Multi-physical-quantity optical fiber sensor system based on long-period fiber bragg grating and Bragg fiber bragg grating

Abstract

The invention relates to the field of optical fiber sensing, and particularly discloses a multi-physical-quantity optical fiber sensor system based on a long-period fiber grating and a Bragg fiber grating. The system comprises a flat broadband light source light path part, a sensing light path part, an STM32 central controller, a serial port display screen, a pumping source and a photoelectric conversion module, the sensing optical path part is composed of a long-period fiber grating, an optical coupler, a first photoelectric detector, an optical circulator, a Bragg grating and a second photoelectric detector, one end of the long-period fiber grating is connected to the optical coupler, the optical coupler divides the long-period fiber grating into two optical paths, the first optical path is connected to the first photoelectric detector, and the second optical path is connected to the second photoelectric detector; the second optical path passes through the Bragg grating through the optical circulator and then is connected to the second photoelectric detector through the other port of the optical circulator. According to the invention, high-precision measurement of three physical quantities of temperature, liquid concentration and vibration is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of fiber optic sensing, and specifically to a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings. Background Art

[0002] In industrial production and experimental data acquisition, sensor technology plays a crucial role. They are not only used for accurately measuring physical quantities but also play a core role in the collection and analysis of experimental data. However, with the continuous development of science and technology, traditional electronic sensors gradually show their limitations in some application scenarios, such as insufficient sensitivity and susceptibility to interference. These problems are particularly prominent in physical experiments that require high precision and high stability.

[0003] In this context, fiber optic sensors, with their significant advantages such as optical signal transmission, electromagnetic interference resistance, and high sensitivity, show great application potential. Currently, fiber optic sensor technology has developed various types, including sensors based on principles such as fiber Bragg gratings (FBG), Mach - Zehnder interferometers (MZI), and Michelson interferometers. These sensors have their unique advantages in measurement accuracy, sensitivity, and applicability, but there are also some limitations, such as cost, complexity, and multi - parameter measurement capabilities.

[0004] In industrial production and experimental data acquisition, temperature, vibration, and liquid concentration are three key physical quantities. The accurate measurement of these three physical quantities is crucial for ensuring the accuracy of experimental data. However, existing fiber optic sensors often can only measure a single physical quantity, and it is difficult to measure temperature, vibration, or liquid concentration simultaneously or independently. Moreover, they often need to be used in conjunction with expensive spectrometers for measurement, which limits their use in a wider range of application scenarios.

[0005] Therefore, it is necessary to design a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings to solve the above - mentioned technical problems. Summary of the Invention

[0006] Aiming at the above - mentioned problems of the prior art, the present invention provides a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings, which can achieve high - precision measurement of three physical quantities, namely temperature, vibration, and concentration, without relying on a spectrometer, has a low cost, and also has good scalability and is easy to upgrade.

[0007] To achieve the above object, the present invention proposes a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings. The system includes a flat broadband light source optical path part, a sensing optical path part, an STM32 central control unit, a serial port display screen, a pump source, and a photoelectric conversion module. The sensing optical path part consists of a long - period fiber grating, an optical coupler, a first photodetector, an optical circulator, a Bragg grating, and a second photodetector. One end of the long - period fiber grating is connected to the optical coupler, and the optical coupler divides it into two optical paths. Optical path one is connected to the first photodetector, and optical path two passes through the Bragg grating via the optical circulator and is then connected to the second photodetector through the other port of the optical circulator.

[0008] Preferably, the flat broadband light source optical path part includes an erbium - doped gain fiber, a wavelength - division multiplexer, and an optical mirror. The erbium - doped gain fiber consists of a first erbium - doped gain fiber and a second erbium - doped gain fiber. One port of the wavelength - division multiplexer is connected to the pump source, and the other two ports are respectively connected to the first erbium - doped gain fiber and the second erbium - doped gain fiber. The first erbium - doped gain fiber is connected to the optical mirror.

[0009] Preferably, both the first erbium - doped gain fiber and the second erbium - doped gain fiber use low - concentration erbium - doped gain fibers. The erbium - doped gain fiber uses a single - mode fiber, the output laser is in the 1550nm band, the dispersion coefficient is - 21.4ps 2 / km, the length of the first erbium - doped gain fiber is 6 meters, and the length of the second erbium - doped gain fiber is 2 meters.

[0010] Preferably, the reflectivity of the optical mirror is above 99%, the insertion loss is not greater than 0.2dB, and the wavelength - division multiplexer uses a fiber device multiplexing wavelengths of 980nm and 1550nm.

[0011] Preferably, the flat broadband light source part is connected to the long - period fiber grating through the second erbium - doped gain fiber and is connected to the sensing optical path part to form the light source input of the sensing optical path part.

[0012] Preferably, the pump source is a semiconductor laser, the output laser center wavelength is 980nm, and the output power range is 80mW - 200mW. The output optical power and the intracavity optical power coupling ratios corresponding to the optical coupler are divided into three categories: 1:99, 10:90, and 20:80.

[0013] Preferably, the STM32 central control unit includes dual - channel ADC acquisition and dual - channel serial communication. The dual - channel ADCs respectively acquire the signals of the first photodetector and the second photodetector. One serial communication controls the output power of the pump source, and the other serial communication communicates with the serial port display screen.

[0014] Preferably, the optoelectronic conversion module uses a current-to-voltage amplifier with a gain of 100,000 times and an input frequency range of 1 Hz - 1 MHz; both the first photodetector and the second photodetector use indium gallium arsenide photodiode detectors with a photosensitive surface of Ф3 mm, and the spectral range is 800 - 1700 nm.

[0015] Preferably, the working wavelength of the sensor system is 1530 - 1570 nm, the insertion loss is not greater than 0.8 dB, the isolation is not less than 40 dB, the return loss is not less than 50 dB, and the extinction ratio is not less than 20 dB.

[0016] Preferably, the center wavelength of the reflection peak of the Bragg grating is 1548 nm, and the reflectivity is 90%, which is used for temperature sensing measurement; the resonance peak of the long-period fiber grating is 1550 nm, which is used for concentration and vibration measurement.

[0017] Therefore, the present invention proposes a multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings, and its beneficial effects are as follows:

[0018] (1) The system of the present invention based on long-period fiber gratings and Bragg fiber gratings can achieve high-precision measurement of three physical quantities, namely temperature, vibration and concentration, without relying on a spectrometer. By adjusting the usage method, the system can also achieve precise measurement of concentration and vibration, improving the diversity and accuracy of measurement.

[0019] (2) The present invention utilizes the resonance peak characteristics of the long-period fiber grating to convert the wavelength change of the reflection peak of the Bragg grating into a light intensity change, so as to accurately sense the temperature. At the same time, under the condition that the connection relationship remains unchanged, the long-period fiber grating is used as the concentration and vibration sensing unit, and the wavelength of the reflection peak of the Bragg grating remains unchanged. The change of the resonance peak of the long-period fiber grating is converted into a light intensity change to realize the measurement of concentration and vibration. The first photodetector is used as the reference arm to correct the interference factors in front, and then realize high-sensitivity sensing measurement.

[0020] (3) The overall cost of the instrument of the present invention is relatively low, and it has good scalability and upgrade potential. On the basis of keeping the connection relationship unchanged, the system can flexibly adapt to different application scenarios. This cost-effectiveness and flexibility make the system not only suitable for commercial transformation to meet the needs of specific industries, but also have the potential to become a teaching instrument, which helps to popularize fiber optic sensing technology in the fields of education and scientific research.

[0021] The technical solutions of the present invention will be further described in detail below with reference to the drawings and embodiments. Description of the Drawings

[0022] Figure 1It is a schematic structural diagram of a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings of the present invention;

[0023] Figure 2 It is a physical diagram of a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings of the present invention;

[0024] Figure 3 It is the corresponding relationship between the measured temperature and the ratio of the output voltage of a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings of the present invention;

[0025] Figure 4 It is the spectral image of a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings of the present invention excited by a 64 - Hz vibration source.

[0026] Reference numerals

[0027] 1. Pump source; 2. Wavelength division multiplexer; 3. First erbium - doped gain fiber; 4. Optical mirror; 5. Second erbium - doped gain fiber; 6. Long - period fiber grating; 7. Optical coupler; 8. Optical circulator; 9. Bragg grating; 10. First photodetector; 11. Second photodetector; 12. STM32 central control; 13. Serial port display screen. Detailed implementation manners

[0028] To make the technical solutions, advantages and objectives of the present invention clearer, the technical solutions of the embodiments of the present invention will be described clearly and completely below. The described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts belong to the protection scope of this application.

[0029] Unless otherwise defined, the technical terms or scientific terms used in the present invention should have the ordinary meaning understood by those of ordinary skill in the art within the field to which the present invention belongs.

[0030] As Figure 1-2 shown, the present invention provides a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings. The system includes a flat broadband light source optical path part, a sensing optical path part, an STM32 central control 12, a serial port display screen 13, a pump source 1, and a photoelectric conversion module;

[0031] The flat broadband light source optical path part includes erbium - doped gain fibers, a wavelength division multiplexer 2, and an optical mirror 4; the erbium - doped gain fibers are composed of a first erbium - doped gain fiber 3 and a second erbium - doped gain fiber 5.

[0032] The first erbium-doped gain fiber 3 and the second erbium-doped gain fiber 5 adopt single-mode fibers, which are used to achieve population inversion and generate stimulated emission amplification of light. Both the first erbium-doped gain fiber 3 and the second erbium-doped gain fiber 5 are selected as single-mode fibers of Coherent SM-EDF980HP highly doped gain fibers, with a length of 15 m, the output laser being in the 1550 nm band, and the dispersion coefficient being -21.4 ps 2 / km, where the length of the first erbium-doped gain fiber 3 is 6 m and the length of the second erbium-doped gain fiber 5 is 2 m.

[0033] The pump source 1 is a semiconductor laser, and the output band of the semiconductor laser is 980 nm. The actual output power range of the semiconductor laser is controlled between 80 - 200 mW. When the power is below 80 mW, the power of part of the output of the flat broadband light source is relatively low, and the photodetector cannot detect the light intensity. When the power is above 200 mW, the first erbium-doped gain fiber 3 will excite more amplified spontaneous emission (ASE), and excitation light will be generated in the 1530 nm and 1560 nm bands, affecting the flatness of the output spectrum of the flat broadband light source.

[0034] The wavelength division multiplexer 2 adopts an optical fiber device multiplexing wavelengths of 980 nm and 1550 nm, and its function is to separate the light in the 980 nm band and the light in the 1550 nm band, with an insertion loss not greater than 0.2 dB. One port of the wavelength division multiplexer 2 is connected to the pump source 1, and the other two ports are respectively connected to the first erbium-doped gain fiber 3 and the second erbium-doped gain fiber 5. The first erbium-doped gain fiber 3 is connected to the optical mirror 4.

[0035] The reflectivity of the optical mirror 4 is above 99%, which is used to reflect the light of the first erbium-doped gain fiber 3 back to achieve the extension of the erbium-doped gain fiber. A second erbium-doped gain fiber 5 with a length of 2 meters is added behind the wavelength division multiplexer 2. By using the ASE in the C band as a secondary pump source, the light intensity in the L band is effectively increased. At the same time, since the total number of erbium particles in the erbium-doped fiber is greater than the saturation number, these excess erbium particles absorb the light in the C band, causing the peak near 1530 nm to gradually decay, and the overall spectrum becomes flatter.

[0036] The 980 nm laser emitted from the pump source 1 passes through one port of the wavelength division multiplexer 2, passes through the first erbium-doped gain fiber 3 and the optical mirror 4, and then passes through the first erbium-doped gain fiber 3 again, and is introduced into the second erbium-doped gain fiber 5 by the wavelength division multiplexer 2 to complete the operation of the entire flat broadband light source.

[0037] The sensing optical path part consists of a long-period fiber grating 6, an optical coupler 7, a first photodetector 10, an optical circulator 8, a Bragg grating 9, and a second photodetector 11.

[0038] The long-period fiber grating 6 is an optical component made by periodically changing the refractive index in the fiber core. The core working principle is mode coupling. When the difference in propagation constants between the core fundamental mode and the cladding mode matches the reciprocal of the grating period, light resonance occurs at a specific wavelength / resonant wavelength, resulting in an increase in the transmission loss at that wavelength.

[0039] One end of the long-period fiber grating 6 is connected to an optical coupler 7, which divides the light into two optical paths. The first optical path is connected to a first photodetector 10, and the second optical path passes through a Bragg grating 9 via an optical circulator 8 and is then connected to a second photodetector 11 through another port of the optical circulator 8.

[0040] The output optical power of the optical coupler 7 and the in-cavity optical power coupling ratio are 1:99, 10:90, or 20:80. In specific embodiments, an optical coupler 7 with a different power ratio is selected according to the situation to make the light intensity entering the first photodetector 10 reach a detectable level.

[0041] The Bragg grating 9 is selected to have a reflection peak center wavelength that matches the resonant wavelength of the long-period fiber grating 6 and the difference is no more than 3 nm. When the external temperature causes the center wavelength of the Bragg grating 9 to change, it can be reflected through the resonant wavelength of the long-period fiber grating.

[0042] The STM32 central control 12 includes dual-channel ADC acquisition and dual-channel serial communication. The dual-channel ADCs respectively acquire the signals of the first photodetector 10 and the second photodetector 11. One serial communication controls the output power of the pump source 1, and the other serial communication communicates with the serial display screen 13.

[0043] The photoelectric conversion module uses a current-to-voltage amplifier with a gain of 100,000 times and an input frequency range of 1 Hz - 1 MHz. Both the first photodetector 10 and the second photodetector 11 use indium gallium arsenide photodiode detectors with a photosensitive surface of Ф3 mm, and the spectral range is 800 - 1700 nm.

[0044] The working wavelength of the multi-physical quantity fiber optic sensor system based on the long-period fiber grating and the Bragg fiber grating is 1530 - 1570 nm, the insertion loss is not greater than 0.8 dB, the isolation is not less than 40 dB, the return loss is not less than 50 dB, and the extinction ratio is not less than 20 dB.

[0045] Therefore, the present invention provides a multi - physical - quantity fiber optic sensor system based on long - period fiber gratings and Bragg fiber gratings. Without relying on a spectrometer, this system can achieve high - precision measurement of three physical quantities: temperature, vibration, and concentration. This instrument not only has a relatively low cost but also has good scalability and is easy to upgrade, especially suitable for commercial transformation to meet the vibration and temperature sensing requirements in deep - sea power systems. In addition, the present invention can be used as a teaching tool, playing a key role in the practical sessions of college physics or optoelectronic information - related experimental courses, providing valuable experimental learning experiences for students.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions of the present invention or make equivalent replacements, and these modifications or equivalent replacements do not enable the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A multi-physical quantity optical fiber sensor system based on long period fiber grating and Bragg fiber grating, characterized in that: The system comprises a flat broadband light source optical path part, a sensing optical path part, an STM32 central control, a serial port display screen, a pump source, and a photoelectric conversion module; the sensing optical path part is composed of a long-period fiber grating, an optical coupler, a first photodetector, an optical circulator, a Bragg grating, and a second photodetector; one end of the long-period fiber grating is connected to the optical coupler and is divided into two optical paths by the optical coupler, wherein the first optical path is connected to the first photodetector, and the second optical path is connected to the second photodetector through the optical circulator, the Bragg grating, and the other port of the optical circulator.

2. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 1, characterized in that: The optical path of the flat broadband light source includes an erbium-doped gain fiber, a wavelength division multiplexer, and an optical reflector; the erbium-doped gain fiber consists of a first erbium-doped gain fiber and a second erbium-doped gain fiber; one port of the wavelength division multiplexer is connected to a pump source, and the other two ports are respectively connected to the first erbium-doped gain fiber and the second erbium-doped gain fiber, and the first erbium-doped gain fiber is connected to the optical reflector.

3. The multi-physical quantity optical fiber sensor system based on long period fiber grating and Bragg fiber grating according to claim 2, characterized in that: The first erbium-doped gain fiber and the second erbium-doped gain fiber both use low-concentration erbium-doped gain fibers. The erbium-doped gain fibers use single-mode fibers, and the output laser is in the 1550nm band, with a dispersion coefficient of -21.4ps. 2 / km, the length of the first erbium-doped gain fiber is 6 meters, and the length of the second erbium-doped gain fiber is 2 meters.

4. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 2, characterized in that: The reflectivity of the optical reflector is above 99%, the insertion loss is not greater than 0.2 dB, and the wavelength division multiplexer adopts an optical fiber device with wavelengths of 980 nm and 1550 nm multiplexing.

5. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 2, characterized in that: The flat broadband light source part is connected to the long period fiber grating through the second erbium-doped gain fiber, and is connected to the sensing optical path part, forming the light source input of the sensing optical path part.

6. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 1, characterized in that: The pump source is a semiconductor laser, the output laser center wavelength is 980nm, and the output power ranges from 80mW to 200mW; the output optical power and intracavity optical power coupling ratios corresponding to the optical coupler are divided into three categories: 1:99, 10:90, and 20:

80.

7. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 1, characterized in that: The STM32 central control includes dual-channel ADC acquisition and dual-channel serial port communication. The dual-channel ADC respectively acquires signals from the first photodetector and the second photodetector. One serial port communication controls the output power of the pump source, and the other serial port communication communicates with the serial port display screen.

8. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 1, characterized in that: The photoelectric conversion module adopts a current-to-voltage amplifier with a gain of 100,000 times and an input frequency range of 1Hz-1MHz; the first photodetector and the second photodetector both adopt indium gallium arsenide photodiode detectors with a photosensitive surface of Ф3mm and a spectral range of 800-1700nm.

9. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 1, characterized in that: The sensor system has an operating wavelength of 1530-1570 nm, an insertion loss of no more than 0.8 dB, an isolation of no less than 40 dB, a return loss of no less than 50 dB, and an extinction ratio of no less than 20 dB.

10. The multi-physical quantity optical fiber sensor system based on long period fiber grating and fiber Bragg grating according to claim 1, characterized in that: The reflection peak center wavelength of the Bragg grating is 1548nm, the reflectivity is 90%, and it is used for temperature sensing measurement; the resonance peak of the long-period fiber grating is 1550nm, and it is used for concentration and vibration measurement.

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