A multi-parameter gas sensing system based on graphene microsphere cavities

Abstract

The present invention belongs to the field of biochemical sensing technology and specifically provides a multi-parameter gas sensing system based on a graphene microsphere cavity. This system addresses the low sensitivity and inability to perform multi-parameter sensing in existing fiber-optic gas sensors. The system comprises a vacuum cavity 1, a graphene microsphere cavity 2, a micro-nano optical fiber 3, a fixture 4, a tunable narrow-linewidth laser 5, a polarization controller 6, a single-mode circulator 7, a 2×2 single-mode coupler 8, a photodetector 9, a spectrum analyzer 10, and an optical spectrum analyzer 11. The sensor, constructed using the graphene microsphere cavity and the micro-nano optical fiber, utilizes multi-order Brillouin signals excited by the multi-mode characteristics of the graphene microsphere cavity. Based on the differences in frequency shifts caused by different gases, the sensor achieves multi-parameter gas sensing through multi-parameter cross-calculation. The system also offers advantages such as high sensitivity, fast response time, and compact size.

Description

Technical Field

[0001] The present invention belongs to the field of biochemical sensing technology, and specifically provides a multi-parameter gas sensing system based on a graphene microsphere cavity, which realizes the multi-parameter gas sensing function by utilizing the frequency response differences of multi-order Brillouin signals to different types of gases. Background Art

[0002] Sensors, as the front end of information acquisition, are the eyes, nose, and ears of modern information and communication systems, and play a very important role in modern science and technology. Gas sensors, as an important development direction in the sensor field, are increasingly receiving attention. Unlike biochemical sensing, a major feature of gas sensing is the detection of the concentration of small gas molecules. However, since gases are nanomolecules, their interaction with traditional materials is very weak and difficult to respond.

[0003] Currently, gas sensors primarily encompass several areas: gas chromatography, electrochemistry, and photoelectron detection based on novel materials. Gas chromatography, which uses FTIR technology to detect gas absorption spectra, offers the advantage of multi-parameter resolution. However, this method suffers from relatively low sensitivity, slow integration speed, and a large instrument footprint. Electrochemistry also suffers from shortcomings such as slow response, low sensitivity, poor electromagnetic interference resistance, and difficulty in achieving multi-parameter sensing capabilities. Therefore, it is crucial to design gas sensors that combine high sensitivity, fast response, and multi-parameter sensing capabilities.

[0004] Fiber-optic sensors based on fiber-optic sensing technology are gaining increasing attention due to their high sensitivity, resistance to electromagnetic interference, and fast response speed. Sensors designed by combining different fiber structures with two-dimensional materials with different properties have advantages such as high sensitivity, good biocompatibility, miniaturization, and integration. They are of great value in the field of multifunctional, highly sensitive, rapid on-site detection, especially gas detection. Currently, representative gas sensors are based on micro-nano fiber structures and D-shaped fiber-based gas sensors. Both have significant advantages in miniaturization, integration, and resistance to electromagnetic interference. However, due to the structural limitations of the devices themselves, the interaction length between light and matter is limited, which limits further improvements in the sensitivity of fiber-optic gas sensors. At the same time, current fiber-optic sensing technology faces problems such as a limited number of channels and the simultaneous influence of the measured gas concentration and other signals (temperature, humidity, vibration) on the transmitted optical signal. This reduces the sensing sensitivity of the measured gas and makes it difficult to measure multiple parameters. Summary of the Invention

[0005] The purpose of the present invention is to address the problems of low sensitivity and inability to perform multi-parameter sensing in existing optical fiber gas sensors, and to provide a multi-parameter gas sensing system based on a graphene microsphere cavity. The present invention adopts a graphene microsphere cavity and a micro-nano optical fiber to form a sensor, utilizes the multi-order Brillouin signal excited by the multi-mode characteristics of the graphene microsphere cavity, and based on the difference in frequency drift caused by different types of gases to the multi-order Brillouin signal, finally realizes a highly sensitive multi-parameter gas sensing function through a multi-parameter cross solution.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A multi-parameter gas sensing system based on a graphene microsphere cavity comprises: a vacuum cavity 1, a graphene microsphere cavity 2, a micro-nano optical fiber 3, a fixture 4, a tunable narrow linewidth laser 5, a polarization controller 6, a single-mode circulator 7, a 2×2 single-mode coupler 8, a photodetector 9, a spectrum analyzer 10, and an optical spectrum analyzer 11; the system is characterized in that:

[0008] The graphene microsphere cavity 2, micro-nano optical fiber 3 and clamp 4 are all placed in a vacuum cavity, and the graphene microsphere cavity is placed on the clamp; the tunable narrow linewidth laser 5 emits a pump light signal, and the light signal passes through the polarization controller 6 and is transmitted from the first port of the single-mode circulator 7 to the second port and enters the micro-nano optical fiber 3. The light signal transmitted through the micro-nano optical fiber 3 is coupled into the graphene microsphere cavity 2, and the graphene microsphere cavity 2 generates multi-order Brillouin signals. The even-order Brillouin signals are output to the 2×2 single-mode coupler 8 along with the forward light signal, and the odd-order Brillouin signals are transmitted from the second port of the single-mode circulator 7 to the third port along with the reverse light signal and output to the 2×2 single-mode coupler 8. The 2×2 single-mode coupler 8 couples the forward light signal and the reverse light signal and outputs them to the photodetector 9 and the spectrum analyzer 11. The photodetector 9 is connected to the spectrum analyzer 10.

[0009] Furthermore, the graphene microsphere cavity and the micro-nano optical fiber constitute a gas sensor based on the graphene microsphere cavity. The graphene microsphere cavity is composed of a microsphere cavity 2-1 and a single-layer graphene 2-2. The diameter of the microsphere cavity is 600 to 800 microns. The single-layer graphene is attached to the upper hemisphere surface of the microsphere cavity and the vertical distance from the equatorial plane is 150 to 250 microns. The area of the single-layer graphene is greater than 2×10 3 square micron, the distance between the micro-nano optical fiber and the graphene microsphere cavity is less than 0.5 nanometers.

[0010] Furthermore, the quality factor of the graphene microsphere cavity is greater than 5×10 7 The radius of the micro-nano optical fiber is less than 1 micron, and the loss of the micro-nano optical fiber is less than 0.1 dB / km.

[0011] Furthermore, the frequency of the optical signal emitted by the tunable narrow linewidth laser is located in any resonance mode of the graphene microsphere cavity.

[0012] Furthermore, the sweep frequency range of the tunable narrow linewidth laser is 1550-1551 nanometers, the minimum scanning accuracy of the laser is less than 100 Hz, and the output laser linewidth is less than 1 kHz.

[0013] Furthermore, the fixture is equipped with a temperature controller to ensure that the system operates at a constant temperature.

[0014] Furthermore, the multi-parameter gas sensing method according to the multi-parameter gas sensing system based on the graphene microsphere cavity is characterized by comprising the following steps:

[0015] Step 1: Dry nitrogen is introduced into the vacuum chamber to make the pressure inside the chamber equal to standard atmospheric pressure, and the beat frequency signal in the spectrum of the multi-order Brillouin signal in the initial state is measured. N is the order of the multi-order Brillouin signal;

[0016] Step 2: calibrate the sensitivity coefficient matrix of the multi-parameter mixed gas to be measured;

[0017] For the nth gas, within the gas sensing concentration range Internal equal spacing setting M n Each calibration concentration The gas sample is passed into the vacuum chamber for measurement to obtain the corresponding beat frequency signal

[0018] Then calculate the corresponding frequency drift

[0019] Will Respectively Perform linear fitting and obtain the fitting coefficients in turn The fitting coefficient is used as the sensitivity coefficient;

[0020] After calibrating the sensitivity coefficients of all gases, the sensitivity coefficient matrix S is obtained:

[0021]

[0022] Step 3: Pass the multi-parameter mixed gas to be measured into the vacuum chamber and measure the corresponding beat frequency signal Then the frequency drift is calculated

[0023] Substitute the frequency drift into the following formula:

[0024]

[0025] Then the concentrations of the 1st to Nth gases in the multi-parameter mixed gas to be measured are calculated as follows:

[0026] Furthermore, the value range of N is 1 to 6.

[0027] Based on the above technical solution, the beneficial effects of the present invention are:

[0028] A multi-parameter gas sensing system based on a graphene microsphere cavity is proposed. The sensor is composed of a graphene microsphere cavity and a micro-nano optical fiber. Based on the optical Brillouin effect, the multi-mode characteristics of the graphene microsphere cavity excite multi-order Brillouin signals. Through the design of specific structural parameters in the sensor (the diameter of the microsphere cavity is 600 to 800 microns, the single-layer graphene is attached to the upper hemisphere surface of the microsphere cavity, and the vertical distance from the equatorial plane is 150 to 250 microns, and the area of the single-layer graphene is greater than 2×10 3 Square microns, the distance between the micro-nano optical fiber and the graphene microsphere cavity is less than 0.5 nanometers), so that the graphene only coincides with the high-order optical modes related to the generation of multi-order Brillouin signals. When gas molecules are adsorbed on the graphene, the refractive index of the graphene changes, which only causes the Brillouin signal frequency to drift; different types of gases cause different Brillouin signal frequency drifts. Based on the difference in frequency drift, a high-sensitivity multi-parameter gas sensing function is finally achieved through multi-parameter cross-solution.

[0029] Moreover, the number of gas types in the present invention is the same as the order of the multi-order Brillouin signal generated by the graphene microsphere cavity. By adjusting the frequency of the input pump light signal, the order of the multi-order Brillouin signal can be adjusted, thereby adapting the number of gas types to be detected in the mixed gas.

[0030] At the same time, even-order and odd-order Brillouin signals are emitted from the transmission end and reflection end of the micro-nano optical fiber respectively, and then the optical signals at the transmission end and reflection end are coupled and output through a 2×2 single-mode coupler. This design can significantly improve the signal-to-noise ratio of multi-order Brillouin signals.

[0031] In summary, the present invention proposes a multi-parameter gas sensing system based on a graphene microsphere cavity, which can realize the concentration measurement of more than three gas components, and significantly improves the sensitivity based on the unique cavity characteristics of the graphene microsphere cavity, and the measurement sensitivity of various gases is better than 1ppm; at the same time, the present invention adopts heterodyne frequency demodulation to break through the time limit required by traditional signal intensity integration, and the real-time response time of the signal is less than 2s; it can be seen that the present invention has the advantages of high sensitivity, fast response time and small size while realizing the multi-parameter gas sensing function. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1Schematic diagram of the structure of the multi-parameter gas sensing system based on graphene microsphere cavity in the present invention;

[0033] Figure 2 Schematic diagram of the structure of the gas sensor based on the graphene microsphere cavity of the present invention;

[0034] Figure 3 Spectrum diagram of the third-order Brillouin signal in an embodiment of the present invention;

[0035] Figure 4 This is a spectrum diagram of the beat frequency of the third-order Brillouin signal in an embodiment of the present invention;

[0036] Figure 5 10 ppm CO2 gas spectrum response diagram of the multi-parameter gas sensing system in an embodiment of the present invention;

[0037] Among them: 1 is a vacuum cavity, 2 is a graphene microsphere cavity, 3 is a micro-nano optical fiber, 4 is a clamp, 5 is a tunable narrow-linewidth laser, 6 is a polarization controller, 7 is a single-mode circulator, 8 is a 2×2 single-mode coupler, 9 is a photodetector, 10 is a spectrum analyzer, and 11 is an optical spectrum analyzer. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solutions and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0039] This embodiment provides a multi-parameter gas sensing system based on a graphene microsphere cavity, which relies on the high-order Brillouin excitation caused by the multi-mode characteristics of the graphene microsphere cavity, so that it has the characteristics of multi-parameter and high-sensitivity sensing; the multi-parameter gas sensing system is as follows Figure 1 As shown, it includes: a vacuum cavity 1, a graphene microsphere cavity 2, a micro-nano optical fiber 3, a fixture 4, a tunable narrow linewidth laser 5, a polarization controller 6, a single-mode circulator 7, a 2×2 single-mode coupler 8, a photodetector 9, a spectrum analyzer 10 and an optical spectrum analyzer 11; more specifically:

[0040] The graphene microsphere cavity 2 and the micro-nano optical fiber 3 constitute a gas sensor based on the graphene microsphere cavity. The graphene microsphere cavity 2 is composed of a microsphere cavity 2-1 and a single-layer graphene 2-2. The microsphere cavity is prepared by melting the end of the optical fiber through electrode discharge in a special optical fiber fusion splicer. The diameter of the obtained microsphere cavity is 600 to 800 microns. The maximum diameter of the microsphere cavity perpendicular to the optical fiber is regarded as the equatorial plane. The single-layer graphene is attached to the upper hemisphere surface of the microsphere cavity, and the vertical distance from the equatorial plane is 150 to 250 microns. The area of the single-layer graphene is greater than 2×10 3square micrometers, the radius of the micro-nano optical fiber is less than 1 micron, and the distance between the micro-nano optical fiber and the graphene microsphere cavity is less than 0.5 nanometers; specifically: in this embodiment, the radius of the micro-nano optical fiber is 1 micron, the radius of the microsphere cavity is 700 microns, the single-layer graphene is transferred to the surface of the silica microsphere cavity by a dry transfer method, the vertical distance from the equatorial plane is 200 microns, and the transferred graphene area is 2.4×10 3 square micrometer;

[0041] The graphene microsphere cavity 2, micro-nano optical fiber 3 and clamp 4 are all placed in the vacuum cavity 1, and the graphene microsphere cavity 2 is placed on the clamp 4. The clamp 4 has a temperature controller and a stable temperature at 25°. The graphene microsphere cavity, micro-nano optical fiber and the clamp with a stable temperature are all placed in the vacuum cavity, which can avoid the influence of ambient temperature instability and other gas components in the air on the test results to the greatest extent; the tunable narrow linewidth laser 5 is used as a pump input to emit a light signal, and the light signal is transmitted from the first port of the single-mode circulator 7 to the second port after passing through the polarization controller 6 and enters the micro-nano optical fiber 3. The light signal transmitted through the micro-nano optical fiber 3 is coupled into the graphene microsphere cavity 2, and the graphene microsphere cavity 2 generates a multi-order Brillouin signal , the even-order Brillouin signal is output to the 2×2 single-mode coupler 8 along with the forward light signal (transmitted light signal), and the odd-order Brillouin signal is transmitted from the second port of the single-mode circulator 7 to the third port along with the reverse light signal (reflected light signal) and output to the 2×2 single-mode coupler 8. The 2×2 single-mode coupler 8 couples the forward light signal and the reverse light signal and outputs them to the photodetector 9 and the spectrum analyzer 11. The photodetector 9 is connected to the spectrum analyzer 10. Specifically: in this embodiment, the sweep frequency range of the tunable narrow-linewidth laser is: 1550~1551 nanometers, the laser linewidth is: 1kHz, and the minimum scanning accuracy is: 100Hz. The selection of this parameter can significantly improve the efficiency and stability of the output multi-order Brillouin signal.

[0042] Based on the multi-parameter gas sensing system described above, the frequency of the optical signal emitted by the tunable narrow-linewidth laser is controlled so that the frequency of the optical signal transmitted through the micro-nano optical fiber falls within any resonant mode of the graphene microsphere cavity, thereby controlling the order of the generated Brillouin signal. The directions of the multiple Brillouin orders in the graphene microsphere cavity are different. Odd-order Brillouin signals propagate in the opposite direction of the pump light in the graphene microsphere cavity, i.e., the reverse optical signal (reflected optical signal). Even-order Brillouin signals propagate in the same direction as the pump light in the graphene microsphere cavity, i.e., the forward optical signal (transmitted optical signal). The mixed gas to be measured is introduced into the vacuum cavity. When the graphene attached to the microsphere cavity adsorbs gas molecules, it will change the refractive index of the Brillouin high-order mode that coincides with the graphene, and thus change the corresponding Brillouin high-order mode frequency. Due to the different effects of different types of gas molecules on the refractive index, the frequency of the corresponding high-order Brillouin signal changes. By analyzing the influence of different types of gases on multi-order Brillouin signals, the corresponding multi-parameter sensing function is realized. It should be noted that the order of the Brillouin signal determines the number of parameters, that is, an N-order Brillouin signal can realize multi-parameter sensing of N gases. In other words, when multi-parameter sensing of N gases is required, it is only necessary to control the order of the generated Brillouin signal to N.

[0043] In this embodiment, in order to achieve multi-parameter sensing of three gases, ammonia, carbon dioxide, and nitrogen dioxide, the frequency of the optical signal coupled to the graphene microsphere cavity is adjusted (located in any resonant mode of the graphene microsphere cavity), so that the pump light outputs a third-order Brillouin signal through the graphene microsphere cavity. By adjusting the polarization, the signal-to-noise ratio of the Brillouin signal can be improved. During the measurement process: first, dry nitrogen is introduced into the vacuum cavity as the background atmosphere (so that the pressure in the cavity is standard atmospheric pressure), and the spectrum diagram and the spectrum diagram in the initial state are measured; as shown in FIG. Figure 3 The figure shows the spectrum of the third-order Brillouin signal collected by the spectrum analyzer, which has four resonance peaks f pump 、f A 、f B With f c , f pump is the input pump light signal, f A 、f B With f c are the three Brillouin signals excited by the pump light. The number of Brillouin signals displayed on the spectrometer is the order of the excited Brillouin signals. pump With f A 、f A With f B 、f B With f c , the beat frequency signal and Corresponding to Figure 4 The beat frequency signal in the spectrum diagram shown and like Figure 4 The figure shows the spectrum of the third-order Brillouin signal acquired by the spectrum analyzer, which has three beat frequency signals. and Then, the three gases with preset concentrations are introduced into the vacuum chamber respectively. After about 1 minute of the gas introduction, the corresponding third-order Brillouin signal data are collected using an optical spectrum analyzer and a frequency spectrum analyzer, and the sensitivity coefficient matrix S is calibrated based on the data; finally, the mixed gas to be tested is introduced into the vacuum chamber, the third-order Brillouin signal data is measured, and the concentrations of the three gases are calculated based on the data.

[0044] Specifically: the sensitivity coefficient of each gas is calibrated to obtain the sensitivity coefficient matrix S of multi-parameter sensing; for the first gas, in the gas sensing concentration range Set M1 calibration concentrations at equal intervals within the The gas sample is measured to obtain the corresponding beat frequency signal and Then calculate the corresponding frequency drift and

[0045]

[0046] like Figure 5 The figure shows the frequency drift for 10 ppm CO2 gas in this embodiment;

[0047] Will Respectively Perform linear fitting and use the fitting coefficient as the sensitivity coefficient to obtain the sensitivity coefficients of the first gas under the three beat frequency signals in turn. and

[0048] The sensitivity coefficients of the second and third gases are calibrated as above, and the corresponding sensitivity coefficients are obtained. and Then the sensitivity coefficient matrix S of the multi-parameter sensing for the three gases of ammonia, carbon dioxide and nitrogen dioxide in this embodiment is obtained:

[0049]

[0050] Based on the sensitivity coefficient matrix S of the multi-parameter sensor, the mixed gas to be measured is measured to obtain the beat frequency signal and Then the frequency response is calculated and

[0051]

[0052] Substitute the frequency response into the following formula:

[0053]

[0054] The concentrations of the first, second and third gases in the mixed gas to be measured are calculated as and

[0055] It should be noted that: in the above-mentioned sensitivity coefficient calibration process, for each gas, the gas sensing concentration range can be the same or different, the number of calibration concentrations can be the same or different, and the intervals between calibration concentrations can be the same or different, which will not affect the technical solution of the present invention.

[0056] The above description is only a specific embodiment of the present invention. Any feature disclosed in this specification, unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes; all disclosed features, or all steps in the methods or processes, except for mutually exclusive features and / or steps, can be combined in any way.

Claims

1. A multi-parameter gas sensing system based on a graphene microsphere cavity, comprising: A vacuum cavity (1), a graphene microsphere cavity (2), a micro-nano optical fiber (3), a fixture (4), a tunable narrow linewidth laser (5), a polarization controller (6), a single-mode circulator (7), a 2×2 single-mode coupler (8), a photodetector (9), a spectrum analyzer (10) and an optical spectrum analyzer (11); characterized in that: The graphene microsphere cavity (2), the micro-nano optical fiber (3) and the fixture (4) are all placed in a vacuum cavity, and the graphene microsphere cavity is placed on the fixture (4); the tunable narrow linewidth laser (5) emits a pump light signal, and the light signal passes through a polarization controller (6) and is transmitted from the first port of a single-mode circulator (7) to the second port and enters the micro-nano optical fiber (3); the light signal transmitted through the micro-nano optical fiber (3) is coupled into the graphene microsphere cavity (2); the graphene microsphere cavity (2) generates multi-order Brillouin signals, and the even-order Brillouin signals are output to a 2×2 single-mode coupler (8) along with the forward light signal; the odd-order Brillouin signals are transmitted from the second port of the single-mode circulator (7) to the third port and output to the 2×2 single-mode coupler (8) along with the reverse light signal; the 2×2 single-mode coupler (8) couples the forward light signal and the reverse light signal and outputs them to a photodetector (9) and a spectrum analyzer (11); the photodetector (9) is connected to the spectrum analyzer (10).

2. The multi-parameter gas sensing system based on graphene microsphere cavity according to claim 1, characterized in that: The graphene microsphere cavity and the micro-nano optical fiber constitute a gas sensor based on the graphene microsphere cavity. The graphene microsphere cavity is composed of a microsphere cavity (2-1) and a single-layer graphene (2-2). The diameter of the microsphere cavity is 600 to 800 microns. The single-layer graphene is attached to the upper hemisphere surface of the microsphere cavity and the vertical distance from the equatorial plane is 150 to 250 microns. The area of the single-layer graphene is greater than 2×10 3 square micron, the distance between the micro-nano optical fiber and the graphene microsphere cavity is less than 0.5 nanometers.

3. The multi-parameter gas sensing system based on graphene microsphere cavity according to claim 1, characterized in that: The frequency of the optical signal emitted by the tunable narrow linewidth laser is located in any resonance mode of the graphene microsphere cavity.

4. The multi-parameter gas sensing system based on graphene microsphere cavity according to claim 1, characterized in that: The quality factor of the graphene microsphere cavity is greater than 5×10 7 .

5. The multi-parameter gas sensing system based on graphene microsphere cavity according to claim 1, characterized in that: The radius of the micro-nano optical fiber is less than 1 micron, and the loss of the micro-nano optical fiber is lower than 0.1 dB / km.

6. The multi-parameter gas sensing system based on graphene microsphere cavity according to claim 1, characterized in that: The sweep frequency range of the tunable narrow linewidth laser is 1550-1551 nanometers, the minimum scanning accuracy of the laser is less than 100 Hz, and the output laser linewidth is less than 1 kHz.

7. The multi-parameter gas sensing system based on graphene microsphere cavity according to claim 1, characterized in that: The fixture is equipped with a temperature controller to prevent the influence of temperature changes on the sensing results.

8. The multi-parameter gas sensing method of the multi-parameter gas sensing system based on the graphene microsphere cavity according to claim 1, characterized in that: The following steps are involved: Step 1: Dry nitrogen is introduced into the vacuum chamber to make the pressure inside the chamber equal to standard atmospheric pressure, and the beat frequency signal in the spectrum of the multi-order Brillouin signal in the initial state is measured. N is the order of the multi-order Brillouin signal; Step 2: calibrate the sensitivity coefficient matrix of the multi-parameter mixed gas to be measured; For the nth gas, within the gas sensing concentration range Internal equal spacing setting M n Each calibration concentration The gas sample is passed into the vacuum chamber for measurement to obtain the corresponding beat frequency signal n=1,2,...,N,m=1,2,...,M n ; Then calculate the corresponding frequency drift Will Respectively Perform linear fitting and obtain the fitting coefficients in turn The fitting coefficients are used as sensitivity coefficients; After calibrating the sensitivity coefficients of all gases, the sensitivity coefficient matrix S is obtained: Step 3: Pass the multi-parameter mixed gas to be measured into the vacuum chamber and measure the corresponding beat frequency signal Then the frequency drift is calculated Substitute the frequency drift into the following formula: The concentrations of the first to N gases in the multi-parameter mixed gas to be measured are calculated as follows:

9. The multi-parameter gas sensing method of the multi-parameter gas sensing system based on the graphene microsphere cavity according to claim 8, characterized in that: The value of N ranges from 1 to 6.

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