical signal.

[0137] S602 , the coupler couples the optical signal emitted by the laser into two paths, one of which is transmitted to the orthogonal modulator as detection light, and the other is transmitted to the coherent receiver as local oscillator light.

[0138] S603: The first RF transmitting unit generates a first RF signal and a second RF signal that have a second frequency and are orthogonal to each other.

[0139] S604 , the orthogonal modulator modulates the orthogonal first radio frequency signal and the second radio frequency signal onto the detection light of the first polarization state to obtain a detection light pulse signal.

[0140] S605 , the optical fiber circulator inputs the detection light pulse signal into the optical fiber under test, and outputs the signal light generated in the optical fiber under test to a coherent receiver.

[0141] S606: The coherent receiver obtains four electrical signals according to the local oscillator light and the signal light, where the four electrical signals include two orthogonal electrical signals in the first polarization state of the signal light and two orthogonal electrical signals in the second polarization state of the signal light.

[0142] S607 , the radio frequency analog-to-digital conversion unit converts the four orthogonal electrical signals to obtain two digital signals of the first polarization state of the signal light and two digital signals of the second polarization state of the signal light.

[0143] S608, the frequency band calculation unit calculates the spectrum of the signal light according to the two digital signals of the first polarization state of the signal light and the two digital signals of the second polarization state of the signal light, wherein the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency.

[0144] In a possible implementation, with reference to FIG. 15 a, S607 includes:

[0145] A digitally controlled oscillator generates a radio frequency signal of a first frequency, a first mixer mixes the electrical signal output by the coherent receiver with the radio frequency signal of the first frequency, a first filter filters out high-frequency components in the mixed signal to convert the electrical signal to a baseband, and a first analog-to-digital converter converts the electrical signal converted to the baseband into a digital signal, wherein the first frequency is the center sampling frequency of the first analog-to-digital converter.

[0146] In another possible implementation, with reference to FIG. 15 b, S607 includes:

[0147] A digitally controlled oscillator generates a radio frequency signal at a first frequency. A first mixer mixes the electrical signal output by the coherent receiver with the radio frequency signal at the first frequency. A first filter filters out high-frequency components from the mixed signal to convert the electrical signal to baseband. A first analog-to-digital converter converts the converted baseband electrical signal into an in-phase digital signal. A 90° phase shifter shifts the phase of the radio frequency signal at the first frequency by 90°. A second mixer mixes the phase-shifted radio frequency signal with the electrical signal output by the coherent receiver. A second filter filters out high-frequency components from the mixed signal to convert the electrical signal to baseband. A second analog-to-digital converter converts the converted baseband electrical signal into a quadrature digital signal.

[0148] In some possible implementations, in order to ensure that the frequency distribution of the first detection signal and the frequency distribution of the second signal obtained by the signal receiving device are within the sampling range of the ADC, the method further includes:

[0149] S609A, when the frequency range of the first detection signal does not match the first frequency range, or when the frequency range of the second detection signal does not match the second frequency range, the first RF transmitting unit is used to adjust the second frequency, and / or the RF analog-to-digital converter is used to adjust the first frequency.

[0150] S609B: When the absolute value of the frequency range of the first detection signal intersects the absolute value of the frequency range of the second detection signal, the first RF transmitting unit adjusts the second frequency.

[0151] In some possible implementations, the signal transmitting device further includes a second RF transmitting unit, which can transmit a third RF signal and a fourth RF signal having a third frequency and being orthogonal to each other. The orthogonal modulator can adjust the third RF signal and the fourth RF signal to the second polarization state of the probe light. In this case, to adjust the quality of the signal received by the signal receiving device, the method further includes:

[0152] S609C: The second RF transmitting unit adjusts the third frequency and the time delay between the signal transmitted by the second RF transmitting unit and the signal transmitted by the first RF transmitting unit according to the fitting accuracy of the BOTDR signal and / or the phase noise of the φOTDR signal.

[0153] It should be noted that S609A, S609B, and S609C can be executed simultaneously, or only part of them can be executed, and can be adjusted according to the actual needs of the optical fiber sensing device operation project.

[0154] In the above example, the frequency band calculation unit, the signal quality calculation unit, etc. can be implemented by a hardware circuit, such as an integrated circuit for implementing the above functions, or the frequency band calculation unit, the signal quality calculation unit, etc. can also be integrated into a calculator, and the above functions can be implemented by a software algorithm. The above-mentioned first RF signal transmitting unit, the second RF signal transmitting unit, etc. can be implemented by a signal generator or other structure.

[0155] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

Claims

1. A signal receiving device, characterized in that, The signal receiving device includes a coherent receiver, a radio frequency analog-to-digital conversion unit, and a frequency band calculation unit; The coherent receiver is configured to obtain four electrical signals based on the local oscillator light and the signal light generated in the optical fiber under test. The four electrical signals include two quadrature electrical signals in the first polarization state and two quadrature electrical signals in the second polarization state; The radio frequency analog-to-digital conversion unit is configured to convert the four electrical signals to obtain two digital signals in the first polarization state and two digital signals in the second polarization state; The frequency band calculation unit is configured to calculate the spectrum of the signal light according to the two digital signals in the first polarization state and the two digital signals in the second polarization state. The spectrum includes a first detection signal located in the positive frequency and a second detection signal located in the negative frequency.

2. The signal receiving device according to claim 1, wherein The coherent receiver includes four output terminals. The radio frequency analog-to-digital conversion unit includes four radio frequency analog-to-digital converters. The four radio frequency analog-to-digital converters are respectively and correspondingly connected to the four output terminals of the coherent receiver; The radio frequency analog-to-digital converter includes a digital control oscillator, a first mixer, a first filter, and a first analog-to-digital converter; The output terminal of the digital control oscillator is connected to the first input terminal of the first mixer. The second input terminal of the first mixer is connected to the output terminal of the coherent receiver; the output terminal of the first mixer is connected to the input terminal of the first filter. The output terminal of the first filter is connected to the input terminal of the first analog-to-digital converter. The output terminal of the first analog-to-digital converter is connected to the frequency band calculation unit; The digital control oscillator is configured to generate a radio frequency signal with a first frequency. The first mixer is configured to mix one of the electrical signals output by the coherent receiver with the radio frequency signal. The first filter is configured to filter out the high-frequency components in the mixed signal to convert the electrical signal to the baseband; the first analog-to-digital converter is configured to convert the electrical signal converted to the baseband into a digital signal. Wherein, the center sampling frequency of the first analog-to-digital converter is the first frequency.

3. The signal receiving device according to claim 2, wherein The radio frequency analog-to-digital converter further includes a 90° phase shifter, a second mixer, a second filter, and a second analog-to-digital converter; The output terminal of the digital control oscillator is further connected to the input terminal of the 90° phase shifter. The output terminal of the 90° phase shifter is connected to the first input terminal of the second mixer. The second input terminal of the second mixer is connected to the output terminal of the coherent receiver. The output terminal of the second mixer is connected to the input terminal of the second filter. The output terminal of the second filter is connected to the input terminal of the second analog-to-digital converter. The output terminal of the second analog-to-digital converter is connected to the frequency band calculation unit; The digital controlled oscillator is used to generate a radio frequency signal of a first frequency. The 90° phase shifter is used to shift the phase of the radio frequency signal by 90°. The mixer is used to mix an electrical signal output by the coherent receiver with the phase-shifted radio frequency signal. The second filter is used to filter out high-frequency components in the mixed signal to convert the electrical signal to the baseband. The second analog-to-digital converter is used to convert the electrical signal converted to the baseband into a digital signal, where the center sampling frequency of the second analog-to-digital converter is the first frequency.

4. The signal receiving device according to any one of claims 1 to 3, characterized in that, Wherein the first detection signal is a phase-sensitive optical time domain reflectometer signal, and the second detection signal is a Brillouin optical time domain reflectometer BOTDR signal.

5. The signal receiving device according to any one of claims 1 to 4, characterized in that The first detection signal and the second detection signal are detection signals generated by scattering of the same detection optical pulse, or the first detection signal and the second detection signal are detection signals generated by different detection optical pulses.

6. The signal receiving device according to claim 4, wherein The signal receiving device further includes a signal quality calculation unit, and the signal quality calculation unit is used to determine the fitting accuracy of the BOTDR signal and the phase noise of the signal.

7. A signal transmitting device, characterized in that, The signal transmitting device includes a laser, a coupler, a first radio frequency transmitting unit, a quadrature modulator, and an optical fiber circulator. The laser is used to emit an optical signal. The optical signal emitted by the laser is coupled into two paths by the coupler. One path is transmitted to the quadrature modulator as the detection optical signal, and the other path is transmitted to the coherent receiver as the local oscillator optical signal. The first radio frequency transmitting unit is used to generate a first radio frequency signal and a second radio frequency signal with a second frequency and orthogonal phases. The quadrature modulator is used to modulate the first radio frequency signal and the second radio frequency signal with orthogonal phases onto the detection optical signal in the first polarization state to obtain a detection optical pulse signal. The optical fiber circulator is used to connect the fiber under test. The optical fiber circulator is used to input the detection optical pulse signal into the fiber under test, and the optical fiber circulator is also used to output the signal optical signal generated in the fiber under test.

8. The signal transmitting device according to claim 7, wherein, The signal transmitting device further includes a second transmitting unit. The second radio frequency transmitting unit is used to generate a third radio frequency signal and a fourth radio frequency signal with a third frequency and orthogonal phases. The quadrature modulator is further used to modulate the third radio frequency signal and the fourth radio frequency signal with orthogonal phases onto the detection optical signal in the second polarization state.

9. The signal transmitting device according to claim 7 or 8, characterized in that, The first radio frequency transmitting unit is further used to adjust the magnitude of the second frequency.

10. The signal transmitting device according to claim 8, wherein The second radio frequency transmitting unit is further used to adjust the magnitude of the third frequency, and the time delay between the signal generated by the second radio frequency transmitting unit and the signal generated by the first radio frequency transmitting unit.

11. An optical fiber sensing device, characterized in that, The fiber optic sensing device includes: a laser, a coupler, a first radio frequency transmitting unit, a quadrature modulator, an optical fiber circulator, a coherent receiver, a frequency band calculation unit, and a radio frequency analog-to-digital conversion unit. The optical signal emitted by the laser is coupled into two paths by the coupler. One path is transmitted to the quadrature modulator as the detection optical signal, and the other path is transmitted to the coherent receiver as the local oscillator optical signal. The first radio frequency transmitting unit is used to generate a first radio frequency signal and a second radio frequency signal with a second frequency and orthogonal phases. The quadrature modulator is used to modulate the first radio frequency signal and the second radio frequency signal with orthogonal phases onto the detection optical signal in the first polarization state to obtain a detection optical pulse signal. The optical fiber circulator is used to connect the optical fiber under test, and is used to input the detection optical pulse signal into the optical fiber under test. The optical fiber circulator is also used to output the signal light generated in the optical fiber under test to the coherent receiver; The coherent receiver is used to obtain four electrical signals based on the local oscillator light and the signal light generated in the optical fiber under test. The four electrical signals include two quadrature electrical signals in the first polarization state and two quadrature electrical signals in the second polarization state; The radio frequency analog-to-digital conversion unit is used to convert the four electrical signals to obtain two digital signals in the first polarization state and two digital signals in the second polarization state; The frequency band calculation unit is used to calculate the spectrum of the signal light according to the two digital signals in the first polarization state and the two digital signals in the second polarization state. The spectrum includes a first detection signal at positive frequency and a second detection signal at negative frequency.

12. The optical fiber sensing device according to claim 11, characterized in that, The coherent receiver includes four output terminals. The radio frequency analog-to-digital conversion unit includes four radio frequency analog-to-digital converters. The four radio frequency analog-to-digital converters are respectively and correspondingly connected to the four output terminals of the coherent receiver; The radio frequency analog-to-digital converter includes a digital control oscillator, a first mixer, a first filter, and a first analog-to-digital converter; The output terminal of the digital control oscillator is connected to the first input terminal of the first mixer. The second input terminal of the first mixer is connected to the output terminal of the coherent receiver; The output terminal of the first mixer is connected to the input terminal of the first filter. The output terminal of the first filter is connected to the input terminal of the first analog-to-digital converter. The output terminal of the first analog-to-digital converter is connected to the frequency band calculation unit; The digital control oscillator is used to generate a radio frequency signal with a first frequency. The first mixer is used to mix a path of electrical signal output by the coherent receiver with the radio frequency signal; The first filter is used to filter out the high-frequency components in the mixed signal to convert the electrical signal to the baseband; The first analog-to-digital converter is used to convert the electrical signal converted to the baseband into a digital signal, where the center sampling frequency of the first analog-to-digital converter is the first frequency.

13. The optical fiber sensing device according to claim 11 or 12, characterized in that, The radio frequency analog-to-digital converter further includes a 90° phase shifter, a second filter, and a second analog-to-digital converter; The output terminal of the digital control oscillator is further connected to the input terminal of the 90° phase shifter. The output terminal of the 90° phase shifter is connected to the first input terminal of the second mixer. The second input terminal of the second mixer is connected to the output terminal of the coherent receiver. The output terminal of the second mixer is connected to the input terminal of the second filter. The output terminal of the second filter is connected to the input terminal of the second analog-to-digital converter. The output terminal of the second analog-to-digital converter is connected to the frequency band calculation unit; The digital controlled oscillator is used to generate a radio frequency signal with a first frequency. The 90° phase shifter is used to shift the phase of the radio frequency signal by 90°. The mixer is used to mix one path of the electrical signal output by the coherent receiver with the phase-shifted radio frequency signal. The second filter is used to filter out the high-frequency components in the mixed signal to convert the electrical signal to the baseband. The second analog-to-digital converter is used to convert the electrical signal converted to the baseband into a digital signal, where the center sampling frequency of the second analog-to-digital converter is the first frequency.

14. The optical fiber sensing device according to any one of claims 11 to 13, characterized in that, The first detection signal is a phase-sensitive optical time domain reflectometer signal, and the second detection signal is a Brillouin optical time domain reflectometer BOTDR signal.

15. The optical fiber sensing device according to any one of claims 11 to 14, characterized in that, The first detection signal and the second detection signal are detection signals generated by the pulse scattering of the first polarization state of the probe light.

16. The optical fiber sensing device according to any one of claims 11 to 14, characterized in that, The signal transmitting device further includes a second transmitting unit. The second radio frequency transmitting unit is used to generate a third radio frequency signal and a fourth radio frequency signal with a third frequency and orthogonal phases. The quadrature modulator is further used to modulate the third radio frequency signal and the fourth radio frequency signal with orthogonal phases onto the probe light of the second polarization state. The frequency band calculation unit is used to calculate the spectrum of the signal light according to the two paths of digital signals of the first polarization state and the two paths of digital signals of the second polarization state. The spectrum includes a first detection signal located in the positive frequency and a second detection signal located in the negative frequency. Among them, the first detection signal is a detection signal generated by the pulse scattering of the first polarization state of the probe light, and the second detection signal is a detection signal generated by the pulse scattering of the second polarization state of the probe light.

17. The optical fiber sensing device according to any one of claims 11 to 16, characterized in that, In the case where the frequency range of the first detection signal does not match the first frequency range, or the frequency range of the second detection signal does not match the second frequency range, the first radio frequency transmitting unit is used to adjust the second frequency, and / or the radio frequency analog-to-digital converter is used to adjust the first frequency.

18. The optical fiber sensing device according to any one of claims 11 to 16, characterized in that, The first radio frequency transmitting unit is further used to adjust the second frequency in the case where there is an intersection between the absolute value of the frequency range of the first detection signal and the absolute value of the frequency range of the second detection signal.

19. The optical fiber sensing device according to any one of claims 16 to 18, characterized in that, The first detection signal is a phase-sensitive optical time domain reflectometer signal, the second detection signal is a Brillouin optical time domain reflectometer BOTDR signal, and the fiber optic sensing device further includes a signal quality calculation unit, and the signal quality calculation unit is used to determine the fitting accuracy of the BOTDR signal and the phase noise of the signal.

20. The fiber optic sensing device according to claim 19, characterized in that, The second radio frequency transmitting unit is further configured to adjust the magnitude of the third frequency according to the fitting accuracy of the BOTDR signal and / or the phase noise of the signal, and the time delay between the signal transmitted by the second radio frequency transmitting unit and the signal transmitted by the first radio frequency transmitting unit.

21. A signal processing method, characterized in that The method is applied to the fiber optic sensing device according to any one of claims 11 to 20. The method includes: The laser emits an optical signal. The coupler couples the optical signal emitted by the laser into two paths, one of which is transmitted to the quadrature modulator as the probe light, and the other is transmitted to the coherent receiver as the local oscillator light. The first radio frequency transmitting unit generates a first radio frequency signal and a second radio frequency signal with a second frequency and orthogonal phases. The quadrature modulator modulates the first radio frequency signal and the second radio frequency signal with orthogonal phases onto the probe light of the first polarization state to obtain a probe light pulse signal. The fiber optic circulator inputs the probe light pulse signal into the fiber under test, and outputs the signal light generated in the fiber under test to the coherent receiver. The coherent receiver obtains four paths of electrical signals according to the local oscillator light and the signal light. The four paths of electrical signals include two paths of electrical signals with orthogonal phases of the first polarization state and two paths of electrical signals with orthogonal phases of the second polarization state. The radio frequency analog-to-digital conversion unit converts the four-way electrical signals to obtain two-way digital signals of the first polarization state and two-way digital signals of the second polarization state; The frequency band calculation unit calculates the spectrum of the signal light according to the two-way digital signals of the first polarization state and the two-way digital signals of the second polarization state, and the spectrum includes a first detection signal located at a positive frequency and a second detection signal located at a negative frequency.

22. The signal processing method according to claim 21, wherein The method further includes: In the case where the frequency range of the first detection signal does not match the first frequency range, or the frequency range of the second detection signal does not match the second frequency range, the first radio frequency transmitting unit adjusts the second frequency, and / or the radio frequency analog-to-digital converter is used to adjust the first frequency.

23. The signal processing method according to claim 21, wherein The method further includes: In the case where there is an intersection between the absolute value of the frequency range of the first detection signal and the absolute value of the frequency range of the second detection signal, the first radio frequency transmitting unit adjusts the second frequency.

24. The signal processing method according to claim 21, wherein The method further includes: The second radio frequency transmitting unit is based on the fitting accuracy of the BOTDR signal and / or the The phase noise of the signal adjusts the magnitude of the third frequency and the time delay between the signal transmitted by the second radio frequency transmitting unit and the signal transmitted by the first radio frequency transmitting unit.

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