2-micron-waveband three-parameter optical fiber sensor based on inclined optical fiber Bragg grating
Technical Field
The invention relates to the field of optical fiber sensors, in particular to a 2-micron-waveband three-parameter optical fiber sensor based on a tilted fiber Bragg grating, which can sense temperature, axial strain and environmental refractive index simultaneously.
Background
Theoretical and experimental studies on the 2 μm band are currently in a rapidly growing stage. Tm3+, Ho3+ ion doped fiberglass materials have a wide gain bandwidth range from 1.7 μm to 2.1 μm with good overlap with atmospheric gas absorption lines, such as H2O and CO2, making them well suited for CO2 gas detection and other sensing measurements. Moreover, the working bandwidth also provides a wide operating range for the laser in the safe band of human eyes. Due to these advantages, devices operating in the 2 μm band can be widely used in the fields of medicine, biology, lidar, remote sensing, military technology, etc.
Measurement of temperature, axial strain and ambient refractive index (SRI) is an important process in biochemical engineering, environmental monitoring and medical science. The optical fiber sensor has gained wide attention due to its advantages of small volume, fast response, strong operability, etc. In the field of optical fiber sensing, the application and research of fiber gratings have also become very popular and practical. The optical fiber Bragg grating sensor is mainly used for measuring stress strain, temperature and humidity, but the Bragg wavelength is sensitive to changes of stress and temperature, so that the problem of cross talk is difficult to eliminate. Although Long Period Fiber Gratings (LPFGs) have excellent performance for measurement of the ambient refractive index, their high cross-sensitivity to perturbations of the ambient environment is not negligible.
Tilted fiber Bragg gratings, because of their unique physical structure, which include the advantages of fiber Bragg gratings and long-period fiber Bragg gratings, can successfully overcome these disadvantages and show great potential in the simultaneous measurement of various parameters. However, in the manufacturing design of the existing inclined fiber Bragg grating, the inclined angle is too large, the wave band range is wide, and only the temperature and the refractive index can be measured simultaneously, so that the defects of slow response of a sensor, low measurement precision and insufficient environmental adaptability exist.
Disclosure of Invention
Aiming at the defects, the invention provides a 2-micron-waveband three-parameter optical fiber sensor based on a tilted fiber Bragg grating, which can sense the temperature, the axial strain and the ambient refractive index simultaneously.
The purpose of the invention is realized by the following technical scheme:
a2 mu m waveband three-parameter fiber sensor based on a tilted fiber Bragg grating comprises a wide spectrum light source (101), a first single-mode fiber (102), a tilted fiber Bragg grating (103), a second single-mode fiber (104) and a spectrometer (105), and is characterized in that:
the wide-spectrum light source (101) is connected with one end of the first single-mode fiber (102) through a fiber connector, the other end of the first single-mode fiber (102) is connected with one end of the inclined fiber Bragg grating (103), the other end of the inclined fiber Bragg grating (103) is connected with one end of the second single-mode fiber (104), and the other end of the second single-mode fiber (104) is connected with the spectrometer (105) through a fiber connector.
Preferably, the first single-mode fiber (102) and the tilted fiber Bragg grating (103) are connected by a fiber connector or fusion spliced by a fiber fusion splicer.
Preferably, the tilted fiber Bragg grating (103) and the second single-mode fiber (104) are connected by a fiber connector or fusion spliced by a fiber fusion splicer.
Preferably, the tilted fiber Bragg grating (103) is fabricated using a phase mask method of ultraviolet exposure.
Preferably, the phase mask needs to be inclined by 2 degrees when the inclined fiber Bragg grating (103) is manufactured.
Preferably, the core mode transmission peak wavelength, the 25 th order cladding mode transmission peak wavelength and the 28 th order cladding mode transmission peak wavelength of the tilted fiber Bragg grating (103) are taken as characteristic wavelengths of the optical fiber sensor.
Preferably, the optical fiber sensor senses the temperature, the axial strain and the environmental refractive index simultaneously, and realizes real-time detection of the temperature to be detected, the axial strain and the environmental refractive index.
A method for measuring a 2 μm band three-parameter fiber sensor using a tilted fiber Bragg grating is characterized by: the method comprises the following steps:
step one, a temperature calibration process: light emitted by a wide-spectrum light source (101) is incident on the inclined fiber Bragg grating, when the temperature changes, the transmission spectrum of the inclined fiber Bragg grating (103) can drift, and a spectrometer (105) is used for detecting the changes of the core mode transmission peak wavelength, the 25 th-order cladding mode transmission peak wavelength and the 28 th-order cladding mode transmission peak wavelength of the inclined fiber Bragg grating (103) to obtain a sensitivity coefficient related to the temperature;
step two, an axial strain calibration process: fixing two ends of the tilted fiber Bragg grating (103) on a stress adjusting frame, and stretching the tilted fiber Bragg grating (103) to generate strain; when the strain occurs, the transmission spectrum of the tilted fiber Bragg grating (103) can shift, and the spectrometer (105) is used for detecting the changes of the core mode transmission peak wavelength, the 25 th-order cladding mode transmission peak wavelength and the 28 th-order cladding mode transmission peak wavelength of the tilted fiber Bragg grating (103) to obtain the sensitivity coefficient related to the axial strain;
step three, the environmental refractive index calibration process: when the refractive index of liquid around the tilted fiber Bragg grating (103) changes, the transmission spectrum of the tilted fiber Bragg grating can drift, and the spectrometer (105) is used for detecting the changes of the core mode transmission peak wavelength, the 25 th order cladding mode transmission peak wavelength and the 28 th order cladding mode transmission peak wavelength of the tilted fiber Bragg grating (103) to obtain the sensitivity coefficient related to the environmental refractive index.
And step four, combining the temperature, the axial strain and the ambient refractive index sensitivity coefficient, and the core mold transmission peak wavelength, the 25 th order cladding mold transmission peak wavelength and the 28 th order cladding mold transmission peak wavelength variation to realize sensing measurement.
The invention has the beneficial effects that:
1. the optical fiber sensor designed by the invention can simultaneously sense the temperature, the axial strain and the environmental refractive index, and realize the real-time detection of the temperature to be detected, the axial strain and the environmental refractive index;
2. the sensor probe has the advantages of small volume, quick response, high precision, strong operability and the like.
Drawings
FIG. 1 is a schematic diagram of a 2 μm waveband three-parameter fiber sensor based on a tilted fiber Bragg grating according to the present invention;
FIG. 2 is a transmission spectrum of a tilted fiber Bragg grating (103) according to the present invention.
Detailed Description
Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.
It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Example 1:
as shown in fig. 1, a 2 μm waveband three-parameter fiber sensor based on a tilted fiber Bragg grating comprises a wide spectrum light source (101), a first single mode fiber (102), a tilted fiber Bragg grating (103), a second single mode fiber (104), and a spectrometer (105); the wide-spectrum light source (101) is connected with one end of the first single-mode fiber (102) through a fiber connector, the other end of the first single-mode fiber (102) is connected with one end of the inclined fiber Bragg grating (103) through a fiber connector or through a fusion splicer, the other end of the inclined fiber Bragg grating (103) is connected with one end of the second single-mode fiber (104) through a fiber connector or through a fusion splicer, and the other end of the second single-mode fiber (104) is connected with the spectrometer (105) through a fiber connector.
The inclined fiber Bragg grating (103) is manufactured by using an ultraviolet exposure phase mask method, the length of the inclined fiber Bragg grating is 2cm, the phase mask needs to be inclined when the inclined fiber Bragg grating is manufactured, and the inclination angle is 2 degrees.
As shown in fig. 2, the tilted fiber Bragg grating (103) Mandrel transmission peak wavelength lambdacore1944.5nm, and the wavelength of the transmission peak of the cladding mode ranges from 1905nm to 1942.7nm, and the transmission peak of the cladding mode contains 38-step transmission peak of the cladding mode; the core-mode transmission peak wavelength lambda of the tilted fiber Bragg grating (103) is selectedcore25 th order cladding mode transmission peak wavelength lambdacladding,25And a 28 th order cladding mode transmission peak wavelength lambdacladding,28As the characteristic wavelength of the three-parameter sensing of the present invention.
The emission spectrum range of the wide-spectrum light source (101) is 1200-2050nm, and the whole transmission peak range of the inclined fiber Bragg grating (103) is covered;
example 2:
the 2-micron-waveband three-parameter optical fiber sensor based on the inclined optical fiber Bragg grating needs to be subjected to parameter calibration before sensing measurement, and the calibration process is as follows:
1. temperature T calibration process: placing the inclined fiber Bragg grating (103) into a temperature control box, and placing the rest part out of the temperature control box; light emitted by the wide-spectrum light source (101) is incident on the inclined fiber Bragg grating, when the temperature is not changed, the transmission spectrum of the inclined fiber Bragg grating (103) cannot shift, and when the temperature is changed, the transmission spectrum of the inclined fiber Bragg grating (103) can shift; the temperature of the temperature control box is gradually increased from 30 ℃ to 80 ℃, and the wavelength lambda of the mandrel transmission peak of the inclined fiber Bragg grating (103) is detected by the spectrometer (105)core25 th order cladding mode transmission peak wavelength lambdacladding,25And a 28 th order cladding mode transmission peak wavelength lambdacladding,28The variation and the sensitivity coefficient K of the three resonance peak wavelengths with respect to the temperature are obtained through data processingcore,T、Kcladding,25,T、Kcladding,28,T。
2. And (3) an axial strain epsilon calibration process: fixing two ends of the tilted fiber Bragg grating (103) on a stress adjusting frame, and stretching the tilted fiber Bragg grating (103) to generate strain; the light emitted by the wide-spectrum light source (101) is incident on the inclined fiber Bragg grating (103), and when no response occurs on the inclined fiber Bragg grating (103)When changed, the transmission spectrum of the tilted fiber Bragg grating (103) can not shift, and when the tilted fiber Bragg grating is strained, the transmission spectrum of the tilted fiber Bragg grating can shift; axial strain gradually increases from 0 to 3500 mu epsilon, and the core mode transmission peak wavelength lambda of the tilted fiber Bragg grating (103) is detected by the spectrometer (105)core25 th order cladding mode transmission peak wavelength lambdacladding,25And a 28 th order cladding mode transmission peak wavelength lambdacladding,28Changing and obtaining sensitivity coefficient K of three resonance peak wavelengths related to axial strain of the tilted fiber Bragg grating (103) through data processingcore,ε、Kcladding,25,ε、Kcladding,28,ε。
3. Ambient refractive index n
extA calibration process: placing the tilted fiber Bragg grating (103) in a container filled with a liquid with a known refractive index, and placing the rest of the container outside, wherein the refractive index of the liquid in the container can be accurately adjusted and changed; light emitted by the wide-spectrum light source (101) is incident on the inclined fiber Bragg grating (103), and when the refractive index of liquid around the inclined fiber Bragg grating (103) is changed, the transmission spectrum of the inclined fiber Bragg grating can shift; the refractive index of the liquid gradually increases from 1.35749 to 1.47399, and the wavelength λ of the mandrel transmission peak of the tilted fiber Bragg grating (103) is detected by the spectrometer (105)
core25 th order cladding mode transmission peak wavelength lambda
cladding,25And a 28 th order cladding mode transmission peak wavelength lambda
cladding,28The sensitivity coefficients of the three resonance peak wavelengths with respect to the environmental refractive index of the tilted fiber Bragg grating (103) are changed and obtained through data processing, namely 0,
4. Combining temperature, axial strain and ambient refractive index variations DeltaT,. DELTA.. epsilon,. DELTA.nextAnd sensitivity coefficient and wavelength lambda of transmission peak of the core model core25 th order cladding mode transmission peak wavelength lambdacladding,25And a 28 th order cladding mode transmission peak wavelength lambdacladding,28Variation quantity Delta lambdacore、△λcladding,25、△λcladding,28Obtaining the sensitivity momentThe matrix is as follows:
the variation quantity delta T, delta epsilon and delta n of the temperature, the axial strain and the ambient refractive index can be obtained through a reverse-push matrixextThe variation quantity delta lambda of the transmission peak wavelength of the core mold, the transmission peak wavelength of the 25 th order cladding mold and the transmission peak wavelength of the 28 th order cladding moldcore、△λcladding,25、△λcladding,28For implementing a sensing measurement:
the above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.