CN112129426A - Raman sensing temperature measurement system and method with single end injected with multi-core optical fiber - Google Patents
Raman sensing temperature measurement system and method with single end injected with multi-core optical fiber Download PDFInfo
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- CN112129426A CN112129426A CN202011005451.6A CN202011005451A CN112129426A CN 112129426 A CN112129426 A CN 112129426A CN 202011005451 A CN202011005451 A CN 202011005451A CN 112129426 A CN112129426 A CN 112129426A
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- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/32—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using changes in transmittance, scattering or luminescence in optical fibres
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Abstract
The invention provides a single-end injection multicore optical fiber Raman sensing temperature measurement system and a method, wherein a signal processing module and a fan-in fan-out module are arranged, any two fiber cores are taken from the multicore optical fiber for measurement when the temperature measurement is carried out on the multicore optical fiber, a pulse laser generates pumping pulse, the pumping pulse is injected into a fiber core 1 of the fan-in module through a wavelength division multiplexer, the pumping pulse is output from the fiber core 1 of the fan-out module and injected into a fiber core 2 of the fan-out module through a single-mode optical fiber after passing through the multicore optical fiber core 1, and the pumping pulse returns to the fan-in module; raman scattering signals generated by the multi-core optical fiber core 1 and the multi-core optical fiber core 2 are filtered out stokes and anti-stokes optical signals through a wavelength division multiplexer, under the triggering of a pulse laser synchronous control signal, a signal acquisition module synchronously acquires the Raman scattering signals, and the averaged signals are input into a signal processing module for temperature demodulation. According to the invention, double-end measurement of the fiber core 1 is realized through single-end measurement, and the influence of wavelength-dependent loss and local loss on the measurement temperature is eliminated.
Description
Technical Field
The invention relates to a temperature measurement system and a method, in particular to a Raman sensing temperature measurement system and a Raman sensing temperature measurement method for realizing double-end measurement accuracy by injecting a multi-core fiber into a single end.
Background
The distributed Raman optical fiber sensing system has the advantages of long measuring distance, electromagnetic interference resistance, portability, insulation and the like, and is widely applied to the fields of electric power petroleum pipelines, large-scale buildings, tunnel bridges and the like which need real-time temperature monitoring. In the traditional single-ended Raman temperature measurement method, a pulse light source is coupled into an optical fiber, Stokes light and anti-Stokes light power in Raman scattering signals are detected simultaneously, and the two are divided to demodulate the temperature:
wherein P isas(z) and Ps(z) anti-Stokes and Stokes optical powers, C, respectively, at fiber position zas(z) and Cs(z) is a constant determined by the position z of the optical fiber, and is related to incident light power, anti-Stokes wavelength, etc., h is a Planckian constant, Δ ν is the frequency difference between Raman scattered light and incident light, k is a Boltzmann constant, αas(x)、αs(x) The loss of anti-stokes light, respectively stokes light at fiber position x, and t (z) is the temperature distribution over the fiber.
In the single-ended Raman temperature measurement method, the temperature demodulation result comprises
Shows that the temperature measurement result is subjected to lightAnti-stokes light and stokes light in the fiber are affected by position-dependent losses. In an extreme environment such as nuclear radiation, or when the optical fiber is bent, the loss of the anti-stokes light and the stokes light changes, resulting in a large temperature error. The traditional double-end Raman temperature measurement method adopts an optical fiber loop structure, and the light source is injected from the head end or the tail end of the sensing optical fiber in a time-sharing manner through switching of an optical switch, so that forward Raman scattering signals and backward Raman scattering signals are measured respectively. In the double-end Raman temperature measurement method, for anti-Stokes and Stokes signals, signals obtained by forward and backward measurement are respectively subjected to geometric averaging to obtain loop anti-Stokes and Stokes optical signals, and the loop anti-Stokes and Stokes optical signals are divided to demodulate the loop temperature:
wherein P isAS_LoopAnd PS_LoopPower of loop anti-Stokes and Stokes optical signals, CAS_ForAnd CS_ForConstants, C, representing the position dependence of the anti-Stokes and Stokes light signals, respectively, during forward measurementsAS_BackAnd CS_BackRespectively, representing the position-dependent constants of the anti-stokes and stokes optical signals for back-measurement. In the double-end Raman temperature measurement method, the wavelength-dependent loss is the same at each point on the optical fiber loop
And the error of the local temperature measurement result caused by wavelength-dependent loss is eliminated. However, in practical application, the double-end raman temperature measurement method needs to arrange an optical fiber loop, and an optical switch is needed to switch an input port during measurement, so that a temperature curve on the optical fiber loop can be obtained through two measurements.
Disclosure of Invention
The invention provides a novel distributed Raman fiber temperature measurement system and a novel distributed Raman fiber temperature measurement method, which overcome the defects of the prior art in the background art.
The invention provides a single-ended injection multi-core fiber Raman sensing temperature measurement system which comprises a pulse laser, a wavelength division multiplexer, a photoelectric conversion module and a signal acquisition module, wherein the signal processing module and a fan-in and fan-out module are arranged, the fan-in and fan-out module comprises a fan-in module and a fan-out module, the fan-in module comprises a fan-in module core 1, the fan-out module comprises a fan-out module fiber core 1 and a fan-out module fiber core 2,
when the temperature of the multi-core optical fiber is measured, two fiber cores are taken from the multi-core optical fiber for measurement, the two fiber cores are marked as a multi-core optical fiber core 1 and a multi-core optical fiber core 2, a pulse laser generates pumping pulses, the pumping pulses are injected into a fan-in module fiber core 1 through a wavelength division multiplexer, the pumping pulses are output from the fan-out module fiber core 1 and injected into the fan-out module fiber core 2 through a single-mode optical fiber after passing through the multi-core optical fiber core 1, and the pumping pulses return to the fan-in module through the multi-core optical fiber core 2 to form an optical fiber loop; raman scattering signals generated by the multi-core optical fiber core 1 and the multi-core optical fiber core 2 are filtered out stokes and anti-stokes optical signals through a wavelength division multiplexer, and enter a photoelectric conversion module to be converted into electric signals; under the trigger of the pulse laser synchronous control signal, the signal acquisition module synchronously acquires Raman scattering signals, and the averaged signals are input into the signal processing module for temperature demodulation.
Moreover, the number of the fiber cores of the multi-core optical fiber is more than 2, different fiber cores have the same refractive index distribution, the length difference of the different fiber cores is less than 5cm/km, and the crosstalk between the fiber cores is less than-40 dB/km.
Moreover, the insertion loss of 1550nm wavelength of the multi-core fan-in fan-out module is less than 1.5dB, the return loss is greater than 45dB, and the crosstalk among the cores is less than-50 dB.
The invention also provides a single-ended injection multi-core fiber Raman sensing temperature measurement method which is used for the single-ended injection multi-core fiber Raman sensing temperature measurement system.
Moreover, the temperature measuring process comprises the following steps,
step 1, setting the total length of the multi-core optical fiber as L, measuring the total lengths of stokes and anti-stokes optical signals of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 as 2L, wherein the z position and the 2L-z position on the stokes and anti-stokes optical signals both correspond to the z position on the multi-core optical fiber, and the environmental temperature of the z position is T (z), the anti-stokes and anti-stokes optical signal ratios of the z position and the 2L-z position are respectively as follows:
wherein, Pas(z) and Ps(z) anti-Stokes and Stokes optical powers, C, respectively, at fiber position zas(z) and Cs(z) is a constant determined by the fiber position z, h is the Planckian constant, Δ ν is the frequency difference between the Raman scattered light and the incident light, k is the Boltzmann constant, αas(x)、αs(x) Loss of anti-stokes light and stokes light at the optical fiber position x respectively;
step 2, obtaining a z-position anti-Stokes double-end measurement signal P according to the result obtained in the step 1as_Double(z) and Stokes double ended measurement signal Ps_Double(z), and further obtaining double-end measurement results of the z-position Stokes and anti-Stokes optical signals as follows:
considering time t, willas(z)、αs(z) is represented by alphaas(z,t)、αs(z, t), the z positions of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 respectively correspond to the z position and the 2L-z position in the measurement result,
αas(z,t)＝αas(2L-z,t)
αs(z,t)＝αs(2L-z,t)
to obtain
The wavelength dependent loss of the double-ended measurement Stokes and anti-Stokes optical signals at each position of the sensing optical fiber is the same
Step 3, eliminating the constant C by scalingasAnd CsThe effect of (a) is achieved as follows,
taking a section of the multi-core optical fiber to be placed in a constant temperature state as a reference, and based on the section of the constant temperature optical fiber, at the time t0, for any point z on the multi-core optical fiber, under the known optical fiber temperature distribution Temp0(z, t0), the anti-Stokes and Stokes double-end measurement signals are respectively Pas_Double(z, t0) and Ps_Double(z, t0), the double-ended measurement calibration results are:
at the time of t1, measuring any point z on the multi-core optical fiber under the temperature distribution Temp1(z, t1) of the optical fiber to be measured, wherein the anti-Stokes and Stokes double-end measurement signals are P respectivelyas_Double(z, t1) and Ps_Double(z, t1), double ended measurement:
the measurement result at the time t1 is divided by the calibration result at the time t0 to obtain:
step 4, assuming that z0 is a point on the constant temperature optical fiber, and when the temperature Temp0(z0, t0) at the time t0 and the temperature Temp1(z0, t1) at the time t1 are both known, the wavelength-dependent loss is calculated as follows:
calculating the average value of delta alpha on the constant temperature optical fiber as
And 5, for any point z on the multi-core fiber except the constant temperature fiber, dividing the measurement result by the calibration result into:
in the case where Δ α has been solved, we obtain:
therefore, the temperature curve on the multi-core optical fiber is obtained through demodulation.
According to the invention, double-end measurement of the fiber core is realized by a single-end measurement method, and the influence of unstable Raman signal light on temperature measurement precision due to optical fiber loss change is eliminated. Compared with the prior art, the invention has the following advantages and beneficial effects:
1. according to the invention, the geometric mean is obtained by multiplying signals at the same positions of two fiber cores, so that a double-end measurement result is obtained, and the wavelength-dependent loss of each point on the sensing optical fiber is
The system and the measuring method can eliminate the influence of static wavelength-dependent loss on temperature measurement.
2. The invention firstly calibrates under the known temperature, and divides the measuring result and the calibrating result, thereby eliminating the influence of the constant coefficient related to the position and further improving the temperature measuring precision.
3. The invention can be applied without arranging an optical fiber loop, only by using a single multi-core optical fiber and without using an optical switch to switch ports, can obtain a temperature measurement result by single measurement, and has the advantages of high measurement speed, simple system structure, less required devices and low cost.
Drawings
Fig. 1 is a structure of a single-ended injection multi-core fiber raman sensing temperature measurement system according to an embodiment of the present invention.
FIG. 2 shows core 1 and core 2 anti-Stokes and Stokes signal measurements of an embodiment of the present invention.
Fig. 3 is a temperature curve of the multi-core fiber demodulated according to the embodiment of the present invention.
Detailed Description
The technical solution of the present invention is specifically described below with reference to the accompanying drawings and examples.
The raman sensing temperature measurement system with single-end injection of the multi-core fiber provided by the embodiment of the invention is shown in fig. 1 and comprises a pulse laser, a wavelength division multiplexer, a photoelectric conversion module, a signal acquisition module, a signal processing module, a fan-in fan-out module and a multi-core fiber.
The fan-in fan-out module comprises a fan-in module and a fan-out module, wherein the fan-in module comprises a fan-in module core 1, and the fan-out module comprises a fan-out module core 1 and a fan-out module core 2.
The number of the fiber cores of the multi-core optical fiber is more than or equal to 2, different fiber cores have the same refractive index distribution, the length difference of the different fiber cores is less than 5cm/km, and the crosstalk between the fiber cores is less than-40 dB/km. According to the current multi-core fiber technology, the multi-core fiber can generally adopt a seven-core fiber, and two cores can be taken from the seven-core fiber for measurement, which are marked as a multi-core fiber core 1 and a multi-core fiber core 2 in the embodiment.
In an embodiment, the pulsed laser generates pump pulses with a wavelength of 1550nm, a peak power of 5W, a pulse width of 10ns and a repetition rate of 10 kHz. The pump pulse generated by the pulse laser is injected into the fiber core 1 of the fan-in module through the wavelength division multiplexer, is output from the fiber core 1 of the fan-out module after passing through the multi-core fiber core 1, is injected into the fiber core 2 of the fan-out module through the single-mode fiber, and returns to the fan-in module through the multi-core fiber core 2 to form an optical fiber loop, and the synchronous control signal generated by the pulse laser is used for triggering the signal acquisition module. The wavelength division multiplexer filters out 1450nm anti-stokes light and 1660nm stokes light of the raman scattered signal in the optical fiber. Stokes and anti-Stokes optical signals are input into a photoelectric conversion module, the photoelectric conversion module consists of two APD photoelectric detectors, and the bandwidth is 100 MHz. The electric signal generated by the photoelectric conversion module is synchronously acquired by a signal acquisition module, the signal acquisition module comprises an analog-to-digital converter with 12bit precision, and the sampling rate is 100 MS/s. The acquired signals are input into a signal processing module to demodulate the temperature. The multi-core fan-in fan-out module 1550nm wavelength insertion loss is less than 1.5dB, the return loss is greater than 45dB, and the inter-core crosstalk is less than-50 dB. The multi-core optical fiber is a seven-core optical fiber, the total length of the optical fiber is 2 kilometers, and the crosstalk between the fiber cores is less than-40 dB/km. The front 50 m of the multi-core optical fiber is arranged in a constant temperature box as a reference optical fiber, 600 m of the multi-core optical fiber is arranged in a cold water bath, and 800 m of the multi-core optical fiber is arranged in a hot water bath. In the temperature measuring process, the temperature of the constant temperature box is 12 ℃, the room temperature is 12 ℃, the temperature of the cold bath is 0 ℃, the temperature of the hot bath is 15 ℃, and the temperature control precision of the cold bath and the hot bath is +/-0.5 ℃.
According to the system, the single-ended injection multi-core fiber Raman sensing temperature measurement method provided by the embodiment of the invention is realized as follows:
step 1, a pulse laser generates pumping pulses, the pumping pulses are injected into a fiber core 1 of a fan-in module through a wavelength division multiplexer, the pumping pulses are output from the fiber core 1 of the fan-out module after passing through a multi-core fiber core 1, the pumping pulses are injected into a fiber core 2 of the fan-out module through a single-mode fiber, and the pumping pulses return to the fan-in module through the multi-core fiber core 2 to form a fiber loop, so that simultaneous measurement of the multi-core fiber core 1 and the multi-core fiber core. Raman scattering signals generated by the multi-core optical fiber core 1 and the multi-core optical fiber core 2 are filtered out stokes and anti-stokes optical signals through a wavelength division multiplexer, and enter a photoelectric conversion module to be converted into electric signals. Under the trigger of a pulse laser synchronous control signal, the signal acquisition module synchronously acquires Raman scattering signals, and the average time of single measurement is preferably 50000 times. The averaged signal is input to a signal processing module for temperature demodulation.
For example, when the total length L of the seven-core optical fiber is 2 km, since the lengths of the different cores of the multi-core optical fiber are approximately the same, the total lengths of the stokes and anti-stokes optical signals of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 measured are 4 km.
The z position and the 2L-z position on the Stokes light signal and the anti-Stokes light signal both correspond to the z position on the multi-core optical fiber, the environmental temperature of the z position is T (z), and the anti-Stokes light signal ratio and the Stokes light signal ratio of the z position and the 2L-z position are respectively as follows:
wherein, Pas(z) and Ps(z) anti-Stokes and Stokes optical powers, C, respectively, at fiber position zas(z) and Cs(z) is a constant determined by the position z of the optical fiber, and is related to incident light power, anti-Stokes wavelength, etc., h is a Planckian constant, Δ ν is the frequency difference between Raman scattered light and incident light, k is a Boltzmann constant, αas(x)、αs(x) Loss of anti-stokes light, respectively stokes light at fiber position x.
The anti-stokes and stokes signal measurement results of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 are shown in fig. 2. As can be seen from FIG. 2, at 500-600 m and 3400-3500 m, the Stokes signal is slightly reduced and the anti-Stokes signal is obviously reduced when the multi-core fiber is placed in the cold water bath. At the positions of 700-800 m and 3200-3300 m, the multi-core fiber is placed in a hot water bath, the Stokes signal is slightly increased, and the anti-Stokes signal is obviously increased.
Step 2, multiplying the formula (1) and the formula (2) and taking geometric mean to obtain the z-position anti-Stokes double-end measurement signal Pas_Double(z) and Stokes double ended measurement signal Ps_Double(z), respectively expressed as:
Pas_Double(z) and Ps_DoubleThe (z) division gives a double ended measurement:
αas(z)、αs(z) may vary with time t due to the external environment, and may be represented as αas(z,t)、αs(z, t), because different cores of the multi-core optical fiber have high consistency and are in the same external environment, the anti-stokes light and the stokes light loss of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 at the z position of the multi-core optical fiber are the same at each moment, in the adopted measuring method, the z positions of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 respectively correspond to the z position and the 2L-z position in the measuring result, namely:
αas(z,t)＝αas(2L-z,t) (6)
αs(z,t)＝αs(2L-z,t) (7)
thus, a double ended measurement can be expressed as:
as can be seen from equation (8), the wavelength dependent loss of the double-ended measurement Stokes and anti-Stokes optical signals at each position of the sensing fiber is the same
Step 3, in the formula (8), constants C at different positions of the optical fiberasAnd CsThese constants are not identical and therefore need to be calibrated first, taking 50 meters of the multicore fiber and placing it in an oven as a reference fiber (i.e. a thermostatted fiber), the oven temperature being known at each moment, atAt the time t0, any point z on the multi-core optical fiber (namely any point on the whole sensing optical fiber) is calibrated under the known optical fiber temperature distribution Temp0(z, t0), and the anti-Stokes and Stokes double-end measurement signals are respectively Pas_Double(z, t0) and Ps_Double(z, t0), so the double ended measurement scale results are:
at the time of t1, measuring any point z on the multi-core fiber under the temperature distribution Temp1(z, t1) of the fiber to be measured, wherein the anti-Stokes and Stokes double-end measurement signals are P respectivelyas_Double(z, t1) and Ps_Double(z, t1), so the double ended measurement is:
the measurement result at time t1 is divided by the calibration result at time t0 to obtain:
as equation (11), the constant C is eliminated by dividing the measurement at time t1 by the calibration at time t0asAnd CsThe influence of (c).
In step 4, z0 is a point on the constant temperature optical fiber, and the temperature Temp0(z0, t0) at time t0 and the temperature Temp1(z0, t1) at time t1 are both known, so that the wavelength dependent loss Δ α can be calculated:
calculating the average value of delta alpha on the constant temperature optical fiber as
for any point z on the multi-core fiber, the measurement result is divided by the calibration result as follows:
in that
Having solved for this, the temperature Temp1(z, t1) at any point z on the multicore fiber at time t1 can be solved:
the temperature curve of the optical fiber can be obtained by demodulation according to the formula (14). The temperature curve obtained by demodulation is shown in fig. 3, and the average temperature of 100m sensing optical fibers in a hot water bath and a cold water bath is marked on the right side of fig. 3, and the error of the average temperature and the set actual temperature is not more than 0.7 ℃.
The single-ended injection multi-core fiber Raman sensing temperature measurement system and the method do not need to switch ports, do not need to arrange an optical fiber loop, can obtain a temperature measurement result by only one-time measurement, have high measurement speed, eliminate temperature measurement errors caused by wavelength-dependent loss and local loss, and effectively improve the temperature measurement precision.
In specific implementation, a person skilled in the art can implement the automatic operation process by using a computer software technology, and a system device for implementing the method, such as a computer-readable storage medium storing a corresponding computer program according to the technical solution of the present invention and a computer device including a corresponding computer program for operating the computer program, should also be within the scope of the present invention.
The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims and their equivalents.
The specific embodiments described herein are merely illustrative of the spirit of the invention. Various modifications or additions may be made to the described embodiments or alternatives may be employed by those skilled in the art without departing from the spirit or ambit of the invention as defined in the appended claims.
Claims (5)
1. The utility model provides a single-ended injection multicore optic fibre raman sensing temperature measurement system, includes pulse laser, wavelength division multiplexer, photoelectric conversion module and signal acquisition module, its characterized in that: arranging a signal processing module and a fan-in fan-out module, wherein the fan-in fan-out module comprises a fan-in module and a fan-out module, the fan-in module comprises a fan-in module core 1, the fan-out module comprises a fan-out module core 1 and a fan-out module core 2,
when the temperature of the multi-core optical fiber is measured, two fiber cores are taken from the multi-core optical fiber for measurement, the two fiber cores are marked as a multi-core optical fiber core 1 and a multi-core optical fiber core 2, a pulse laser generates pumping pulses, the pumping pulses are injected into a fan-in module fiber core 1 through a wavelength division multiplexer, the pumping pulses are output from the fan-out module fiber core 1 and injected into the fan-out module fiber core 2 through a single-mode optical fiber after passing through the multi-core optical fiber core 1, and the pumping pulses return to the fan-in module through the multi-core optical fiber core 2 to form an optical fiber loop; raman scattering signals generated by the multi-core optical fiber core 1 and the multi-core optical fiber core 2 are filtered out stokes and anti-stokes optical signals through a wavelength division multiplexer, and enter a photoelectric conversion module to be converted into electric signals; under the trigger of the pulse laser synchronous control signal, the signal acquisition module synchronously acquires Raman scattering signals, and the averaged signals are input into the signal processing module for temperature demodulation.
2. The single-ended injection multi-core fiber Raman sensing temperature measurement system according to claim 1, wherein: the number of the fiber cores of the multi-core optical fiber is more than 2, different fiber cores have the same refractive index distribution, the length difference of the different fiber cores is less than 5cm/km, and the crosstalk between the fiber cores is less than-40 dB/km.
3. The single-ended injection multi-core fiber Raman sensing temperature measurement system according to claim 1, wherein: the multi-core fan-in fan-out module 1550nm wavelength insertion loss is less than 1.5dB, the return loss is greater than 45dB, and the inter-core crosstalk is less than-50 dB.
4. A single-ended injection multi-core fiber Raman sensing temperature measurement method is characterized by comprising the following steps: the single-ended injection multi-core fiber Raman sensing temperature measurement system used for the method as claimed in any one of claims 1 to 3.
5. The single-ended injection multi-core fiber Raman sensing temperature measurement method according to claim 3, wherein: the temperature measuring process comprises the following steps of,
step 1, setting the total length of the multi-core optical fiber as L, measuring the total lengths of stokes and anti-stokes optical signals of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 as 2L, wherein the z position and the 2L-z position on the stokes and anti-stokes optical signals both correspond to the z position on the multi-core optical fiber, and the environmental temperature of the z position is T (z), the anti-stokes and anti-stokes optical signal ratios of the z position and the 2L-z position are respectively as follows:
wherein, Pas(z) and Ps(z) anti-Stokes and Stokes optical powers, C, respectively, at fiber position zas(z) and Cs(z) is a constant determined by the fiber position z, h is the Planckian constant, Δ ν is the frequency difference between the Raman scattered light and the incident light, k is the Boltzmann constant, αas(x)、αs(x) Loss of anti-stokes light and stokes light at the optical fiber position x respectively;
step 2, obtaining a z-position anti-Stokes double-end measurement signal P according to the result obtained in the step 1as_Double(z) and Stokes double ended measurement signal Ps_Double(z), and further obtaining double-end measurement results of the z-position Stokes and anti-Stokes optical signals as follows:
considering time t, willas(z)、αs(z) is represented by alphaas(z,t)、αs(z, t), the z positions of the multi-core optical fiber core 1 and the multi-core optical fiber core 2 respectively correspond to the z position and the 2L-z position in the measurement result,
αas(z,t)＝αas(2L-z,t)
αs(z,t)＝αs(2L-z,t)
to obtain
The wavelength dependent loss of the double-ended measurement Stokes and anti-Stokes optical signals at each position of the sensing optical fiber is the same
Step 3, eliminating the constant C by scalingasAnd CsThe effect of (a) is achieved as follows,
taking a section of the multi-core optical fiber to be placed in a constant temperature state as a reference, and based on the section of the constant temperature optical fiber, at the time t0, for any point z on the multi-core optical fiber, under the known optical fiber temperature distribution Temp0(z, t0), the anti-Stokes and Stokes double-end measurement signals are respectively Pas_Double(z, t0) and Ps_Double(z, t0), the double-ended measurement calibration results are:
at the time of t1, measuring any point z on the multi-core optical fiber under the temperature distribution Temp1(z, t1) of the optical fiber to be measured, wherein the anti-Stokes and Stokes double-end measurement signals are P respectivelyas_Double(z, t1) and Ps_Double(z, t1), double ended measurement:
the measurement result at the time t1 is divided by the calibration result at the time t0 to obtain:
step 4, assuming that z0 is a point on the constant temperature optical fiber, and when the temperature Temp0(z0, t0) at the time t0 and the temperature Temp1(z0, t1) at the time t1 are both known, the wavelength-dependent loss is calculated as follows:
calculating the average value of delta alpha on the constant temperature optical fiber as
And 5, for any point z on the multi-core fiber except the constant temperature fiber, dividing the measurement result by the calibration result into:
in the case where Δ α has been solved, we obtain:
therefore, the temperature curve on the multi-core optical fiber is obtained through demodulation.
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