A multi-physical quantity fiber sensor system based on long period fiber grating and bragg fiber grating

Abstract

The application 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 display screen, a pump source and a photoelectric conversion module; the sensing light 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, and the optical coupler divides the light path into two light paths; one light path is connected to the first photoelectric detector, and the other light path passes through the optical circulator, passes through the Bragg grating, and is connected to the second photoelectric detector through another port of the optical circulator. The application realizes high-precision measurement of three physical quantities, i.e. temperature, liquid concentration and vibration.

Description

Technical Field

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

[0002] Sensor technology plays a crucial role in industrial production and experimental data acquisition. It is used not only for the precise measurement of physical quantities but also plays a central role in the collection and analysis of experimental data. However, with the continuous development of science and technology, traditional electronic sensors have gradually revealed their limitations in certain applications, such as insufficient sensitivity and susceptibility to interference. These problems are particularly prominent in physical experiments that require high precision and high stability.

[0003] Against this backdrop, fiber optic sensors, with their significant advantages such as optical signal transmission, resistance to electromagnetic interference, and high sensitivity, have demonstrated enormous application potential. Currently, fiber optic sensor technology has evolved into various types, including sensors based on principles such as fiber Bragg gratings (FBGs), Mach-Zehnder interferometers (MZIs), and Michelson interferometers. These sensors each possess unique advantages in measurement accuracy, sensitivity, and applicability, but also have 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. Accurate measurement of these three quantities is crucial for ensuring the accuracy of experimental data. However, existing fiber optic sensors often can only measure one physical quantity at a time, making it difficult to simultaneously or independently measure temperature, vibration, or liquid concentration. Furthermore, they often require the use of expensive spectrometers, limiting their application in a wider range of 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] To address the aforementioned problems in the prior art, this invention provides a multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings. This system enables high-precision measurement of three physical quantities—temperature, vibration, and concentration—without relying on a spectrometer. It is also low-cost, highly scalable, and easy to upgrade.

[0007] To achieve the above objectives, this invention proposes a multi-physical quantity fiber optic sensor system based on a long-period fiber grating and a Bragg fiber grating. The system includes a flat broadband light source optical path, a sensing optical path, an STM32 central control unit, a serial port display, a pump source, and a photoelectric conversion module. The sensing optical path 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, which splits the optical path into two paths. One path is connected to the first photodetector, and the other path passes through the optical circulator, through the Bragg grating, and then through the other port of the optical circulator to the second photodetector.

[0008] Preferably, the flat broadband light source optical path includes an erbium-doped gain fiber, a wavelength division multiplexer, and an optical mirror; the erbium-doped gain fiber is composed 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 connected to the first erbium-doped gain fiber and the second erbium-doped gain fiber, respectively; the first erbium-doped gain fiber is connected to the optical mirror.

[0009] Preferably, both the first and second erbium-doped gain fibers are low-concentration erbium-doped gain fibers. The erbium-doped gain fibers are single-mode fibers, and the output laser light 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.

[0010] Preferably, the optical reflector has a reflectivity of over 99% and an insertion loss of no more than 0.2dB, and the wavelength division multiplexer uses an optical fiber device that multiplexes wavelengths of 980nm and 1550nm.

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

[0012] Preferably, the pump source is a semiconductor laser with an output laser center wavelength of 980nm and an output power range of 80mW-200mW; the output optical power and cavity optical power coupling ratio of the optical coupler are of three types: 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 ADC acquires signals from the first photodetector and the second photodetector respectively. One channel of serial communication controls the output power of the pump source, and the other channel communicates with the serial display screen.

[0014] Preferably, the photoelectric conversion module uses 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 use indium gallium arsenide photodiode detectors with a photosensitive surface of Ф3mm and a spectral range of 800-1700nm.

[0015] Preferably, the sensor system operates at a wavelength of 1530-1570nm, with an insertion loss of no more than 0.8dB, an isolation of no less than 40dB, a return loss of no less than 50dB, and an extinction ratio of no less than 20dB.

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

[0017] Therefore, this invention proposes a multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings, which has the following advantages:

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

[0019] (2) This invention utilizes the resonant peak characteristics of long-period fiber gratings to convert the wavelength change of the reflection peak of Bragg gratings into a change in light intensity, thereby accurately sensing temperature; at the same time, under the condition that the connection relationship remains unchanged, long-period fiber gratings are used as concentration and vibration sensing units, and the wavelength of the reflection peak of Bragg gratings remains unchanged, so that the change of the resonant peak of long-period fiber gratings is converted into a change in light intensity, thereby realizing the measurement of concentration and vibration; the first photodetector is used as a reference arm to correct for interference factors in front, thereby realizing high-sensitivity sensing measurement.

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

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

[0022] Figure 1This is a schematic diagram of the structure of a multi-physical quantity fiber optic sensor system based on a long-period fiber grating and a Bragg fiber grating according to the present invention.

[0023] Figure 2 This is a physical diagram of a multi-physical quantity fiber optic sensor system based on a long-period fiber grating and a Bragg fiber grating according to the present invention.

[0024] Figure 3 This invention relates to the relationship between the measured temperature and the output voltage ratio in a multi-physical quantity fiber optic sensor system based on a long-period fiber optic grating and a Bragg fiber grating.

[0025] Figure 4 This invention relates to a multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings, which is excited by a 64Hz vibration source.

[0026] Figure Labels

[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 unit; 13. Serial port display screen. Detailed Implementation

[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 clearly and completely described below. The described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the protection scope of this application.

[0029] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0030] like Figure 1-2 As 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 section, a sensing optical path section, an STM32 central control unit 12, a serial port display screen 13, a pump source 1, and a photoelectric conversion module.

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

[0032] The first erbium-doped gain fiber 3 and the second erbium-doped gain fiber 5 are single-mode fibers 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 single-mode fibers made of highly doped Coherent SM-EDF980HP fiber, with a length of 15m, outputting laser light in the 1550nm band with a dispersion coefficient of -21.4ps. 2 / km, wherein the length of the first erbium-doped gain fiber 3 is 6m and the length of the second erbium-doped gain fiber 5 is 2m.

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

[0034] The wavelength division multiplexer 2 uses fiber optic devices that multiplex wavelengths of 980nm and 1550nm. Its function is to separate light in the 980nm band and light in the 1550nm band, with an insertion loss of no more than 0.2dB. One port of the wavelength division multiplexer 2 is connected to the pump source 1, and the other two ports are connected to the first erbium-doped gain fiber 3 and the second erbium-doped gain fiber 5, respectively. The first erbium-doped gain fiber 3 is connected to the optical reflector 4.

[0035] The optical reflector 4 has a reflectivity of over 99% and is used to reflect the light from the first erbium-doped gain fiber 3 back to extend the range of the erbium-doped gain fiber. A second erbium-doped gain fiber 5 with a length of 2 meters is added after the wavelength division multiplexer 2. By using the C-band ASE 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 1530nm to gradually attenuate, and the overall spectrum to become flatter.

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

[0037] The sensing optical path 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] Long-period fiber gratings (LPGFs) are optical elements made by periodically changing the refractive index in the fiber core. Their core working principle is mode coupling. When the difference in propagation constant between the fiber core fundamental mode and the cladding mode matches the reciprocal of the grating period, light resonance occurs at a specific wavelength / resonant wavelength, leading to an increase in transmission loss at that wavelength.

[0039] One end of the long-period fiber grating 6 is connected to the optical coupler 7, which splits the optical path into two optical paths. Optical path one is connected to the first photodetector 10, and optical path two passes through the optical circulator 8 and the Bragg grating 9, and then is connected to the second photodetector 11 through the other port of the optical circulator 8.

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

[0041] The center wavelength of the reflection peak of the Bragg grating 9 is selected to match the resonant wavelength of the long-period fiber grating 6, and the difference is no more than 3nm. When the center wavelength of the Bragg grating 9 changes due to the external temperature, it can be reflected by the resonant wavelength of the long-period fiber grating.

[0042] The STM32 central control unit 12 includes dual-channel ADC acquisition and dual-channel serial communication. The dual-channel ADC acquires signals from the first photodetector 10 and the second photodetector 11 respectively. One channel of serial communication controls the output power of the pump source 1, and the other channel 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 1Hz-1MHz. Both the first photodetector 10 and the second photodetector 11 are indium gallium arsenide photodiode detectors with a photosensitive surface of Ф3mm and a spectral range of 800-1700nm.

[0044] The operating wavelength of the multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings is 1530-1570nm, with an insertion loss of no more than 0.8dB, an isolation of no less than 40dB, a return loss of no less than 50dB, and an extinction ratio of no less than 20dB.

[0045] Therefore, this invention provides a multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings. This system can achieve high-precision measurement of three physical quantities—temperature, vibration, and concentration—without relying on a spectrometer. The instrument is not only low-cost but also highly scalable and easily upgraded, making it particularly suitable for commercial applications to meet the vibration and temperature sensing needs of deep-sea power systems. Furthermore, this invention can serve as a teaching tool, playing a crucial role in the practical components of university physics or optoelectronic information experimental courses, providing students with valuable experimental learning experiences.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause 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 fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings, characterized in that, The system includes a flat broadband light source optical path section, a sensing optical path section, an STM32 central control unit, a serial port display screen, a pump source, and a photoelectric conversion module. The sensing optical path section 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, which splits the optical path into two paths. One path is connected to the first photodetector, and the other path passes through the optical circulator, the Bragg grating, and then is connected to the second photodetector through the other end of the optical circulator. The STM32 central control unit includes dual-channel ADC acquisition and dual-channel serial communication. The dual-channel ADC acquires the signals of the first photodetector and the second photodetector respectively. One serial communication channel controls the output power of the pump source, and the other serial communication channel communicates with the serial display screen. The Bragg grating has a reflection peak center wavelength of 1548nm and a reflectivity of 90%, and is used for temperature sensing and measurement; the long-period fiber grating has a resonance peak wavelength of 1550nm and is used for concentration and vibration measurement. The flat broadband light source optical path includes an erbium-doped gain fiber, a wavelength division multiplexer, and an optical mirror; the erbium-doped gain fiber is composed 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 connected to the first erbium-doped gain fiber and the second erbium-doped gain fiber, respectively; the first erbium-doped gain fiber is connected to the optical mirror. The flat broadband light source section is connected to the long-period fiber grating via the second erbium-doped gain fiber, and is also connected to the sensing optical path section to form the light source input of the sensing optical path section.

2. The multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings according to claim 1, characterized in that, Both the first and second erbium-doped gain fibers use low-concentration erbium-doped gain fibers. The erbium-doped gain fibers are single-mode fibers, and the output laser light 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.

3. The multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings according to claim 1, characterized in that, The optical mirror has a reflectivity of over 99% and an insertion loss of no more than 0.2dB. The wavelength division multiplexer uses optical fiber devices that multiplex wavelengths of 980nm and 1550nm.

4. A multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings according to claim 1, characterized in that, The pump source is a semiconductor laser with an output laser center wavelength of 980nm and an output power range of 80mW-200mW; the output optical power and cavity optical power coupling ratios of the optical couplers are 1:99, 10:90, and 20:

80.

5. A multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings according to claim 1, characterized in that, The photoelectric conversion module uses 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 use indium gallium arsenide photodiode detectors with a photosensitive surface of Ф3mm and a spectral range of 800-1700nm.

6. A multi-physical quantity fiber optic sensor system based on long-period fiber gratings and Bragg fiber gratings according to claim 1, characterized in that, The sensor system operates at a wavelength of 1530-1570nm, with an insertion loss of no more than 0.8dB, an isolation of no less than 40dB, a return loss of no less than 50dB, and an extinction ratio of no less than 20dB.

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