Ultra-high-resolution bending temperature sensor based on quasi-linear distribution of fiber core refractive index

Abstract

The present invention discloses an ultra-high resolution bending temperature sensor based on a linear distribution of the core refractive index. The sensor comprises a core-doped single-mode optical fiber cladding, a Bragg grating, and a core-doped single-mode optical fiber core. The core-doped single-mode optical fiber core has a Bragg grating engraved inside the core-doped single-mode optical fiber core, and the core-doped single-mode optical fiber cladding is wrapped around the outside of the core-doped single-mode optical fiber core. The present invention prepares a core-doped single-mode optical fiber by melt-drawing SiO2, Al2O3, Y2O3, and P2O5 materials in a fiber drawing tower according to different mass ratios, and uses a femtosecond laser to write a Bragg grating at its core to prepare an optical fiber sensor, thereby realizing dual-parameter measurement of bending and temperature. At the same time, according to the reflection spectrum characteristics of bending and temperature, the simultaneous measurement of bending and temperature can be realized by decoupling. The sensor has the characteristics of compact structure, simple preparation, high sensitivity, etc.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber sensing technology, in particular to an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of a fiber core refractive index. Background Art

[0002] As one of the important technologies in the field of sensing, fiber optic sensing has been gradually applied in aerospace, oil extraction, bridges and dams, biomedicine, and automation industries due to its unique advantages of anti-electromagnetic interference, compact structure, and high sensitivity. Temperature and bending are two extremely important physical parameters in the field of fiber optic sensing. The realization of fast and highly sensitive measurement of them has always been a hot topic of social concern. At present, based on different sensing principles, fiber optic bending temperature sensors of various types such as interferometer type, grating type, photonic crystal fiber (PCF) type, sapphire fiber type, and multi-core fiber type have been prepared. Most interferometric sensors require multiple fiber optic fusion splicing to prepare, which makes the reproducibility and robustness of the sensor poor. Sensors based on special optical fibers will increase the production cost of the sensor. Long period fiber grating (LPFG) has high detection sensitivity, but generally uses the transmission spectrum of the structure for data analysis and testing, which has great limitations in fiber optic sensing networks. Fiber Bragg Bragg Grating (FBG) can achieve simultaneous measurement of temperature and bending, but its sensitivity is low and it is difficult to distinguish the measurement parameters; ordinary fiber Bragg gratings are made by ultraviolet laser writing, and have poor high temperature resistance. They will gradually decay until they are completely erased in a long-term high temperature environment, which greatly limits the application of fiber Bragg gratings in high temperature environments. Sapphire fiber, as a high-quality single-crystal fiber, has excellent high temperature characteristics and optical and mechanical properties. It can achieve high temperature testing above 1000℃ and has good application value in fiber high temperature sensing, but its cost is very high compared with other optical fibers. In addition, most of the current temperature bending sensors use a single wavelength demodulation method. The simultaneous use of wavelength demodulation for dual physical parameters is bound to cause crosstalk, and the sensitivity and accuracy of the sensor is not high. Therefore, at the current stage, achieving high-precision measurement of fiber temperature and bending is one of the problems that need to be solved in practical applications. Summary of the invention

[0003] The object of the present invention is to provide an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of the core refractive index, so as to solve the problems raised in the above background technology.

[0004] To achieve the above-mentioned purpose, the present invention provides the following technical solution: an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of the core refractive index, the sensor comprising a core-doped single-mode optical fiber cladding, a Bragg grating, and a core-doped single-mode optical fiber core, wherein a Bragg grating is arranged inside the core-doped single-mode optical fiber core, and the core-doped single-mode optical fiber cladding is wrapped around the outside of the core-doped single-mode optical fiber core.

[0005] Preferably, the core-doped single-mode optical fiber is drawn by an optical fiber drawing tower, has a cladding diameter of 125 μm, a core diameter of 10 μm, a numerical aperture of 0.2, and a core refractive index of a quasi-linear distribution.

[0006] Preferably, the core doping materials of the single-mode optical fiber are SiO2, Al2O3, Y2O3 and P2O5; the mass percentages of the core doping materials are: 4.9wt.% Y2O3, 3.2wt.% Al2O3, 2.3wt.% P2O5, 89.6wt.% SiO2.

[0007] Preferably, the Bragg grating is inscribed by a femtosecond laser, the laser wavelength is 800 nm, the pulse width is 200 fs, the maximum output power is 3 W, the writing grating power is 1.2 mJ, and the fiber Bragg grating length is 4 mm.

[0008] Preferably, the preparation method comprises the following steps:

[0009] (1) Using an optical fiber drawing tower to prepare a core-doped single-mode optical fiber;

[0010] (2) Using femtosecond laser micromachining technology to write a fiber Bragg grating in the core of a single-mode optical fiber;

[0011] (3) Perform bending and temperature sensing tests.

[0012] Preferably, in the step (1), the mass proportion of the doping materials is: 4.9wt.% Y2O3, 3.2wt.% Al2O3, 2.3wt.% P2O5, 89.6wt.% SiO2, and the single-mode optical fiber with a cladding diameter of 125μm, a core diameter of 10μm, and a numerical aperture of 0.2 is prepared by drawing in a fiber drawing tower.

[0013] Preferably, in step (2), the wavelength of the femtosecond laser is 800 nm, the repetition frequency is 200 KHz, the pulse width is 200 fs, and the maximum power is 3 W; the writing power is 1.2 mJ, and the length of the written Bragg grating is 4 mm.

[0014] Preferably, in step (3), the bending measurement range is 0-1.2m -1 , the interval is 0.2m -1 ; The temperature test range is 80-1000℃, and the temperature response is shear from 25℃ to 980℃.

[0015] Preferably, the bending test in step (3) adopts a bending test system, which includes a computer, a grating demodulator, a bending test device and a grating sensor head. The computer is connected to the grating demodulator, and the grating demodulator is connected to the grating sensor head. The grating sensor head is placed on the bending test device for bending test, and the test range is 0-1.2m. -1 , the interval is 0.2m -1 , the optical signal is received and demodulated by the grating demodulator, and the computer software terminal can receive and display the real-time reflection spectrum.

[0016] Preferably, the temperature test in step (3) adopts a temperature testing system, and the temperature testing system includes a computer, a grating demodulator, a temperature testing device and a grating sensor head. The computer is connected to the grating demodulator, and the grating demodulator is connected to the grating sensor head. The grating sensor head is placed in the temperature testing device for temperature sensing test, and the test range is 80°C-1000°C.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The sensor uses core-doped single-mode optical fiber, which has the advantages of simple preparation and low cost compared with sensors based on sapphire optical fiber;

[0019] (2) The sensor is sensitive to both bending and temperature, and can measure environmental parameters simultaneously. The bending change only affects the light intensity change of the sensor. The temperature change causes the wavelength of the sensor to drift. By decoupling, the two can be measured simultaneously. Compared with the single wavelength demodulation method, the bending and temperature sensitivity of the sensor is more accurate.

[0020] (3) The sensor only writes the fiber grating on the fiber core and does not involve multiple fusion splicing. The sensor has strong mechanical properties.

[0021] (4) In terms of high temperature testing, the sensor has a fast high temperature response characteristic. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram for preparing core-doped single-mode optical fiber;

[0023] Figure 2 is the optical fiber refractive index distribution diagram;

[0024] Figure 3 It is a schematic diagram of the sensor structure;

[0025] Figure 4 is the reflection spectrum of the sensor;

[0026] Figure 5 This is a diagram of the bending measurement system;

[0027] Figure 6 This is the sensor bending measurement data diagram;

[0028] Figure 7 This is a diagram of the high temperature test system;

[0029] Figure 8 It is the reflection spectrum of the sensor at different temperatures;

[0030] Fig. 9 This is the relationship between the wavelength drift of the sensor and the temperature at different temperatures;

[0031] Fig.10 This is the temperature response time diagram of the sensor from 25℃ to 980℃. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be noted that the terms "upper", "lower", "inner", "outer", "front end", "rear end", "two ends", "one end", "the other end" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] See also Figure 1-10The present invention provides a technical solution: an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of the core refractive index, the sensor comprising a core-doped single-mode optical fiber cladding 1, a Bragg grating 2, and a core-doped single-mode optical fiber core 3, wherein the core-doped single-mode optical fiber core 3 has a Bragg grating 2 engraved inside, and the core-doped single-mode optical fiber cladding 1 is wrapped around the outside of the core-doped single-mode optical fiber core 3; the core-doped single-mode optical fiber 4 is drawn by an optical fiber drawing tower 9, and has a cladding diameter of 125 μm, a core diameter of 10 μm, a numerical aperture of 0.2, and a core refractive index of a quasi-linear distribution; the core-doped single-mode optical fiber core 3 is doped with SiO2 5, Al2O36, Y2O37, and P2O58; and the mass percentages of the core doping materials are: 4.9wt.% Y2O3, 3.2wt.% Al2O3, 2.3wt.% P2O5, and 89.6wt.% SiO2.

[0036] In the present invention, the Bragg grating 2 is written by a femtosecond laser, the laser wavelength is 800nm, the pulse width is 200fs, the maximum output power is 3W, the writing grating power is 1.2mJ, and the fiber Bragg grating length is 4mm.

[0037] In the present invention, the temperature sensor preparation method comprises the following steps:

[0038] (1) Using an optical fiber drawing tower to prepare a core-doped single-mode optical fiber;

[0039] (2) Using femtosecond laser micromachining technology to write a fiber Bragg grating in the core of a single-mode optical fiber;

[0040] (3) Perform bending and temperature sensing tests.

[0041] Among them, in the step (1), the mass proportion of the doping materials is: 4.9wt.% Y2O3, 3.2wt.% Al2O3, 2.3wt.% P2O5, 89.6wt.% SiO2, and the single-mode optical fiber with a cladding diameter of 125μm, a core diameter of 10μm, and a numerical aperture of 0.2 is prepared by drawing in a fiber drawing tower.

[0042] In the step (2), the wavelength of the femtosecond laser is 800 nm, the repetition frequency is 200 KHz, the pulse width is 200 fs, and the maximum power is 3 W; the writing power is 1.2 mJ, and the length of the written Bragg grating is 4 mm.

[0043] In step (3), the bending measurement range is 0-1.2m -1 , the interval is 0.2m -1 ; The temperature test range is 80-1000℃, and the temperature response is shear from 25℃ to 980℃.

[0044] The bending test in step (3) adopts a bending test system, which includes a computer 10, a grating demodulator 11, a bending test device 12 and a grating sensor head 13. The computer 10 is connected to the grating demodulator 11, and the grating demodulator 12 is connected to the grating sensor head 13. The grating sensor head is placed on the bending test device for bending test, and the test range is 0-1.2m. -1 , the interval is 0.2m -1 , the optical signal is received and demodulated by the grating demodulator, and the computer software terminal can receive and display the real-time reflection spectrum.

[0045] The temperature test in step (3) adopts a temperature testing system, which includes a computer 10, a grating demodulator 11, a temperature testing device 14 and a grating sensor head 13. The computer 10 is connected to the grating demodulator 11, and the grating demodulator 11 is connected to the grating sensor head 13. The grating sensor head is placed in the temperature testing device for temperature sensing testing, and the test range is 80°C-1000°C.

[0046] By analogy, the grating at the core is used as a micro-disturbance to the optical fiber, and the perturbation principle of the Maxwell equations is established to derive the grating coupled mode theory. Then, using the orthogonal normalization condition, the coupled mode equation of the mode amplitude can be obtained as follows:

[0047]

[0048] In the formula, It is related to the perturbation of the dielectric constant. By obtaining the perturbation form of the dielectric constant caused by the refractive index modulation, we can get the corresponding perturbation coupled mode equation.

[0049] The present invention prepares a core-doped single-mode optical fiber by melting and drawing SiO2, Al2O3, Y2O3 and P2O5 materials in a fiber drawing tower according to different mass ratios, and uses a femtosecond laser to write a Bragg grating at the core of the fiber to prepare an optical fiber sensor, thereby realizing dual parameter measurement of bending and temperature. At the same time, according to the reflection spectrum characteristics of bending and temperature, the simultaneous measurement of bending and temperature can be realized by decoupling. The sensor has the characteristics of compact structure, simple preparation, high sensitivity, etc.

[0050] It should be noted that, in this article, terms such as "comprises", "includes" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or device including the element.

[0051] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

Claims

1. An ultra-high resolution bending temperature sensor based on a quasi-linear distribution of the fiber core refractive index, characterized in that: The temperature sensor comprises a core-doped single-mode optical fiber cladding (1), a Bragg grating (2), and a core-doped single-mode optical fiber core (3); the Bragg grating (2) is arranged inside the core-doped single-mode optical fiber core (3), and the core-doped single-mode optical fiber cladding (1) is wrapped around the outside of the core-doped single-mode optical fiber core (3); The core-doped single-mode optical fiber core (3) is drawn by an optical fiber drawing tower (4), has a cladding diameter of 125 μm, a core diameter of 10 μm, a numerical aperture of 0.2, and a core refractive index of a quasi-linear distribution; The core (3) of the core-doped single-mode optical fiber is doped with materials including SiO2 (5), Al2O3 (6), Y2O3 (7) and P2O5 (8); the mass percentages of the core doping materials are respectively: 4.9wt.% Y2O3, 3.2wt.% Al2O3, 2.3wt.% P2O5, and 89.6wt.% SiO2.

2. The ultra-high resolution bending temperature sensor based on the quasi-linear distribution of the core refractive index according to claim 1, characterized in that: The Bragg grating (2) is inscribed by a femtosecond laser, the laser wavelength is 800nm, the pulse width is 200fs, the maximum output power is 3W, the writing grating power is 1.2mJ, and the fiber Bragg grating length is 4mm.

3. A method for preparing an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of core refractive index as claimed in claim 1, characterized in that: The preparation method comprises the following steps: (1) Using an optical fiber drawing tower to prepare a core-doped single-mode optical fiber; (2) Using femtosecond laser micromachining technology to write a fiber Bragg grating in the core of a single-mode optical fiber; (3) Perform bending and temperature sensing tests.

4. The method for preparing an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of core refractive index according to claim 3, characterized in that: In the step (2), the wavelength of the femtosecond laser is 800 nm, the repetition frequency is 200 KHz, the pulse width is 200 fs, and the maximum power is 3 W; the writing power is 1.2 mJ, and the length of the written Bragg grating is 4 mm.

5. The method for preparing an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of core refractive index according to claim 3, characterized in that: In step (3), the bending measurement range is 0-1.2m -1 , the interval is 0.2m -1 ; The temperature test range is 80-1000℃, and the temperature response is shear from 25℃ to 980℃.

6. The method for preparing an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of core refractive index according to claim 3, characterized in that: The bending test in step (3) adopts a bending test system, which comprises a computer (9), a grating demodulator (10), a bending test device (11) and a grating sensor head (12). The computer (9) is connected to the grating demodulator (10), the grating demodulator (10) is connected to the bending test device (11), and the grating sensor head is placed on the bending test device to perform the bending test, and the test range is 0-1.2m. -1 , the interval is 0.2m -1 , the optical signal is received and demodulated by the grating demodulator, and the computer software terminal can receive and display the real-time reflection spectrum.

7. The method for preparing an ultra-high resolution bending temperature sensor based on a quasi-linear distribution of core refractive index according to claim 3, characterized in that: The temperature test in step (3) adopts a temperature test system, which comprises a computer (9), a grating demodulator (10), a temperature test device (13) and a grating sensor head (12). The computer (9) is connected to the grating demodulator (10), and the grating demodulator (10) is connected to the temperature test device (13). The grating sensor head is placed in the temperature test device to perform a temperature sensing test, and the test range is 80°C-1000°C.

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