CN106404217B - A kind of temperature demodulation method based on distributed fiber Raman thermometric - Google Patents

Abstract

The invention relates to a temperature demodulation method in a distributed optical fiber Raman temperature measurement system, in particular to a novel temperature demodulation method based on distributed optical fiber Raman temperature measurement. The invention solves the problems of low temperature measurement accuracy and low temperature measurement efficiency of the system caused by the temperature demodulation method in the existing distributed optical fiber Raman temperature measurement system. A new temperature demodulation method based on distributed optical fiber Raman temperature measurement, the method includes the following steps: Step 1: build a distributed optical fiber Raman temperature measurement system; Raman scattering, so that each position of the optical fiber to be tested produces back-transmitted Stokes light and anti-Stokes light; Step 3: Interpolate Stokes light; Step 4: Loss Stokes light and anti-Stokes light Compensation; step five: performing temperature demodulation on the optical fiber to be tested. The invention is applicable to a distributed optical fiber Raman temperature measurement system.

Description

A temperature demodulation method based on distributed optical fiber Raman temperature measurement

technical field

The invention relates to a temperature demodulation method in a distributed optical fiber Raman temperature measurement system, in particular to a temperature demodulation method based on distributed optical fiber Raman temperature measurement.

Background technique

The distributed optical fiber Raman temperature measurement system is realized by using the spontaneous Raman scattering effect in the optical fiber, combined with Optical Time Domain Reflectometry (OTDR), which can be used for distributed, continuous, and real-time measurement of spatial temperature field distribution. A new type of sensing system. Compared with traditional electronic temperature sensors, the distributed optical fiber Raman temperature measurement system has the advantages of anti-electromagnetic interference, high voltage resistance, high precision, and simple structure, so it is widely used in power cable temperature monitoring, structural health monitoring, dam leakage monitoring and other fields.

In the distributed optical fiber Raman temperature measurement system, the commonly used temperature demodulation method is to use Stokes light as the reference channel, use anti-Stokes light as the signal channel, and then use the wavelength ratio of the two lights to demodulate the temperature information. However, practice has shown that the existing temperature demodulation method has the following problems due to its own principle limitations: First, due to the different wavelengths of Stokes light and anti-Stokes light, their propagation speeds in the optical fiber are different, so the same position is scattered back The Stokes light and anti-Stokes light arrive at the data acquisition card at different times, resulting in that the Stokes light and anti-Stokes light collected by the data acquisition card at the same time do not come from the same position, which leads to signal misalignment, which leads to the measurement of the system. The temperature accuracy is low. Second, in the existing temperature demodulation method, in order to eliminate the fiber loss and demodulate the temperature information, the entire optical fiber to be tested must be placed at a constant temperature for calibration before temperature measurement (if the optical fiber to be tested is replaced, adjusted If the laser power is changed or any system component is replaced, the calibration process must be performed again), which leads to cumbersome operation and low temperature measurement efficiency of the system. Based on this, it is necessary to invent a brand-new temperature demodulation method to solve the problems of low temperature measurement accuracy and low temperature measurement efficiency of the system caused by the temperature demodulation method in the existing distributed optical fiber Raman temperature measurement system.

Contents of the invention

In order to solve the problems of low temperature measurement accuracy and low temperature measurement efficiency caused by the temperature demodulation method in the existing distributed optical fiber Raman temperature measurement system, the present invention provides a temperature solution based on distributed optical fiber Raman temperature measurement. tune method.

The present invention is realized by adopting the following technical solutions:

A temperature demodulation method based on distributed optical fiber Raman temperature measurement, the method comprises the following steps:

Step 1: Build a distributed optical fiber Raman temperature measurement system;

The distributed optical fiber Raman temperature measurement system includes a Raman thermometer, a first high-precision constant temperature bath, a second high-precision constant temperature bath, an optical fiber to be tested, a first temperature sensor, and a second temperature sensor;

Described Raman thermometer comprises pulse laser, WDM, the first APD, the second APD, the first LNA, the second LNA, data acquisition card, computer; Wherein, the output end of pulse laser is connected with the input end of WDM; WDM The two output terminals of the first APD are respectively connected to the input terminal of the first APD and the input terminal of the second APD; the output terminal of the first APD is connected to the input terminal of the first LNA; the output terminal of the second APD is connected to the input terminal of the second LNA connection; the output end of the first LNA and the output end of the second LNA are connected with the input end of the data acquisition card; the output end of the data acquisition card is connected with the input end of the computer; the computer and the pulse laser are bidirectionally connected;

The front end of the optical fiber to be tested is connected to the common end of the WDM; the middle part of the optical fiber to be tested is respectively wound with a first reference optical fiber ring and a second reference optical fiber ring; the first reference optical fiber ring is placed in the first high-precision constant temperature bath; The two reference optical fiber rings are placed in the second high-precision constant temperature tank; the first temperature sensor is installed on the first high-precision constant temperature tank; the second temperature sensor is installed on the second high-precision constant temperature tank; the first temperature sensor and the second temperature The sensors are bidirectionally connected with the computer;

Step 2: Set the temperature value of the first high-precision constant temperature bath to T ₁ , and set the temperature value of the second high-precision constant temperature bath to T ₂ ; then, start the Raman thermometer, and the laser pulse emitted by the pulse laser passes through the WDM Incident to the optical fiber to be tested; when the laser pulse propagates in the optical fiber to be tested, spontaneous Raman scattering occurs, so that each position of the optical fiber to be tested produces Stokes light and anti-Stokes light transmitted backward;

The Stokes light enters the data acquisition card sequentially through the WDM, the first APD, and the first LNA, and the data acquisition card performs analog-to-digital conversion on the Stokes light, thereby obtaining the light intensity curve of the Stokes light, which contains an Inferne Spikes caused by Ole reflection;

The anti-Stokes light enters the data acquisition card through the WDM, the second APD, and the second LNA in turn, and the data acquisition card performs analog-to-digital conversion on the anti-Stokes light, thereby obtaining the light intensity curve of the anti-Stokes light, the light intensity curve also contains a spike due to Fresnel reflection;

Step 3: Interpolate the Stokes light according to the peak position in the light intensity curve of the Stokes light and the peak position in the light intensity curve of the anti-Stokes light, so that the Stokes light and anti-Stokes light generated at the same position of the optical fiber to be tested are - Stokes light takes the same time to reach the data acquisition card;

Step 4: performing loss compensation on Stokes light and anti-Stokes light according to the position of the first reference fiber ring and the position of the second reference fiber ring;

Step 5: Perform temperature demodulation on the optical fiber under test according to the Stokes light and anti-Stokes light after loss compensation.

Compared with the temperature demodulation method in the existing distributed optical fiber Raman temperature measurement system, a kind of temperature demodulation method based on distributed optical fiber Raman temperature measurement of the present invention has the following advantages: First, the present invention adopts The Stokes light is interpolated so that the Stokes light scattered back from the same position and the anti-Stokes light arrive at the data acquisition card at the same time, thus effectively avoiding signal misalignment and thus effectively improving the temperature measurement accuracy of the system. Second, the present invention compensates for the loss of Stokes light and anti-Stokes light, so that the optical fiber to be tested does not need to be calibrated before temperature measurement, thereby effectively simplifying the operation and effectively improving the temperature measurement efficiency of the system.

The invention effectively solves the problems of low temperature measurement accuracy and low temperature measurement efficiency of the system caused by the temperature demodulation method in the existing distributed optical fiber Raman temperature measurement system, and is suitable for the distributed optical fiber Raman temperature measurement system.

Description of drawings

Fig. 1 is a schematic structural diagram of a distributed optical fiber Raman temperature measurement system in the present invention.

Fig. 2 is a schematic diagram of measurement positions of Stokes light and anti-Stokes light before interpolation processing.

Fig. 3 is a schematic diagram of light intensity curves of Stokes light and anti-Stokes light before interpolation processing.

Fig. 4 is a schematic diagram of measurement positions of Stokes light and anti-Stokes light after interpolation processing.

Fig. 5 is a schematic diagram of light intensity curves of Stokes light and anti-Stokes light after interpolation processing.

Fig. 6 is a schematic diagram of light intensity curves of Stokes light and anti-Stokes light before loss compensation.

Fig. 7 is a schematic diagram of light intensity curves of Stokes light and anti-Stokes light after loss compensation.

In Figure 1: 1-pulse laser, 2-WDM (wavelength division multiplexer), 3-first APD (first avalanche photodiode), 4-second APD (second avalanche photodiode), 5-first LNA (the first low-noise amplifier), 6-the second LNA (the second low-noise amplifier), 7-data acquisition card, 8-computer, 9-the first high-precision constant temperature bath, 10-the second high-precision constant temperature bath, 11 - the optical fiber to be tested, 12 - the first temperature sensor, 13 - the second temperature sensor, and the dotted box part represents a Raman thermometer.

In Fig. 2: a represents the Raman pyrometer, and the dotted box part represents the optical fiber to be tested.

In Fig. 4: a represents the Raman pyrometer, and the dotted box part represents the optical fiber to be tested.

Detailed ways

A temperature demodulation method based on distributed optical fiber Raman temperature measurement, the method comprises the following steps:

Step 1: Build a distributed optical fiber Raman temperature measurement system;

The distributed optical fiber Raman temperature measurement system includes a Raman thermometer, a first high-precision constant temperature bath 9, a second high-precision constant temperature bath 10, an optical fiber to be tested 11, a first temperature sensor 12, and a second temperature sensor 13;

Described Raman thermometer comprises pulsed laser 1, WDM2, the first APD3, the second APD4, the first LNA5, the second LNA6, data acquisition card 7, computer 8; Wherein, the output end of pulsed laser 1 and the input of WDM2 The two output terminals of WDM2 are respectively connected with the input terminal of the first APD3 and the input terminal of the second APD4; the output terminal of the first APD3 is connected with the input terminal of the first LNA5; the output terminal of the second APD4 is connected with the second APD4 The input end of LNA6 is connected; The output end of the first LNA5 and the output end of the second LNA6 are all connected with the input end of data acquisition card 7; The output end of data acquisition card 7 is connected with the input end of computer 8; Computer 8 and pulse laser 1 two-way connection;

The front end of the optical fiber 11 to be tested is connected to the common end of WDM2; the middle part of the optical fiber 11 to be tested is respectively wound with a first reference optical fiber ring and a second reference optical fiber ring; the first reference optical fiber ring is placed in the first high-precision constant temperature bath 9 Middle; the second reference optical fiber ring is placed in the second high-precision constant temperature tank 10; the first temperature sensor 12 is installed on the first high-precision constant temperature tank 9; the second temperature sensor 13 is installed on the second high-precision constant temperature tank 10; Both the first temperature sensor 12 and the second temperature sensor 13 are bidirectionally connected with the computer 8;

Step 2: Set the temperature value of the first high-precision constant temperature tank 9 to T ₁ , and set the temperature value of the second high-precision constant temperature tank 10 to T ₂ ; then, start the Raman thermometer, and the laser pulse laser 1 sends The pulse is incident on the optical fiber 11 to be tested through the WDM2; spontaneous Raman scattering occurs when the laser pulse propagates in the optical fiber 11 to be tested, thereby causing back-transmitted Stokes light and anti-Stokes light to be generated at each position of the optical fiber 11 to be tested;

The Stokes light enters the data acquisition card 7 through the WDM2, the first APD3, and the first LNA5 in turn, and the data acquisition card 7 performs analog-to-digital conversion on the Stokes light, thereby obtaining the light intensity curve of the Stokes light, which contains a factor Spikes caused by Fresnel reflections;

The anti-Stokes light enters the data acquisition card 7 through the WDM2, the second APD4, and the second LNA6 in turn, and the data acquisition card 7 performs analog-to-digital conversion on the anti-Stokes light, thereby obtaining the light intensity curve of the anti-Stokes light. The strong curve also contains a spike due to Fresnel reflection;

Step 3: According to the peak position in the light intensity curve of the Stokes light and the peak position in the light intensity curve of the anti-Stokes light, the Stokes light is interpolated, so that the Stokes light and The time when the anti-Stokes light reaches the data acquisition card 7 is the same;

Step 4: performing loss compensation on Stokes light and anti-Stokes light according to the position of the first reference fiber ring and the position of the second reference fiber ring;

Step 5: Perform temperature demodulation on the optical fiber 11 to be tested according to the loss-compensated Stokes light and anti-Stokes light.

In said step three, the specific steps of interpolation processing are as follows:

Let the peak position in the light intensity curve of Stokes light be L _{1 max} , let the peak position in the light intensity curve of anti-Stokes light be L _{2 max} , then the difference L _c =|L _{1 max} -L _{2 max} | ; Then, the difference L _c is rounded to the nearest integer, and let Wherein, φ _s (L) represents the light intensity value of the Stokes light generated at a certain position of the optical fiber 11 to be tested; L represents the distance between the position and the front end of the optical fiber 11 to be tested.

In the step four, the specific steps of loss compensation are as follows:

The distance between the position of the first reference fiber ring and the front end of the optical fiber 11 to be tested is _L1 , and the distance between the position of the second reference fiber ring and the front end of the optical fiber 11 to be tested is _L2 ;

According to the light intensity curve of Stokes light, determine that the light intensity value of the Stokes light that the position of the first reference fiber ring produces is φ _s1 , determine the light intensity value of the Stokes light that the position of the second reference fiber ring produces is φ _s2 ;

Calculate the loss coefficient α _o +α _s of the optical fiber 11 to be tested for the Stokes light; the specific calculation formula is as follows:

In the formula (1): α _o represents the loss coefficient of the laser pulse per unit length in the optical fiber 11 to be tested; α _s represents the loss coefficient of the Stokes light per unit length in the optical fiber 11 to be tested; h represents Planck’s constant; Δv Indicates the Raman frequency shift of the fiber; K indicates the Boltzmann constant;

According to the light intensity curve of the anti-Stokes light, determine the light intensity value of the anti-Stokes light generated by _the position of the first reference fiber ring, determine the light intensity value of the anti-Stokes light generated by the position of the second reference fiber ring is φ _a2 ;

Calculate the loss coefficient α _o +α _a of the optical fiber 11 to be tested for anti-Stokes light; the specific calculation formula is as follows:

In the formula (2): α _o represents the loss coefficient of the laser pulse per unit length in the optical fiber 11 to be tested; α _a represents the loss coefficient of the anti-Stokes light per unit length in the optical fiber 11 to be tested; h represents Planck’s constant ; Δv represents the Raman frequency shift of the fiber; K represents the Boltzmann constant.

In the step five, the specific temperature demodulation formula is as follows:

In formula (3): T represents the temperature value of a certain position of optical fiber 11 to be tested; φ _s represents the light intensity value of the Stokes light that this position produces; φ _a represents the light intensity value of the anti-Stokes light that this position produces; L represents the distance between the position and the front end of the optical fiber 11 to be tested; φ _s1 represents the light intensity value of the Stokes light produced by the position of the first reference fiber ring; φ _a1 represents the anti-Stokes produced by the position of the first reference fiber ring The light intensity value of light; φ _s2 represents the light intensity value of the Stokes light that the position of the second reference fiber ring produces; φ _a2 represents the light intensity value of the anti-Stokes light that the position of the second reference fiber ring produces; L ₁ represents the first The distance between the position of a reference optical fiber ring and the front end of the optical fiber 11 to be tested; _L2 represents the distance between the position of the second reference optical fiber ring and the front end of the optical fiber 11 to be tested; h represents Planck's constant; Δv represents the optical fiber The Raman frequency shift; K represents the Boltzmann constant.

During specific implementation, the wavelength of the pulsed laser is 1550.1 nm, the pulse width is 10 ns, and the repetition frequency is 8 KHz. The working wavelength of the WDM is 1550nm/1450nm/1663nm. The first APD has a bandwidth of 80 MHz and a spectral response range of 900-1700 nm. The second APD has a bandwidth of 80 MHz and a spectral response range of 900-1700 nm. The bandwidth of the first LNA is 100MHz. The bandwidth of the second LNA is 100MHz. The number of channels of the data acquisition card is 4, the sampling rate is 100M/s, and the bandwidth is 100MHz. The optical fiber to be tested is a common multimode optical fiber.

Claims (4)

1. a kind of temperature demodulation method based on distributed fiber Raman thermometric, it is characterised in that：This method comprises the following steps：

Step 1：Build distributed fiber Raman temp measuring system；

The distributed fiber Raman temp measuring system includes Raman temperature measurer, the first high-precision thermostat bath (9), the second high-accuracy and constant Warm slot (10), testing fiber (11), the first temperature sensor (12), second temperature sensor (13)；

The Raman temperature measurer include pulse laser (1), WDM (2), the first APD (3), the 2nd APD (4), the first LNA (5), 2nd LNA (6), data collecting card (7), computer (8)；Wherein, the input terminal of the output end of pulse laser (1) and WDM (2) Connection；Two output ends of WDM (2) are connect with the input terminal of the input terminal of the first APD (3) and the 2nd APD (4) respectively；First The output end of APD (3) is connect with the input terminal of the first LNA (5)；The input terminal of the output end and the 2nd LNA (6) of 2nd APD (4) Connection；The output end of first LNA (5) and the output end of the 2nd LNA (6) are connect with the input terminal of data collecting card (7)；Data The output end of capture card (7) is connect with the input terminal of computer (8)；Computer (8) is bi-directionally connected with pulse laser (1)；

The front end of testing fiber (11) is connect with the common end of WDM (2)；The middle section of testing fiber (11) is wound with respectively One reference optical fiber ring and the second reference optical fiber ring；First reference optical fiber ring is positioned in the first high-precision thermostat bath (9)；Second ginseng Fiber optic loop is examined to be positioned in the second high-precision thermostat bath (10)；First temperature sensor (12) is installed on the first high-precision thermostat bath (9) on；Second temperature sensor (13) is installed on the second high-precision thermostat bath (10)；First temperature sensor (12) and second Temperature sensor (13) is bi-directionally connected with computer (8)；

Step 2：Set the temperature value of the first high-precision thermostat bath (9) to T₁, by the temperature of the second high-precision thermostat bath (10) Value is set as T₂；Then, start Raman temperature measurer, the laser pulse that pulse laser (1) is sent out is incident on to be measured through WDM (2) Optical fiber (11)；When being propagated in testing fiber (11) spontaneous Raman scattering occurs for laser pulse, so that testing fiber (11) Each position generate backwards to transmission Stokes light and anti-Stokes light；

Stokes light is incident on data collecting card (7), data collecting card through WDM (2), the first APD (3), the first LNA (5) successively (7) analog-to-digital conversion is carried out to Stokes light, thus obtains the light intensity curve of Stokes light, comprising one because of phenanthrene in the light intensity curve Spike caused by Nie Er reflections；

Anti-Stokes light is incident on data collecting card (7) through WDM (2), the 2nd APD (4), the 2nd LNA (6) successively, and data are adopted Truck (7) carries out analog-to-digital conversion to anti-Stokes light, thus obtains the light intensity curve of anti-Stokes light, the light intensity curve In equally include a spike caused by Fresnel reflection；

Step 3：According to the point in the light intensity curve of peak location and anti-Stokes light in the light intensity curve of Stokes light Peak position, to Stokes light carry out interpolation processing so that testing fiber (11) same position generate Stokes light and The time that anti-Stokes light reaches data collecting card (7) is identical；

Step 4：According to the position of the position of the first reference optical fiber ring and the second reference optical fiber ring, to Stokes light and anti- Stokes light carries out loss balancing；

Step 5：According to the Stokes light and anti-Stokes light after loss balancing, to testing fiber (11) into trip temperature solution It adjusts.

2. a kind of temperature demodulation method based on distributed fiber Raman thermometric according to claim 1, it is characterised in that： In the step 3, interpolation processing is as follows：

If the peak location in the light intensity curve of Stokes light is L_{1 max}If the spike in the light intensity curve of anti-Stokes light Position is L_{2 max}, then its difference L_c=| L_{1 max}-L_{2 max}|；Then, to difference L_cIt handles, and enables using with regard to nearest integer roundingWherein, φ_s(L) light for the Stokes light that a certain position of testing fiber (11) generates is indicated Intensity values；L indicates the distance between the front end of the position and testing fiber (11).

3. a kind of temperature demodulation method based on distributed fiber Raman thermometric according to claim 1, it is characterised in that： In the step 4, loss balancing is as follows：

If the distance between the position of the first reference optical fiber ring and the front end of testing fiber (11) are L₁If the second reference optical fiber ring The distance between the front end of position and testing fiber (11) be L2；

According to the light intensity curve of Stokes light, determine that the light intensity value for the Stokes light that the position of the first reference optical fiber ring generates is φ_s1, determine that the light intensity value for the Stokes light that the position of the second reference optical fiber ring generates is φ_s2；

Calculate loss factor α o+ α of the testing fiber (11) to Stokes light_s；Specific formula for calculation is as follows：

In formula (1)：α o indicate loss factor of the laser pulse in testing fiber (11) under unit length；α_sIndicate Stokes Loss factor of the light in testing fiber (11) under unit length；H indicates Planck's constant；Δ v indicates the Raman frequency shift of optical fiber Amount；K indicates Boltzmann constant；

According to the light intensity curve of anti-Stokes light, the anti-Stokes light that the position of the first reference optical fiber ring generates is determined Light intensity value is φ_a1, determine that the light intensity value for the anti-Stokes light that the position of the second reference optical fiber ring generates is φ_a2；

Calculate loss factor α of the testing fiber (11) to anti-Stokes light_o+α_a；Specific formula for calculation is as follows：

In formula (2)：α_oIndicate loss factor of the laser pulse in testing fiber (11) under unit length；α_aIndicate anti- Loss factor of the Stokes light in testing fiber (11) under unit length；H indicates Planck's constant；Δ v indicates the drawing of optical fiber Graceful frequency shift amount；K indicates Boltzmann constant.

4. a kind of temperature demodulation method based on distributed fiber Raman thermometric according to claim 1, it is characterised in that： In the step 5, it is as follows that actual temp demodulates formula：

In formula (3)：T indicates the temperature value of a certain position of testing fiber (11)；φ_sIndicate the Stokes light that the position generates Light intensity value；φ_aIndicate the light intensity value for the anti-Stokes light that the position generates；L indicates the position and testing fiber (11) The distance between front end；φ_s1Indicate the light intensity value for the Stokes light that the position of the first reference optical fiber ring generates；φ_a1Indicate first The light intensity value for the anti-Stokes light that the position of reference optical fiber ring generates；φ_s2Indicate what the position of the second reference optical fiber ring generated The light intensity value of Stokes light；φ_a2Indicate the light intensity value for the anti-Stokes light that the position of the second reference optical fiber ring generates；L₁Table Show the distance between the front end of the position and testing fiber (11) of the first reference optical fiber ring；L₂Indicate the position of the second reference optical fiber ring It sets and the distance between the front end of testing fiber (11)；H indicates Planck's constant；Δ v indicates the Raman frequency shift amount of optical fiber；K tables Show Boltzmann constant.