CN106323498A - Distributed optical fiber temperature sensor - Google Patents

Abstract

The invention relates to a distributed optical fiber temperature sensor, comprising a pulsed fiber laser, a first optical isolator, a circulator and an optical fiber Raman amplifier connected in sequence; the circulator is connected to a third wavelength division multiplexer; the third The wavelength division multiplexer is connected to the photoelectric conversion signal processing unit; the photoelectric conversion signal processing unit is connected to the data acquisition unit; the data acquisition unit is connected to the temperature demodulation unit. The technical solution of the invention is suitable for long-distance temperature measurement and disaster warning over 50Km.

Description

A Distributed Optical Fiber Temperature Sensor

Technical field:

The invention relates to the technical field of optical fiber sensing, and more particularly relates to a distributed optical fiber temperature sensor.

Background technique:

Optical fiber sensing technology is a new type of sensing technology that emerged with the development of optical fiber technology and optical fiber communication technology in the 1970s. It uses light waves as the sensing signal and optical fiber as the transmission medium to perceive and detect external signals. It is very different from traditional electrical sensors in terms of sensing methods, sensing principles, and signal detection and processing.

The application of distributed fiber optic temperature sensors based on the principle of backward Raman scattering is becoming more and more mature. There are already various types of fully distributed fiber optic sensor products at home and abroad, and they have begun to be embedded and equipped in electric power, ports, petroleum and petrochemical transportation, and railways. , bridges, tunnels, roads, buildings, water supply systems, dams and coal mines and other facilities. But it still can't meet the application requirements in terms of measuring length (distance), spatial resolution, temperature measurement accuracy, reliability, multi-parameter and intelligence. Especially in long-distance oil and gas pipelines with high distance requirements, higher requirements are put forward for the transmission distance of distributed optical fiber temperature measurement.

The existing temperature measurement technology based on the principle of backward Raman scattering is limited by the light pulse energy injected into the sensing fiber, and the sensing distance is limited, generally less than 15Km. Using the current common injection optical amplification technology, that is, EDFA (erbium-doped fiber amplification) or traditional Raman amplifier technology amplification, can significantly increase the optical pulse energy injected into the fiber, but due to the uneven power amplification of EDFA technology, that is, the amplification is flat The problem of poor accuracy, and the above two technologies are easy to excite the stimulated Raman scattering effect in the optical fiber, that is, the nonlinear effect, and it is impossible to realize the distributed temperature sensing with a distance greater than 30Km.

Invention content:

The purpose of the present invention is to provide a distributed optical fiber temperature sensor, which can realize long-distance transmission exceeding 50km.

In order to achieve the above object, the present invention adopts the following technical solutions: a distributed optical fiber temperature sensor, comprising sequentially connected pulsed fiber lasers, the first optical isolator, circulator and fiber Raman amplifier; the circulator is connected to the third wave A division multiplexer; the third wavelength division multiplexer is connected to a photoelectric conversion signal processing unit; the photoelectric conversion signal processing unit is connected to a data acquisition unit; the data acquisition unit is connected to a temperature demodulation unit.

The fiber Raman amplifier includes the first Raman pump laser, the second optical isolator, the first wavelength division multiplexer, sensing fiber, the second wavelength division multiplexer 6, and the third optical isolator connected in sequence and the second Raman pump laser; the first wavelength division multiplexer is connected to the circulator.

The pulsed fiber laser 1 sends pulsed light to the first optical isolator; port 1 of the circulator 3 is connected to the first optical isolator; port 2 of the circulator 3 is connected to the first wave The R port of the multiplexer is connected; the 4COM port of the first wavelength division multiplexer is connected to the sensing fiber; the end of the sensing fiber is connected to the COM port of the second wavelength division multiplexer; The T port of the first wavelength division multiplexer is connected to the first Raman pump laser 9; the T port of the second wavelength division multiplexer is connected to the second optical isolator 7.

The 1660nm Raman scattered light and the 1450nm anti-Stokes Raman scattered light amplified by bidirectional Raman enter the third wavelength division multiplexer through the R port of the first wavelength division multiplexer and the third port of the circulator device; the two output ports of the 3rd wavelength division multiplexer respectively output the backward Raman scattered light of 1450nm and 1660nm, and carry out photoelectric conversion and signal amplification processing by the photoelectric conversion signal processing unit; the data acquisition unit Complete signal accumulation and upload the data to the temperature demodulation unit in the host computer.

The central wavelength of the pulsed laser is 1550nm, its spectral width is 0.1nm, the pulsed width of the pulsed laser is 5-100ns, the peak power is 1-100W, and the repetition frequency is 100Hz-1MHz.

The transmission wavelength of the T terminal of the first wavelength division multiplexer and the T terminal of the second wavelength division multiplexer is 1360 ± 15nm, and the respective R terminal reflection wavelengths are 1450 ± 15nm and 1660 ± 15nm respectively; The isolation of the multiplexer is greater than 45dB.

The operating wavelength ranges of the second optical isolator and the third optical isolator are both 1360nm±30nm, and the isolation is greater than 60dB.

The wavelengths of the first Raman pump laser and the second Raman pump laser are both 1360nm, the 3dB spectral width of each Raman pump laser is 0.1nm, and the respective output powers are 100-800mW.

The T-end transmission bands of the third wavelength division multiplexer are 1450±15nm and 1660±15nm, and the isolation is greater than 60dB.

The response wavelength of the photoelectric conversion signal processing unit is 1000-1700nm, the responsivity is 6-9A/W, and the bandwidth is 100MHz-300MHz.

Compared with the closest prior art, the technical solution provided by the present invention has the following excellent effects

1. The technical solution of the present invention avoids the use of relays to extend the sensing distance, and does not need to add workstations along the sensing optical fiber, which can effectively solve the cost problem and significantly reduce the construction difficulty;

2. The technical solution of the present invention adopts the Raman amplification method, so that the backscattering signal of the system along the long-distance sensing line is evenly amplified, and the dynamic range of the effective signal is improved;

3. The technical solution of the present invention has simple structure and good signal-to-noise ratio;

4. The technical solution of the present invention is suitable for long-distance temperature measurement and disaster warning above 50Km;

5. The technical solution of the present invention uses the pump light in the 1360nm band to separately perform Raman amplification on the Raman anti-Stokes backscattered light, and adopts a bidirectional amplification method with a gain of nearly 30dB, without changing the anti-Stokes The anti-Stokes signal is amplified under the condition of signal-to-noise ratio, which greatly prolongs the sensing distance of the distributed optical fiber temperature measurement system.

Description of drawings

Fig. 1 is the schematic diagram of the sensor structure provided by the technical solution of the present invention;

Among them, 1-pulse fiber laser, 2-the first optical isolator, 3-circulator, 4-the first wavelength division multiplexer, 5-sensing fiber, 6-the second wavelength division multiplexer, 7-the first 2 optical isolator, 8- the third optical isolator, 9- the first Raman pump laser, 10- the second Raman pump laser, 11- the third wavelength division multiplexer, 12- photoelectric conversion signal processing unit , 13-data acquisition unit, 14-temperature demodulation unit.

detailed description

Below in conjunction with embodiment the invention is described in further detail.

Example 1:

The invention of this example provides a kind of distributed optical fiber temperature sensor, as shown in Figure 1, comprises pulse fiber laser 1, the first optical isolator 2, circulator 3, the first wavelength division multiplexer 4, sensing fiber 5, The second wavelength division multiplexer 6, the second optical isolator 7, the third optical isolator 8, the first Raman pump laser 9, the second Raman pump laser 10, the third wavelength division multiplexer 11, A photoelectric conversion signal processing unit 12 , a data acquisition unit 13 , and a temperature demodulation unit 14 . The pulsed fiber laser 1 emits pulsed light and is connected to the first optical isolator 2, which is used to prevent the reflected light in the optical path from damaging the pulsed laser. Port 1 of the circulator 3 is connected to the first optical isolator 2, port 2 is connected to the R port of the first wavelength division multiplexer 4, and the COM port of the first wavelength division multiplexer 4 is connected to the sensing fiber. The end of the sensing fiber is connected to the COM end of the second wavelength division multiplexer 6, and the T ends of the first wavelength division multiplexer 4 and the second wavelength division multiplexer 6 are connected to the first Raman pump laser 9 and the first Raman pump laser 9 respectively. 2 optical isolator 7, the second Raman pump laser 10, and the third optical isolator 8. The 1660nm Raman scattered light and the 1450nm anti-Stokes Raman scattered light amplified by bidirectional Raman pass through the first wavelength division multiplexer The R port of the device 4 and the port 3 of the circulator 3 enter the third wavelength division multiplexer 8, and the two output ports of the third wavelength division multiplexer 11 respectively output the backward Raman scattered light of 1450nm and 1660nm, and the The photoelectric conversion and signal processing unit 12 performs photoelectric conversion and signal amplification processing, and the data acquisition unit 13 completes signal accumulation and uploads the data to the upper computer temperature demodulation unit 14 .

By the first wavelength division multiplexer 4, the second wavelength division multiplexer 6, the first Raman pump laser 9, the second Raman pump laser 10, the second optical isolator 7, the third optical isolator 8 Together with the sensing fiber 5, it constitutes a bidirectional S-band fiber Raman amplifier.

The first wavelength division multiplexer, the second wavelength division multiplexer and the third wavelength division multiplexer are all 3-port devices, which are R (reflection), T (transmission) and COM (communication) ports respectively.

The working principle of the fiber Raman amplifier is: the 1360nm Raman pump laser has a Raman scattering effect in the sensing fiber, which can amplify the signal light with a wavelength of 1446nm and has a bandwidth of 6THz, and the converted wavelength amplification range is 45nm, 1450nm The Raman anti-Stokes light in the wavelength band just falls within the gain bandwidth of the 1360nm pump light, and will be amplified by the strong pump light. Wherein, the first and second Raman pump lasers play the role of backward and forward Raman amplification respectively. This kind of distributed amplification can overcome the shortcomings of centralized optical fiber amplifiers. The transmission line and amplification are carried out in the optical fiber, so the coupling loss is small, the noise is low, and the gain stability is good.

The fully distributed optical fiber temperature sensor of the fusion first-order Raman amplification effect is characterized in that the first, second, and third wavelength division multiplexers are 3-port devices, which are respectively R (reflection), T (transmission) , COM (communication) port.

The central wavelength of the pulse laser 1 is 1550nm, the spectral width is 0.1nm, the laser pulse width is adjustable from 5 to 100ns, the peak power is adjustable from 1 to 100W, and the repetition frequency is adjustable from 100Hz to 1MHz.

The optical isolator 2 has an operating wavelength range of 1550nm±30nm, and an isolation degree>60dB.

The circulator 3 has an operating wavelength range of 1550nm±30nm, and an isolation degree>50dB.

For the first wavelength division multiplexer 4 and the second wavelength division multiplexer 6, the transmission wavelength at the T terminal is 1360±15nm, the reflection wavelength at the R terminal is 1450±15nm, 1660±15nm, and the isolation is greater than 45dB.

The sensing fiber 5 can be a G651-50/125 μm or 62.5/125 μm multimode fiber or a G652-9/125 μm communication single-mode fiber or special material coated fiber (polyimide, carbon coating, metal coating cover).

The optical isolators 7 and 8 have an operating wavelength range of 1360nm±30nm and an isolation degree of >60dB

The first and second Raman pump lasers 9 and 10 have a wavelength of 1360nm, a 3dB spectral width of 0.1nm, and an adjustable output power of 100-800mW.

In the third wavelength division multiplexer 11, the transmission bands at the T (transmission) end are 1450±15nm and 1660±15nm respectively, and the isolation is greater than 60dB.

The photoelectric conversion and signal processing unit 12 includes an InGaAs photoelectric conversion module with a response wavelength of 1000-1700 nm, a responsivity of 6-9 A/W, and a bandwidth of 100 MHz-300 MHz.

The data acquisition unit 13 has a sampling rate of 100-500 MSPS, a sampling precision of 8-14 bits, and supports hardware accumulation function.

The temperature demodulation unit includes a temperature demodulation algorithm and a host computer to realize this function.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Those of ordinary skill in the art should understand with reference to the above embodiments that the specific implementation methods of the present invention can still be modified or equivalent. Replacement, any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the protection scope of the claims of the present invention pending application.

Claims (10)

1. A distributed optical fiber temperature sensor, characterized in that: comprise sequentially connected pulse fiber lasers, the 1st optical isolator, circulator and optical fiber Raman amplifier; said circulator connects the 3rd wavelength division multiplexer; The third wavelength division multiplexer is connected to the photoelectric conversion signal processing unit; the photoelectric conversion signal processing unit is connected to the data acquisition unit; the data acquisition unit is connected to the temperature demodulation unit. 2. A kind of distributed optical fiber temperature sensor as claimed in claim 1, is characterized in that: described optical fiber Raman amplifier comprises the 1st Raman pump laser device, the 2nd optical isolator, the 1st wavelength division multiplexer connected in sequence A user, a sensing fiber, a second wavelength division multiplexer 6, a third optical isolator and a second Raman pump laser; the first wavelength division multiplexer is connected to the circulator. 3. A kind of distributed optical fiber temperature sensor as claimed in claim 2, is characterized in that: described pulse fiber laser 1 sends pulsed light to described 1st optical isolator; 1 port of described circulator 3 and described The 1st optical isolator is connected; 2 ports of the circulator 3 are connected with the R port of the 1st wavelength division multiplexer; the 4COM ports of the 1st wavelength division multiplexer are connected to transmit the sensing optical fiber; The end of the sensing fiber is connected to the COM port of the second wavelength division multiplexer; the T end of the first wavelength division multiplexer is connected to the first Raman pump laser 9; the second wave The T port of the demultiplexer is connected to the second optical isolator 7 . 4. A kind of distributed optical fiber temperature sensor as claimed in claim 3, it is characterized in that: 1660nm Raman scattered light and the 1450nm anti-Stokes Raman scattered light through the two-way Raman amplification pass through the first wavelength division The R port of the multiplexer and the 3 ports of the circulator enter the 3rd wavelength division multiplexer; the two output ports of the 3rd wavelength division multiplexer respectively output the backward Raman scattered light of 1450nm and 1660nm, and The photoelectric conversion signal processing unit performs photoelectric conversion and signal amplification processing; the data acquisition unit completes signal accumulation and uploads the data to the temperature demodulation unit in the host computer. 5. A kind of distributed optical fiber temperature sensor as claimed in claim 1, it is characterized in that: the center wavelength of described pulse laser is 1550nm, and its spectral width is 0.1nm, and the pulse width of described pulse laser is 5～100ns, The peak power is 1~100W, and the repetition frequency is 100Hz~1MHz. 6. A kind of distributed optical fiber temperature sensor as claimed in claim 2, it is characterized in that: the transmission wavelength of the T end of the first wavelength division multiplexer and the T end of the second wavelength division multiplexer is 1360 ± 15nm , and the reflection wavelengths of the respective R terminals are 1450±15nm and 1660±15nm respectively; the isolation of each wavelength division multiplexer is greater than 45dB. 7. A distributed optical fiber temperature sensor according to claim 2, characterized in that: the operating wavelength range of the second optical isolator and the third optical isolator are both 1360nm±30nm, and the isolation degrees are both greater than 60dB. 8. A kind of distributed optical fiber temperature sensor as claimed in claim 2, is characterized in that: the wavelength of described the 1st Raman pump laser and the 2nd Raman pump laser are 1360nm, each Raman pump The 3dB spectral width of the laser is 0.1nm, and the respective output powers are 100-800mW. 9. A distributed optical fiber temperature sensor according to claim 1, characterized in that: the T-end transmission bands of the third wavelength division multiplexer are 1450±15nm and 1660±15nm, and the isolation is greater than 60dB. 10. A distributed optical fiber temperature sensor according to claim 1, characterized in that: the response wavelength of the photoelectric conversion signal processing unit is 1000-1700nm, the responsivity is 6-9A/W, and the bandwidth is 100MHz-300MHz .