Distributed optical fiber vibration sensing system

Abstract

The invention relates to the technical field of optical sensing, and particularly discloses a distributed optical fiber vibration sensing system, which comprises an IQ modulator, an acoustic optical modulator, an erbium-doped optical fiber amplifier, an optical circulator, a coherent optical receiver and a polarization controller, the optical signal output end of the IQ modulator is connected with the optical signal input end of the acoustic optical modulator; the optical signal output end of the acoustic optical modulator is connected with the input end of the erbium-doped optical fiber amplifier, and the output end of the erbium-doped optical fiber amplifier is connected with the optical signal input end of the optical circulator; a first optical signal output end of the optical circulator is connected with an optical fiber to be measured, and a second optical signal output end of the optical circulator is connected with a signal optical port of the coherent optical receiver; the input end of the polarization controller is used for acquiring a second optical signal emitted from the laser, and the output end of the polarization controller is connected with the local oscillation optical port of the coherent optical receiver.

Description

Technical Field

[0001] The present application relates to the field of optical sensing technology, and in particular to a distributed optical fiber vibration sensing system. Background Art

[0002] Distributed Acoustic Sensing (DAS) is an optical fiber-based optoelectronic device that uses the sensitivity of optical fiber to sound (vibration) for continuous distributed measurement. The system senses and reconstructs sound / vibration information by detecting the phase change caused by sound waves in the optical fiber, and has many unique advantages and a wide range of applications. DAS technology is mainly based on coherent Rayleigh scattering and optical time domain reflectometry (OTDR) measurement technology. When external sound waves act on the sensing optical fiber, they cause a small strain (or vibration) in the optical fiber, which in turn causes a phase change in the signal transmitted in the optical fiber. By detecting this phase change, the detection and positioning of the acoustic signal can be achieved. Specifically, the laser emits a light pulse along the optical fiber, and some of the light interferes with the incident light in the pulse in the form of backscattering. The interference light is reflected back and received by the signal processing device. Since the speed of light remains constant, the acoustic vibration of each meter of optical fiber can be calculated.

[0003] However, in order to achieve high resolution, the traditional coherent DAS system needs to increase the bandwidth of the optical pulse, which means that a high sampling rate is required to collect the reflected signal, thereby increasing the cost of the system. At the same time, the increase in the bandwidth of the optical pulse in the frequency domain means that the energy entering the optical fiber per unit time is reduced, thereby limiting the detectable distance. To this end, many solutions have been proposed to reduce the sampling rate and system cost while maintaining the longest possible detection distance. Among them, the most effective method is to change the detection pulse into a linear frequency modulated pulse. Although traditional acousto-optic modulators can also generate frequency modulated pulse signals, their bandwidth range is limited, resulting in limited detection resolution. In order to increase the bandwidth of the pulse, using commercial optical communication devices to generate broadband frequency modulated pulse signals is an effective method with controllable cost. However, traditional commercial optical communication devices have the problem of low extinction ratio, which leads to limited signal-to-noise ratio and detection distance of the detection signal. Therefore, how to further improve the performance of commercial optical communication devices in optical fiber sensing systems and maintain low-cost characteristics is one of the key issues that need to be solved in the current field of optical fiber sensing. Summary of the invention

[0004] The purpose of the present application is to provide a distributed optical fiber vibration sensing system to solve the problem of low extinction ratio of traditional commercial optical communication devices in the prior art, which leads to limited signal-to-noise ratio and detection distance of the detection signal.

[0005] To achieve the above-mentioned purpose, the embodiment of the present application provides a distributed optical fiber vibration sensing system, including: an IQ modulator, an acousto-optic modulator, an erbium-doped fiber amplifier, an optical circulator, a coherent optical receiver, and a polarization controller, wherein:

[0006] The optical signal input end of the IQ modulator is used to obtain the first optical signal emitted from the laser, and the optical signal output end of the IQ modulator is connected to the optical signal input end of the acousto-optic modulator;

[0007] The optical signal output end of the acousto-optic modulator is connected to the input end of the erbium-doped fiber amplifier, and the output end of the erbium-doped fiber amplifier is connected to the optical signal input end of the optical circulator;

[0008] The first optical signal output end of the optical circulator is connected to the optical fiber to be tested, and the second optical signal output end of the optical circulator is connected to the signal optical port of the coherent optical receiver;

[0009] The input end of the polarization controller is used to obtain the second optical signal emitted from the laser, and the output end of the polarization controller is connected to the local oscillator optical port of the coherent optical receiver.

[0010] Optionally, it also includes:

[0011] A coupler, wherein two output ends of the coupler are respectively connected to the optical signal input end of the IQ modulator and the input end of the polarization controller.

[0012] Optionally, it also includes:

[0013] A laser, wherein the output end of the laser is connected to the input end of the coupler.

[0014] Optionally, it also includes:

[0015] An arbitrary waveform generator, wherein the output end of the arbitrary waveform generator is connected to the two electrical signal input ends of the IQ modulator.

[0016] Optionally, it also includes:

[0017] A function generator, wherein the output end of the function generator is connected to the pulse electrical signal port of the acousto-optic modulator.

[0018] Optionally, it also includes:

[0019] A data acquisition card, wherein two input terminals of the data acquisition card are respectively connected to two electrical signal output terminals of the coherent optical receiver.

[0020] Optionally, the second optical signal is received as local oscillator light in coherent beat frequency with the reflected optical signal, and the polarization controller is used to ensure that the polarization state of the signal as local oscillator light is consistent with the polarization state of the local oscillator light port of the coherent optical receiver.

[0021] Optionally, after the first optical signal enters the IQ modulator, a linear frequency modulated pulse electrical signal is generated by the arbitrary waveform generator, and the linear frequency modulated pulse electrical signal is modulated onto the first optical signal by the IQ modulator, and the modulated first optical signal is then shifted by the acousto-optic modulator to further improve the extinction ratio of the optical pulse;

[0022] After being amplified in the erbium-doped fiber amplifier, the first optical signal enters the optical fiber link to be tested through the optical circulator.

[0023] The embodiments of the present application have the following advantages:

[0024] Compared with the existing technology, the distributed optical fiber vibration sensing system provided by the above technical solution can achieve the generation of high extinction ratio and broadband modulated pulse signals through cascaded IQ modulators and acousto-optic modulators. The use of inner heterodyne reception in the receiving process can effectively reduce the sampling rate requirements and control the cost of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for the implementation methods or the description of the prior art. Obviously, the drawings described below are only exemplary, and for ordinary technicians in this field, other implementation drawings can be derived from the provided drawings without creative work.

[0026] Figure 1 A schematic diagram of the overall system architecture of a distributed optical fiber vibration sensing system provided for at least one embodiment of the present application;

[0027] Figure 2 A schematic diagram of a spectrum loaded into an IQ modulator of a distributed optical fiber vibration sensing system provided by at least one embodiment of the present application;

[0028] Figure 3 A schematic diagram of a spectrum of a distributed optical fiber vibration sensing system after frequency shift by an acousto-optic modulator provided in at least one embodiment of the present application;

[0029] Figure 4 A schematic diagram of positioning vibration points of a distributed optical fiber vibration sensing system provided by at least one embodiment of the present application;

[0030] Figure 5A time domain diagram of a demodulated vibration point signal of a distributed optical fiber vibration sensing system provided in at least one embodiment of the present application. DETAILED DESCRIPTION

[0031] The following is a description of the implementation of the present application by specific specific embodiments. People familiar with the technology can easily understand other advantages and effects of the present application from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0032] In the description of the present application, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application. Unless otherwise clearly specified and limited, the terms "set", "install", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be a connection between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0033] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0034] The present application embodiment provides a distributed optical fiber vibration sensing system, referring to Figures 1 to 5 , including: IQ modulator, acousto-optic modulator, erbium-doped fiber amplifier, optical circulator, coherent optical receiver, polarization controller, among which,

[0035] The optical signal input end of the IQ modulator is used to obtain the first optical signal emitted from the laser, and the optical signal output end of the IQ modulator is connected to the optical signal input end of the acousto-optic modulator;

[0036] The optical signal output end of the acousto-optic modulator is connected to the input end of the erbium-doped fiber amplifier, and the output end of the erbium-doped fiber amplifier is connected to the optical signal input end of the optical circulator;

[0037] The first optical signal output end of the optical circulator is connected to the optical fiber to be tested, and the second optical signal output end of the optical circulator is connected to the signal optical port of the coherent optical receiver;

[0038] The input end of the polarization controller is used to obtain the second optical signal emitted from the laser, and the output end of the polarization controller is connected to the local oscillator optical port of the coherent optical receiver.

[0039] In some embodiments, it also includes:

[0040] A coupler, wherein two output ends of the coupler are respectively connected to the optical signal input end of the IQ modulator and the input end of the polarization controller.

[0041] In some embodiments, it also includes:

[0042] A laser, wherein the output end of the laser is connected to the input end of the coupler.

[0043] In some embodiments, it also includes:

[0044] An arbitrary waveform generator, wherein the output end of the arbitrary waveform generator is connected to the two electrical signal input ends of the IQ modulator. The two electrical signal input ports of the IQ modulator correspond to the real part and the imaginary part of the electrical signal respectively.

[0045] In some embodiments, it also includes:

[0046] A function generator, wherein the output end of the function generator is connected to the pulse electrical signal port of the acousto-optic modulator.

[0047] In some embodiments, it also includes:

[0048] A data acquisition card, wherein two input terminals of the data acquisition card are respectively connected to two electrical signal output terminals of the coherent optical receiver. The two electrical signal output terminals of the coherent optical receiver respectively correspond to the real part and the imaginary part of the electrical signal.

[0049] Specifically, Figure 1 The overall system architecture diagram for the implementation of this application describes that after the laser is divided into two optical signals, namely the first optical signal and the second optical signal, after the coupler, the second optical signal is used as the local oscillator light to perform coherent beat frequency reception with the reflected optical signal, and the second optical signal first enters the polarization controller. The polarization controller is used to ensure that the polarization state of the signal as the local oscillator light is consistent with the polarization state of the local oscillator light port of the coherent optical receiver.

[0050] The first optical signal enters the IQ modulator, generates a linear frequency modulated pulse electrical signal through an arbitrary waveform generator, and modulates the linear frequency modulated pulse electrical signal onto the first optical signal through the IQ modulator. The modulated first optical signal is then shifted by the acousto-optic modulator to further improve the extinction ratio of the optical pulse. The function generator is used to generate a pulse signal and load it onto the acousto-optic modulator, so that the light can pass through when the pulse is at a high level, but cannot pass through when the pulse is at a low level. After that, the first optical signal is amplified in the erbium-doped fiber amplifier and enters the optical fiber link to be tested through the optical circulator. Due to the Rayleigh scattering effect in the optical fiber, the optical signal will generate a reflected optical signal during transmission. The reflected optical signal enters the coherent optical receiver through the first optical signal output end and the second optical signal output end of the optical circulator. Finally, the electrical signal generated by the coherent receiver is converted into a digital signal in the data acquisition card and further processed as a digital signal.

[0051] Specifically, Figure 2 Schematic diagram of the spectrum of the frequency modulated electrical signal generated by the arbitrary waveform generator loaded into the IQ modulator. In some embodiments, the spectrum range of the single sideband frequency modulated signal is defined as -100 MHz to -300 MHz, and the bandwidth of the signal is 200 MHz.

[0052] Specifically, Figure 3 It is a spectrum diagram after the frequency shift of the acousto-optic modulator. In some embodiments, it is assumed that the frequency shift of the acousto-optic modulator is 200MHz, which is also the fixed frequency shift of the common commercial acousto-optic modulator. After the frequency shift, the signal spectrum range of the frequency-modulated light pulse changes from -100MHz to +100MHz, thereby ensuring that the signal can be received in an intra-differential manner. Since the upper limit of the bandwidth has changed from 300MHz to 100MHz, according to the sampling theorem, this changes the sampling rate from the traditional 600MHz to 200MHz. It should be pointed out that the bandwidth of the optical signal is related to the detection accuracy. The larger the bandwidth value, the higher the detection accuracy. In some embodiments, the bandwidth value of the optical signal is still 200MHz, thereby ensuring that the detection accuracy will not be affected by the spectrum shift.

[0053] Specifically, Figure 4 1 is a vibration point location map obtained after the digital signal processing process in some embodiments. It can be seen that the location of the vibration point can be clearly identified.

[0054] Specifically, Figure 5 After the vibration point is found, the time domain waveform of the vibration point is restored. It can be seen that the sine waveform of the vibration point can also be accurately restored.

[0055] In summary, compared with the prior art, in a distributed coherent photoacoustic wave sensing system, the present application can achieve the generation of a high extinction ratio and a broadband modulated pulse signal by cascading an IQ modulator and an acousto-optic modulator, and utilizes an inner heterodyne reception method during the receiving process to effectively reduce the sampling rate requirements and control the cost of the system.

[0056] The principles of this application system are as follows:

[0057] In the process of pulse generation, an IQ modulator is used to generate a single-sideband broadband frequency-modulated pulse. The modulated optical pulse is then passed through an acousto-optic modulator to further improve the frequency shift and extinction ratio. It should be noted that after the optical pulse is frequency-shifted, its center frequency is consistent with the frequency of the transmitting laser. Therefore, the reception of this pulse needs to adopt an intra-heterodyne reception method. This also ensures that the sampling frequency of the data acquisition card only needs to be greater than the bandwidth of the optical pulse, thereby reducing the sampling rate required for data acquisition, effectively reducing the power consumption and cost of the coherent light distributed vibration fiber optic sensing system while improving the quality of the detection pulse.

[0058] Note that, unless otherwise directly stated, all features disclosed in this specification (including any attached claims, abstracts and drawings) may be replaced by alternative features for achieving the same, equivalent or similar purposes. Therefore, unless otherwise explicitly stated, each feature disclosed is only an example of a group of equivalent or similar features. Where used, further, preferably, further and more preferably are simple beginnings for elaborating another embodiment based on the aforementioned embodiment, and the content of the further, preferably, further or more preferably followed by the combination with the aforementioned embodiment constitutes a complete construction of another embodiment. Several further, preferably, further or more preferably settings following the same embodiment can be arbitrarily combined to form another embodiment.

[0059] In the implementation of functions and steps, the corresponding functions and steps in various embodiments may also occur in a different order than shown. For example, two consecutive functions and steps may actually be performed or implemented substantially in parallel, and they may sometimes be performed or implemented in the opposite order, depending on the functions involved.

[0060] Although the present application has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made to the present application. Therefore, these modifications or improvements made without departing from the spirit of the present application all fall within the scope of protection claimed in the present application.

Claims

1. A distributed optical fiber vibration sensing system, characterized in that: include: IQ modulator, acousto-optic modulator, erbium-doped fiber amplifier, optical circulator, coherent optical receiver, polarization controller, among which, The optical signal input end of the IQ modulator is used to obtain the first optical signal emitted from the laser, and the optical signal output end of the IQ modulator is connected to the optical signal input end of the acousto-optic modulator; The optical signal output end of the acousto-optic modulator is connected to the input end of the erbium-doped fiber amplifier, and the output end of the erbium-doped fiber amplifier is connected to the optical signal input end of the optical circulator; The first optical signal output end of the optical circulator is connected to the optical fiber to be tested, and the second optical signal output end of the optical circulator is connected to the signal optical port of the coherent optical receiver; The input end of the polarization controller is used to obtain the second optical signal emitted from the laser, and the output end of the polarization controller is connected to the local oscillator optical port of the coherent optical receiver.

2. The distributed optical fiber vibration sensing system according to claim 1, characterized in that: Also includes: A coupler, wherein two output ends of the coupler are respectively connected to the optical signal input end of the IQ modulator and the input end of the polarization controller.

3. The distributed optical fiber vibration sensing system according to claim 2, characterized in that: Also includes: A laser, wherein the output end of the laser is connected to the input end of the coupler.

4. The distributed optical fiber vibration sensing system according to claim 1, characterized in that: Also includes: An arbitrary waveform generator, wherein the output end of the arbitrary waveform generator is connected to the two electrical signal input ends of the IQ modulator.

5. The distributed optical fiber vibration sensing system according to claim 1, characterized in that: Also includes: A function generator, wherein the output end of the function generator is connected to the pulse electrical signal port of the acousto-optic modulator.

6. The distributed optical fiber vibration sensing system according to claim 1, characterized in that: Also includes: A data acquisition card, wherein two input terminals of the data acquisition card are respectively connected to two electrical signal output terminals of the coherent optical receiver.

7. The distributed optical fiber vibration sensing system according to claim 1, characterized in that: The second optical signal is received as local oscillator light by coherent beat frequency with the reflected optical signal, and the polarization controller is used to ensure that the polarization state of the signal as local oscillator light is consistent with the polarization state of the local oscillator light port of the coherent optical receiver.

8. The distributed optical fiber vibration sensing system according to claim 1, characterized in that: After the first optical signal enters the IQ modulator, the arbitrary waveform generator generates a linear frequency modulated pulse electrical signal, and the linear frequency modulated pulse electrical signal is modulated onto the first optical signal by the IQ modulator. The modulated first optical signal is then shifted by the acousto-optic modulator to further improve the extinction ratio of the optical pulse. After being amplified in the erbium-doped fiber amplifier, the first optical signal enters the optical fiber link to be tested through the optical circulator.

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