CN111678583A - Optical fiber vibration measuring device and method for improving light source noise - Google Patents
Optical fiber vibration measuring device and method for improving light source noise Download PDFInfo
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- G—PHYSICS
- 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35306—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement
- G01D5/35329—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using an interferometer arrangement using interferometer with two arms in transmission, e.g. Mach-Zender interferometer
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
- G01D5/26—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light
- G01D5/32—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light
- G01D5/34—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells
- G01D5/353—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre
- G01D5/35338—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable characterised by optical transfer means, i.e. using infrared, visible, or ultraviolet light with attenuation or whole or partial obturation of beams of light the beams of light being detected by photocells influencing the transmission properties of an optical fibre using other arrangements than interferometer arrangements
- G01D5/35354—Sensor working in reflection
- G01D5/35358—Sensor working in reflection using backscattering to detect the measured quantity
- G01D5/35361—Sensor working in reflection using backscattering to detect the measured quantity using elastic backscattering to detect the measured quantity, e.g. using Rayleigh backscattering
Abstract
The invention provides an optical fiber vibration measurement device and method for improving light source noise, which relate to the field of optical fiber distributed vibration measurement.A feed-forward loop of a light source noise suppression feed-forward structure obtains two mutually orthogonal interference optical signals based on an optical fiber interferometer and a 90-degree optical mixer, and respectively outputs the two interference optical signals to a photoelectric balance detector 1 and a photoelectric balance detector 2, converts the two interference optical signals into two interference electrical signals and outputs the two interference electrical signals to a tracker; the method is characterized in that a light source noise suppression feedforward structure is used for suppressing the phase noise of continuous light output by a laser, and the phase noise is added to classical light
In the measuring device, the phase noise of the laser is reduced, and the measuring precision of the external vibration signal is further improved.
Description
Technical Field
The disclosure relates to the field of optical fiber distributed vibration measurement, and in particular to an optical fiber vibration measurement device and method for improving light source noise.
Background
The statements in this section merely provide background information related to the present disclosure and may not necessarily constitute prior art.
The optical time domain reflection measurement technology is an essential technology in optical cable construction, maintenance and monitoring, and is based on the principle of backward scattering and Fresnel reverse of light, and utilizes the backward scattering light wave generated when pulse light wave propagates in an optical fiber to obtain the information of energy (amplitude) attenuation, so that the optical time domain reflection measurement technology can be used for measuring the optical fiber attenuation, joint loss, optical fiber fault point positioning, knowing the loss distribution condition of the optical fiber along the length and the like.
With the continuous improvement of measurement techniques, phase-sensitive optical time-domain reflectometry, for example, has emerged
The technology,
Vibration measurement technique and based on quadratic difference
A method of measurement;
the inventors have found that for the difference based on two
According to the measuring method, when the measured environment vibrates, due to the influence of a vibration event, the sensing optical fibers behind the vibration point carry vibration information, and the sensing optical fibers in front of the vibration point do not carry vibration information. Thus, the distance D can be selectedABThe point A and the point B preliminarily eliminate the adverse effect on the measurement caused by the phase noise of the laser through phase difference, wherein the point A carries vibration information after the vibration point, and the point B does not carry vibration information before the vibration point. Further, the distance between the vibration points is selected to be DCDThe phase difference is made between the points C and D to obtain C, D phase change information between the two points. By calculating the distance DABAnd DCDThe proportional relation can eliminate the performance influence of the laser phase noise on the sensing system, compensate the measurement phase drift caused by the frequency drift in real time and improve the measurement precision of the external vibration signal, but the method is a digital signal processing method, does not reduce the laser phase noise at all and is difficult to further improve the measurement precision of the external vibration signal.
Disclosure of Invention
The disclosure aims to provide an optical fiber vibration measurement device and method with improved light source noise, which can reduce the phase noise of emergent laser and further improve the measurement accuracy of external vibration signals by adding a frequency tracking feedforward structure in the traditional phase sensitive optical time domain reflection measurement device.
The first purpose of this disclosure is to provide an optical fiber vibration measuring device with improved light source noise, which adopts the following technical scheme:
the feed-forward structure acquires continuous light and divides the continuous light into two paths, one path of continuous light sequentially passes through the interferometer, the photoelectric balance detector, the tracker, the preamplifier and the voltage-controlled oscillator, then is input into the single-side-band modulator together with the other path of continuous light, and outputs the continuous light subjected to phase noise suppression;
the measuring structure acquires continuous light subjected to phase noise suppression and divides the continuous light into two paths, wherein one path of continuous light passes through the acousto-optic modulator, the optical amplifier and the circulator and then is input into the sensing optical fiber, and backward Rayleigh scattered light carrying vibration information is coupled with the other path of continuous light and then is output to the processor through the photoelectric detector;
and the sensing optical fiber is connected with the circulator and used for acquiring the environmental vibration information along the optical fiber.
Furthermore, the interferometer divides the acquired one path of continuous light into two orthogonal interference light signals, and the two interference light signals are respectively input into the first light balance detector and the second light balance detector to be converted into two paths of interference electric signals and then input into the tracker.
Further, the tracker inputs the two acquired interference electrical signals into a preamplifier together, and drives the voltage-controlled oscillator to generate a continuous optical signal and output the continuous optical signal to the single-sideband modulator.
Furthermore, the other path of the continuous light passes through the first delay optical fiber and then is output to the single-sideband modulator, and a second delay optical fiber is arranged in the interferometer and used for adjusting the time difference of the primary difference acquired by the tracker.
Furthermore, after the continuous light obtained by the test structure is divided into two paths, the sensing optical fiber obtains one path of continuous light, emits backward Rayleigh scattering light through a port of the circulator, and is coupled with the other path of continuous light serving as local reference light to generate a coherent signal.
A second object of the present disclosure is to provide an optical fiber vibration measuring method with improved light source noise, comprising the steps of:
acquiring continuous light and dividing the continuous light into two paths in a feed-forward structure;
respectively processing two paths of continuous light and then jointly carrying out single-side band modulation to inhibit the phase noise of a light source;
dividing the continuous light subjected to the light source phase noise suppression into two paths;
one path is subjected to acousto-optic modulation and optical amplification and then is input into a sensing optical fiber through a circulator;
the circulator outputs backward Rayleigh scattering light with environmental vibration information generated in the sensing optical fiber and is coupled with the other path of continuous light to generate a coherent signal;
and processing the coherent signals to acquire the environmental vibration information along the sensing optical fiber.
Further, the feedforward mechanism specifically processes the continuous light by:
processing one path of continuous light by an interferometer to obtain two paths of orthogonal interference signals, namely an I path and a Q path;
the I path interference signal is multiplied by the Q path signal after being subjected to time averaging, and the Q path interference signal is multiplied by the I path signal after being subjected to time averaging and negation;
adding the two paths of signals obtained in the last step, and performing amplitude normalization processing to obtain an estimated value of the first-order differential light source phase noise;
amplifying the extracted first-order differential light source phase noise estimated value, and driving a voltage-controlled oscillator to output an oscillation signal;
and an oscillation signal output by the voltage-controlled oscillator and the other path of continuous light enter the single-side-band modulator together for modulation after passing through the delay optical fiber.
Further, the light source phase noise is adjusted by adjusting the sensitivity of the voltage-controlled oscillator and the estimated value of the section of differential light source noise.
Further, the backward rayleigh scattering light carries the environmental vibration information received by the sensing optical fiber and exits through the port of the circulator.
Further, the other path of continuous light coupled with the backward Rayleigh scattering light is used as local reference light.
Compared with the prior art, the utility model has the advantages and positive effects that:
(1) the method is characterized in that a light source noise suppression feedforward structure is used for suppressing the phase noise of continuous light output by a laser, and the phase noise is added to classical light
In the measuring device, the phase noise of the laser is reduced, and the measuring precision of an external vibration signal is further improved;
(2) in a feedforward loop of a light source noise suppression feedforward structure, two mutually orthogonal interference optical signals are obtained based on an optical fiber interferometer and a 90-degree optical mixer and are respectively output to a photoelectric balance detector 1 and a photoelectric balance detector 2, converted into two interference electrical signals and output to a tracker. The method avoids the frequency drift problem existing when single-path interference optical signals are adopted to carry out first-order differential light source phase noise estimation, and improves the measurement precision of the first-order differential light source phase noise, thereby being beneficial to inhibiting the light source phase noise and improving the measurement precision of external vibration signals.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure and are not to limit the disclosure.
Fig. 1 is a schematic diagram of a structure and a flow of optical fiber vibration measurement in embodiments 1 and 2 of the present disclosure;
fig. 2 is a structural diagram of a tracker in embodiments 1 and 2 of the present disclosure.
Detailed Description
It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the disclosure. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments according to the present disclosure. As used herein, the singular forms "a", "an", and/or "the" are intended to include the plural forms as well, and it should be understood that when the terms "comprises" and/or "comprising" are used in this specification, they specify the presence of stated features, steps, operations, devices, components, and/or combinations thereof;
for convenience of description, the words "up", "down", "left" and "right" in this disclosure, if any, merely indicate that the directions of movement are consistent with those of the figures themselves, and are not limiting in structure, but merely facilitate the description of the invention and simplify the description, rather than indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present disclosure.
As described in the background, the prior art is twice differenced
The measuring method is a digital signal processing method, the phase noise of the laser is not reduced fundamentally, and the measuring precision of the external vibration signal is difficult to further improve; in view of the above problems, the present disclosure provides an optical fiber vibration measurement apparatus and method with improved light source noise.
Light source noise: the linewidth of the laser cannot be infinitely narrow and there is always some phase noise (otherwise known as "frequency drift"). When pulsed light is transmitted in an optical fiber, the intensity of a backward Rayleigh scattering signal is affected by phase noise of the detected light to generate jitter, so that the signal-to-noise ratio of a measurement signal is reduced, and positioning and measurement errors of a measured vibration signal even fail.
To pair
For a system, the phase noise of the laser may reduce the measurement accuracy of the system and the spatial resolution of the system. Therefore, it is important to improve the phase noise of the optical wave. On one hand, the stability of the optical wave frequency can be improved and the phase noise can be reduced by improving the laser material, keeping the environmental temperature and humidity and the atmospheric pressure stable and the like; on the other hand, the adverse effects of the optical wave phase noise on the vibration measurement precision and the space positioning can be inhibited by designing a new optical path structure and a new data processing method.
For the former, on the basis of the existing laser manufacturing process and constant temperature, humidity and pressure treatment technology, the technology is not a technical method which is easy to realize in a short period; for the latter, a more general method is to use a quadratic difference method, which is an improved method of pure digital signal processing.
Based on quadratic difference
The detailed working principle of the measuring method is as follows:
in the classic
On the basis of the system structure, continuous light emitted by a narrow linewidth laser is divided into two paths through a coupler with a specific power ratio, wherein one path of continuous light is converted into pulse light with a specific width and period through an acousto-optic Modulator (AOM) with a frequency shift function, the pulse light enters a port of a circulator 1 after being subjected to power compensation through an Optical Amplifier (generally, an Erbium Doped Fiber Amplifier (EDFA)), and then enters a sensing Optical Fiber through the port of the circulator 3 to obtain vibration measurement information along the Optical Fiber, and backward scattered light which carries environmental vibration information and is generated in the sensing Optical Fiber passes through the port of the circulator 3 again and exits from the port of the circulator 2.
The other path of continuous light which is branched after the continuous light emitted by the light source passes through the coupler with the specific power ratio is used as local reference light. The local reference light and the backward Rayleigh scattered light emitted from the port 2 of the circulator generate coherent signals through a coupler with the ratio of 50:50, the coherent signals are converted into electric signals through a photoelectric detector and enter a data acquisition card, digital signals are obtained, data processing is carried out on the electric signals, and environmental vibration information along the optical fiber is obtained.
However, based on quadratic differences
The measuring method is a digital signal processing method, does not reduce the phase noise of the laser at all, and does not consider the feasible scheme of improving and suppressing the phase noise of the measurement by the optical path structure.
Example 1
In an exemplary embodiment of the present disclosure, as shown in fig. 1-2, an optical fiber vibration measuring device with improved light source noise is provided.
The device comprises: the device comprises a laser, a light source noise suppression feedforward structure, a coupler 3, an acousto-optic modulator, an erbium-doped fiber amplifier, a circulator, a sensing fiber, a coupler 4, a photoelectric detector, a data acquisition card, a signal generator and a processor.
The narrow-linewidth continuous light emitted by the laser passes through the light source noise suppression feedforward structure, enters the coupler 3 with a specific power ratio, and is divided into two paths, wherein one path of continuous light is subjected to acousto-optic modulation with a frequency shift function and is converted into pulse light with a specific width and a specific period, the pulse light enters the port 1 of the circulator after being subjected to power compensation through the optical amplifier, and then is emitted through the port 3 of the circulator to enter the sensing optical fiber, so that vibration measurement information along the optical fiber is obtained, backward Rayleigh scattering light which carries environmental vibration information and is generated in the sensing optical fiber passes through the port 3 of the circulator again and is emitted from the port 2 of the circulator.
The other continuous light which is divided after the continuous light emitted by the light source passes through the coupler 3 with the specific power ratio is used as the local reference light. The local reference light and the backward Rayleigh scattered light emitted from the port of the circulator 2 generate coherent signals through the coupler 4 in a ratio of 50:50, the coherent signals are converted into electric signals through the photoelectric detector and enter the data acquisition card, the digital signals are obtained and are subjected to data processing in the processor, and the environmental vibration information along the optical fiber is obtained.
The method is characterized in that a light source noise suppression feedforward structure is used for suppressing the phase noise of continuous light output by a laser, and the phase noise is added to classical light
In the measuring device, the phase noise of the laser is reduced, and the measuring precision of the external vibration signal is further improved.
The light source noise suppression feed-forward structure comprises: coupler 1, delay fiber 1, feed forward loop, single sideband modulator.
The laser emits narrow-linewidth continuous light, the narrow-linewidth continuous light is divided into two paths through a 50:50 coupler 1, the path 1 directly enters a single-side band modulator through a delay optical fiber 1, and the path 2 enters the single-side band modulator through a feedforward loop. The delay optical fiber 1 realizes propagation delay control of the 1 st path of continuous light, and ensures that two paths of continuous light from the coupler 1 to the single side band modulator have the same delay time.
The feed forward loop comprises: the device comprises a coupler 2, a delay optical fiber 2, a 90-degree optical mixer, a photoelectric balance detector 1, a photoelectric balance detector 2, a tracker, a preamplifier and a voltage-controlled oscillator.
The 2 nd path of continuous light output by the coupler 1 is divided into two paths through the coupler 2 with the ratio of 50:50, wherein one path of continuous light directly enters the 90-degree optical mixer, and the other path of continuous light enters the 90-degree optical mixer through the delay optical fiber 2. The coupler 2, the transmission fiber without the delay fiber, the transmission fiber with the delay fiber 2, and the 90-degree optical mixer constitute a classical mach-zehnder fiber interferometer, the difference in the length of the interference arms being determined by the delay fiber 2. Based on the Mach-Zehnder optical fiber interferometer, the 90-degree optical mixer obtains two mutually orthogonal interference optical signals, respectively outputs the two interference optical signals to the photoelectric balance detector 1 and the photoelectric balance detector 2, converts the two interference optical signals into two interference electric signals and outputs the two interference electric signals to the tracker. The tracker obtains the light source phase noise of the primary difference, and transmits the light source phase noise to the preamplifier, and the time difference of the primary difference is determined by the delay optical fiber 2. The preamplifier amplifies the light source phase noise of the primary difference, drives the voltage-controlled oscillator, generates continuous optical signals and outputs the continuous optical signals to the single-sideband modulator.
The single sideband modulator receives the continuous light passing through the delay optical fiber 1 and the continuous light of the feedforward loop for frequency synthesis, and the continuous light with the output light source phase noise improved enters the coupler 3.
Based on the Mach-Zehnder optical fiber interferometer, the 90-degree optical mixer obtains two mutually orthogonal interference optical signals, respectively outputs the two interference optical signals to the photoelectric balance detector 1 and the photoelectric balance detector 2, converts the two interference optical signals into two interference electric signals and outputs the two interference electric signals to the tracker. The method avoids the frequency drift problem existing when single-path interference optical signals are adopted to carry out first-order differential light source phase noise estimation, and improves the measurement precision of the first-order differential light source phase noise, thereby being beneficial to inhibiting the light source phase noise and improving the measurement precision of external vibration signals.
The 90-degree optical mixer outputs two paths of orthogonal (I path and Q path) interference electric signals to the tracker.
For the tracker, in this embodiment, it includes: averager 1, averager 2, multiplier 1, inverter, multiplier 2 and adder. The I path interference electric signal passes through the averager 1, calculates the signal average value in the time T and transmits the signal average value to the multiplier 1. The multiplier 1 multiplies the signal average value output from the averager 1 by the Q-path signal and outputs the result to the adder. The Q path interference electric signal passes through the averager 2 to obtain the signal average value in the time T, and the Q path interference electric signal is inverted by the phase inverter and then transmitted to the multiplier 2. The multiplier 2 multiplies the average value of the signal output from the averager 2 by the I-path signal and outputs the result to the adder. The adder adds the two paths of input signals to obtain primary differential light source phase noise, and transmits the primary differential light source phase noise to the preamplifier.
Example 2
In another exemplary embodiment of the present disclosure, as shown in fig. 1-2, a method for fiber optic vibration measurement with improved source noise is provided.
wherein A represents the amplitude of light waves, v0Representing the frequency of the optical wave, with a constant 193.5THz (corresponding to a wavelength of 1550 nm) or 229.0THz (corresponding to a wavelength of 1310 nm), θ (t) representing the phase noise of the light source, and t representing time.
And 2, dividing the continuous light of the laser into two paths, wherein 1 path obtains two paths (an I path and a Q path) of orthogonal interference signals by using a classical Mach-Zehnder interferometer:
I(t)＝Bcos(2πν0τ+Δθ(t)) (2)
Q(t)＝Bsin(2πν0τ+Δθ(t)) (3)
Δθ(t)＝θ(t)-θ(t-τ) (4)
where B represents the interference signal amplitude, Δ θ (t) represents the first-order differential light source phase noise, and τ represents the time delay caused by the mach-zehnder interferometer interferometric arm length. And τ is selected to be short in time so that Δ θ (t) satisfies:
Δθ(t)＜＜1 (5)
and 3, multiplying the I path interference signal by the Q path signal after time averaging, multiplying the Q path interference signal by the I path signal after time averaging and negation, and obtaining:
where T represents the length of time for averaging. Since laser phase noise is a bounded zero-mean random process, taking the time average to be zero, we get:
and 4, adding the two paths of signals obtained in the previous step to obtain:
the amplitude normalization processing is performed on the above formula, and since τ is selected to be shorter time, according to formula (5), the estimated value of the first-order difference light source phase noise can be obtained:
and 5, amplifying the extracted first-order differential light source phase noise, and driving a voltage-controlled oscillator to output an oscillation signal:
wherein v is1Indicating the natural frequency of oscillation, k, of the voltage-controlled oscillatorVCOIndicating the sensitivity, k, of the voltage-controlled oscillatorAMPShowing the magnification.
And 6, enabling continuous light output by the voltage-controlled oscillator to enter a single-side band modulator, enabling the other path of the continuous light of the laser to enter the single-side band modulator through a delay optical fiber, and ensuring that the time delay of the two paths of continuous light is equal through the delay optical fiber. The single-sideband modulator modulates the continuous light of the laser by using the oscillation signal output by the voltage-controlled oscillator to obtain:
by adjusting the parameter kVCOAnd kAMPSo that 2 π kVCOkAMPτ is 1, the light source phase noise θ (t) can be suppressed significantly.
And 7, after passing through a feed-forward structure of light source noise suppression, the light source continuous light enters a coupler 3 with a specific power ratio and is divided into two paths, wherein one path of continuous light is subjected to acousto-optic modulation with a frequency shift function and is converted into pulse light with a specific width and a specific period, the pulse light enters a port of a circulator 1 after being subjected to power compensation through an optical amplifier, and then the pulse light is emitted through a port 3 of the circulator and enters a sensing optical fiber to obtain vibration measurement information along the optical fiber, and backward Rayleigh scattering light which carries environmental vibration information and is generated in the sensing optical fiber passes through the port 3 of the circulator again and is emitted from a port 2 of the circulator.
The other continuous light which is divided after the continuous light emitted by the light source passes through the coupler 3 with the specific power ratio is used as the local reference light. The local reference light and the backward Rayleigh scattered light emitted from the port of the circulator 2 generate coherent signals through the coupler 4 in a ratio of 50:50, the coherent signals are converted into electric signals through the photoelectric detector and enter the data acquisition card, the digital signals are obtained and are subjected to data processing in the processor, and the environmental vibration information along the optical fiber is obtained.
When the vibration of the detected environment occurs, the sensing optical fibers behind the vibration point carry vibration information due to the influence of the vibration event, and the sensing optical fibers in front of the vibration point do not carry vibration information;
thus, the distance D can be selectedABPoint A and point B, the phase difference is used for preliminarily eliminating the difference between the points A and B due to the laserPhase noise adversely affects the measurement, where point a carries vibration information after the vibration point and point B does not carry vibration information before the vibration point.
Further, the distance between the vibration points is selected to be DCDThe phase difference is made between the points C and D to obtain C, D phase change information between the two points. By calculating the distance DABAnd DCDThe proportional relation of the frequency offset and the phase offset can further eliminate the influence of residual laser phase noise on the performance of a sensing system, compensate the measurement phase drift caused by the frequency drift in real time and further improve the measurement precision of external vibration signals.
Wherein the content of the first and second substances,
indicating the external vibration that needs to be measured,
the phase difference between the points a and B is shown,
the phase difference between the points C and D is shown.
It is to be noted that, if the distance is DCDThe point C and the point D are behind the vibration point, the phase information of the point C and the point D is added with the phase information caused by the external vibration detected by the sensing optical fiber, and the same signals as the point C and the point D before the vibration point can be obtained after the phase difference is made
Therefore, the C point and the D point can compensate the measurement phase drift caused by the residual phase noise of the laser in real time whether the C point and the D point are selected to be before or after the vibration point.
The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure, and various modifications and changes may be made to the present disclosure by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.
Claims (10)
1. An optical fiber vibration measuring device with improved noise of a light source, comprising:
the feed-forward structure acquires continuous light and divides the continuous light into two paths, one path of continuous light sequentially passes through the interferometer, the photoelectric balance detector, the tracker, the preamplifier and the voltage-controlled oscillator, then is input into the single-side-band modulator together with the other path of continuous light, and outputs the continuous light subjected to phase noise suppression;
the measuring structure acquires continuous light subjected to phase noise suppression and divides the continuous light into two paths, wherein one path of continuous light passes through the acousto-optic modulator, the optical amplifier and the circulator and then is input into the sensing optical fiber, and backward Rayleigh scattered light carrying vibration information is coupled with the other path of continuous light and then is output to the processor through the photoelectric detector;
and the sensing optical fiber is connected with the circulator and used for acquiring the environmental vibration information along the optical fiber.
2. The light vibration measuring device with improved light source noise as claimed in claim 1, wherein the interferometer divides the obtained continuous light into two orthogonal interference light signals, and inputs the two interference light signals into the first light balance detector and the second light balance detector respectively and then inputs the two interference electric signals into the tracker.
3. The optical fiber vibration measuring device with improved optical source noise as claimed in claim 2, wherein the tracker drives the voltage controlled oscillator to generate a continuous optical signal and output the continuous optical signal to the single-sideband modulator after inputting the two obtained interference electrical signals into the preamplifier.
4. The optical fiber vibration measuring apparatus with improved noise of light source as claimed in claim 1, wherein the other path of the continuous light is outputted to the single side band modulator through a first delay optical fiber, and a second delay optical fiber is provided in the interferometer for adjusting the time difference of the primary difference acquired by the tracker.
5. The apparatus according to claim 1, wherein the continuum obtained by the test structure is divided into two paths, and the sensing fiber obtains one path of continuum and emits backward rayleigh scattered light through the circulator port, and couples with the other path of continuum as local reference light to generate a coherent signal.
6. An optical fiber vibration measurement method with improved light source noise is characterized by comprising the following steps:
acquiring continuous light and dividing the continuous light into two paths in a feed-forward structure;
respectively processing two paths of continuous light and then jointly carrying out single-side band modulation to inhibit the phase noise of a light source;
dividing the continuous light subjected to the light source phase noise suppression into two paths;
one path is subjected to acousto-optic modulation and optical amplification and then is input into a sensing optical fiber through a circulator;
the circulator outputs backward Rayleigh scattering light with environmental vibration information generated in the sensing optical fiber and is coupled with the other path of continuous light to generate a coherent signal;
and processing the coherent signals to acquire the environmental vibration information along the sensing optical fiber.
7. The method for fiber optic vibration measurement with improved noise from light sources of claim 6 wherein the feedforward mechanism processes the continuous light by:
processing one path of continuous light by an interferometer to obtain two paths of orthogonal interference signals, namely an I path and a Q path;
the I path interference signal is multiplied by the Q path signal after being subjected to time averaging, and the Q path interference signal is multiplied by the I path signal after being subjected to time averaging and negation;
adding the two paths of signals obtained in the last step, and performing amplitude normalization processing to obtain an estimated value of the first-order differential light source phase noise;
amplifying the extracted first-order differential light source phase noise estimated value, and driving a voltage-controlled oscillator to output an oscillation signal;
and an oscillation signal output by the voltage-controlled oscillator and the other path of continuous light enter the single-side-band modulator together for modulation after passing through the delay optical fiber.
8. The method of claim 7, wherein the optical source phase noise is adjusted by adjusting a sensitivity of a voltage controlled oscillator and an estimated value of a section of differential optical source noise.
9. The method of claim 6, wherein the backward Rayleigh scattered light carries environmental vibration information received by the sensing fiber and exits through the circulator port.
10. The method for fiber optic vibration measurement with improved noise in the light source of claim 6 wherein another continuous beam of light optically coupled to the backward rayleigh scattered beam is used as the local reference beam.
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