CN113237570A - Low-coherence distributed optical fiber sensor based on wavelength light splitting - Google Patents
Low-coherence distributed optical fiber sensor based on wavelength light splitting Download PDFInfo
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- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- 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
- G01K11/3206—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 at discrete locations in the fibre, e.g. using Bragg scattering
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- G—PHYSICS
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
- G01H9/004—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means using fibre optic sensors
Abstract
The invention discloses a low coherence distributed optical fiber sensor based on wavelength light splitting, which relates to the technical field of optical fiber sensing and measurement and comprises a broadband light source, a circulator, a 3 x 3 optical fiber coupler, a time delay optical fiber, a first narrow-band reflector, a second narrow-band reflector, a first wavelength division multiplexer, a second wavelength division multiplexer, a first single-mode optical fiber, a second single-mode optical fiber and a photoelectric detector, wherein the broadband light source is connected with the circulator through the first narrow-band reflector; the invention is provided with two narrow-band reflectors with different central wavelengths on a transmission optical fiber, and sensing is realized by detecting the non-dissimilarity phase difference formed by the clockwise transmission light and the anticlockwise transmission light in different time passing through a disturbance point; through wavelength division multiplexing and signal demodulation, subtracting the two groups of signals to obtain signals sensed by the second single-mode optical fiber, so that the separation of a transmission channel and a sensing channel of the sensor is realized; therefore, the filtering of environmental noise caused by external vibration perturbation and temperature change is realized, and the noise accumulated in the long-distance optical fiber transmission process is eliminated.
Description
Technical Field
The invention belongs to the technical field of optical fiber sensing and measurement, and particularly relates to a low-coherence distributed optical fiber sensor based on wavelength light splitting; the method has good application prospect in the fields of safety detection of communication main lines, power transmission lines, natural gas pipelines and petroleum pipelines, optical fiber perimeter security and the like.
Background
With the development of the technological level, in the field of real-time monitoring of important production and living facilities such as intelligent materials, communication main lines, power transmission lines, oil and gas pipelines, bridges and dams and the like, a distributed optical fiber sensing system is widely researched due to the characteristics of no blind spot in sensing, convenience in network formation, electromagnetic interference resistance and the like, is put into use and gradually plays an important role. A distributed sensing system based on a low coherence interference technology is one of the research hotspots in the sensing field due to the advantages of simple structure, low manufacturing cost and the like.
However, in the field of safety detection of long-distance transmission systems, such as oil and gas pipelines, noise caused by external environment temperature or vibration is applied to a path between a control end and a remote sensing optical fiber, and the noise is accumulated in a signal transmission process, so that the signal-to-noise ratio of the system is reduced, the overall performance of the system is affected, and the noise is difficult to effectively suppress.
Disclosure of Invention
In order to solve the problems existing in the scheme, the invention provides a low-coherence distributed optical fiber sensor based on wavelength splitting. Based on the low coherence interference technology, two fiber Bragg gratings with different central wavelengths are respectively inserted into different positions on an original transmission light path, the original transmission light path is divided into a transmission part and a sensing part, a fiber section in front of a first fiber Bragg grating is the transmission part, and a fiber section between the two fiber Bragg gratings is the sensing part; through subsequent signal processing, the filtering of environmental noise caused by external vibration perturbation and temperature change is realized, and noise accumulated in the long-distance optical fiber transmission process is eliminated.
The purpose of the invention can be realized by the following technical scheme:
a low coherence distributed optical fiber sensor based on wavelength splitting is characterized in that two narrow-band reflectors with different central wavelengths are arranged on a transmission optical fiber, an original transmission optical path is separated into a transmission part and a sensing part through wavelength splitting and subsequent signal processing, an optical fiber section in front of a first optical fiber Bragg grating is the transmission part, and an optical fiber section between the two optical fiber Bragg gratings is the sensing part; the separation of the sensor transmission channel and the sensor channel is realized.
Furthermore, the optical fiber sensor comprises a broadband light source, a circulator, a 3 x 3 optical fiber coupler, a time delay optical fiber, a first narrow-band reflector, a second narrow-band reflector, a first wavelength division multiplexer, a second wavelength division multiplexer, a first single-mode optical fiber, a second single-mode optical fiber and a photoelectric detector;
the optical fiber sensor realizes sensing in the following modes:
s1: the first narrow-band reflector reflects a wavelength λ1Of light of wavelength λ1The light emitted by the broadband light source is injected into the 3 multiplied by 3 optical fiber coupler through the circulator and then is output, wherein one path of light is transmitted clockwise: the first single-mode fiber, the first narrow-band reflector, the first single-mode fiber, the 3 × 3 fiber coupler and the delay fiber sequentially pass through, and then are split by the 3 × 3 fiber coupler again, one part of the split light reaches the first wavelength division multiplexer, the other part of the split light reaches the second wavelength division multiplexer through the circulator, and the split light is output to the photoelectric detector after being demultiplexed;
the other path is transmitted anticlockwise: the light is split by the 3 x 3 optical fiber coupler, one part of the light reaches the first wavelength division multiplexer, the other part of the light reaches the second wavelength division multiplexer through the circulator, and the light is also demultiplexed and then respectively reaches the photoelectric detector; sensing is realized by detecting the non-anisotropic phase difference formed by the clockwise transmission light and the anticlockwise transmission light passing through the disturbance point at different times;
s2: the second narrow-band reflector only reflects wavelengths λ2Of light of wavelength λ2Optical transmission path and wavelength of lambda1Adding a second single mode fiber to the light phase of (1); subtracting the two groups of signals through wavelength division multiplexing and signal demodulation to obtain a signal sensed by the second single-mode fiber; the first single-mode fiber only plays a transmission role, and the second single-mode fiber plays a sensing role, so that the separation of a transmission channel and a sensing channel of the sensor is realized;
because of adopting a broadband light source, light with unmatched optical path difference can not form interference; the light circulating in the ring after passing through the delay fiber for many times can not consider the multi-beam interference effect because the light intensity is too small.
Further, the wavelength is λ2The light is sensitive to disturbance signals on the first single-mode fiber and the second single-mode fiber, and the number of the photoelectric detectors is four;
further, the wavelength is λ1Is sensitive to a perturbation signal on the first single mode fibre.
Further, the narrow-band reflector is one of a Fiber Bragg Grating (FBG), a fabry-perot filter (FPF), and a Wavelength Division Multiplexer (WDM); and the center wavelengths of the first narrow band reflector and the second narrow band reflector are different.
Further, the broadband light source is one of a super radiation diode (SLD), an Amplified Spontaneous Emission (ASE) and a Light Emitting Diode (LED), and the spectral range of the broadband light source covers the central wavelengths of the first narrow-band reflector and the second narrow-band reflector.
Compared with the prior art, the invention has the beneficial effects that:
based on the low coherence interference technology, two fiber Bragg gratings with different central wavelengths are respectively inserted into different positions on an original transmission light path, the original transmission light path is divided into a transmission part and a sensing part, a fiber section in front of a first fiber Bragg grating is the transmission part, and a fiber section between the two fiber Bragg gratings is the sensing part; through subsequent signal processing, the filtering of environmental noise caused by external vibration perturbation and temperature change is realized, and noise accumulated in the long-distance optical fiber transmission process is eliminated.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a diagram of an apparatus of a low coherence distributed optical fiber sensor based on wavelength division according to the present invention.
Fig. 2 is a block diagram of detection and signal demodulation in the present invention.
FIG. 3 is an experimental spectrum diagram of a noise signal when the length of the sensing fiber is 10 m.
Fig. 4 is an experimental frequency spectrum diagram of a signal to be measured when the length of the sensing fiber is 10 m.
FIG. 5 is a graph of the experimental spectrum of the residual noise for a sensing fiber length of 10 m.
FIG. 6 is a graph of experimental spectrum of noise signal when the length of sensing fiber is 20 m.
Fig. 7 is an experimental spectrum diagram of a signal to be measured when the length of the sensing fiber is 20 m.
FIG. 8 is a graph of the experimental spectrum of the residual noise for a sensing fiber length of 20 m.
FIG. 9 is a graph of experimental spectrum of noise signal when the length of sensing fiber is 50 m.
FIG. 10 is an experimental spectrum chart of a signal to be measured when the length of the sensing fiber is 50 m.
FIG. 11 is a graph of the experimental spectrum of the residual noise for a sensing fiber length of 50 m.
In the figure: 1. a broadband light source; 2. a circulator; 3. a 3 × 3 fiber coupler; 4. a delay fiber; 5. a first narrow band reflector; 6. a second narrow band reflector; 7. a first wavelength division multiplexer; 8. a second wavelength division multiplexer; 9. a first single mode optical fiber; 10. a second single mode optical fiber; 11. a photodetector.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the following embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1-11, a low coherence distributed optical fiber sensor based on wavelength division is provided with two narrow band reflectors with different central wavelengths on a transmission optical fiber, and separates an original transmission optical path into a transmission part and a sensing part through wavelength division and subsequent signal processing, wherein an optical fiber segment before a first fiber bragg grating is the transmission part, and an optical fiber segment between two fiber bragg gratings is the sensing part; the separation of a sensor transmission channel and a sensor channel is realized;
the device comprises a broadband light source 1, a circulator 2, a 3 x 3 optical fiber coupler 3, a delay optical fiber 4, a first narrow-band reflector 5, a second narrow-band reflector 6, a first wavelength division multiplexer 7, a second wavelength division multiplexer 8, a first single-mode optical fiber 9, a second single-mode optical fiber 10 and a photoelectric detector 11;
the optical fiber sensor realizes sensing in the following modes:
s1: the first narrow band reflector 5 reflects a wavelength λ1Of light of wavelength λ1The light emitted by the broadband light source 1 is injected into the 3 multiplied by 3 optical fiber coupler 3 through the circulator 2 and then is output, wherein one path of light is transmitted clockwise: the light is split by the 3 × 3 optical fiber coupler 3 again, one part of the light reaches the first wavelength division multiplexer 7, the other part of the light reaches the second wavelength division multiplexer 8 through the circulator 2, and the light is output to the photoelectric detector 11 after being demultiplexed;
the other path is transmitted anticlockwise: the light is split by the 3 x 3 optical fiber coupler 3, one part of the light is transmitted to the first wavelength division multiplexer 7, the other part of the light is transmitted to the second wavelength division multiplexer 8 by the circulator 2, and the light is also demultiplexed and then transmitted to the photoelectric detector 11 respectively; sensing is realized by detecting the non-anisotropic phase difference formed by the clockwise transmission light and the anticlockwise transmission light passing through the disturbance point at different times;
s2: the second narrow band reflector 6 reflects only wavelengths lambda2Of light of wavelength λ2Optical transmission path and wavelength of lambda1The second single mode fiber 10 is added compared to the light of (1); subtracting two sets of signals by de-wavelength division multiplexing and signal demodulationObtaining a signal sensed by the second single-mode fiber 10; namely, the first single-mode fiber 9 only plays a transmission role, and the second single-mode fiber 10 plays a sensing role, so that the separation of a transmission channel and a sensing channel of the sensor is realized;
the broadband light source 1 is an ASE light source with the center wavelength of 1550nm and the bandwidth of 35nm, light emitted by the broadband light source 1 enters the 3 x 3 optical fiber coupler 3 after passing through the circulator 2, and the splitting ratio of the 3 x 3 optical fiber coupler 3 is 1: 1: 1; the first narrow band reflector 5 reflects a wavelength λ1Other wavelengths of light are transmitted into the sensing fiber, and the second narrow-band reflector 6 reflects light with a wavelength lambda2Light of (2), light of other wavelengths being transmitted; as the system belongs to a phase modulation type, only light forming interference can carry phase information of a noise point, for example, as shown in fig. 1, 1-2-3-4-3-5-6-5-3 and 1-2-3-5-6-5-3-4-3 two paths of light form interference, light of other light paths need to pass through the 3 x 3 optical fiber coupler 3 more than 3 times, although paired light capable of mutually interfering exists, the intensity of the paired light is too small, and therefore the paired light can be ignored. The light forming interference enters a first wavelength division multiplexer 7 and a second wavelength division multiplexer 8 for wavelength division, and respectively enters 4 different photoelectric detectors 11; accessing light of the 4 paths of photoelectric detectors 11 into a Labview program through a data acquisition card, adding two paths of light with the same wavelength and subtracting two paths of light in pairs respectively, and performing cross multiplication on the in-phase added and subtracted alternating current parts after differentiation to obtain two paths of light which are subtracted and integrated; in the same way, the other two paths are also the same. Subtracting the two paths of light after final integration to obtain residual noise;
in the experiment, because the specifications of the light splitting devices are not completely consistent and have deviation, the amplitudes of the four paths of light accessed to the Labview program from the photoelectric detector 11 through the data acquisition card are changed, and the amplitudes of the four paths of light are consistent through the adjusting knob. When the length of the experimental delay optical fiber 4 is 2000m, the length of the transmission optical fiber is 100m, and the length of the sensing optical fiber is 10 m; the frequency of the noise signal is 400Hz, and the amplitude is 400 mv; the frequency of the signal to be measured is 700Hz, and the amplitude is 370 mv. The spectra of the noise signal and the residual noise signal were measured by Labview. We can see from fig. 3-5 that the noise spectrum is reduced by about 40dB, i.e. the residual noise signal amplitude is reduced to one percent of the noise signal, which achieves the elimination of the noise on the transmission fiber, and is consistent with the theory; by changing the frequency of the noise signal, and keeping other conditions unchanged, the noise reduction effect is found to be in a decreasing trend along with the increase of the frequency, and the experimental result is consistent with the theory, as shown in fig. 6-11; by changing the length of the sensing fiber without changing other conditions, the noise reduction effect tends to decrease with the increase of the length of the sensing fiber, and the experimental results are consistent with theory, as shown in fig. 3-5 at 10m of the sensing fiber, fig. 6-8 at 20m of the sensing fiber, and fig. 9-11 at 50m of the sensing fiber.
The working principle of the invention is as follows:
a low-coherence distributed optical fiber sensor based on wavelength light splitting is characterized in that when the sensor works, the wavelength range of light waves emitted by a broadband light source 1 is large, and only the wavelength is lambda after the light waves pass through a first narrow-band reflector 51The light will be reflected back, and at this time, each photodetector 11 receives the light of four different paths, wherein only two paths of light, namely path 1 and path 2, can interfere due to equal optical path, and an interference signal is generated; after the light wave passes through the second narrow-band reflector 6, only the wavelength is lambda2The light will be reflected back, each photodetector 11 will also receive the light of four different paths, wherein the two paths of light, path 3 and path 4, will interfere because of the equal optical path length, generate another set of interference signals; the light rays of other light paths need to pass through the 3 x 3 optical fiber coupler 3 more than 3 times, although paired light rays which can interfere with each other exist, the intensity is ignored due to too small intensity; sensing is realized by detecting the non-anisotropic phase difference formed by the clockwise transmission light and the anticlockwise transmission light passing through the disturbance point at different times; subtracting the two groups of signals through wavelength division multiplexing and signal demodulation to obtain signals sensed by the second single-mode fiber 10; namely, the first single-mode fiber 9 only plays a transmission role, and the second single-mode fiber 10 plays a sensing role, so that the separation of a transmission channel and a sensing channel of the sensor is realized; in the long-distance transmission process, the direct distance between the sensing optical fiber and the local control end and the noise introducing position have no influence on the magnitude of residual noise, so that the noise introduced everywhere can be uniformly filtered in a longer transmission distance without the difference between the introducing position and the sensing area; fruit of Chinese wolfberryThe noise filter filters environmental noise caused by external vibration perturbation and temperature change, and eliminates noise accumulated in the long-distance optical fiber transmission process.
In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
The foregoing is merely exemplary and illustrative of the present invention and various modifications, additions and substitutions may be made by those skilled in the art to the specific embodiments described without departing from the scope of the invention as defined in the following claims.
Claims (6)
1. A low coherence distributed optical fiber sensor based on wavelength light splitting is characterized in that two narrow-band reflectors with different central wavelengths are arranged on a transmission optical fiber, an original transmission optical path is separated into a transmission part and a sensing part through the wavelength light splitting and subsequent signal processing, an optical fiber section in front of a first optical fiber Bragg grating is the transmission part, and an optical fiber section between two optical fiber Bragg gratings is used as the sensing part; the separation of the sensor transmission channel and the sensor channel is realized.
2. The low coherence distributed optical fiber sensor based on wavelength division according to claim 1, characterized by comprising a broadband light source (1), a circulator (2), a 3 x 3 optical fiber coupler (3), a time delay optical fiber (4), a first narrow band reflector (5), a second narrow band reflector (6), a first wavelength division multiplexer (7), a second wavelength division multiplexer (8), a first single mode optical fiber (9), a second single mode optical fiber (10) and a photodetector (11);
the optical fiber sensor realizes sensing in the following modes:
s1: the first narrow-band reflector (5) reflects a wavelength λ1Of light of wavelength λ1The light emitted by the broadband light source (1) is injected into the 3 multiplied by 3 optical fiber coupler (3) through the circulator (2) and then is output, wherein one path of light is transmitted clockwise: the light is split by the first single mode fiber (9), the first narrow band reflector (5), the first single mode fiber (9), the 3 x 3 fiber coupler (3) and the delay fiber (4) in sequence and the 3 x 3 fiber coupler (3), one part of the light reaches the first wavelength division multiplexer (7), the other part of the light reaches the second wavelength division multiplexer (8) through the circulator (2), and the light is output to the photoelectric detector (11) after being demultiplexed;
the other path is transmitted anticlockwise: the light is split by the 3 x 3 optical fiber coupler (3) through the delay optical fiber (4), the 3 x 3 optical fiber coupler (3), the first single-mode optical fiber (9), the first narrow-band reflector (5) and the first single-mode optical fiber (9) in sequence, one part of the light reaches the first wavelength division multiplexer (7), the other part of the light reaches the second wavelength division multiplexer (8) through the circulator (2), and the light are respectively transmitted to the photoelectric detector (11) after being demultiplexed; sensing is realized by detecting the non-anisotropic phase difference formed by the clockwise transmission light and the anticlockwise transmission light passing through the disturbance point at different times;
s2: the second narrow-band reflector (6) reflects only the wavelength λ2Of light of wavelength λ2Optical transmission path and wavelength of lambda1A second single mode fibre (10) is added to the light phase of (1); subtracting the two groups of signals by de-wavelength division multiplexing and signal demodulation to obtain signals sensed by the second single-mode fiber (10); namely, the first single-mode fiber (9) only plays a transmission role, and the second single-mode fiber (10) plays a sensing role, so that the separation of a transmission channel and a sensing channel of the sensor is realized.
3. The low coherence distributed optical fiber sensor based on wavelength division according to claim 2, wherein the wavelength is λ2Is sensitive to disturbance signals on the first single-mode fiber (9) and the second single-mode fiber (10); the number of the photoelectric detectors (11) is four.
4. According to claimThe low coherence distributed optical fiber sensor based on wavelength division as claimed in claim 2, wherein the wavelength is λ1Is sensitive to a disturbing signal on the first single mode fibre (9).
5. A wavelength-division-based low-coherence distributed optical fiber sensor according to claim 1 or 2, wherein the narrow-band reflector is one of a Fiber Bragg Grating (FBG), a fabry-perot filter (FPF), a Wavelength Division Multiplexer (WDM); and the center wavelengths of the first narrow-band reflector (5) and the second narrow-band reflector (6) are different.
6. The wavelength-splitting-based low coherence distributed optical fiber sensor according to claim 2, wherein the broadband light source (1) is one of a super radiation diode (SLD), an Amplified Spontaneous Emission (ASE) and a Light Emitting Diode (LED), and the spectral range of the broadband light source (1) covers the central wavelengths of the first narrow-band reflector (5) and the second narrow-band reflector (6).
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