CN115931105A - Single-ended distributed optical fiber vibration sensor system and signal processing method - Google Patents
Single-ended distributed optical fiber vibration sensor system and signal processing method Download PDFInfo
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Abstract
The invention discloses a single-ended distributed optical fiber vibration sensor system and a signal processing method, wherein the system comprises the following steps: the device comprises a laser source, an electro-optic modulator, an optical fiber to be tested, piezoelectric ceramics, a 1 x 2 coupler, a mixer, an oscilloscope and a PC (personal computer) terminal; the laser emitted by the laser source is loaded with carrier frequency by the electro-optical modulator and then is transmitted to the optical fiber to be tested; the optical fiber to be detected is affected by vibration of an external environment, then the optical phase conducted inside the optical fiber is changed, the piezoelectric ceramic generates vibration signals to modulate the phase information of the optical fiber to be detected, then the modulated optical signals are transmitted to the 1 x 2 coupler to be divided into signal light and local oscillator light, and then the signal light and the local oscillator light are respectively transmitted to the frequency mixer to be subjected to coherent frequency mixing, and phase change is obtained through demodulation; and the PC side demodulates the phase change acquired by the oscilloscope to acquire the vibration information of the external environment. The single-ended distributed optical fiber vibration sensor system has the advantages of large dynamic range, long measurement distance, low cost and measurement stability.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a single-ended distributed optical fiber vibration sensor system and a signal processing method.
Background
The distributed optical fiber vibration sensor is used for carrying out large-area remote monitoring on the seabed, and the local environment change of the seabed caused by marine earthquake or gas hydrate exploitation can be fed back in real time, so that more intelligent decision, better safety and maximum yield can be made. Cables in excess of 120 km are criss-crossed at the sea floor, which is a hidden infrastructure for implementing the internet. It would be a significant breakthrough if the optical fibers within these fiber optic cables could become distributed seismic detection sensors in addition to functioning properly.
Currently, distributed vibration technologies are mainly classified into two categories: OFDR (Optical Frequency Domain Reflection) and OTDR (Optical Time-Domain Reflectometer). The OTDR has a simple basic structure, relatively good dynamic response capability and a detection range of dozens of kilometers, and can respond to vibration information in real time; however, the OTDR system also has the disadvantages of low signal-to-noise ratio, difficulty in realizing full-range sensitivity, difficulty in balancing resolution and dynamic range, and the like. The OFDR can be satisfied, and the OFDR has the advantages of high sensitivity and high spatial resolution; there are two limitations to the OFDR system at the same time: the limitation of source phase noise and coherence and the limitation of source sweep nonlinearity. In addition, the two technologies are based on back scattering, scattered light is very weak, so that the power of a light source must be increased in order to improve the signal-to-noise ratio and the detection range, an obvious nonlinear effect is introduced, an additional optical amplifier is used for long-distance sensing, the complexity of an actual system is increased, the manufacturing cost of a distributed system is greatly increased due to a high-power and ultra-narrow-line-width laser, the cost of the long-distance distributed system is high, and a serious nonlinear effect is caused.
Accordingly, the prior art is yet to be improved and developed.
Disclosure of Invention
The invention mainly aims to provide a single-ended distributed optical fiber vibration sensor system and a signal processing method, and aims to solve the problems of small measurement range, short sensing distance, complex equipment and high cost of the existing distributed vibration sensor.
To achieve the above object, the present invention provides a single-ended distributed optical fiber vibration sensor system, including:
the device comprises a laser source, an electro-optic modulator, an optical fiber to be tested, piezoelectric ceramics, a 1 x 2 coupler, a mixer, an oscilloscope and a PC (personal computer) terminal; the laser source, the electro-optic modulator, the optical fiber to be measured, the piezoelectric ceramic, the 1 x 2 coupler, the frequency mixer, the oscilloscope and the PC end are connected in sequence;
the laser source is used for emitting laser, and the laser is loaded with carrier frequency through the electro-optical modulator and then transmitted to the optical fiber to be tested;
the optical fiber to be measured is influenced by the vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1-x 2 coupler;
the 1 x 2 coupler is used for dividing phase information into signal light and local oscillator light and then respectively transmitting the signal light and the local oscillator light to the frequency mixer, and the frequency mixer is used for performing coherent frequency mixing on the local oscillator light and the signal light and demodulating to obtain phase change;
the oscilloscope is used for acquiring the phase change acquired by the frequency mixer, and the PC terminal is used for demodulating the phase change acquired by the oscilloscope so as to acquire the vibration information of the external environment.
The single-ended distributed optical fiber vibration sensor system is characterized in that the frequency mixer is a port 90-degree optical frequency mixer;
the port 90-degree optical mixer is used for performing coherent mixing on the local oscillator light and the signal light, so that the relative phase difference of the four output ports is respectively 0 degrees, 90 degrees, 180 degrees and 270 degrees.
The single-ended distributed optical fiber vibration sensor system is characterized in that the port 90-degree optical mixer comprises a quarter-wave plate, two half-wave plates and three polarization splitting prisms.
The single-ended distributed optical fiber vibration sensor system is characterized in that the optical fiber to be detected consists of a single-mode optical fiber.
The single-ended distributed optical fiber vibration sensor system is characterized in that the wavelengths of the local oscillation light and the signal light are the same.
The single-ended distributed optical fiber vibration sensor system is characterized in that the laser source is a semiconductor laser.
The single-ended distributed optical fiber vibration sensor system is characterized in that the linewidth of the semiconductor laser is 50kHz.
In addition, in order to achieve the above object, the present invention further provides a signal processing method based on the single-ended distributed optical fiber vibration sensor system, wherein the signal processing method includes:
the laser source emits laser, and the laser is loaded with carrier frequency through the electro-optical modulator and then is transmitted to the optical fiber to be tested;
the optical fiber to be measured is influenced by the vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1-x 2 coupler;
the 1 x 2 coupler divides phase information into signal light and local oscillation light and then respectively transmits the signal light and the local oscillation light to the frequency mixer, and the frequency mixer performs coherent frequency mixing on the local oscillation light and the signal light and demodulates the local oscillation light to obtain phase change;
the oscilloscope collects the phase change obtained by the mixer, and the PC terminal demodulates the phase change collected by the oscilloscope to obtain the vibration information of the external environment.
The signal processing method, wherein the signal processing method further comprises:
and when the phase of the optical fiber to be tested is changed due to the vibration influence, the time delay is solved by cross-correlation by utilizing the time delay relation of the two phases so as to determine the position of an external event.
The signal processing method includes, when the phase of the optical fiber to be measured is changed due to the influence of vibration, using the time delay relationship of the two phases to solve the time delay through cross-correlation to determine the position of the external event, and then:
the intensity of the external event is analyzed as well as the frequency information.
In the present invention, the single-ended distributed optical fiber vibration sensor system includes: the device comprises a laser source, an electro-optic modulator, an optical fiber to be tested, piezoelectric ceramics, a 1 x 2 coupler, a mixer, an oscilloscope and a PC (personal computer) terminal; the laser source, the electro-optic modulator, the optical fiber to be measured, the piezoelectric ceramic, the 1 x 2 coupler, the frequency mixer, the oscilloscope and the PC end are connected in sequence; the laser source is used for emitting laser, and the laser is loaded with carrier frequency through the electro-optical modulator and then transmitted to the optical fiber to be tested; the optical fiber to be measured is influenced by vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates vibration signals to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1 x 2 coupler; the 1 x 2 coupler is used for dividing phase information into signal light and local oscillator light and then respectively transmitting the signal light and the local oscillator light to the frequency mixer, and the frequency mixer is used for performing coherent frequency mixing on the local oscillator light and the signal light and demodulating to obtain phase change; the oscilloscope is used for acquiring the phase change acquired by the frequency mixer, and the PC terminal is used for demodulating the phase change acquired by the oscilloscope so as to acquire the vibration information of the external environment. The single-ended distributed optical fiber vibration sensor system has the advantages of large dynamic range, long measurement distance, low cost and measurement stability, can well detect vibration signals, and can efficiently measure high-frequency vibration.
Drawings
FIG. 1 is a schematic diagram of a preferred embodiment of a single-ended distributed fiber optic vibration sensor system according to the present invention;
FIG. 2 is a functional schematic diagram of a mixer in a preferred embodiment of the single-ended distributed fiber optic vibration sensor system of the present invention;
FIG. 3 is a schematic diagram of a mixer in a preferred embodiment of the single-ended distributed fiber optic vibration sensor system of the present invention;
FIG. 4 is a schematic diagram of the output of a mixer in a preferred embodiment of the single-ended distributed fiber optic vibration sensor system of the present invention;
FIG. 5 is a schematic diagram of a forward transmission based distributed vibration sensing system of the present invention;
FIG. 6 is a schematic diagram of the present invention, when the optical fiber is affected by vibration, the phase is changed and the time delay can be solved by cross-correlation using the time delay relationship of two phases;
fig. 7 is a flow chart of a signal processing method based on a single-ended distributed optical fiber vibration sensor system according to a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention clearer and clearer, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The invention introduces the phase shift of light in the optical fiber caused by disturbance signals, and when the embedded sensing optical fiber is subjected to the pressure, heat transfer or bending of a disturbance source, physical parameters such as the refractive index, the length, the diameter and the like of the section of the optical fiber are changed along with the elastic optical effect and the thermal strain effect of the optical fiber, so that the phase shift containing disturbance information is generated in the transmission light in the fiber core, namely the modulation of the external disturbance on the phase of the transmission light is realized. If the total length of the sensing optical fiber is L, the refractive index is n, the optical wavelength is lambda, and the phase shift of a certain fixed frequency light wave passing through the sensing optical fiber
Expressed as:
wherein beta is a propagation constant and is directly influenced by the effective refractive index of the optical fiber;
when there is external disturbance, the phase shift amount
Expressed as:
wherein the content of the first and second substances,
respectively expressed as phase shift caused by the change of the length of the sensing optical fiber caused by elastic deformation and the change of the refractive index of the optical fiber caused by elasto-optical effectThe phase shift caused by the change and the phase shift caused by the change of the fiber core diameter caused by the Poisson effect are respectively expressed as the fiber length change, the propagation constant change, the refractive index change and the fiber core diameter change. />
Due to the fact that
Ratio->
And &>
More than two orders of magnitude smaller and is therefore omitted, i.e. the amount of phase shift->
The approximate representation is:
wherein, the first and the second end of the pipe are connected with each other,
and &>
Respectively representing the phase shift caused by the change of the length of the sensing optical fiber caused by elastic deformation and the phase shift caused by the change of the refractive index of the optical fiber caused by elasto-optical effect.
For phase shift caused by length change of sensing optical fiber due to elastic deformation
According to the strain theory, the strain quantity epsilon of each direction of the sensing optical fiber is i Describing, let epsilon be the positive strain vector borne by the sensing fiber, when the sensing fiber is subjected to external disturbance of longitudinal pressure P, there are:
wherein epsilon x 、ε y 、ε z The strain quantities of the sensing optical fiber in the X direction, the Y direction and the Z direction are respectively, E is the Young modulus of elasticity of the sensing optical fiber, mu is the Poisson ratio of the optical fiber, and the phase change caused by the length change in the Z direction is as follows:
phase shift caused by refractive index change of optical fiber due to elasto-optical effect
According to the principle of elasticity mechanics, refractive index change and the amount epsilon of the applied anisotropic strain are obtained by the elasto-optical tensor and the principal strain tensor of the quartz optical fiber i The relationship of (c) is:
wherein, P m ＝(P 11 -P 12 )/2，ΔB i ＝-2Δn i /n i 3 Fourth order tensor P ij Is a constant.
For quartz optical fibres has epsilon x ＝ε y 、n i = n, so the refractive index variation of the sensing fiber in the X, Y and Z directions is obtained as follows:
whereby the elasto-optical effect causes a phase shift due to a change in the refractive index of the fibre
Comprises the following steps:
therefore, the amount of phase shift caused by external disturbance
Expressed as:
from the above formula, it can be seen that the phase shift of the transmission light is proportional to the optical fiber isotropic strain caused by disturbance, the actual dynamic external disturbance can be regarded as a function of time t, and the phase change function can be obtained by combining with the demodulation means during the post-processing
The type of external disturbance can be easily distinguished, and a sensing system with the optical fiber as a sensing element is realized.
As shown in fig. 1, the single-ended distributed optical fiber vibration sensor system according to the preferred embodiment of the present invention includes: the device comprises a laser source, an electro-optic modulator, an optical fiber to be tested, piezoelectric ceramics, a 1 x 2 coupler, a mixer, an oscilloscope and a PC (personal computer) terminal; the laser source, the electro-optical modulator, the optical fiber to be measured, the piezoelectric ceramic, the 1 x 2 coupler, the frequency mixer, the oscilloscope and the PC end are connected in sequence.
Specifically, the laser source is configured to emit laser, and load a carrier frequency (so that a signal frequency band is shifted to a high frequency) through the electro-optical modulator and transmit the carrier frequency to the optical fiber to be tested; the optical fiber to be measured is influenced by the vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1-x 2 coupler; the 1 x 2 coupler is used for dividing phase information into signal light and local oscillator light and then respectively transmitting the signal light and the local oscillator light to the frequency mixer, and the frequency mixer is used for performing coherent frequency mixing on the local oscillator light and the signal light and demodulating to obtain phase change; the oscilloscope is used for acquiring the phase change acquired by the frequency mixer, and the PC terminal is used for demodulating the phase change acquired by the oscilloscope so as to acquire the vibration information of the external environment.
The optical fiber to be detected is also called a sensing unit, and the sensing unit consists of a Single Mode Fiber (SMF) which is dozens of kilometers long; the 1 x 2 coupler and the mixer form a demodulation unit; the sensing unit can be influenced by the vibration of the external environment, so that the optical phase conducted inside the optical fiber is changed, the demodulation unit demodulates the phase to obtain the change of the phase, and the vibration information of the external environment is obtained. The invention has large dynamic range, long measuring distance, low cost and measuring stability.
Wherein the mixer is a port 90 ° optical mixer; the port 90-degree optical mixer performs coherent mixing on the local oscillation light and the signal light, so that the relative phase difference of the four output ports is respectively 0 degrees, 90 degrees, 180 degrees and 270 degrees. The photocurrent direct-current components obtained by the port balance detectors of 0 degrees and 180 degrees and 90 degrees and 270 degrees are respectively equal, so that two coherent signals can be obtained by respective subtraction, the relative phase difference of the two signals is 90 degrees, and the relative strength is K 1 K 2 /K 3 K 4 ，K 1 、K 2 、K 3 、K 4 Representing the intensity factor, as shown in FIG. 2, E S Representing signal light, E LO Indicating local oscillator light, 90 ° Hybrid indicating port 90 ° optical mixer, i being an imaginary unit.
As shown in fig. 3, the port 90 ° optical mixer includes a quarter-wave plate, two half-wave plates, and three polarization splitting prisms. Signal light P in fig. 3 i And local oscillator light P LO The same wavelength (1064 nm) was passed through a polarizer into a 90 ℃ optical mixer as linearly polarized light. The 1 is a quarter wave plate, and the fast (slow) axis direction of the quarter wave plate forms 45 degrees with the polarization direction of the local oscillation light, so that the local oscillation light becomes circularly polarized light after passing through the 1. 2. 4, 6 are both Polarizing Beam Splitters (PBS), so that the P light component is only transmitted and the S light component is only reflected (P and S light components can be understood as the decomposition of a planar light vector into two mutually perpendicular directions). 3.5 is a half wave plate, the fast (slow) axis direction of which is in line with the S (P) light direction22.5 degrees, so that the linearly polarized light on the two branches after passing through the second branch 2 is changed into linearly polarized light with the polarization direction of 45 degrees with the P light after being optically rotated by 3 degrees. Finally, the light of the two branches is split by PBS to obtain four output lights with relative phase differences of 0 degree, 90 degrees, 180 degrees and 270 degrees. The polarization beam splitter prism is an optical element which is characterized in that a multilayer film structure is plated on the inclined plane of a right-angle prism, then a cubic structure is glued, the P polarization component is completely transmitted, and most of S polarization component is reflected (at least more than 90%) after the light passes through the multilayer film structure for multiple times at the Brewster angle by utilizing the properties that the P polarization transmission rate is 1 and the S polarization transmission rate is less than 1 when the light is incident at the Brewster angle. The incident interference light intensity can be as shown in fig. 4, and only the ac component remains after the difference between the output light intensities at the two ends, so that the actual phase can be calculated by using the tangent calculation method.
Further, the structure of the distributed vibration sensing system based on forward transmission is shown in fig. 5, where PMM denotes a plane mirror, TDF (Time Delay Fiber) denotes a Time Delay Fiber, FTU (Fiber Test Unit) denotes a Fiber Test Unit, mixer denotes a Mixer, PC denotes a computer, and LD (Laser Diode) denotes a Laser Diode (i.e., a Laser source); the semiconductor laser is the light source (that is, laser source) of this system, and the semiconductor laser linewidth is 50kHz, and the light that narrow linewidth laser sent first enters into the Circulator (CIR), and the phase change that sensing fiber produced can be carried by the light signal, and the end is through 50: in a 50 beam splitter and two paths of light respectively Electro-optical modulators (EOM, electro-optical Modulator), the Electro-optical Modulator needs a signal generator to drive the Electro-optical Modulator, the driving frequency is dozens of MHz, the voltage peak-to-peak value (Vpp) is 3.5V, the acousto-optical Modulator modulates continuous light and generates a signal shift frequency of dozens of MHz, the signal shift frequency is reflected by a circulator and enters 50: in the 50 beam splitters, an optical signal is divided into two paths to be coherently superposed in a mixer, and the optical signal is converted into an electrical signal through a Balanced detector (BPD), the bandwidth of the Balanced detector is 500MHz, and the output signal is finally acquired by an Acquisition card (DAQ).
The distributed vibration sensing principle is explained below, where the phases of light accumulate at different places as it passes through the fiber, and thus the two paths are:
P1:a→b→c→d→c→b→a；P2:a→b→c→f→c→b→a；
the resulting phases of the different paths can be expressed as:
Phase1:
Phase2:
wherein t1= nL bcdcb C is the delay time of the d terminal, t2= nL bcfcb And/c is the delay time of the f end, omega 1 is the working frequency of the d end EOM, and omega 2 is the working frequency of the f end EOM.
By means of time delay, the phase obtained by self-coherence is realized:
wherein the content of the first and second substances,
and &>
Light output from the delay fiber at the receiving end is represented;
tdelay＝nL delay/c and respectively carrying out difference derivation on the phases:
where Δ t = t2-t1, as can be derived from a simple derivation:
from the above equation, when the optical fiber is affected by vibration, the phase changes, and the time delay relationship of two phases is utilized, and the time delay can be solved through cross-correlation as shown in fig. 6, so as to determine the position L of the external event bcfcb ＝t 2cn . By analysing phase changes simultaneously
And &>
The strength and frequency information of the external event is obtained.
The invention provides a single-ended distributed optical fiber vibration sensor system, and experimental results show that the single-ended distributed optical fiber vibration sensor system has the advantages of large frequency range, long sensing distance, low cost and good stability, and can be used for well detecting vibration signals; the distributed vibration optical fiber sensor can carry out efficient measurement on high-frequency vibration.
Further, as shown in fig. 7, the signal processing method based on the single-ended distributed optical fiber vibration sensor system of the present invention includes:
s10, the laser source emits laser, and the laser is loaded with carrier frequency through the electro-optic modulator and then is transmitted to the optical fiber to be tested;
s20, changing the optical phase conducted inside the optical fiber after the optical fiber to be detected is influenced by vibration of an external environment, and transmitting the modulated optical phase information of the optical fiber to be detected to the 1 x 2 coupler after the piezoelectric ceramic generates a vibration signal;
s30, the 1-by-2 coupler divides the phase information into signal light and local oscillation light and then respectively transmits the signal light and the local oscillation light to the frequency mixer, and the frequency mixer performs coherent frequency mixing on the local oscillation light and the signal light and demodulates the local oscillation light to obtain phase change;
and S40, the oscilloscope collects the phase change obtained by the mixer, and the PC terminal demodulates the phase change collected by the oscilloscope to obtain the vibration information of the external environment.
In addition, the detection frequency range of the distributed vibration optical fiber sensor can be changed, and the detection distance can be changed; the type of fiber may vary, such as being replaced by a special fiber that is sensitive to vibrations, or by other types of fiber, such as: multi-core fibers, polarization maintaining fibers, etc.
In summary, the present invention provides a single-ended distributed optical fiber vibration sensor system and a signal processing method, where the single-ended distributed optical fiber vibration sensor system includes: the device comprises a laser source, an electro-optic modulator, an optical fiber to be tested, piezoelectric ceramics, a 1 x 2 coupler, a mixer, an oscilloscope and a PC (personal computer) terminal; the laser source, the electro-optic modulator, the optical fiber to be tested, the piezoelectric ceramic, the 1 x 2 coupler, the mixer, the oscilloscope and the PC end are sequentially connected; the laser source is used for emitting laser, and the laser is loaded with carrier frequency through the electro-optical modulator and then transmitted to the optical fiber to be tested; the optical fiber to be measured is influenced by the vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1-x 2 coupler; the 1 × 2 coupler is used for dividing phase information into signal light and local oscillator light and then respectively transmitting the signal light and the local oscillator light to the frequency mixer, and the frequency mixer is used for performing coherent frequency mixing on the local oscillator light and the signal light and demodulating the local oscillator light to obtain phase change; the oscilloscope is used for acquiring the phase change acquired by the mixer, and the PC terminal is used for demodulating the phase change acquired by the oscilloscope so as to acquire the vibration information of the external environment. The single-ended distributed optical fiber vibration sensor system has the advantages of large dynamic range, long measurement distance, low cost and measurement stability, can well detect vibration signals, and can efficiently measure high-frequency vibration.
Of course, it will be understood by those skilled in the art that all or part of the processes of the methods of the embodiments described above can be implemented by instructing relevant hardware (such as a processor, a controller, etc.) through a computer program, and the program can be stored in a computer readable storage medium, and when executed, the program can include the processes of the embodiments of the methods described above. The computer readable storage medium may be a memory, a magnetic disk, an optical disk, etc.
It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.
Claims (10)
1. A single-ended distributed optical fiber vibration sensor system, the distributed optical fiber vibration sensor system comprising: the device comprises a laser source, an electro-optic modulator, an optical fiber to be tested, piezoelectric ceramics, a 1 x 2 coupler, a mixer, an oscilloscope and a PC (personal computer) terminal; the laser source, the electro-optic modulator, the optical fiber to be tested, the piezoelectric ceramic, the 1 x 2 coupler, the mixer, the oscilloscope and the PC end are sequentially connected;
the laser source is used for emitting laser, and the laser is loaded with carrier frequency through the electro-optical modulator and then transmitted to the optical fiber to be tested;
the optical fiber to be measured is influenced by the vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1-x 2 coupler;
the 1 x 2 coupler is used for dividing phase information into signal light and local oscillator light and then respectively transmitting the signal light and the local oscillator light to the frequency mixer, and the frequency mixer is used for performing coherent frequency mixing on the local oscillator light and the signal light and demodulating to obtain phase change;
the oscilloscope is used for acquiring the phase change acquired by the mixer, and the PC terminal is used for demodulating the phase change acquired by the oscilloscope so as to acquire the vibration information of the external environment.
2. The single-ended distributed fiber optic vibration sensor system of claim 1, wherein the mixer is a port 90 ° optical mixer;
the port 90-degree optical mixer is used for carrying out coherent mixing on local oscillation light and signal light, so that relative phase differences of the four output ports are respectively 0 degrees, 90 degrees, 180 degrees and 270 degrees.
3. The single-ended distributed fiber optic vibration sensor system of claim 2, wherein the port 90 ° optical mixer comprises one quarter wave plate, two half wave plates, and three polarization splitting prisms.
4. The single-ended distributed fiber optic vibration sensor system of claim 1, wherein the optical fiber under test is comprised of a single mode fiber.
5. The single-ended distributed optical fiber vibration sensor system according to claim 1, wherein the local oscillator light and the signal light have the same wavelength.
6. The single-ended distributed fiber optic vibration sensor system of claim 1, wherein the laser source is a semiconductor laser.
7. The single-ended distributed fiber optic vibration sensor system of claim 6, wherein the semiconductor laser has a linewidth of 50kHz.
8. A method for processing signals based on the single-ended distributed optical fiber vibration sensor system according to any one of claims 1 to 7, wherein the method for processing signals comprises:
the laser source emits laser, and the laser is loaded with carrier frequency through the electro-optical modulator and then is transmitted to the optical fiber to be tested;
the optical fiber to be measured is influenced by the vibration of the external environment, the optical phase conducted inside the optical fiber is changed, and the piezoelectric ceramic generates a vibration signal to modulate the phase information of the optical fiber to be measured and then transmits the modulated phase information to the 1-x 2 coupler;
the 1 x 2 coupler divides phase information into signal light and local oscillation light and then respectively transmits the signal light and the local oscillation light to the frequency mixer, and the frequency mixer performs coherent frequency mixing on the local oscillation light and the signal light and demodulates the local oscillation light to obtain phase change;
the oscilloscope collects the phase change obtained by the frequency mixer, and the PC terminal demodulates the phase change collected by the oscilloscope to obtain the vibration information of the external environment.
9. The signal processing method of claim 8, further comprising:
when the phase of the optical fiber to be tested is changed due to the vibration influence, the time delay is solved through cross-correlation by utilizing the time delay relation of the two phases so as to determine the position of an external event.
10. The signal processing method according to claim 9, wherein when the phase of the optical fiber under test is changed due to the vibration, the time delay is solved by cross-correlation using the time delay relationship of the two phases to determine the position of the external event, and then further comprising:
the intensity of the external event is analyzed as well as the frequency information.
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