CN109211289B - Spontaneous Brillouin scattering optical fiber sensing method and device based on circularly polarized light interference - Google Patents
Spontaneous Brillouin scattering optical fiber sensing method and device based on circularly polarized light interference Download PDFInfo
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- 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
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Abstract
本发明公开了一种基于圆偏振光干涉的自发布里渊散射光纤传感方法与装置。窄线宽激光器发出的连续激光信号经过第一光分束耦合器分为两路。第一路被电光强度调制器转换为脉冲光信号后，经过环形器输入传感光纤中传输，在传输路径上产生频移与被测物理量相关联的后向散射光信号。第二路光信号经过偏振控制器将线偏振光转化为圆偏振光后，输入第二光分束耦合器，与经过环形器的后向散射光信号发生干涉，干涉后的光信号经过平衡探测器转化为电信号，再由混频器和滤波器通过电域扫频获得后向散射光信号布里渊频移和强度信息，最终获得传感光纤的物理量变化。本发明克服了现有自发布里渊散射光纤传感方法偏振失配的问题，能够获得稳定的干涉信号输出。
The invention discloses a self-published Brillouin scattering optical fiber sensing method and device based on circularly polarized light interference. The continuous laser signal emitted by the narrow linewidth laser is divided into two paths through the first optical beam splitting coupler. After the first path is converted into a pulsed light signal by the electro-optical intensity modulator, it is input into the sensing fiber through the circulator for transmission, and a backscattered light signal whose frequency shift is associated with the measured physical quantity is generated on the transmission path. After the second optical signal is converted into circularly polarized light by the polarization controller, it is input into the second optical beam splitter coupler, and interferes with the backscattered optical signal passing through the circulator, and the interfered optical signal is detected by balance Then, the mixer and filter are used to obtain the Brillouin frequency shift and intensity information of the backscattered light signal through frequency sweeping in the electrical domain, and finally the physical quantity change of the sensing fiber is obtained. The invention overcomes the problem of polarization mismatch in the existing self-published Brillouin scattering optical fiber sensing method, and can obtain stable interference signal output.
Description
Technical Field
The invention relates to the technical field of optical fiber sensing, in particular to a spontaneous Brillouin scattering optical fiber sensing method and device based on circularly polarized light interference.
Background
In the optical fiber sensing technology, an optical fiber not only serves as a channel for transmitting light, but also serves as a sensing unit. At present, a distributed optical fiber sensing system based on a scattering principle is mainly based on three scattering technologies of Rayleigh scattering, Raman scattering and Brillouin scattering. The distributed optical fiber sensing system based on the spontaneous Brillouin scattering can detect two physical quantities of strain and temperature, and the Brillouin scattering is divided into spontaneous Brillouin scattering and stimulated Brillouin scattering.
Currently, a distributed optical fiber sensing system of brillouin scattering mainly relates to three technologies: the method comprises a Brillouin optical time domain reflection technology, a Brillouin optical time domain analysis technology and a Brillouin optical frequency domain analysis technology.
When spontaneous Brillouin scattering optical fiber sensing is involved, the optical fiber sensing system is mainly based on the Brillouin optical time domain reflection technology. The optical signal generates Brillouin scattering when transmitted in the sensing optical fiber, and simultaneously generates Brillouin frequency shift. When the external temperature changes or the sensing optical fiber is subjected to stress changes, the Brillouin frequency shift generates corresponding changes, and the variation of the Brillouin frequency shift and the temperature variation or the stress variation are in a linear relation.
As described above, the changes in strain and temperature with respect to the brillouin shift are as follows:
at a certain temperature T0The relationship between strain and frequency shift is:
υ(T0,ε)＝υ(T0,0)[1+(Δnε+ΔΕε+Δρε+ΔKε)ε] (1)
wherein Δ nε、ΔΕε、Δρε、ΔKεThe refractive index, young's modulus, medium density, and poisson's ratio, respectively, are changes that are constant in the sensing fiber. Based on the above equation (1), it is known that the strain and the brillouin frequency shift are in a linear relationship at a certain temperature.
Similarly, when the strain ∈ is zero, the relationship between the amount of change in temperature and the frequency shift is:
υ(T,0)＝υ(T0,0)[1+(Δn+ΔE+Δρ+ΔK)ΔT] (2)
where Δ n, Δ E, Δ ρ, and Δ K are constants in the sensing fiber with zero strain, and based on the above equation (2), the temperature change amount and the frequency shift change are linear when the strain is zero.
As described above, the spontaneous brillouin scattering optical fiber sensing system measures a physical quantity change based on a linear relationship between a change amount of temperature and stress generated at a certain point of a sensing optical fiber and a brillouin frequency shift amount, thereby achieving the purpose of optical fiber sensing. The Brillouin frequency shift is measured by obtaining a Brillouin scattering spectrum by using an electrical domain frequency sweeping method, namely, the local oscillation frequency v of microwaves is adjustedOSo that the frequency and Brillouin frequency shift vBThe phase difference is within dozens of megahertz, and then the local oscillation frequency is continuously adjusted to scan the whole Brillouin spectrum width delta vBWherein when the local oscillator frequency vOEqual to brillouin frequency shift vBThe output signal strength is maximum. Based on the method, frequency shift information of the Brillouin scattering spectrum can be obtained by using a frequency sweeping method, and then the microwave local oscillation frequency v is adjustedOThe whole Brillouin scattering spectrum signal can pass through the low-pass filter and the band-pass filter, so that a Lorentz curve of the Brillouin scattering spectrum is obtained, the intensity of Brillouin scattering light is obtained by integrating the Lorentz curve, and finally frequency shift and intensity information of Brillouin scattering can be obtained, so that measurement of temperature change and strain is realized.
Therefore, the optical fiber sensing system of the invention achieves the sensing purpose by measuring the change quantity of the Brillouin frequency shift and utilizing the linear relation between the change quantity of the Brillouin frequency shift and the change quantities of the temperature and the stress. Meanwhile, the invention detects the Brillouin frequency shift by using a coherent detection method, namely, the Brillouin frequency shift is detected by the interference action of the reference light and the backward scattering light. However, the random change of the polarization state of the backscattered light cannot keep the polarization consistent with the linear polarization of the reference light, i.e., the problem of polarization mismatch is generated, so that the interference effect is not ideal, and further the output optical power is randomly fluctuated, so that the output optical power cannot reach an optimal value, errors exist in the measurement of the brillouin spectrum generated after the photoelectric detector and the frequency sweep, and the measurement accuracy of the optical fiber sensing system is reduced.
As described above, the random change of the polarization state of the backscattered light and the linear polarization of the reference light generate a polarization angle, which causes a polarization mismatch phenomenon, thereby affecting the output optical power. Based on the above, the relationship between the polarization angle θ of the two beams of light and the power of the two beams of light after interference is analyzed as follows:
let the jones matrix of the incident optical signal be:
wherein e1(t) and e2(t) is expressed as two orthogonal unit vectors on the fiber transverse electric field.
The optical signal may generate birefringence in the sensing fiber due to the sensing fiber being squeezed or bent by an external force or due to the imperfect material of the sensing fiber. Based on this, let the jones matrix of the light somewhere incident on the fiber be:
wherein Q1Is a birefringent Jones matrix, e1' (t) and e2' (t) is the two orthogonal unit vectors of the light field somewhere.
In the interference process, the interference effect is optimal when the polarization state of the backscattered light is consistent with that of the reference light, and interference cannot be generated when the polarization state of the backscattered light is orthogonal to that of the reference light, namely, the backscattered light cannot be received by heterodyne. Therefore, when analyzing the light intensity after interference, the polarization state of the backscattered light and the polarization state of the reference light are considered, and the jones matrix in the formula (4) is improved as follows:
wherein A is3Is a Jones matrix, Q, after considering the interference of polarization states of two optical signals2Is a Jones matrix of pairs of reference states of polarization, e1"(t) and e2"(t) denotes a unit vector when the polarization state of the backscattered light coincides with and is orthogonal to the polarization state of the reference light, respectively.
As described above, the expression (5) not only represents the jones matrix of the light beam in which the backscattered light and the reference light interfere with each other, but also reflects the direction of the polarization state of the backscattered light and the polarization state of the reference light.
Therefore, in the optical fiber sensing system of spontaneous brillouin scattering, if the continuous light as the reference light is linearly polarized light, the jones matrix is:
when the sensing optical fiber is subjected to the conditions of external pressure and the like, the sensing optical fiber generates birefringence, and the birefringence Jones matrix is as follows:
the angle θ is the phase delay angle between the backscattered light signal and the reference light, i.e. the angle between the polarization directions of the two beams. Matrix Q in formula (5)2For a jones matrix, i.e., heterodyne components, for a reference polarization state pair, the expression for the jones matrix is:
accordingly, formula (5) is:
A3＝Q2Q1A1
namely:
from the above equation (9), a matrix expression of a vector in which the polarization state of the backscattered light coincides with the polarization state of the reference light and a vector in which the polarization states of the two light signals are orthogonal can be obtained.
Thus, the ratio of the power of the backscattered light received by the heterodyning to the total backscattered light optical power is as follows:
it can be seen from the formula (10) that when the polarization angle θ between the backscattered light and the circularly polarized light is zero, the backscattered light is completely received by heterodyne, when the polarization angle θ is not zero, the interference occurs polarization mismatch, and the backscattered light cannot completely interfere, so that the interference effect is not ideal, a random fluctuation phenomenon occurs to a signal detected by a detector, the output optical power cannot reach an optimal value, and an error exists in measurement of brillouin spectrum generated after the photodetector and the frequency sweep, thereby reducing the measurement accuracy of the optical fiber sensing system.
In order to eliminate the above-mentioned influence caused by polarization mismatch, five schemes are mainly adopted to eliminate the phenomenon of polarization mismatch at present, namely: polarization control technology, polarization maintaining fiber technology, polarization diversity receiving technology, polarization expanding technology and polarization scrambler.
The polarization maintaining fiber technology utilizes polarization maintaining fiber to collimate the polarization direction of incident light to eliminate polarization mismatch: the polarization direction is kept on the main axis of the polarization-maintaining optical fiber, so that an optical signal with stable polarization state is obtained. However, the polarization maintaining fiber is disadvantageous for long-distance transmission due to its high cost and large loss compared with the common fiber. The polarization control technology is characterized in that a feedback system is formed, and the polarization state of continuous reference light is changed to the polarization state of astigmatism so as to avoid the existence of a polarization included angle in two interference beams of light signals, but the running efficiency of the system is greatly reduced due to the complex feedback loop. The polarization diversity receiving technology is that light signals after interference of continuous reference light and backward scattering light are averagely distributed on 2 polarization films, the polarization angles of the polarization films have a pi/2 difference, the polarization angles are respectively detected by 2 photoelectric detectors, and finally branch signals are processed in an overlapping mode to eliminate the influence of polarization mismatch. The more polarizing films that need to be used, the more desirable the result, if the polarization mismatch is to be eliminated as much as possible, but at this time the system operation speed is reduced, and the complexity of the polarization diversity receiver of this technique is almost twice that of the standard receiver, with the cost increasing. The polarization spreading technique is to spread the power of reference light or signal light to the whole polarization state in each bit in the time domain, and ensure that more than half of the power is received, but the requirement on an intermediate frequency filter in the technique is very high, and the complexity of the system is higher than that of the polarization diversity receiving technique. The utilization of the polarization scrambler is a better solution provided based on the four schemes, and the polarization mismatch elimination of the optical fiber sensing system is realized by continuously changing the polarization direction of the reference light by means of the polarization scrambler, so that the reference light can show a polarization state matched with the back scattering light in a certain period, and the polarization mismatch is eliminated. However, the scheme requires that the offset disturbing frequency of the offset scrambler is high, the offset disturbing frequency which can be achieved at present is 700MHz, the requirement on a system in practice is far from being achieved, and statistical uniform distribution in the sampling time of optical fiber sensing cannot be ensured.
Disclosure of Invention
In view of the above, in order to solve the above problems in the prior art, the present invention provides a method and an apparatus for sensing a spontaneous brillouin scattering optical fiber based on circularly polarized light interference.
The invention solves the problems through the following technical means:
on one hand, the invention provides a spontaneous Brillouin scattering optical fiber sensing method based on circularly polarized light interference, which comprises the following steps:
at a light source transmitting end, a continuous laser signal is divided into two paths after passing through a first optical beam splitting coupler; the first path of continuous laser signals are modulated into pulse light signals to enter the sensing optical fiber for transmission, the pulse light signals can generate backward Brillouin scattering light signals at a certain position of the sensing optical fiber after being transmitted for a certain distance, and the frequency shift of the backward scattering light signals is related to the measured strain and the temperature variation, so that the backward scattering light is used as signal light; and a second path of continuous laser signal is used as reference light, after the linear polarization state reference light is converted into the circular polarization state reference light, the reference light enters a second optical beam splitting coupler to interfere with the backscattered light signal, the interfered optical signal is converted into an electrical signal by a balance detector, and finally strain and temperature information at the sensing optical fiber is measured by measuring Brillouin frequency shift quantity.
Further, before the second path of reference light interferes with the backward scattering light signal with the randomly changed polarization state of the first path of reference light, the polarization state of the reference light is converted into a circular polarization state after passing through the polarization controller, namely the problem that the interference effect is not ideal due to the fact that the polarization states of the two paths of light are not consistent during interference is solved by means of the characteristics that the vibration direction of circular polarized light rotates at a high speed and changes uniformly.
On the other hand, the invention also provides a spontaneous Brillouin scattering optical fiber sensing device based on circularly polarized light interference, which comprises a narrow linewidth laser, a first optical splitting coupler, an electro-optical intensity modulator, a circulator, a polarization controller, a second optical splitting coupler, a balance detector, a microwave signal generator, a mixer, a low-pass filter, a band-pass filter and a data processing module, wherein the narrow linewidth laser is connected with the first optical splitting coupler; the narrow linewidth laser outputs a continuous laser signal, and the continuous laser signal divides a light path into two paths through the first optical beam splitting coupler; the first path of continuous laser signals are converted into pulse light signals by the electro-optical intensity modulator, the pulse light signals enter the sensing optical fiber after passing through the circulator, and the pulse light signals generate backward scattering light in the transmission process; the polarization state of the second path of linearly polarized continuous laser signal serving as reference light is changed into a circular polarization state after passing through the polarization controller; the method comprises the steps that a circular polarization continuous laser signal and a backward scattering light signal are interfered in a second optical beam splitter coupler, the interfered optical signal is subjected to photoelectric conversion through a balance detector to form an electric signal, electric domain frequency sweeping is carried out through a microwave signal generator and a frequency mixer to obtain frequency shift information of a Brillouin scattering spectrum, a Lorentz curve of the Brillouin scattering spectrum is obtained through a low-pass filter and a band-pass filter, so that intensity information of the Brillouin scattering spectrum is obtained, and finally, acquisition processing is carried out through a data processing module to obtain strain and temperature information of the position.
Further, before the second path of reference light interferes with the backward scattering light signal with the randomly changed polarization state of the first path of reference light, the polarization state of the reference light is converted into a circular polarization state after passing through the polarization controller, namely the problem that the interference effect is not ideal due to the fact that the polarization states of the two paths of light are not consistent during interference is solved by means of the characteristics that the vibration direction of circular polarized light rotates at a high speed and changes uniformly.
Compared with the prior art, the invention has the beneficial effects that at least:
1. compared with the currently adopted depolarization technology, the invention utilizes the characteristics that the vibration direction of circularly polarized light rotates at high speed and changes uniformly, and takes the circularly polarized light as reference light to interfere with the backward scattering light with randomly changing polarization state, so that the optical fiber sensing system can obtain stable interference signal output.
2. Compared with the existing spontaneous Brillouin scattering system with the polarization mismatch elimination technology, the system depolarization module only needs to add the polarization controller to eliminate polarization, so that the device of the optical fiber sensing system is simple, and the cost of the system is low.
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 is a schematic diagram of a spontaneous Brillouin scattering optical fiber sensing device based on circularly polarized light interference;
FIG. 2 is a schematic diagram of a polarization controller with coaxial optical fibers.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. It should be noted that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments, and all other embodiments obtained by those skilled in the art without any inventive work based on the embodiments of the present invention belong to the protection scope of the present invention.
The invention relates to a spontaneous Brillouin scattering optical fiber sensing method and device based on circularly polarized light interference. In order to eliminate the polarization mismatch generated when the backward scattering light with randomly changed polarization state interferes with the continuous light with linearly polarized state, the invention utilizes the interference of the circularly polarized light with uniformly distributed vibration and high change rate and the backward scattering light with randomly changed polarization state, so the output light power after interference is not lost due to the polarization mismatch.
Example 1
The invention provides a spontaneous Brillouin scattering optical fiber sensing method based on circularly polarized light interference, which comprises the following steps of:
at the light source transmitting end, the continuous laser signal is divided into two paths after passing through the first optical beam splitting coupler. The first path of continuous laser signals are modulated into pulse light signals, the pulse light signals enter the sensing optical fiber to be transmitted, after the pulse light signals are transmitted for a certain distance, backward Brillouin scattering light signals can be generated at a certain position of the sensing optical fiber, the frequency shift of the backward scattering light signals is related to the measured strain and temperature variation, and therefore the backward scattering light is used as signal light. And a second path of continuous laser signal is used as reference light, after the linear polarization state reference light is converted into the circular polarization state reference light, the reference light enters a second optical beam splitting coupler to interfere with the backscattered light signal, the interfered optical signal is converted into an electrical signal by a balance detector, and finally strain and temperature information at the sensing optical fiber is measured by measuring Brillouin frequency shift quantity.
As described above, the present invention solves the problem of polarization mismatch by using the characteristics that the vibration directions of circularly polarized light are statistically uniformly distributed and the change rate is very fast, so as to make the reference light circularly polarized, and ensure that the polarization state of the reference light is rapidly changed within the sampling time of the optical fiber sensor, so that the polarization states of the backscattered light and the reference light are matched in the second optical beam splitting coupler. According to the invention, circularly polarized light is adopted to eliminate the influence of polarization mismatch on interference.
When the circularly polarized light as the reference light interferes with the backscattered light, the ratio of the intensity after interference to the intensity before interference, i.e., the contrast, can be used as a reference value for considering the interference effect. Since any polarization state can be decomposed into two linear polarization states, when the contrast ratio of interference of reference light and backward scattering light is calculated, the calculation of the interference contrast ratio of circularly polarized light and linearly polarized light is simplified.
Based on this, the principle of interference of circularly polarized light and linearly polarized light is as follows:
let the vector wave be
The expression for circularly polarized light of (c) is:
in the above formula
And
are unit vectors of x and y axes respectively, i.e. the circularly polarized light is decomposed into two orthogonal linearly polarized lights, i.e. the vector wave is
The specific complex expression of the linearly polarized light is as follows:
in the above formulae (12) and (13)
Is complex amplitude, k1Wave vector of circularly polarized light, r1Is the radial diameter of the circularly polarized light,
is the phase.
The polarization direction of linearly polarized light interfering with the circularly polarized light is the direction of the x axis, and the vector wave of the linearly polarized light is
The specific complex expression is as follows:
in the above formula
Is the complex amplitude, k, of linearly polarized light2Is the wave vector of linearly polarized light, r2Is the sagittal diameter of the linearly polarized light,
is the phase.
Wherein for convenient comparison:
the contrast ratio at which linearly polarized light and circularly polarized light interfere is calculated based on the above-described relation. From the above conditions, the polarization direction of linearly polarized light is the x-axis direction. Therefore, when the two beams interfere, the linearly polarized light cannot interfere with the y-axis component of the circularly polarized light.
Then the interfered light field
Comprises the following steps:
the formula of the light intensity I after interference is as follows:
wherein the light intensity I is obtained by first applying a light field
And conjugation thereof
The product is then time averaged. After calculation:
wherein Re { } is the fraction of complex number in which real number is taken, since
Are all mixed with
Orthogonal, therefore, the above formula (17) is:
in the above formula, the linearly polarized light intensity E02The value is 1, and therefore, the above formula is:
the contrast ratio of the interference of the two beams is:
the above-mentioned principle of interference between circularly polarized light and linearly polarized light is used to derive that when the circularly polarized light amplitude is linearly polarized light
The contrast ratio of time-doubled circularly polarized light to linearly polarized light is
The contrast value is ideal. The invention adopts circularly polarized light, and has the advantages of eliminating polarization mismatch by using the characteristics of statistically uniform distribution and very fast change rate of the vibration direction of the circularly polarized light.
Therefore, when circularly polarized light is used as the reference light, it should be ensured that the polarization direction of the circularly polarized light is rotated by a sufficient number of circles within the sampling time of the fiber sensor to achieve a statistically uniform distribution of the polarization direction in order to solve the problem of polarization mismatch. Based on this, the number of circles that circularly polarized light rotates within the sampling range of the fiber sensor is calculated as follows:
let the expression of circularly polarized light E be:
as described above
And
the unit vectors of the x and y axes, respectively, i.e. circularly polarized light, are resolved into two orthogonal linearly polarized light, a is the amplitude of circularly polarized light, k is the wavevector, z is the distance of light propagation, and ω is the electric vector polarization frequency, which is related to the wavelength of the incident light. When the wavelength λ of incident light in the system is 1550nm, the light speed c is 3 × 108m/s, thenThe polarization frequency of the circularly polarized light is:
when the spatial resolution Δ L is constant, the circularly polarized reference light interferes with the backscattered light at the position of the optical fiber to be measured when the strain and temperature variation at a certain position of the optical fiber are to be measured. For the interference situation to be ideal, the change in the direction of oscillation of the circularly polarized light must be rotated a sufficient number of revolutions during the time Δ t through the spatial resolution Δ L. Then:
where n is the index of refraction, T is the period of one revolution, and X is the number of revolutions within the time Δ T. By substituting formula (23) for formula (24):
wherein
That is, the period T and the frequency f are reciprocal, and the above equation (25) is an expression of the rotation angle in the time of the time Δ T passing through the spatial resolution Δ L, and the rotation angle is in a proportional relationship with the polarization frequency.
Therefore, the frequency of circularly polarized light is 1.94 × 10 according to the formula (22)11KHz, substituting into equation (25), indicates that the angle of circularly polarized light is 0.59X 10 in the system with spatial resolution of 0.1 m6rad is 94413 times 2 π.
As described above, in a system with a spatial resolution of 0.1 meter, the circularly polarized polarization state can complete tens of thousands of cycles of polarization change. Therefore, when the circularly polarized light interferes with the circularly polarized light in any polarization state, the circularly polarized light electric vector can be rapidly changed, so that the condition of phase mismatch of the two beams of light is eliminated.
Therefore, the application of the circularly polarized light can ensure that enough circles are rotated in the sampling time of the optical fiber sensing, so that the polarization directions are statistically and uniformly distributed, the operation is simple, and the running load of the system cannot be increased.
Preferably, before the second path of continuous reference light enters the second optical splitting coupler, the continuous linear polarized light is converted into circular polarized light by the polarization controller, and the circular polarized light is input into the second optical splitting coupler and interferes with the backscattered light signal passing through the circulator.
Example 2
As shown in fig. 1, the present invention further provides a spontaneous brillouin scattering optical fiber sensing device based on circularly polarized light interference, which includes a narrow linewidth laser, a first optical splitting coupler, an electro-optical intensity modulator, a circulator, a polarization controller, a second optical splitting coupler, a balanced detector, a microwave signal generator, a mixer, a low-pass filter, a band-pass filter, and a data processing module. Continuous optical signals emitted by the narrow linewidth laser are divided into two paths of continuous optical signals through a first optical beam splitting coupler with a beam splitting ratio of 50: 50. The first path of continuous light signals are modulated into pulse light signals through the electro-optic intensity modulator, the pulse light signals after passing through the circulator enter the sensing optical fiber, the pulse light signals are transmitted for a certain distance and then generate backward scattering light signals at a certain position of the sensing optical fiber, the signals comprise Rayleigh scattering signals and Brillouin scattering signals, and then the backward scattering light is output through an outlet of the circulator. The second path of continuous light passes through the first light beam splitting coupler with the beam splitting ratio of 50:50 to be used as reference light, and is input into the polarization controller to modulate continuous light signals into reference light in a circular polarization state. After entering a second optical beam splitting coupler with a beam splitting ratio of 50:50, the reference light interferes with the backward scattering light, and an optical signal after interference is converted into an electric signal by a balance detector. The electric signal is swept through the microwave signal generator and the frequency mixer to obtain frequency shift information of the Brillouin scattering spectrum, then a Lorentz curve of the Brillouin scattering spectrum is obtained through the low-pass filter and the band-pass filter to obtain intensity information of the Brillouin scattering spectrum, and finally the strain and temperature information of the position is obtained through acquisition processing of the data processing module.
Shown in fig. 2 is a fiber coaxial polarization controller from THORLABS. In the device of the present invention, the polarization controller shown in fig. 2 will be used to change the polarization state of the reference light. In fig. 2, the fiber coaxial polarizer generates birefringence by rotating and pressurizing the fiber, and generates a fast axis and a slow axis orthogonal to each other, thereby acting as a wave plate, and thus the polarization state of the reference light can be changed into a circular polarization state.
Compared with the prior art, the invention has the beneficial effects that at least:
1. compared with the currently adopted depolarization technology, the invention utilizes the characteristics that the vibration direction of circularly polarized light rotates at high speed and changes uniformly, and takes the circularly polarized light as reference light to interfere with the backward scattering light with randomly changing polarization state, so that the optical fiber sensing system can obtain stable interference signal output.
2. Compared with the existing spontaneous Brillouin scattering system with the polarization mismatch elimination technology, the system depolarization module only needs to add the polarization controller to eliminate polarization, so that the device of the optical fiber sensing system is simple, and the cost of the system is low.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (2)
1. A spontaneous Brillouin scattering optical fiber sensing method based on circularly polarized light interference is characterized by comprising the following steps:
at a light source transmitting end, a continuous laser signal is divided into two paths after passing through a first optical beam splitting coupler; the first path of continuous laser signals are modulated into pulse light signals to enter the sensing optical fiber for transmission, the pulse light signals can generate backward Brillouin scattering light signals at a certain position of the sensing optical fiber after being transmitted for a certain distance, and the frequency shift of the backward scattering light signals is related to the measured strain and the temperature variation, so that the backward scattering light is used as signal light; a second path of continuous laser signals is used as reference light, after linear polarization state reference light is converted into circular polarization state reference light, the reference light enters a second optical beam splitter coupler to interfere with backscattered light signals, the interfered optical signals are converted into electric signals by a balance detector, and finally strain and temperature information at the sensing optical fiber is measured by measuring Brillouin frequency shift quantity;
before the second path of reference light interferes with the backward scattering light signal with the randomly changed polarization state of the first path of reference light, the polarization state of the reference light is converted into a circular polarization state after passing through the polarization controller, namely the problem that the interference effect is not ideal due to the fact that the polarization states of the two paths of light are not consistent during interference is solved by utilizing the characteristics that the vibration direction of circular polarized light rotates at a high speed and changes uniformly;
when the circularly polarized light is used as reference light, the circularly polarized light rotates enough circles in the polarization direction within the sampling time of the optical fiber sensor, so that the polarization direction is statistically and uniformly distributed, and the number of circles of the circularly polarized light rotating within the sampling range of the optical fiber sensor is calculated as follows:
let the expression of circularly polarized light E be:
as described above
And
the unit vectors of the x and y axes, i.e. the circularly polarized light is decomposed into two orthogonal linearly polarized lights, A is the amplitude of the circularly polarized light, k is the wave vector, and z is the light propagationDistance, ω, is the electric vector polarization frequency, which is related to the incident light wavelength; when the wavelength λ of incident light in the system is 1550nm, the light speed c is 3 × 108m/s, the polarization frequency of the circularly polarized light is:
when the spatial resolution Δ L is constant, the reference light of circular polarization interferes with the back scattering light of the optical fiber to be measured to measure the strain and temperature variation of the optical fiber, and in order to make the interference ideal, the vibration direction variation of the circular polarization must rotate enough circumference within the time Δ t passing through the spatial resolution Δ L, then:
wherein n is a refractive index, T is a period of one circle of rotation, X is a number of circles of rotation within Δ T time, and formula (23) is substituted for formula (24):
wherein
That is, the period T and the frequency f are reciprocal, the above equation (25) is an expression of the rotation angle in the time of the time Δ T passing through the spatial resolution Δ L, and the rotation angle is in a direct proportion relationship with the polarization frequency;
therefore, the frequency of circularly polarized light is 1.94 × 10 according to the formula (22)11KHz, substituting into equation (25) shows that in the system with spatial resolution of 0.1 m, circularly polarized lightIs 0.59X 106rad is 94413 times 2 π.
2. A spontaneous Brillouin scattering optical fiber sensing device based on circularly polarized light interference applied to the method of claim 1, which comprises a narrow linewidth laser, a first optical beam splitting coupler, an electro-optical intensity modulator, a circulator, a polarization controller, a second optical beam splitting coupler, a balance detector, a microwave signal generator, a mixer and a data processing module;
the narrow linewidth laser outputs a continuous laser signal, and the continuous laser signal divides a light path into two paths through the first optical beam splitting coupler;
the first path of continuous laser signals are converted into pulse light signals by the electro-optical intensity modulator, the pulse light signals enter the sensing optical fiber after passing through the circulator, and the pulse light signals generate backward scattering light in the transmission process;
the polarization state of the second path of linearly polarized continuous laser signal serving as reference light is changed into a circular polarization state after passing through the polarization controller;
the circularly polarized continuous laser signal and the backward scattering light signal are interfered in a second optical beam splitting coupler, the interfered optical signal is subjected to photoelectric conversion through a balance detector to form an electric signal, electric domain frequency sweeping is carried out through a microwave signal generator and a frequency mixer to obtain Brillouin scattering frequency spectrum information, and finally, the Brillouin scattering frequency spectrum information is acquired and processed through a data processing module to obtain strain and temperature information of the position;
before the second path of reference light interferes with the backward scattering light signal with the randomly changed polarization state of the first path of reference light, the polarization state of the reference light is converted into a circular polarization state after passing through the polarization controller, namely the problem that the interference effect is not ideal due to the fact that the polarization states of the two paths of light are not consistent during interference is solved by utilizing the characteristics that the vibration direction of circular polarized light rotates at a high speed and changes uniformly.
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Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6285808A (en) * | 1985-09-03 | 1987-04-20 | Daiichi Denshi Kogyo Kk | Fiber strain sensor |
| CN101320502A (en) * | 2008-07-22 | 2008-12-10 | 北京航空航天大学 | Optical fiber perimeter alarm method and device for realizing anti-polarization fading |
| CN101825499A (en) * | 2010-05-18 | 2010-09-08 | 华北电力大学（保定） | Method for measuring sea water temperature profile based on optical fiber Brillouin scattering principle |
| CN101975626A (en) * | 2010-10-13 | 2011-02-16 | 华中科技大学 | Brillouin scattering based distributive fiber sensing system |
| CN102279444A (en) * | 2011-07-26 | 2011-12-14 | 南京大学 | Passive device for eliminating polarization noise in Brillouin optical fiber sensor |
| CN102937416A (en) * | 2012-11-20 | 2013-02-20 | 南京大学 | Fully-distributed optical fiber strain and vibration sensing method and device based on cross-polarization state changeover |
| CN103580758A (en) * | 2012-07-26 | 2014-02-12 | 富士通株式会社 | Optical transmission system and method for monitoring polarization dependent characteristics of optical transmission line |
| WO2015067292A1 (en) * | 2013-11-05 | 2015-05-14 | Omnisens Sa | Single-end brillouin optical distributed sensing device and method |
| JP2017053645A (en) * | 2015-09-07 | 2017-03-16 | 横河電機株式会社 | Optical fiber characteristic measurement device |
Family Cites Families (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102322880B (en) * | 2011-08-18 | 2013-06-05 | 天津大学 | Polarization sensitive distributive optical frequency domain reflection disturbance sensor and demodulation method |
-
2018
- 2018-10-19 CN CN201811223809.5A patent/CN109211289B/en active Active
Patent Citations (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6285808A (en) * | 1985-09-03 | 1987-04-20 | Daiichi Denshi Kogyo Kk | Fiber strain sensor |
| CN101320502A (en) * | 2008-07-22 | 2008-12-10 | 北京航空航天大学 | Optical fiber perimeter alarm method and device for realizing anti-polarization fading |
| CN101825499A (en) * | 2010-05-18 | 2010-09-08 | 华北电力大学（保定） | Method for measuring sea water temperature profile based on optical fiber Brillouin scattering principle |
| CN101975626A (en) * | 2010-10-13 | 2011-02-16 | 华中科技大学 | Brillouin scattering based distributive fiber sensing system |
| CN102279444A (en) * | 2011-07-26 | 2011-12-14 | 南京大学 | Passive device for eliminating polarization noise in Brillouin optical fiber sensor |
| CN103580758A (en) * | 2012-07-26 | 2014-02-12 | 富士通株式会社 | Optical transmission system and method for monitoring polarization dependent characteristics of optical transmission line |
| CN102937416A (en) * | 2012-11-20 | 2013-02-20 | 南京大学 | Fully-distributed optical fiber strain and vibration sensing method and device based on cross-polarization state changeover |
| WO2015067292A1 (en) * | 2013-11-05 | 2015-05-14 | Omnisens Sa | Single-end brillouin optical distributed sensing device and method |
| JP2017053645A (en) * | 2015-09-07 | 2017-03-16 | 横河電機株式会社 | Optical fiber characteristic measurement device |
Non-Patent Citations (2)
| Title |
|---|
| A Novel Detection Method of Brillouin Backscattered Light in Optical Fiber;Tianying Chang et al;《IEEE Sensors Journal》;20090430;第29卷(第4期);第430-434页 * |
| 布里渊散射谱相干检测的消偏振衰落技术;刘迪仁等;《光学学报》;20050930;第25卷(第9期);第1191-1194页 * |
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