Signal receiving device, transmitting device and optical fiber sensing device

Abstract

The invention provides a signal receiving device, a signal transmitting device and an optical fiber sensing device, relates to the technical field of optical fiber sensing, and is used for solving the problems that the requirement for equipment is high when an existing optical fiber sensing device detects Rayleigh scattering and Brillouin scattering at the same time and the like. The signal receiving device comprises a coherent receiver, a radio frequency analog-to-digital conversion unit and a frequency band calculation unit, the coherent receiver is used for obtaining four electric signals with orthogonal phases according to the local oscillation light and the signal light, and the radio frequency analog-to-digital conversion unit converts the four electric 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 is used for calculating the frequency spectrum of the signal light according to the two paths of digital signals of the first polarization state of the signal light and the two paths of digital signals of the second polarization state of the signal light, and the frequency spectrum comprises a phi OTDR signal located at the positive frequency and a BOTDR signal located at the negative frequency.

Description

Technical Field

[0001] 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

[0002] When the optical fiber is affected by the external environment (such as temperature, stress, vibration, etc.), the intensity, phase, frequency and other parameters of the light transmitted in the optical fiber will change accordingly. By detecting these parameters of the transmitted light, the corresponding physical quantities can be obtained. This technology is called optical fiber sensing technology. Distributed optical fiber sensing technology uses the optical fiber itself as a sensor. By measuring the intensity, phase or frequency shift of the scattered light at each point on the optical fiber, the temperature, stress, vibration and other information on the optical fiber path can be obtained to monitor these physical quantities.

[0003] The combination of phase-sensitive optical time-domain reflectometer and Brillouin optical time-domain reflectometer is a form of multi-parameter sensing. It realizes the sensing of vibration, temperature, and stress through the simultaneous detection of Rayleigh scattering and Brillouin scattering. However, when detecting both at the same time, its detection performance has high requirements on the bandwidth of the receiver. Summary of the invention

[0004] 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, so as to improve the problem that the current optical fiber sensing device has high requirements on the equipment when simultaneously detecting Rayleigh scattering and Brillouin scattering.

[0005] In a first aspect, a signal receiving device is provided, comprising 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 two electrical signals have the same frequency and a phase difference of 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, and the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency.

[0006] The signal receiving device provided in the embodiment of the present application receives the signal light by using a coherent receiver, 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 , YQ 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-channel 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. In this way, a set of transceiver can be used to simultaneously receive the BOTDR signal and Signals can be used to monitor multiple parameters such as vibration, temperature, and strain. Compared with traditional fiber optic sensing devices, the solution provided in the embodiments 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 a positive frequency, and the frequency coverage range requirement is high; the solution provided in the present application samples the first detection signal at a positive frequency and the second detection signal at a negative frequency, and the frequency coverage range requirement for the coherent receiver and ADC in the signal receiving device can be reduced by half.

[0007] In a 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 requirements on the performance of the analog-to-digital converter can be relaxed.

[0008] In a 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, and 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 collect the in-phase (I) and quadrature (Q) signals respectively. Compared with using only one ADC to collect signals on the I channel, using two ADCs to collect I and Q signals respectively doubles the frequency range of the signals that can be collected, reducing the requirements for the ADC sampling bandwidth.

[0009] 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.

[0010] In a possible implementation, the first detection signal and the second detection signal are detection signals generated by scattering of the same detection light pulse, or the first detection signal and the second detection signal are detection signals generated by different detection light pulses. If the first detection signal and the second detection signal are detection signals generated by scattering of the same detection 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 sampling frequency of the ADC can be adjusted in a limited range. When the first detection signal and the second detection signal are detection signals generated by scattering of different detection light pulses, for example, the first detection signal is generated by the first detection light pulse, and the second detection signal is generated by the second detection light pulse, there is no limit to the frequency difference between the first detection signal and the second detection signal. The frequency distribution of the first detection signal and the second detection signal can be adjusted by adjusting the frequency of the first detection light pulse and the second detection light pulse, so that the sampling frequency of the ADC can be flexibly adjusted.

[0011] In a possible implementation, 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 φOTDR signal.

[0012] 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.

[0013] In a 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 detection light output by the orthogonal modulator has two polarization states, and 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.

[0014] The solution provided in the embodiment of the present application can modulate radio frequency signals of different frequencies onto two polarization states of the detection light respectively. The two polarization states do not affect each other, and 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 can be collected. 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 frequencies of the first detection signal and the second detection signal can adapt to the working frequency bands of different signal receiving devices.

[0015] In a possible implementation, the first RF transmitting unit is also used 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, and the first detection signal can be sampled at the positive frequency and the second detection signal can be sampled at the negative frequency at the same time, thereby reducing the requirements for the ADC sampling bandwidth.

[0016] In a possible implementation manner, the second RF transmitting unit is further used 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.

[0017] In a third aspect, a fiber optic sensing device is provided, which includes: a laser, a coupler, a first RF transmitting unit, an orthogonal modulator, an optical fiber circulator, a coherent receiver, an RF 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 RF transmitting unit is used to generate a first RF signal and a second RF signal that are orthogonal to a second frequency; 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 the optical fiber to be measured, and the optical fiber circulator is used to transmit the detection light to the coherent receiver; A photometric pulse signal is input 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 to a coherent receiver; the coherent receiver is used to obtain four orthogonal electrical signals according to 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 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 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, and the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency.

[0018] The optical fiber sensing device provided in the embodiment of the present application, wherein the signal receiving device receives the signal light by using a coherent receiver, 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-channel 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 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 transceiver can be used to simultaneously receive the BOTDR signal and Signals can be used to monitor multiple parameters such as vibration, temperature, and strain. Compared with traditional fiber optic sensing devices, the solution provided in the embodiments 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 a positive frequency, and the frequency coverage range requirement is high. The solution provided in the present application samples the first detection signal at a positive frequency and the second detection signal at a negative frequency, and the frequency coverage range requirement for the coherent receiver and ADC in the signal receiving device can be reduced by half.

[0019] In a 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.

[0020] In a 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, and 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.

[0021] 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.

[0022] 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.

[0023] In a 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.

[0024] 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. The flexible adjustment of the first detection signal and the second detection signal can adapt to the working frequency bands of different signal receiving devices.

[0025] 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.

[0026] In a possible implementation manner, 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.

[0027] In a 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.

[0028] In a 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.

[0029] In a fourth aspect, a signal processing method is provided, and the method 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 that are orthogonal to a second frequency; 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.

[0030] In a possible implementation, the method also 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.

[0031] In a possible implementation manner, the method further includes: when an absolute value of the frequency range of the first detection signal intersects with an absolute value of the frequency range of the second detection signal, the first RF transmitting unit adjusts the second frequency.

[0032] In a possible implementation, the method further includes: the second RF transmitting unit adjusts the magnitude of the third frequency according to the fitting accuracy of the BOTDR signal and / or the phase noise of the φOTDR signal, and the time delay between the signal transmitted by the second RF transmitting unit and the signal transmitted by the first RF transmitting unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagrams of several light scatterings provided in embodiments of the present application;

[0034] Figure 2 A schematic diagram of Rayleigh scattering provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of a distributed optical fiber sensing technology provided in an embodiment of the present application;

[0036] Figure 4 A schematic diagram of a fiber optic sensing device for multi-yield detection provided in an embodiment of the present application;

[0037] Figure 5 A schematic diagram of the frequency difference between Rayleigh scattered light and Brillouin scattered light provided in an embodiment of the present application;

[0038] Figure 6 A schematic diagram of an optical fiber sensing device provided in an embodiment of the present application;

[0039] Figure 7 A schematic diagram of a first polarization state of a detection light provided in an embodiment of the present application;

[0040] Figure 8 A schematic diagram of the spectrum of the signal light provided in the embodiment of the present application;

[0041] Fig. 9 A comparison chart of two ADC acquisition frequency bands provided in an embodiment of the present application;

[0042] Fig.10 A schematic diagram of another optical fiber sensing device provided in an embodiment of the present application;

[0043] Fig.11 is a schematic diagram of double-sideband modulation;

[0044] Fig.12 It is a schematic diagram of single sideband modulation;

[0045] Fig.13 A schematic diagram of a detection signal and its mirror image signal;

[0046] Fig.14 A schematic diagram of a coherent receiver provided in an embodiment of the present application;

[0047] Fig.15 A schematic diagram of a radio frequency analog-to-digital converter provided in an embodiment of the present application;

[0048] Fig.16 A comparison chart of the sampling ranges of two analog-to-digital converters provided in an embodiment of the present application;

[0049] Fig.17 A schematic diagram of a radio frequency analog-to-digital converter provided in an embodiment of the present application;

[0050] Fig.18A schematic diagram of a signal quality curve of a detection signal provided in an embodiment of the present application;

[0051] Fig.19 A sampling schematic diagram of another analog-to-digital converter provided in an embodiment of the present application;

[0052] Fig. 20 A schematic diagram of another optical fiber sensing device provided in an embodiment of the present application;

[0053] Fig.21 A schematic diagram of a first polarization state and a second polarization state of a detection light provided in an embodiment of the present application;

[0054] Fig. 22 A schematic diagram of the spectrum of the signal light provided in the embodiment of the present application;

[0055] Fig.23 A schematic diagram of a signal quality curve of another detection signal provided in an embodiment of the present application;

[0056] Fig.24 A schematic diagram of another optical fiber sensing device provided in an embodiment of the present application;

[0057] Fig.25 A flowchart of a signal processing method provided in an embodiment of the present application. DETAILED DESCRIPTION

[0058] 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 "plurality" refers to two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. 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 thereof 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.

[0059] The embodiments of the present application use words such as "first" and "second" to distinguish objects with similar names, functions or effects. Those skilled in the art will understand that words such as "first" and "second" do not limit the quantity and execution order. The term "coupled" is used to indicate electrical connection, including direct connection through wires or connection terminals or indirect connection through other devices. Therefore, "coupled" should be regarded as a broad electronic communication connection.

[0060] 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 as "exemplary" or "for example" in this application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0061] When light propagates in an optical fiber, due to the inhomogeneity or nonlinearity of the optical fiber's refractive index, part of the incident light will deviate from the original propagation direction and propagate in any direction. This phenomenon is called light scattering. Among these scattered lights in any direction, a small part of the scattered light will propagate in the opposite direction of the incident direction, which is called backscattered light.

[0062] There are three main types of backscattered light in optical fibers: Rayleigh scattering, Brillouin scattering, and Raman scattering, and their scattering mechanisms are different. Among them, Raman scattering and Brillouin scattering will change the frequency of light, so they are called inelastic scattering; Rayleigh scattering, which does not change the frequency of light, is called elastic scattering.

[0063] Raman scattering and Brillouin scattering are caused by the interaction of light with optical phonons and acoustic phonons, respectively, causing a frequency shift upward or downward. Figure 1 As shown in the figure, under the action of optical phonons in the optical fiber, the optical frequency produces a frequency shift of about 13THz, resulting in Raman scattered light; and under the action of acoustic phonons, the optical frequency produces a frequency shift of about 11GHz, resulting in Brillouin scattered light. The light moving in the direction of decreasing frequency is called Stokes light, and the light moving 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 analyzer (BOTDA), are based on these two inelastic scattering mechanisms to achieve sensing.

[0064] Rayleigh scattering is mainly caused by the inhomogeneity of the medium in the optical fiber. Figure 2 As shown in the figure, in the production of optical fiber, due to factors such as the production process, some random refractive index fluctuations are inevitably introduced into the optical fiber. Figure 2 The black dots in the figure indicate that when the probe light propagates in the optical fiber, random scattered light propagating in all directions will be generated at these refractive index fluctuations. A small part of these scattered lights will propagate backwards and meet the propagation conditions of single-mode optical fiber, thus returning from the scattering location to the incident end of the probe light. These backward Rayleigh scattered lights become the basis of distributed optical fiber sensing based on Rayleigh scattering.

[0065] 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 than traditional electromechanical sensors and more convenient to use; optical fiber is inexpensive, has a wide working bandwidth range, and low loss, and can achieve long-distance and large-range sensing; optical fiber is resistant to compression and stretching, 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.

[0066] The basic principle of distributed optical fiber sensing technology is as follows: Figure 3 As shown in the figure, the laser generates a light source, which is modulated into a light pulse by a modulator and then injected into the optical fiber under test through an optical fiber circulator; the backscattered light generated in the optical fiber is transmitted backward and received by a photodetector to obtain intensity information. Backscattered light includes Rayleigh scattered light, Brillouin scattered light, etc. Due to the existence of optical fiber loss, the intensity of backscattered light decays exponentially along the optical fiber, and the magnitude of optical fiber loss can be measured by the speed of exponential decay; the sudden increase in local signal indicates the presence of a high reflection point; the sudden increase in local attenuation indicates the presence of a loss point or a breakpoint. The optical time-domain reflectometer (OTDR) made according to this principle is widely used in fields such as communications to detect the status of optical fiber links.

[0067] Common optical time domain reflectometers include phase-sensitive optical time domain reflectometer (ΦOTDR) and Brillouin optical time domain reflectometer (BOTDR). ΦOTDR uses the interference effect between backward Rayleigh scattered light and is an interference scattering type fiber optic sensing technology with many advantages such as high sensitivity, long measurement distance, simple structure and easy implementation. Since Rayleigh scattered light has stronger power than Brillouin scattered light and Raman scattered light, it can reduce the average signal processing time and enable it to have the ability to measure vibration. Therefore, it is only necessary to detect the changes in Rayleigh scattered light in the optical fiber to detect the vibration of the optical fiber.

[0068] BOTDR utilizes the Brillouin scattering of optical fiber. In ordinary single-mode quartz optical fiber, the core material has thermo-optic effect and elastic-optic effect. These two effects affect the speed of sound in the optical fiber material, and the change of 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.

[0069] Combining with BOTDR is a form of multi-parameter sensing. It realizes the simultaneous sensing of vibration, temperature and stress by monitoring Rayleigh scattering signal and Brillouin scattering signal simultaneously. The characteristics of Brillouin scattering and Rayleigh scattering are: the frequency interval between the two is large, about 11GHz, the distribution range of Brillouin scattering is wide (hundreds of MHz to GHz), and the scattering coefficient is relatively weak (Rayleigh scattering and Brillouin scattering coefficients are -81dB / ns and -93dB / ns respectively). When the two are detected simultaneously, the detection performance has high requirements on the bandwidth of the receiver, the stray / harmonic interference of the system, etc. If the Rayleigh scattering signal and Brillouin scattering signal are sampled and spectrum analyzed at the same time, the performance and working frequency range requirements of the sampling equipment and spectrum analysis equipment are very high, resulting in sampling difficulties, low sampling accuracy, high equipment cost and other problems.

[0070] Figure 4The invention shows a fiber optic sensing device for multi-parameter detection. The laser light emitted by the laser is divided into two paths through the first fiber optic coupler, one of which is modulated into a light pulse by an optical pulse modulator, and the other is connected to the second fiber optic coupler; the light pulse is connected to the first port of the fiber optic circulator, and the second port of the fiber optic circulator outputs the light pulse, which is injected into the optical fiber under test through the optical interface; the backscattered light of the light pulse in the optical fiber under test enters the second port of the fiber optic circulator through the optical interface, and then enters the second fiber optic coupler through the third port of the fiber optic circulator; the second fiber optic coupler makes the connected laser and the backscattered light coherently generate envelope information, and outputs the envelope information to the balanced photoelectric detector; the balanced The photoelectric detector converts the envelope information into a radio frequency signal, and amplifies the radio frequency signal through a low noise amplifier and then connects it to the power divider; since the first filter corresponds to the Rayleigh scattering signal band, that is, the 200MHz carrier frequency band, and the second filter corresponds to the Brillouin scattering signal band, that is, the carrier frequency band of about 10.8GHz; the power divider divides the radio frequency signal input therein into two paths, one of which is filtered by the first filter to obtain a Rayleigh scattering signal, and the Rayleigh scattering signal is connected to the first channel of the data acquisition and processing module; the other radio frequency signal is filtered by the second filter to obtain a Brillouin scattering signal, and the Brillouin scattering signal is connected to the signal input end of the mixer. The local oscillation signal output by the frequency synthesizer is connected to the local oscillation input end of the mixer, and the mixer mixes the Brillouin scattering signal and the local oscillation signal to obtain a baseband signal, which is filtered by a low-pass filter and connected to the second channel of the data acquisition and processing module.

[0071] 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, 200 data about each position along the optical fiber and the scattering power are first saved, and then the 200 power values ​​corresponding to each position along the optical fiber are fast Fourier transformed to obtain the vibration information of each position along the optical fiber under test.

[0072] The data acquisition and processing module extracts the time domain, frequency domain and power information of the corresponding frequency synthesizer sweep frequency point, i.e., the Brillouin signal, 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 information and strain information of the measured optical fiber.

[0073] Figure 4 The scheme shown uses a large bandwidth balanced receiver to receive the signal and separates it through a first filter and a second filter. For BOTDR signals, the separated RF source (frequency synthesizer) and mixer are used to mix and filter them, transfer them to baseband, and then pass them through multiple ADCs. By collecting the signal and BOTDR signal, it is possible to detect the Brillouin scattering signal and Rayleigh scattering signal at the same time. Based on signal multiplexing perception and demodulation, it is possible to monitor multiple parameters such as vibration, temperature and strain of the measured optical fiber.

[0074] However, the above scheme still has some disadvantages. 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, combined with reference Figure 5 , the frequency of Rayleigh scattered light (f A ) and the frequency of the Brillouin scattered light (f B ) has a frequency difference of about 11GHz in the spectrum, so for Figure 4 For the scheme shown, the frequency synthesizer, receiver, mixer, filter, etc. must be able to cover a frequency range greater than 11 GHz to achieve complete sampling. The signal and BOTDR signal have high requirements on the performance of the equipment; moreover, the above scheme cannot be flexibly controlled The receiving frequency of the signal and the BOTDR signal. In actual engineering applications, the detection performance has high requirements on the spurious-free dynamic range, total harmonic distortion and other indicators of the transceiver system.

[0075] 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 on the frequency range covered by the equipment while realizing the monitoring of multiple parameters such as vibration, temperature and strain.

[0076] For example, see Figure 6 , Figure 6 The schematic diagram of the structure of a fiber optic sensing device provided in an embodiment of the present application is shown. 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, a 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, and the detection light pulse generates scattering in the optical fiber under test to obtain a signal light, and the signal receiving device is used to receive the signal light and process it.

[0077] 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 with a second frequency (f2) and orthogonal to each other, that is, the first RF signal has the same frequency as the second RF signal and has 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 detection 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 detection light, such as Figure 7 As shown, a detection light pulse signal with a period of T is obtained. The optical fiber circulator 204 is used to input the detection light pulse signal into the optical fiber under test. The detection light will be scattered in the optical fiber under test to obtain signal light. The optical fiber 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 according to 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, which 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, which is used to perform frequency band calculation on the digital signal output by the RF analog-to-digital converter 206 to obtain a spectrum, such as Figure 8 As shown, the spectrum includes a first detection signal at a positive frequency and a second detection signal at a negative frequency. The frequency difference between the first detection signal and the second detection signal is vB, where vB refers to the Brillouin frequency shift.

[0078] 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 detection light pulses, 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.

[0079] 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) 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 ), and 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 corresponding to the second polarization state of the signal light (Y I , Y Q ), where each polarization state includes an in-phase (I) signal and a quadrature (Q) signal, so that for the I signal of the first polarization state (i.e., X I ) and Q-channel signal (i.e. X Q ) is Fourier transformed in the complex plane, and the spectrum obtained by taking the modulus and then squaring 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 signal, the second detection signal is a BOTDR signal, or the first detection signal is a BOTDR signal, the second detection signal is signal; for the second polarization state I signal (ie Y I ) and Q 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 in the optical fiber rotate, when calculating the frequency band of the first polarization state and the second polarization state of the signal light, I and Y Q The spectrum obtained by frequency band calculation is the same as that of X I and X Q The frequency 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.

[0080] On this basis, the signal transmitting device adjusts the second frequency (f2), which is the frequency of the first RF signal and the second RF signal transmitted by the first RF transmitting unit, so that the frequencies of the first detection signal and the second detection signal are distributed near the center sampling frequency of the analog to digital converter (ADC) (which is recorded as the first frequency (f1) in the embodiment of the present application), and 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 transceiver devices can simultaneously receive BOTDR signals and Signals can be used to monitor 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 a positive frequency and the second detection signal at a negative frequency can reduce the requirements for the ADC's coverage frequency range. Fig. 9 As shown in Figure a, Figure 4 The scheme shown here requires balanced photodetectors, low noise amplifiers, etc. to cover a frequency range of 11 GHz, see Fig. 9 As shown in Figure b, in the optical fiber sensing device provided by the present application, the signal receiving device can sample at both the positive frequency and the negative frequency, so that the frequency coverage requirement of the signal receiving device is reduced by half, which can be reduced to 5.5GHz. On the other hand, sampling the first detection signal at the positive frequency and sampling the second detection signal at the negative frequency can reduce the BOTDR signal and Spectrum crosstalk and harmonic crosstalk between signals can improve the detection accuracy of the system.

[0081] Combination Figure 1 It can be seen that 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, but when Brillouin scattering occurs, it may scatter to high frequency or low frequency. If the Brillouin frequency shift vB is about 11GHz, that is, if f is the frequency of the probe light, then the frequency of the Brillouin scattered light generated may be f±11GHz. Therefore, the first detection signal at the positive frequency may be the BOTDR signal, and the second detection signal at the negative frequency may be signal; or, the first detection signal at the positive frequency may be The signal, the second detection signal at the negative frequency may be a BOTDR signal. However, since the intensity of the Brillouin scattered light signal scattered to a low frequency is greater than the intensity of the Brillouin scattered light signal scattered to a high frequency, in the embodiment of the present application, the Brillouin scattered light is taken as an example to be scattered to a low frequency, that is, the frequency of the Brillouin scattered light signal is f-vB.

[0082] 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, signal, sampling the BOTDR signal at a negative frequency. The frequency difference between the 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 the negative frequency and the positive frequency respectively, the center sampling frequency of the ADC should be around 5.5 GHz. The signal frequency is about 6GHz, and the BOTDR signal frequency is about -4Ghz, so an ADC with a center sampling frequency of about 5GHz (-5GHz) can be selected. The frequency of the signal (6GHz) is close to 5GHz, and the frequency of the BOTDR signal (-4GHz) is close to -5GHz, so the ADC can sample at the positive frequency. signal, and can also sample the BOTDR signal at a negative frequency.

[0083] Will The signal is set to sample at the positive frequency and the BOTDR signal is sampled at the negative frequency to reduce The crosstalk between the signal and the BOTDR signal, however, due to the imperfect coherent receiver, the negative frequency signal may also leak a small part to the positive frequency to form an image, and the positive frequency signal may also leak a small part to the negative frequency to form an image. Therefore, in order to avoid The signal is affected by the crosstalk of the mirror signal of the BOTDR signal, or the BOTDR signal is prevented from being affected by Signal crosstalk, The absolute values ​​of the frequencies of the signal and the BOTDR signal are close but different, or the absolute values ​​of the frequency ranges of the two signals do not cross, e.g. The frequency of the mirror image of the signal is different from the frequency of the BOTDR signal, or the frequency of the mirror image of the BOTDR signal is different from The frequencies of the signals are different.

[0084] For example, The frequency of the signal is about 6GHz, the frequency of the BOTDR signal is about -4Ghz, and the frequency of the mirror signal of the BOTDR signal is about +4Ghz. The frequency of the mirror signal of the signal is about 6GHz, so The frequency of the signal is offset from the frequency of the mirror signal of the BOTDR signal. The frequencies of the mirror signals of a signal are staggered to reduce the crosstalk between them.

[0085] For example, in one possible implementation, see Fig.10 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 used to generate two orthogonal baseband frequency modulation signals, such as an orthogonal first baseband frequency modulation signal and a second baseband frequency modulation signal, wherein the first baseband frequency modulation signal can be expressed as x i , the second baseband FM signal can be expressed as x q . For example, x i =cos(2πΔf1t),x q =sin(2πΔf1t).

[0086] The first baseband RF unit 211 transmits the generated first baseband frequency modulation signal and the second baseband frequency modulation signal to the first pulse generating unit 212. The first pulse generating unit 212 generates a first baseband pulse frequency modulation signal with a pulse width of τ according to the first baseband frequency modulation signal. The first pulse generating unit 212 generates a second baseband pulse frequency modulation signal with a pulse width of τ according to the second baseband frequency modulation signal. The first baseband pulse frequency modulation signal can be expressed as x pi , the second baseband pulse frequency modulation signal can be expressed as x pq . For example,

[0087] 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.

[0088] 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 and avoid the occurrence of double sideband signals.

[0089] Traditional modulators can only modulate the intensity or phase of the signal. If only the intensity or phase of the signal is modulated, a double-sideband signal will often be generated. Fig.11 , that is, when 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, the BOTDR signal and There will be strong interference between the signals. For example, the frequency of the BOTDR signal in the embodiment of the present application is at the negative frequency. The frequency of the signal is at the positive frequency. If only the intensity or phase of the signal is modulated, double-sideband modulation is used. For the signal, a negative frequency Signal, negative frequency Signal and positive frequency The signal strength is similar, the negative frequency The signal will cause strong interference to the BOTDR signal at the negative frequency.

[0090] 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 simultaneously, and the signal can be modulated to a single sideband. Fig.12 , only the positive frequency signal is modulated, and the negative frequency has no signal and will not cause interference. However, in the above example, due to the imperfection of the coherent receiver, 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. See Fig.13 The intensity of the image signal is much smaller than the signal intensity generated by the double-sideband modulation at the negative frequency. The crosstalk of the signal to the BOTDR signal is converted into The image component of the signal will interfere with the BOTDR signal. The crosstalk of the signal is converted into the image component of the BOTDR signal The crosstalk of signals is greatly reduced, which improves the system performance.

[0091] The orthogonal modulator 203 modulates the orthogonal first RF signal and the second RF signal into the detection light (for example, in this case, the detection light is single-polarized light) to form a detection light pulse signal. The detection 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 detection light pulse in the optical fiber under test can be output to the coherent receiver 205 through the optical fiber circulator 204.

[0092] In one possible implementation, the fiber optic circulator 204 includes a first end, a second end, and a third end. The first end of the fiber optic circulator 204 is connected to the output end of the orthogonal modulator 203, the second end of the fiber optic circulator 204 is connected to the optical fiber under test, and the third end of the fiber optic circulator 204 is connected to the input end of the coherent receiver 205.

[0093] The coherent receiver 205 is an optoelectronic hybrid device, which is used to receive signal light and local oscillator light, and after polarization diversity and optical orthogonal mixing, optoelectronic conversion is performed to output electrical signals in two orthogonal polarization states. In each polarization state, two electrical signal outputs orthogonal in phase are obtained. Exemplarily, 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, and to receive local oscillator light, and to 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 conversion.

[0094] See also Fig.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 the signal light of any polarization state, decompose it into the orthogonal first polarization state and second polarization state, and output four signals: X I , X Q , Y I and Y Q .

[0095] The RF analog-to-digital conversion unit 206 is used to convert the four-way signals output by the coherent receiver 205: I , X Q , Y I and Y Q 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. The embodiment of the present application takes one of the RF analog-to-digital converters as an example, for example, to convert X I For example, in one possible implementation, Fig.15As shown in FIG. 1 , the RF analog-to-digital converter 206 includes a numerically controlled oscillator (NCO) 2061, a mixer 2062, a first filter 2063, and a first analog-to-digital converter (ADC) 2064. The output end of the NCO 2061 is connected to the first input end of the first mixer 2062, and the second input end of the first mixer 2062 is connected to the output end 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), and the mixed signal is filtered by the first filter 2063 and transmitted to the first ADC 2064 for sampling, so as to convert the analog signal into a digital signal. Here, the first frequency (f1) is the central sampling frequency of the first ADC 2064.

[0096] 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 downconverted to the 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.

[0097] In the above example, an ADC is used to I To sample analog signals, Fig.16 As shown in Figure a, only positive frequency signals (i.e., f1~f1+ω) can be sampled, and negative frequency signals (f1-ω~f1) cannot be sampled. In order to increase the bandwidth, negative frequency signals are sampled at the same time, as shown in Fig.15 As shown in Figure b, two ADCs can also be used toI 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, denoted 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 orthogonal path I q and the digital signal X in the same phase I i together as X I digital signal.

[0098] 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 also 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, the second input of the second mixer 2066 is connected to the output of the coherent receiver 207 (for example, the coherent receiver 205 outputs 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 the 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 central sampling frequency of the second analog-to-digital converter 2068 is the first frequency. I The analog signal of the channel and the RF signal after phase shifting by 90° are sampled to obtain the orthogonal channel signal, which is recorded as X I q. In this way, X is obtained by sampling two ADCs. I i signal and X I q signal, and then combine the two signals into one to get X I i+j 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.

[0099] Setting two ADCs to sample positive and negative frequency signals respectively can double the ADC sampling bandwidth. Fig.16 As shown in Figure b, the original bandwidth was ω only in the case of positive frequency sampling. When two ADCs are set to sample positive and negative frequencies, the sampling frequency range covers f1-ω~f1+ω, and the bandwidth is 2ω. The sampling bandwidth is doubled, which can improve the accuracy of the system.

[0100] The above is based on X I The coherent receiver 205 outputs four polarization signals X I , X Q , Y I and Y Q Therefore, the RF analog-to-digital conversion unit 206 needs to sample and convert the above four signals, see Fig.17 , which is equivalent to providing four of the above-mentioned RF analog-to-digital converters 206_A, 206_B, 206_C and 206_D, which will not be described in detail in the embodiment of the present application.

[0101] 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 according to the four digital signals to obtain a spectrum, wherein 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.

[0102] For example, the frequency band calculation unit 207 calculates the orthogonal X I Road signal and X Q The signal is transformed by Fourier in the complex plane, modulo-squared, and recorded as |f(X I +jX Q )| 2 , for the orthogonal Y I Road signal and Y Q The signal is transformed by Fourier in the complex plane, and then squared and recorded as |f(Y I +jY Q )| 2 , and then sum them to get the spectrum:

[0103] |f(X I +jX Q )| 2 +|f(Y I +jY Q )| 2

[0104] 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, 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 are summed. 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 Q are 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 in the two polarization states, and then the power is obtained after taking the square of the modulus, which is equivalent to averaging the signals in the two polarization states. After averaging, the interference between the polarization states can be overcome, making the signal more stable and improving the accuracy of the system.

[0105] The frequency band calculation unit 207 performs frequency band calculation according to the four-channel digital signal to obtain a spectrum, wherein 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 the preset frequency range. For example, the first detection signal is signal, the second detection signal is a BOTDR signal as an example, The bandwidth of the first frequency range of the signal is approximately ±10 MHz, and the 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 signal matches the first frequency range, that is, judging Whether the frequency range of the 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 The signal and BOTDR signal are both within the ADC acquisition frequency band.

[0106] Exemplarily, the signal receiving device further includes a signal quality calculation unit 208, which is used to determine the BOTDR signal and The quality of the signal can be measured in one possible implementation through some indicators such as the fitting accuracy of the BOTDR signal, The signal quality is judged by indicators such as the phase noise of the signal.

[0107] For example, when the optical fiber sensor 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 determine the fitting accuracy of the BOTDR signal under different sizes of the second frequency and The first RF transmitting unit 210 then calculates the phase noise of the BOTDR signal according to the fitting accuracy and The second frequency is adjusted according to the phase noise of the signal until it is adjusted to the fitting accuracy of the BOTDR signal and The phase noise of the signal meets 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.

[0108] For example, combined with Fig.18 , Fig.18 The f2 obtained by sweeping the frequency f2 and the BOTDR signal and Schematic diagram of the relationship between signal quality, for example, indicator 1 is the fitting accuracy of the BOTDR signal, and indicator 2 is the phase noise of the OTDR signal. According to the threshold value of indicator 1, a range of f2 can be selected, and according to the threshold of indicator 2, a range of f2 can be selected. The intersection of these two ranges is the optional working range. When f2 is set to a frequency within this working range, both indicators 1 and 2 can meet the requirements.

[0109] In some other possible implementations, the width of the light pulse or the period of the light pulse can be adjusted accordingly in the same way. After determining the optimal parameters, the optical fiber sensing device can work on the basis of setting the above parameters and realize simultaneous detection of vibration, temperature, and stress under the optimal state.

[0110] In some possible implementations, the optical fiber under test may be formed by fusion-joining multiple optical fibers of different types, and the stress on the optical fiber is relatively large, so that the spectrum of the BOTDR signal obtained by the signal receiving device exceeds the acquisition frequency band of the ADC. In this case, the complete BOTDR signal can be detected by multiple detections to achieve ultra-wide range detection.

[0111] For example, assuming that the acquisition frequency range of the ADC is 200MHz, and the frequency range of the BOTDR signal may exceed 300Mhz, refer to Fig.19 , when the center sampling frequency of the ADC is f1 (or -f1), only The signal and part of the BOTDR signal are collected, and the BOTDR signal cannot be collected completely. In this way, the BOTDR signals sampled multiple times can be spliced ​​to form a complete BOTDR signal by adjusting the ADC center sampling frequency and sampling multiple times. For example, the ADC center sampling frequency is adjusted from f1 (-f1) to f1` (or -f1`). When the ADC center sampling frequency is adjusted twice, it is necessary to leave a certain overlapping area in the ADC acquisition frequency range before and after the adjustment, so that part of the same signal can be sampled during the two samplings. The same part of the BOTDR signal in the two samplings is used as an anchor point, and the BOTDR signals sampled twice are spliced ​​to obtain a complete BOTDR signal, thereby realizing ultra-large-scale detection.

[0112] 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 also be integrated into a computer to implement the above functions through software algorithms.

[0113] In the above example, the signal transmitting device adjusts the first RF signal and the second RF signal to a polarization state of the detection light to form a detection light pulse signal, and only uses a single pulse for multi-parameter detection. The flexibility of the frequency band control of the scattered signal is greatly limited, which is strongly related to 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 measurement accuracy of the system. On this basis, the embodiment of the present application also provides another implementation method, which uses a multi-pulse method for multi-parameter detection.

[0114] For example, Fig. 20 The schematic diagram of another optical fiber sensing device provided by an embodiment of the present application is shown, including a signal transmitting device and a signal receiving device. The signal transmitting device includes a laser 301, a coupler 302, a first radio frequency transmitting unit 310, a second radio frequency transmitting unit 320, a double-biased quadrature modulator 303 and an optical fiber circulator 304. The signal receiving device includes a coherent receiver 305, a radio frequency analog-to-digital conversion unit 306, a frequency band calculation unit 307 and a signal quality calculation unit 308. Compared with Figure 6 For the optical fiber sensing device shown, Fig. 20 The signal transmitting device of the optical fiber sensor device shown in the figure further includes a second radio frequency transmitting unit 320, and the remaining structures are the same as those of FIG. Figure 6 The optical fiber sensing device shown is basically the same, and the embodiment of the present application is only briefly described. The second RF transmitting unit 320 is used to generate a third RF signal and a fourth RF signal with a frequency of a third frequency (f3) and orthogonal. 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. Here, the first polarization state and the second polarization state are two orthogonal polarization states. Therefore, the orthogonal modulator in the embodiment of the present application is a dual-polarization orthogonal modulator 303.

[0115] 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, i =cos(2πΔf3t),y q =sin(2πΔf3t).

[0116] The second baseband RF unit 321 transmits the generated third baseband frequency modulation signal and the fourth baseband frequency modulation signal to the second pulse generating unit 322. The second pulse generating unit 322 generates a third baseband pulse frequency modulation signal with a pulse width of τ according to the third baseband frequency modulation signal. The second pulse generating unit 322 generates a fourth baseband pulse frequency modulation signal with a pulse width of τ according to the fourth baseband frequency modulation signal. The third baseband pulse frequency modulation signal can be expressed as y pi , the fourth baseband pulse frequency modulation signal can be expressed as y pq . For example,

[0117] 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.

[0118] See also Fig.21 As shown, the dual-bias orthogonal modulator 303 can modulate the orthogonal first RF signal and the second RF signal onto the detection light of the first polarization state, and modulate the orthogonal third RF signal and the fourth RF signal onto the detection light of the second polarization state to form a detection light pulse signal. Therefore, the embodiment of the present application selects a dual-bias orthogonal modulator for modulation. Among them, the pulse period of the detection light pulse is T, and the pulse width is τ. In a 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 on the first polarization state and the pulse on the second polarization state is t12, t12<T, for example, T can be 500 microseconds, and t12 is 499 microseconds.

[0119] For the sake of illustration, the pulse formed by modulating the first RF signal and the second RF signal with a frequency of f2 onto the detection light of the first polarization state is recorded as p1, and the pulse formed by modulating the third RF signal and the fourth RF signal with a frequency of f3 onto the detection light of the second polarization state is recorded as p2. Since both p1 and p2 generate backscattered light, the signal received by the coherent receiver 305 includes the pulse generated by the p1 pulse. signal and BOTDR signal, including the p2 pulse Signal and BOTDR signal. In order to improve the signal quality, it can be sampled in different polarization states. Signal and BOTDR signal, for example, the p1 pulse generated by the first polarization state can be sampled Signal, sampling the BOTDR signal generated by the p2 pulse in the second polarization state, which can improve the linearity of the system. And because the two polarization states are independent of each other, the frequencies of f2 and f3 can be flexibly adjusted to improve the performance of the system.

[0120] For example, in Figure 6 In the fiber optic sensor device shown, only a single polarization pulse is generated. signal and BOTDR signal, The frequency difference between the signal and the BOTDR signal is the Brillouin frequency shift vB, which is about 11 GHz. If the same type of ADC is used to sample the BOTDR signal at negative frequencies and at positive frequencies, The signal requires the central sampling frequency of the ADC 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 sensor device will also be affected.

[0121] However, in the solution provided in the embodiment of the present application, the sampling is generated by the p1 pulse. Signal, sampling the BOTDR signal generated by the p2 pulse, such as the p1 pulse The frequency of the signal is f2, and the BOTDR signal frequency generated by the p2 pulse is about f3-vB. By adjusting f2 and f3, the ADC can be sampled at any central sampling frequency (i.e., the first frequency f1). Signal and BOTDR signal are sampled, see Fig. 22 , the coherent receiver 305 outputs X I , X Q , Y I and Y Q The four-channel signals are converted into digital signals by the radio frequency analog-to-digital conversion unit 306 and then calculated by the frequency band calculation unit 307 to restore the spectrum.

[0122] Exemplarily, the frequency band calculation unit 307 performs frequency band calculation based on four digital signals to obtain a spectrum, where the spectrum includes frequency distribution of a first detection signal at a positive frequency and a second detection signal at a 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.

[0123] For example, the first detection signal is The second detection signal is a BOTDR signal, for example, the frequency band calculation unit 307 can obtain a frequency f2 after performing frequency band calculation. The signal and frequency of the BOTDR signal are about f3-vB. The p2 pulse generates Signal (i.e. frequency f3) The signal) may be outside the acquisition frequency band of the ADC and will not be sampled. The frequency width of the signal is about ±10MHz, and the frequency width of the BOTDR signal is about ±150MHz. The frequency band calculation unit 307 determines Whether the frequency range of the signal is within the range of ±10MHz, whether the frequency range of the BOTDR signal is within the range of ±150MHz, if not, the second frequency (f2) of the first RF signal and the second RF signal generated by the first RF transmitting unit 310 can be adjusted, and the third frequency (f3) of the third RF signal and the fourth RF signal generated by the second RF transmitting unit 320 can also be adjusted, or the central sampling frequency f1 of the ADC in the RF analog-to-digital converter can also be fine-tuned to ensure The signal and BOTDR signal are both within the ADC acquisition frequency band.

[0124] In the embodiment of the present application, the RF analog-to-digital converter samples the p1 pulse of the first polarization state to generate The BOTDR signal generated by the p2 pulse of the signal and the second polarization state is sampled at different polarization states signal and BOTDR signal, which can improve the linearity of the system, and because 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 signal and the BOTDR signal, for example, in the above example, The signal and the BOTDR signal are generated by the same (polarization state) detection light pulse. In order to use the same type of ADC to sample the BOTDR signal at negative frequency and at positive frequency Signal, due to The frequency difference between the signal and the BOTDR signal is the Brillouin frequency shift vB, which requires the central sampling frequency of the ADC to be set near vB / 2. In the embodiment of the present application, the sampling frequency generated by the p1 pulse is Signal, sampling the BOTDR signal generated by the p2 pulse, such as the p1 pulse The signal is f2, and the BOTDR signal frequency generated by the p2 pulse is approximately f3-vB. The frequency difference between the 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 above embodiment, f1 is limited to around 5.5GHz) can be cancelled. The center sampling frequency f1 of the ADC can also be adjusted according to the demand, which can improve the performance of the system. For example, if the sampling performance of the ADC near 5.5GHz is not good, the ADC can be operated at a center sampling frequency of around 10GHz, and then by adjusting f2 and f3, the The signal and the BOTDR signal both fall within the acquisition frequency band of the ADC.

[0125] In some possible implementations, in order 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 RF signal and the second RF signal can be in the range of vB to 0, and the frequency f3 of the third RF signal and the fourth RF signal can be in the range of 0 to vB. For example, f2 can be 4.7 GHz and f3 can be 6.0 GHz. However, in order to achieve the same type of ADC sampling signal and BOTDR signal, The absolute values ​​of the frequencies of the signal and the BOTDR signal are similar, but not the same.

[0126] Exemplarily, the optical fiber sensing device further includes a signal quality calculation unit 308, which is used to determine the BOTDR signal and The quality of the signal, in a possible implementation, can be judged by some indicators, for example, the above indicators can include the fitting accuracy of the BOTDR signal, Phase noise of the signal, etc.

[0127] 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 determine the fitting accuracy of the BOTDR signal under different third frequencies (f3) and time delay t12. The second RF transmitting unit 320 can be based on the fitting accuracy of the BOTDR signal and the phase noise of the signal. The phase noise of the signal selects an appropriate third frequency (f3) and time delay t12. In the subsequent operation of the optical fiber sensing device, the third frequency (f3) and time delay t12 of the radio frequency signal emitted by the second radio frequency transmitting unit 320 are adjusted to improve the signal quality.

[0128] For example, combined with Fig.23 , Fig.23The second RF transmitting unit 320 sweeps the frequency f3 and t12 to obtain f3 or t12 and the BOTDR signal and Schematic diagram of the relationship between signal quality, for example, indicator 1 is the fitting accuracy of the BOTDR signal, and indicator 2 is the phase noise of the OTDR signal. According to the threshold value of indicator 1, a range of f3 or t12 can be selected, and according to the threshold of indicator 2, a range of f3 and t12 can be selected. The intersection of these two ranges is the optional working range. When f3 or t12 is set within this working range, both indicators 1 and 2 can meet the requirements, which can improve the BOTDR signal and Signal quality: the optical fiber sensing device can realize the simultaneous detection of vibration, temperature and stress under the optimal state.

[0129] In the above example, a dual-polarization quadrature modulator is used to modulate the orthogonal first RF signal and the second RF signal onto a detection light of a first polarization state, and the third RF signal and the fourth RF signal are modulated onto a detection light of a second polarization state for detection. In some other possible implementations, different RF pulses can also be modulated onto detection light of the same polarization state.

[0130] For example, see Fig.24 The embodiment of the present application provides another optical fiber sensing device, including a signal transmitting device and a signal receiving device, wherein the signal transmitting device includes a laser 401, a coupler 402, a first radio frequency transmitting unit 410, a second radio frequency transmitting unit 420, an orthogonal modulator 403, a signal synthesizer 409 and an optical fiber circulator 404, and the signal receiving device includes a coherent receiver 405, an radio frequency analog-to-digital conversion unit 406, a frequency band calculation unit 407 and a signal quality calculation unit 408. Fig. 20 For the optical fiber sensing device shown, 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 uses an orthogonal modulator for modulation, but 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, and the combined RF signal is then modulated to the detection light of the same polarization state using the orthogonal modulator 403, which can also achieve an effect similar to modulation to a dual polarization state.

[0131] The optical fiber sensing device provided in the embodiment of the present application uses a coherent receiver to receive the The coherent receiver 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 converter performs down-conversion and analog-to-digital conversion to output two digital electrical signals (X I , X Q ) and two digital signals corresponding to the second polarization state of the signal light (Y I , Y Q ), where each polarization state includes an in-phase (I) signal and a quadrature (Q) signal. The spectrum obtained by performing Fourier transform on the complex plane and square after taking the modulus of the I signal and the Q signal of each polarization state 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 signal, the second detection signal is a BOTDR signal, or the first detection signal is a BOTDR signal, the second detection signal is signal, on this basis, by adjusting the second frequency (f2) of the first RF signal and the second RF signal in the signal transmitting device, or adjusting the third frequency (f3) of the third RF signal and the fourth RF signal, so that the frequency distribution of the first detection signal and the second detection signal is near the central 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 by the same type of ADC, so that the BOTDR signal and Signals can be used to monitor multiple parameters such as vibration, temperature and strain. On the other hand, by using the same type of ADC to sample the first detection signal at a positive frequency and the second detection signal at a negative frequency, the coverage frequency range requirements for the coherent receiver, ADC, etc. of the signal receiving device can be reduced.

[0132] This optical fiber sensing device can be applied to many scenarios, including buried optical fiber intrusion alarm, underground monitoring, bridge health monitoring, urban pipeline corridor monitoring, oil and gas leakage detection, cable ice detection, etc. In the above scenarios, by simultaneously detecting multiple parameters such as vibration, temperature, and stress, the applicable scenarios, detection accuracy, and positioning accuracy of the optical fiber sensing system can be effectively improved.

[0133] For example, in the buried pipeline intrusion alarm scenario, the temperature difference of the area where the pipeline is located can reach more than 30 degrees, which causes the positioning accuracy of the intrusion alarm to be biased. This device can detect vibration and temperature at the same time to compensate for the positioning error caused by the temperature difference. In the oil and gas leakage and pipeline corridor monitoring scenarios, the leakage of liquefied gas and gas transmission gas will cause temperature changes near the leakage point, and simultaneously introduce acoustic parameters such as orifice noise and negative pressure waves. The simultaneous detection of temperature and vibration can effectively improve the sensitivity of pipeline leakage detection. In bridge health monitoring and cable icing monitoring, the static stress on the bridge and cable can be detected to determine whether the cable or bridge is in a healthy working state, and the wind dance and bridge resonance of the cable can be detected by detecting low-frequency vibration. In the underground survey scenario, the component and structure information at different depths of the well can be extracted by distributed detection of the underground vibration waves generated by the active excitation source, and the formation temperature profile can be obtained by temperature detection to provide guidance information for underground mining.

[0134] Combination Fig.25 , Fig.25 The flowchart of the signal processing method of the optical fiber sensing device provided by the embodiment of the present application is shown, including:

[0135] S601, the laser emits an optical signal.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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 the coherent receiver.

[0140] S606, the coherent receiver obtains four electrical signals according to the local oscillator light and the signal light, the four electrical signals including 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.

[0141] 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.

[0142] 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.

[0143] In one possible implementation, combining Fig.15 In Figure a, S607 includes:

[0144] A digitally controlled oscillator generates a radio frequency signal of a first frequency, a first mixer mixes an electrical signal output by a coherent receiver with a 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 a baseband into a digital signal, wherein the first frequency is a central sampling frequency of the first analog-to-digital converter.

[0145] In another possible implementation, combining Fig.15 In Figure b, S607 includes:

[0146] The digital controlled oscillator generates a radio frequency signal of a first frequency, the first mixer mixes the electrical signal output by the coherent receiver with the radio frequency signal of the first frequency, the first filter filters out the high frequency components in the mixed signal to convert the electrical signal to baseband, and the first analog-to-digital converter converts the electrical signal converted to baseband to obtain an in-phase digital signal. The 90° phase shifter shifts the phase of the radio frequency signal of the first frequency by 90°, the second mixer mixes the phase-shifted radio frequency signal with the electrical signal output by the coherent receiver, the second filter filters out the high frequency components in the mixed signal to convert the electrical signal to baseband, and the second analog-to-digital converter converts the electrical signal converted to baseband to obtain an orthogonal digital signal.

[0147] In some possible implementations, in order to make the frequency distribution of the first detection signal and the frequency distribution of the second signal obtained by the signal receiving device fall within the sampling range of the ADC, the method further includes:

[0148] 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.

[0149] 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.

[0150] 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, and the orthogonal modulator can adjust the third RF signal and the fourth RF signal to the second polarization state of the detection light. In this case, in order to adjust the signal quality received by the signal receiving device, the method further includes:

[0151] 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.

[0152] 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 sensor device operation project.

[0153] In the above examples, 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 and other structures.

[0154] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope 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 used to obtain four electrical signals according to the local oscillator light and the signal light generated in the optical fiber under test, wherein the four electrical signals include two electrical signals in a first polarization state with orthogonal phases and two electrical signals in a second polarization state with orthogonal phases; The radio frequency analog-to-digital conversion unit is used to convert the four electrical signals into two digital signals of a first polarization state and two digital signals of a second polarization state; The frequency band calculation unit is used to calculate the spectrum of the signal light according to 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.

2. The signal receiving device according to claim 1, 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, and the four radio frequency analog-to-digital converters are connected to the four output terminals of the coherent receiver in a one-to-one correspondence; The radio frequency analog-to-digital converter comprises a digitally controlled oscillator, a first mixer, a first filter and a first analog-to-digital converter; The output end of the digital controlled oscillator is connected to the first input end of the first mixer, and the second input end of the first mixer is connected to the output end of the coherent receiver; the output end of the first mixer is connected to the input end of the first filter, the output end of the first filter is connected to the input end of the first analog-to-digital converter, and the output end of the first 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 first mixer is used to mix an electrical signal output by the coherent receiver with the radio frequency signal, the first filter is used to filter out high-frequency components in the mixed signal to convert the electrical signal to a baseband; the first analog-to-digital converter is used to convert the electrical signal converted to a 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, characterized in that: The radio frequency 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 digital 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.

4. The signal receiving device according to any one of claims 1 to 3, characterized in that: 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.

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 light pulse, or the first detection signal and the second detection signal are detection signals generated by different detection light pulses.

6. The signal receiving device according to claim 4, characterized in that: The signal receiving device further comprises 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 φOTDR signal.

7. A signal transmitting device, characterized in that: The signal transmitting device includes a laser, a coupler, a first radio frequency 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 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 orthogonal modulator is used to modulate the first radio frequency signal and the second radio frequency signal with orthogonal phases onto the detection light of the first polarization state to obtain a detection light pulse signal; The optical fiber circulator is used to connect 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.

8. The signal transmitting device according to claim 7, characterized in that: The signal transmitting device further 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 phases; The orthogonal modulator is further used to modulate the third radio frequency signal and the fourth radio frequency signal with orthogonal phases onto the detection light of 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, characterized in that: The second RF transmitting unit is further used 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.

11. An optical fiber sensing device, characterized in that: The optical fiber sensing device comprises: a laser, a coupler, a first radio frequency transmitting unit, an orthogonal 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 of which is transmitted to the orthogonal modulator as detection light, and the other is transmitted to the coherent receiver as local oscillator light; 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 orthogonal modulator is used to modulate the first radio frequency signal and the second radio frequency signal with orthogonal phases onto the detection light of the first polarization state to obtain a detection light pulse signal; The optical fiber circulator is used to connect 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 to the coherent receiver; The coherent receiver is used to obtain four electrical signals according to the local oscillator light and the signal light generated in the optical fiber under test, wherein the four electrical signals include two electrical signals in a first polarization state with orthogonal phases and two electrical signals in a second polarization state with orthogonal phases; The radio frequency analog-to-digital conversion unit is used to convert the four electrical signals into 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 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.

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, and the four radio frequency analog-to-digital converters are connected to the four output terminals of the coherent receiver in a one-to-one correspondence; the radio frequency analog-to-digital converter includes a digitally controlled oscillator, a first mixer, a first filter and a first analog-to-digital converter; The output end of the digital controlled oscillator is connected to the first input end of the first mixer, and the second input end of the first mixer is connected to the output end of the coherent receiver; the output end of the first mixer is connected to the input end of the first filter, the output end of the first filter is connected to the input end of the first analog-to-digital converter, and the output end of the first 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, and the first mixer is used to mix an electrical signal output by the coherent receiver with the radio frequency signal; 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.

13. The optical fiber sensing device according to claim 11 or 12, characterized in that: The radio frequency analog-to-digital converter also includes a 90° phase shifter, a second filter and a second analog-to-digital converter; The output end of the digital 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.

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 φOTDR 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 pulse scattering of a first polarization state of the detection 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 RF transmitting unit is used to generate a third RF signal and a fourth RF signal with a third frequency and orthogonal phases; The orthogonal modulator is also used to modulate the third radio frequency signal and the fourth radio frequency signal with orthogonal phases onto the detection 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 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.

17. The optical fiber sensing device according to any one of claims 11 to 16, characterized in that: 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.

18. The optical fiber sensing device according to any one of claims 11 to 16, characterized in that: 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.

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 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.

20. The optical fiber sensing device according to claim 19, characterized in that: The second RF transmitting unit is further used to adjust 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.

21. A signal processing method, characterized in that: The method is applied to the optical fiber sensing device according to any one of claims 11 to 20, and the method comprises: The laser emits a light signal; 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; 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 orthogonal modulator modulates the first radio frequency signal and the second radio frequency signal with orthogonal phases onto the detection light in the first polarization state to obtain a detection light pulse signal; 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 the coherent receiver; The coherent receiver obtains four electrical signals according to the local oscillator light and the signal light, wherein the four electrical signals include two electrical signals in a first polarization state and orthogonal in phase and two electrical signals in a second polarization state and orthogonal in phase; The radio frequency analog-to-digital conversion unit converts 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 calculates the spectrum of the signal light according to 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.

22. The signal processing method according to claim 21, characterized in that: The method further comprises: 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 adjusts the second frequency, and / or the RF analog-to-digital converter is used to adjust the first frequency.

23. The signal processing method according to claim 21, characterized in that: The method further comprises: 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, the first RF transmitting unit adjusts the second frequency.

24. The signal processing method according to claim 21, characterized in that: The method further comprises: The second RF transmitting unit adjusts 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.

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