CN108204857B - Vibration signal detection system and assembly method thereof - Google Patents
Vibration signal detection system and assembly method thereof Download PDFInfo
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- CN108204857B CN108204857B CN201611171524.2A CN201611171524A CN108204857B CN 108204857 B CN108204857 B CN 108204857B CN 201611171524 A CN201611171524 A CN 201611171524A CN 108204857 B CN108204857 B CN 108204857B
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- G01—MEASURING; TESTING
- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention discloses a vibration signal detection system and an assembly method thereof, and belongs to the field of vibration signal detection. The system comprises: the narrow-linewidth laser comprises a narrow-linewidth laser, a preamplifier, a photoelectric detector and at least two cascaded optical fiber filters positioned between the preamplifier and the photoelectric detector, wherein the narrow-linewidth laser is connected with the preamplifier, the bandwidths of the at least two optical fiber filters are equal and are x, and the narrow-linewidth laser can generate continuous laser; the passbands of at least two optical fiber filters have an overlapped part, and the bandwidth y of the overlapped part satisfies: n is more than or equal to y and less than x; wherein n is the linewidth of the narrow linewidth laser, the linewidth of the narrow linewidth laser being within the passband range of the coincident portion. The invention solves the problems that the ASE noise of the optical fiber filter is larger and the signal-to-noise ratio of the signal is reduced in the prior art, and improves the signal-to-noise ratio of the signal. The invention is used for detecting the vibration signal.
Description
Technical Field
The invention relates to the field of vibration signal detection, in particular to a vibration signal detection system and an assembly method thereof.
Background
The phase-sensitive optical time-domain reflectometer (abbreviated as Φ -OTDR) technique is also called as coherent rayleigh scattering-based optical time-domain reflectometer, and can detect vibration signals around the optical fiber by using backward rayleigh scattering light signals emitted from the sensing optical fiber by the narrow-linewidth continuous laser.
In the related art, a fiber vibration detection system based on a Φ -OTDR technique generally includes: because a backward rayleigh scattered light signal is weakened along with the extension of a detection distance, and the backward rayleigh scattered light signal received by the photoelectric detector is weak, which causes difficulty in detecting a vibration signal, a preamplifier (generally a two-stage erbium-doped fiber amplifier) is usually arranged at a port of the optical fiber circulator, the strength of the detection signal is improved by the preamplifier, and an optical fiber filter is connected between the preamplifier and the photoelectric detector for filtering Spontaneous excitation radiation (ASE) noise generated in the process of amplifying the backward rayleigh scattered light signal by the preamplifier.
However, since the bandwidth of the fiber filter (typically 50ghz to 100 ghz) is much larger than the linewidth of the narrow linewidth laser (typically less than 3 khz), when the backward rayleigh scattered light SIGNAL emitted by the laser pulse passes through the fiber filter, the ASE NOISE generated by the preamplifier when amplifying the backward rayleigh scattered light SIGNAL in the passband of the fiber filter also passes through, and the ASE NOISE passing through the fiber filter is large, thereby reducing the SIGNAL-to-NOISE RATIO (SNR).
Disclosure of Invention
In order to solve the problems that the ASE noise of an optical fiber filter is large and the signal to noise ratio of a signal is reduced in the prior art, the embodiment of the invention provides a vibration signal detection system and an assembly method thereof. The technical scheme is as follows:
in one aspect, a vibration signal detection system is provided, including:
the narrow-linewidth laser comprises a narrow-linewidth laser, a preamplifier, a photoelectric detector and at least two cascaded optical fiber filters, wherein the at least two cascaded optical fiber filters are positioned between the preamplifier and the photoelectric detector, the narrow-linewidth laser is connected with the preamplifier, the bandwidths of the at least two optical fiber filters are equal and are x, and the narrow-linewidth laser can generate continuous laser;
the passbands of the at least two optical fiber filters have an overlapped part, and the bandwidth y of the overlapped part satisfies: n is more than or equal to y and less than x;
wherein n is the linewidth of the narrow linewidth laser, the linewidth of the narrow linewidth laser being within the passband range of the coincident portion.
Optionally, the system further includes:
and the acousto-optic modulator, the power amplifier and the first optical fiber circulator are sequentially connected between the narrow linewidth laser and the preamplifier.
Optionally, the at least two optical fiber filters include: a fixed center wavelength optical fiber filter and at least one adjustable center wavelength optical fiber filter.
Optionally, the center wavelength of the fixed-center-wavelength optical fiber filter is equal to the center wavelength of the continuous laser.
Optionally, the at least two fiber filters include at least two fiber grating filters.
Optionally, the system further includes: and the number of the at least two fiber grating filters is equal to that of the at least two second fiber circulators, and the at least two fiber grating filters are correspondingly connected with the at least two second fiber circulators one by one.
Optionally, all the optical fiber filters in the at least two optical fiber filters are optical fiber filters with adjustable central wavelength.
Optionally, x is 50 gigahertz.
Optionally, each of the at least two optical fiber filters is a bandpass type optical fiber filter.
Optionally, the center wavelength of the continuous laser is 1550 nm;
the narrow linewidth laser has a linewidth of less than 3 kilohertz.
Optionally, the system further includes: and the sensing optical fiber is connected with the first optical fiber circulator.
In another aspect, a method for assembling a vibration signal detection system is provided, including:
providing a narrow linewidth laser, a preamplifier and a photodetector;
providing at least two optical fiber filters, the at least two optical fiber filters comprising: the line width of the narrow-linewidth laser is within the range of the passband of the first optical fiber filter, and the bandwidths of the at least two optical fiber filters are equal and are x;
connecting the narrow linewidth laser with the preamplifier;
cascading the at least two fiber filters between the preamplifier and the photodetector, and adjusting the center wavelength of at least one of the at least two fiber filters so that there is an overlap in the pass bands of the at least two fiber filters, and the bandwidth y of the overlap satisfies: n is more than or equal to y and less than x;
wherein n is the linewidth of the narrow linewidth laser.
Optionally, the connecting the narrow linewidth laser and the preamplifier includes:
and connecting the narrow-linewidth laser with the preamplifier through an acousto-optic modulator, a power amplifier and a first optical fiber circulator which are connected in sequence.
Optionally, the at least two optical fiber filters include: a fixed center wavelength optical fiber filter and at least one adjustable center wavelength optical fiber filter,
the adjusting the center wavelength of at least one of the at least two fiber filters includes:
and adjusting the center wavelength of the at least one fiber filter with the adjustable center wavelength.
Optionally, all the optical fiber filters in the at least two optical fiber filters are optical fiber filters with adjustable central wavelength,
the adjusting the center wavelength of at least one of the at least two fiber filters includes:
adjusting a center wavelength of each of the at least two fiber filters.
The technical scheme provided by the embodiment of the invention has the following beneficial effects:
the vibration signal detection system and the assembly method thereof provided by the embodiment of the invention have the advantages that at least two optical fiber filters are cascaded, the overlapped part of the pass bands of the at least two optical fiber filters is used as the pass band of the cascaded optical fiber filters, compared with a single optical fiber filter, the bandwidth of the pass band is reduced, ASE noise generated by a preamplifier out of the range of the pass band of the cascaded optical fiber filters is filtered while backward Rayleigh scattering light signals emitted by laser pulses pass through the pass band of the cascaded optical fiber filters, and when the noise passing through the cascaded optical fiber filters is reduced, the voltage effective value of the noise is correspondingly reduced, so that the signal-to-noise ratio of the signals is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without creative efforts.
Fig. 1-1 is a schematic structural diagram of a vibration signal detection system according to an embodiment of the present invention;
fig. 1-2 are schematic diagrams of linewidths of narrow linewidth lasers provided by embodiments of the present invention;
fig. 2-1 is a schematic diagram illustrating a relationship between a linewidth of a narrow linewidth laser and a passband of a fiber filter according to an embodiment of the present invention;
fig. 2-2 is a schematic diagram of the relationship between the linewidth of another narrow linewidth laser and the passband of a fiber filter according to an embodiment of the present invention;
2-3 are schematic structural diagrams of another vibration signal detection system provided by the embodiment of the invention;
fig. 2-4 are schematic diagrams illustrating a relationship between a line width of a narrow-line-width laser and a passband of a fiber grating filter according to an embodiment of the present invention;
fig. 3 is a flowchart of a method for assembling a vibration signal detection system according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
An embodiment of the present invention provides a vibration signal detection system, as shown in fig. 1-1, including:
the laser comprises a narrow linewidth laser 101, a preamplifier 102 and a photoelectric detector 103, and at least two cascaded optical fiber filters 104 positioned between the preamplifier 102 and the photoelectric detector 103, wherein the narrow linewidth laser 101 is connected with the preamplifier 102, the bandwidths of the at least two optical fiber filters 104 are equal, and are x, and the narrow linewidth laser 101 can generate continuous laser light. The continuous laser may be a laser output of 6 powers or more of 10 within 1 second.
The passbands of the at least two optical fiber filters 104 have an overlap, and the bandwidth y of the overlap satisfies: n is more than or equal to y and less than x; where n is the linewidth of the narrow linewidth laser 101, the linewidth of the narrow linewidth laser 101 is within the passband of the overlap.
It should be noted that the passband of the optical fiber filter refers to a frequency passband through which signals can pass, and the bandwidth of the optical fiber filter refers to the width of the passband of the optical fiber filter, that is, the frequency range difference of the passband; the line width of the narrow-line-width laser refers to a frequency range of laser light generated by the narrow-line-width laser, specifically, as shown in fig. 1-2, the spectral intensity of the laser light generated by the narrow-line-width laser is measured in a frequency domain range, and a difference value between two frequencies (w1, w2) corresponding to a half (V/2) of a peak value V of the spectral intensity is a line width n of the narrow-line-width laser. The continuous laser generated by the narrow linewidth laser can be converted into laser pulses under the modulation of the acousto-optic modulator.
In addition, the signal-to-noise ratio of the signal is formulated as: SNR 20LOG (Vs/Vn); where Vs represents a voltage effective value of the signal, Vn represents a voltage effective value of the noise, SNR (signal-to-noise ratio) is in dB (decibel), and LOG (Vs/Vn) represents logarithm taken as (Vs/Vn).
In summary, in the vibration signal detection system provided in the embodiment of the present invention, at least two optical fiber filters are cascaded, and the overlapping portion of the pass bands of the at least two optical fiber filters is used as the pass band of the cascaded optical fiber filters, compared with a single optical fiber filter, the bandwidth of the pass band is reduced, so that when backward rayleigh scattered light signals emitted by laser pulses pass through the pass band of the cascaded optical fiber filters, ASE noise generated by a preamplifier outside the range of the pass band of the cascaded optical fiber filters is filtered, and when noise passing through the cascaded optical fiber filters is reduced, correspondingly, the voltage effective value of the noise is also reduced, thereby improving the signal-to-noise ratio of the signals.
It is noted that the vibration signal detection system may be a Φ -OTDR system.
Wherein each of the at least two optical fiber filters is a bandpass type optical fiber filter, and bandwidths x of the at least two optical fiber filters are fixed and can be 50GHz (gigahertz); a narrow linewidth laser, having a linewidth of less than 3kHz, produces continuous laser light having a center wavelength of 1550 nanometers. Wherein the wavelength of the laser is inversely proportional to the frequency: wavelength is the speed of light/frequency.
Optionally, the arrangement of at least two optical fiber filters in the vibration signal detection system may include the following three cases:
in a first case, applied to the vibration signal detection system as shown in fig. 1-1, the at least two optical fiber filters may include: a fixed center wavelength optical fiber filter and at least one adjustable center wavelength optical fiber filter. It is assumed that the at least two fiber filters comprise: fig. 2-1 is a schematic diagram of a relationship between a line width n of a narrow-line-width laser and pass bands of two optical fiber filters, as shown in fig. 2-1, an abscissa is frequency and a unit is Hz, and an ordinate is spectral intensity and a unit is decibel (dB), where a pass band of the first optical fiber filter 104a is M1, a pass band of the second optical fiber filter 104b is M2, and bandwidths of the first optical fiber filter and the second optical fiber filter are both x.
It should be noted that the line width of the narrow-line-width laser is within the pass band of the first optical fiber filter.
Alternatively, as shown in fig. 2-1, the center wavelength of the first optical fiber filter may be equal to the center wavelength of the continuous laser, that is, the center wavelength of the first optical fiber filter may be 1550 nm. Since the bandpass type optical fiber filter has the weakest suppression effect on the signal at the center wavelength, when the center wavelength of the first optical fiber filter is equal to the center wavelength of the continuous laser beam, the loss of the signal passing through the first optical fiber filter can be minimized, that is, the backward rayleigh scattered light signal generated by the laser pulse can be maximally passed.
Specifically, the first optical fiber filter may be connected to the preamplifier, the second optical fiber filter is connected in series to the output end of the first optical fiber filter, after the two optical fiber filters are cascaded, the center wavelength of the second optical fiber filter is adjusted, and the overlapping portion y of the passband of the cascaded optical fiber filters is reduced, optionally, y may be n + x/2, where n is the line width of the narrow-line-width laser, so that the ASE noise generated by the preamplifier can be filtered to the maximum extent while the optical signal passes through the cascaded optical fiber filters. In the embodiment of the present invention, the positions of the first optical fiber filter and the second optical fiber filter are not limited, and the second optical fiber filter may be connected to a preamplifier, and the first optical fiber filter may be connected in series to the output end of the second optical fiber filter.
In the second case, applied to the vibration signal detection system as shown in fig. 1-1, all of the at least two optical fiber filters may be optical fiber filters with center wavelength tunable. Assuming that two optical fiber filters with adjustable central wavelengths are arranged in the system, fig. 2-2 is a schematic diagram of a relationship between a line width n of a narrow-line-width laser and pass bands of the two optical fiber filters, as shown in fig. 2-2, an abscissa is frequency in Hz, and an ordinate is spectral intensity in decibels (dB), wherein the pass bands of the two optical fiber filters are M3 and M4, respectively, and the bandwidths of the two optical fiber filters are both x.
Specifically, an optical fiber filter (referred to as an optical fiber filter 1 for ease of description) is connected to the preamplifier, and the center wavelength of the optical fiber filter 1 is adjusted so that the line width of the narrow-line-width laser is within the passband of the optical fiber filter 1. And connecting another optical fiber filter (called as an optical fiber filter 2) to the output end of the optical fiber filter 1, cascading the two optical fiber filters, adjusting the central wavelengths of the cascaded optical fiber filter 1 and the optical fiber filter 2, reducing the overlapped part of the pass bands of the two cascaded optical fiber filters, ensuring that the ASE noise generated by the preamplifier is filtered to the maximum extent while an optical signal passes through the cascaded optical fiber filters.
In a third case, the system is applied to the vibration signal detection system shown in fig. 2-3, the at least two fiber filters may be fiber grating filters, the system may further include at least two second fiber circulators, and the number of the fiber grating filters is the same as the number of the second fiber circulators, and the fiber grating filters are connected in a one-to-one correspondence manner. Assuming that two fiber grating filters are disposed in the system, two second fiber circulators, which are respectively referred to as a second fiber circulator 1091 and a second fiber circulator 1092, are disposed in the system. Fig. 2-4 are schematic diagrams showing a relationship between a line width n of a narrow line width laser and pass bands of two fiber grating filters, as shown in fig. 2-4, where the abscissa is frequency in Hz, and the ordinate is spectral intensity in decibels (dB), reflection pass bands of the two fiber grating filters are M5 and M6, respectively, and reflection spectral bandwidths of the two fiber grating filters are both x.
Specifically, a fiber grating filter (referred to as a fiber grating filter 1 for ease of description) is connected to the preamplifier through a second fiber circulator (referred to as a second fiber circulator 1 for ease of description), so that the line width of the narrow-line-width laser is within the reflection spectrum range of the fiber grating filter 1. And then another fiber grating filter (called as a fiber grating filter 2) is connected to the output end of the second fiber circulator 1 through a second fiber circulator (called as a second fiber circulator 2), after the two fiber grating filters are cascaded through the two second fiber circulators, the central wavelengths of the reflection spectrums of the fiber grating filter 1 and the fiber grating filter 2 are adjusted, the overlapped part of the reflection spectrums of the two cascaded fiber grating filters is reduced, and the ASE noise generated by the preamplifier is furthest filtered while the optical signal passes through the cascaded fiber grating filters.
Further, as shown in fig. 1-1, the system may further include an acousto-optic modulator 105, a power amplifier 106 and a first fiber circulator 107 connected in sequence between the narrow linewidth laser 101 and the preamplifier 102.
It should be noted that the system further includes: a sensing fiber 108 connected to the first fiber circulator 107.
Specifically, in the vibration signal detection system shown in fig. 1-1, a narrow line width laser 101 is used to generate continuous laser light; the acousto-optic modulator 105 is connected with the narrow linewidth laser 101 and is used for modulating continuous laser generated by the narrow linewidth laser 101 into laser pulses; the power amplifier 106 is connected with the acousto-optic modulator 105 and is used for amplifying the laser pulse; the amplified laser pulse is transmitted into the first optical fiber circulator 107 through a port 107a of the first optical fiber circulator 107, and is transmitted into a sensing optical fiber 108 connected with the first optical fiber circulator 107 through a port 107b of the first optical fiber circulator 107, when the laser pulse is transmitted in the sensing optical fiber 108, a backward rayleigh scattered light signal is generated, an optical signal generated by the laser pulse can be transmitted into the first optical fiber circulator 107 through a port 107b of the first optical fiber circulator 107, and is transmitted into a preamplifier 102 connected with the first optical fiber circulator 107 through a port 107c of the first optical fiber circulator 107, and the preamplifier 102 amplifies the optical signal; the amplified optical signal is transmitted to the photodetector 103 through at least two cascaded optical fiber filters 104; the photodetector 103 converts the optical signal into a digital signal, transmits the digital signal to an upper computer through an output end, and detects the digital signal through the upper computer.
Optionally, each of the at least two optical fiber filters may be an optical fiber filter with a lorentz spectrum composed of a single F-P resonant cavity. Optionally, in order to better suppress ASE noise outside the passband of the cascaded fiber filters, each of the at least two fiber filters may be a bandpass fiber filter with a steeper falling edge and a smooth top, and formed by stacking a plurality of F-P resonators.
Alternatively, as shown in fig. 2-3, the system may include an acousto-optic modulator 105, a power amplifier 106 and a first fiber optic circulator 107 connected in series between a narrow linewidth laser 101 and a preamplifier 102.
Specifically, in the vibration signal detection system shown in fig. 2 to 3, a narrow line width laser 101 is used to generate continuous laser light; the acousto-optic modulator 105 is connected with the narrow linewidth laser 101 and is used for modulating continuous laser generated by the narrow linewidth laser 101 into laser pulses; the power amplifier 106 is connected with the acousto-optic modulator 105 and is used for amplifying the laser pulse; the amplified laser pulse is transmitted into the first optical fiber circulator 107 through a port 107a of the first optical fiber circulator 107, and is transmitted into a sensing optical fiber 108 connected with the first optical fiber circulator 107 through a port 107b of the first optical fiber circulator 107, when the laser pulse is transmitted in the sensing optical fiber 108, a backward rayleigh scattered light signal is generated, an optical signal generated by the laser pulse can be transmitted into the first optical fiber circulator 107 through a port 107b of the first optical fiber circulator 107, and is transmitted into a preamplifier 102 connected with the first optical fiber circulator 107 through a port 107c of the first optical fiber circulator 107, and the preamplifier 102 amplifies the optical signal; the amplified optical signal is transmitted to the second fiber circulator 1091 through a port 1091 a of the second fiber circulator 1091, and then transmitted to the fiber grating filter 104 connected to the second fiber circulator 1091 through a port 1091b of the second fiber circulator 1091, after the optical signal is filtered by the fiber grating filter 104, the optical signal is transmitted to the second fiber circulator 1091 through the port 1091b, and then enters the second fiber circulator 1092 through a port 1091c of the second fiber circulator 1091, the second fiber circulator 1092 also has three ports, which are a port 1092a, a port 1092b and a port 1092c, and the specific working process may refer to the working process of the second fiber circulator 1091, which is not described herein; the optical signal is transmitted to the photodetector 103 through the port 1092c of the second fiber optic circulator 1092; the photodetector 103 converts the optical signal into a digital signal, transmits the digital signal to an upper computer through an output end, and detects the digital signal through the upper computer.
In summary, in the vibration signal detection system provided in the embodiment of the present invention, at least two optical fiber filters are cascaded, and a superposed portion of the pass bands of the at least two optical fiber filters is used as the pass band of the cascaded optical fiber filters, compared with a single optical fiber filter, the bandwidth of the pass band is reduced, so that while backward rayleigh scattered light signals emitted by laser pulses pass through the pass band of the cascaded optical fiber filters, ASE noise generated by a preamplifier outside the range of the pass band of the cascaded optical fiber filters is filtered, and when the noise passing through the cascaded optical fiber filters is reduced, correspondingly, the voltage effective value of the noise is also reduced, thereby improving the signal-to-noise ratio of the signals, and the reduction of the ASE noise also improves the accuracy of signal data acquired by a data acquisition card in a photodetector, so as to facilitate the processing of subsequent data.
The embodiment of the invention provides an assembly method of a vibration signal detection system, which comprises the following steps of:
Wherein n is the linewidth of the narrow linewidth laser.
It should be noted that the narrow linewidth laser may generate continuous laser light, and the continuous laser light may be converted into laser pulses under the modulation of the acousto-optic modulator.
In summary, in the vibration signal detection system assembly method provided in the embodiments of the present invention, at least two optical fiber filters are cascaded, and the overlapping portion of the pass bands of the at least two optical fiber filters is used as the pass band of the cascaded optical fiber filters, so that compared with a single optical fiber filter, the bandwidth of the pass band is reduced, ASE noise generated by a preamplifier located outside the pass band range of the cascaded optical fiber filters is filtered while backward rayleigh scattered light signals emitted by laser pulses pass through the pass band of the cascaded optical fiber filters, and when the noise passing through the cascaded optical fiber filters is reduced, the voltage effective value of the noise is correspondingly reduced, thereby improving the signal-to-noise ratio of the signals.
Optionally, as shown in fig. 1-1, connecting the narrow linewidth laser 101 to the preamplifier 102 includes: the narrow-linewidth laser 101 is connected to the preamplifier 102 via an acousto-optic modulator 105, a power amplifier 106 and a first fiber circulator 107, which are connected in sequence.
Optionally, the at least two optical fiber filters may include: a fixed center wavelength optical fiber filter and at least one center wavelength tunable optical fiber filter, the center wavelength of at least one of the at least two optical fiber filters being tuned, comprising: the center wavelength of at least one center wavelength tunable optical fiber filter is adjusted.
By way of example, it is assumed that the at least two fiber filters comprise: a first optical fiber filter with a fixed center wavelength and a second optical fiber filter with an adjustable center wavelength. Specifically, the first optical fiber filter may be connected to the preamplifier, the second optical fiber filter is connected in series to the output end of the first optical fiber filter, after the two optical fiber filters are cascaded, the center wavelength of the second optical fiber filter is adjusted, and the overlapping portion y of the passband of the cascaded optical fiber filter is reduced, optionally, y may be equal to n + and 2, where n is the line width of the narrow-line-width laser, so that the ASE noise generated by the preamplifier can be filtered to the maximum extent while the optical signal passes through the cascaded optical fiber filter. In the embodiment of the present invention, the positions of the first optical fiber filter and the second optical fiber filter are not limited, and the second optical fiber filter may be connected to a preamplifier, and the first optical fiber filter may be connected in series to the output end of the second optical fiber filter.
Optionally, all the optical fiber filters in the at least two optical fiber filters may be optical fiber filters with adjustable center wavelengths, and adjusting the center wavelength of at least one optical fiber filter in the at least two optical fiber filters includes: the center wavelength of each of the at least two fiber filters is adjusted.
By way of example, it is assumed that two center wavelength tunable fiber filters are provided in the system. Specifically, an optical fiber filter (referred to as an optical fiber filter 1 for ease of description) is connected to the preamplifier, and the center wavelength of the optical fiber filter 1 is adjusted so that the line width of the narrow-line-width laser is within the passband of the optical fiber filter 1. And connecting another optical fiber filter (called as an optical fiber filter 2) to the output end of the optical fiber filter 1, cascading the two optical fiber filters, adjusting the central wavelengths of the cascaded optical fiber filter 1 and the optical fiber filter 2, reducing the overlapped part of the pass bands of the two cascaded optical fiber filters, ensuring that the ASE noise generated by the preamplifier is filtered to the maximum extent while an optical signal passes through the cascaded optical fiber filters.
Alternatively, as shown in fig. 2-3, it is assumed that two fiber grating filters are provided in the system. Specifically, a fiber grating filter (referred to as the fiber grating filter 1 for the sake of convenience of description) is connected to the preamplifier through a second fiber circulator (referred to as the second fiber circulator 1 for the sake of convenience of description). And the other fiber grating filter (called as the fiber grating filter 2) is connected with the output port of the second fiber circulator 1 through a second fiber circulator (called as the second fiber circulator 2). The overlapping part of the pass bands of the two cascaded fiber grating filters is reduced, so that ASE noise generated by the preamplifier is filtered to the maximum extent while the optical signal passes through the cascaded fiber grating filters.
In summary, in the vibration signal detection system provided in the embodiment of the present invention, at least two optical fiber filters are cascaded, and a superposed portion of the pass bands of the at least two optical fiber filters is used as the pass band of the cascaded optical fiber filters, compared with a single optical fiber filter, the bandwidth of the pass band is reduced, so that while backward rayleigh scattered light signals emitted by laser pulses pass through the pass band of the cascaded optical fiber filters, ASE noise generated by a preamplifier outside the range of the pass band of the cascaded optical fiber filters is filtered, and when the noise passing through the cascaded optical fiber filters is reduced, correspondingly, the voltage effective value of the noise is also reduced, thereby improving the signal-to-noise ratio of the signals, and the reduction of the ASE noise also improves the accuracy of signal data acquired by a data acquisition card in a photodetector, so as to facilitate the processing of subsequent data.
With regard to the vibration signal detection system assembly method in the above-described embodiment, the specific manner in which the respective steps perform operations has been described in detail in the embodiment related to the system, and will not be described in detail here.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. A vibration signal detection system, comprising:
the narrow-linewidth laser comprises a narrow-linewidth laser, a preamplifier, a photoelectric detector and at least two cascaded optical fiber filters, wherein the at least two cascaded optical fiber filters are positioned between the preamplifier and the photoelectric detector, the narrow-linewidth laser is connected with the preamplifier, the bandwidths of the at least two optical fiber filters are equal and are x, and the narrow-linewidth laser can generate continuous laser;
the passbands of the at least two optical fiber filters have an overlapped part, and the bandwidth y of the overlapped part satisfies: n is less than or equal to y and less than x;
wherein n is the linewidth of the narrow linewidth laser, the linewidth of the narrow linewidth laser being within the passband range of the overlap portion;
the at least two optical fiber filters include: a fiber filter with a fixed central wavelength and at least one fiber filter with an adjustable central wavelength, wherein the central wavelength of the fiber filter with the fixed central wavelength is equal to the central wavelength of the continuous laser;
the optical fiber filter with the fixed central wavelength is connected with the preamplifier, and after the optical fiber filter with the adjustable central wavelength is connected with the output end of the optical fiber filter with the fixed central wavelength in series, the central wavelength of the optical fiber filter with the adjustable central wavelength is adjusted, and the bandwidth y of the overlapped part of the pass bands of the at least two optical fiber filters is reduced, so that y is n + x/2.
2. The system of claim 1, further comprising:
and the acousto-optic modulator, the power amplifier and the first optical fiber circulator are sequentially connected between the narrow linewidth laser and the preamplifier.
3. The system of any of claims 1-2, wherein x is 50 gigahertz.
4. The system according to any of claims 1 to 2, wherein each of said at least two fiber filters is a bandpass type fiber filter.
5. The system of claim 1,
the center wavelength of the continuous laser is 1550 nanometers;
the narrow linewidth laser has a linewidth of less than 3 kilohertz.
6. The system of claim 2, further comprising: and the sensing optical fiber is connected with the first optical fiber circulator.
7. A method of assembling a vibration signal detection system, comprising:
providing a narrow linewidth laser, a preamplifier and a photodetector;
providing at least two optical fiber filters, the at least two optical fiber filters comprising: the line width of the narrow-linewidth laser is within the range of the passband of the first optical fiber filter, and the bandwidths of the at least two optical fiber filters are equal and are x;
connecting the narrow linewidth laser with the preamplifier;
cascading the at least two fiber filters between the preamplifier and the photodetector, and adjusting the center wavelength of at least one of the at least two fiber filters so that there is an overlap in the pass bands of the at least two fiber filters, and the bandwidth y of the overlap satisfies: n is less than or equal to y and less than x;
wherein n is the linewidth of the narrow linewidth laser;
the at least two optical fiber filters include: a fixed center wavelength optical fiber filter and at least one tunable center wavelength optical fiber filter, said tuning the center wavelength of at least one of said at least two optical fiber filters comprising: adjusting the center wavelength of the at least one center wavelength tunable optical fiber filter;
and after the optical fiber filter with the adjustable central wavelength is connected with the output end of the optical fiber filter with the fixed central wavelength in series, the central wavelength of the optical fiber filter with the adjustable central wavelength is adjusted, and the bandwidth y of the overlapped part of the pass bands of the at least two optical fiber filters is reduced, so that the y is n + x/2.
8. The method of claim 7,
said coupling said narrow linewidth laser to said preamplifier comprising:
and connecting the narrow-linewidth laser with the preamplifier through an acousto-optic modulator, a power amplifier and a first optical fiber circulator which are connected in sequence.
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