Interferometric carbon dioxide sensor based on optical fiber Fabry-Perot

Abstract

The utility model discloses an interference type carbon dioxide sensor based on optical fiber Fabry-Perot, and relates to the technical field of optical sensors. Comprising a photoacoustic cell; the hollow microspheres are located in the photoacoustic cell, and the hollow microspheres are of hollow spherical structures made of hollow core optical fibers; the microsphere seams are formed in the hollow microspheres; the gas sensitive film covers the outer surface of the hollow microsphere; one end of the detection optical fiber extends into the photoacoustic cell and is connected with the outer surface of the hollow microsphere. The high-sensitivity pressure sensing of the Fabry-Perot interference structure and the expansion effect of the gas sensitive film are utilized, the gas concentration is converted into FPI bubble pressure, the gas detection sensitivity is extremely high, and ultralow detection limit monitoring can be achieved.

Description

Technical Field

[0001] The present application relates to the technical field of optical sensors, and in particular to a carbon dioxide sensor based on optical fiber Fabry-Perot interferometry. Background Art

[0002] There are many trace gases in the atmosphere, with concentrations in the ppt-ppm range. Although their contents are very low, they have a great impact on the environment, such as greenhouse gas carbon dioxide. Long-term monitoring of greenhouse gases such as carbon dioxide in the region is of great scientific significance for carbon peak and carbon neutrality. Accurate measurement of the concentration of gases such as carbon dioxide is of great significance to the future development of the atmospheric environment.

[0003] In order to implement effective supervision of various types of pollutant gases and pollutant emissions, more and more sensor devices have emerged. These devices mainly achieve type identification and content analysis of the measured object through physical or chemical reactions with the measured object. Most of the existing sensors currently use electricity and related principles as the sensing mechanism. This type of gas sensor has obvious limitations in application. First, because the sensor is based on electrical principles, it cannot be used in flammable and explosive environments. Secondly, the control circuit of the sensor and other related devices are greatly affected by factors such as current, magnetic field and temperature, resulting in a large difference between the test results and the true value. Fiber optic sensors have gradually attracted people's attention due to a series of advantages such as small size, high sensitivity, anti-electromagnetic interference, acid and alkali corrosion resistance, and can be used under extreme conditions such as high temperature, high pressure and strong radiation.

[0004] At present, optical fiber sensors mainly use photoacoustic spectroscopy technology to achieve detection, and this detection technology is relatively mature. The optical fiber acoustic wave sensor in the optical fiber sensor can detect the acoustic wave signal with high sensitivity by measuring the changes in characteristic parameters such as wavelength, intensity, polarization state, and phase of the light mode transmitted in the optical fiber. Based on different sensing mechanisms, optical fiber acoustic wave sensors are mainly divided into fiber grating (FBG) type and optical fiber Fabry-Perot type acoustic wave sensing technology. The conventional FBG sensing structure is suitable for the detection of amplitude-frequency characteristics of low-frequency acoustic longitudinal waves, but the linear or point sensing structure of the conventional FBG cannot achieve efficient coupling of acoustic waves to the sensing area. The acoustic wave has obvious energy loss during the transmission along the optical fiber, which is not conducive to obtaining acoustic wave signals with high signal-to-noise ratio. The optical fiber Fabry-Perot interference sensing technology is mainly based on the phase modulation principle, that is, the acoustic wave information is sensed according to the change of the resonant wavelength or interference phase. Common optical fiber Fabry-Perot interference sensors include intrinsic interference type and extrinsic interference type sensing structures. The intrinsic interference Fabry-Perot structure mainly uses the optical fiber itself as a component of the interference cavity. Since the intrinsic Fabry-Perot cavity is placed in the optical fiber, the overall sensing structure is compact, small and stable, especially sensitive to high-frequency sound information, and has obvious advantages in the measurement of high spatial resolution and broadband sound wave information. However, the reflection surface of the intrinsic Fabry-Perot cavity is generally formed by modulating the refractive index in the optical fiber, so the light reflectivity of the reflection surface is often low, and the formed Fabry-Perot interference spectrum does not have the characteristics of high fringe visibility and high quality factor, which is difficult to meet the needs of high sensitivity and high signal-to-noise ratio sound detection. Different from the intrinsic interference Fabry-Perot sensing structure, the reflection surface of the extrinsic interference Fabry-Perot cavity is generally made of extremely thin functional materials or flattened optical fiber end faces, which have a high light reflectivity (>4%). Therefore, the extrinsic interference Fabry-Perot cavity structure is not limited to the optical fiber itself, and generally uses specific materials or air media to construct the interference cavity. The existing technology generally uses thin film sheets such as graphene, silver film, and silicon wafers to construct the reflective surface of the Fabry-Perot cavity. By appropriately adjusting the structural parameters of the functional film (such as thickness, area, etc.), a sensing structure with different amplitude-frequency response characteristics can be obtained to detect broadband sound wave information.

[0005] For photoacoustic spectroscopy gas detection technology, in order to obtain high signal-to-noise ratio photoacoustic signals and realize full photoacoustic signal detection, it is necessary to rely on high-sensitivity fiber optic Fabry-Perot acoustic wave sensors. However, the existing fiber optic Fabry-Perot acoustic wave sensors mainly sense the changes in ambient sound pressure directly through the end face of the device, resulting in low sensor response sensitivity. Utility Model Content

[0006] The embodiment of the present application provides a carbon dioxide sensor based on optical fiber Fabry-Perot interference, which is used to solve the problem of low sensitivity of the prior art that relies on the end face of the device to sense the change of sound pressure.

[0007] The embodiment of the present application provides a carbon dioxide sensor based on optical fiber Fabry-Perot interferometry, comprising:

[0008] photoacoustic pool;

[0009] The hollow microsphere is located inside the photoacoustic cell and is a hollow spherical structure made of hollow core optical fiber;

[0010] A microsphere seam is provided on the hollow microsphere;

[0011] A gas-sensitive film covers the outer surface of the hollow microsphere;

[0012] One end of the detection optical fiber extends into the photoacoustic cell and is connected to the outer surface of the hollow microsphere.

[0013] In a possible implementation, the photoacoustic cell has an air inlet and an air outlet.

[0014] In a possible implementation, the hollow microspheres are formed by subjecting the hollow core optical fiber to multiple discharge treatments.

[0015] In a possible implementation, the hollow core optical fiber is subjected to multiple discharge treatments to form a closed hollow spherical structure, and a focused femtosecond laser is used to form a micro-spherical gap on the closed hollow spherical structure.

[0016] In a possible implementation, the gas-sensitive membrane is formed by covering the outer surface of the hollow microsphere with nanomaterials using electrospinning technology, a pulling method or a dripping method.

[0017] In a possible implementation, the nanomaterial is ZnO or a polymer material.

[0018] The optical fiber Fabry-Perot interferometer carbon dioxide sensor in this application has the following advantages:

[0019] 1. The fiber-optic Fabry-Perot interferometer carbon dioxide sensor utilizes the high-sensitivity pressure sensing of the Fabry-Perot interferometer (FPI) structure and the expansion effect of the gas-sensitive film to convert the gas concentration into FPI bubble pressure. It has extremely high gas detection sensitivity and can achieve ultra-low detection limit monitoring.

[0020] 2. The hollow microsphere sensing structure made by optical fiber microstructure processing technology has a gas-sensitive film on the surface of the microsphere, which has the advantages of simple process, compactness, and high visibility of interference fringes. Combined with the unique FPI bubble packaging technology, it can sense pressure signals in real time and stably. Combined with the high response sensitivity of the optical fiber sensor, it can achieve high-precision sound wave detection.

[0021] 3. The all-optical fiber Fabry-Perot interferometry carbon dioxide sensing gas detection technology uses a functionally integrated optical fiber sensor as the sensing antenna for photoacoustic information. Its high sensitivity, low noise, and small size are fully adapted to the photoacoustic cell and can effectively improve the overall detection performance of the photoacoustic spectroscopy detection system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is a schematic diagram of the structure of a fiber-optic Fabry-Perot interferometer carbon dioxide sensor provided in an embodiment of the present application.

[0024] Explanation of the accompanying drawings: 100, photoacoustic cell; 110, air inlet; 120, air outlet; 200, hollow microsphere; 210, interference cavity; 220, microsphere gap; 300, gas sensitive film; 400, detection optical fiber. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] Figure 1 The present invention provides a schematic diagram of a carbon dioxide sensor based on an optical fiber Fabry-Perot interferometer. The present invention provides a carbon dioxide sensor based on an optical fiber Fabry-Perot interferometer, comprising:

[0027] Photoacoustic pool 100;

[0028] The hollow microsphere 200 is located inside the photoacoustic cell 100 and is a hollow spherical structure made of a hollow core optical fiber;

[0029] Microsphere seam 220, disposed on hollow microsphere 200;

[0030] The gas-sensitive film 300 covers the outer surface of the hollow microsphere 200;

[0031] One end of the detection optical fiber 400 extends into the photoacoustic cell 100 and is connected to the outer surface of the hollow microsphere 200 .

[0032] Exemplarily, the photoacoustic cell 100 has an air inlet 110 and an air outlet 120. The gas to be detected outside the photoacoustic cell 100 enters the photoacoustic cell 100 at a certain flow rate under the transportation of equipment such as an air pump, and the gas inside the photoacoustic cell 100 is discharged from the air outlet 120 at the same flow rate, so as to avoid inaccurate detection results caused by the pressure difference between the inside and the outside. When the carbon dioxide in the gas contacts the gas-sensitive film 300, the gas-sensitive film 300 will generate a pressure corresponding to the concentration of carbon dioxide in the gas, and the pressure will act on the hollow microsphere 200. Under the action of pressure, due to the presence of the microsphere gap 200, the hollow microsphere 200 will be deformed, specifically, the hollow microsphere 200 is squeezed and lengthened in the axial direction parallel to the microsphere gap 200. This deformation will directly affect the interference of the optical signal input from the detection optical fiber 400 on the inner surface of the hollow microsphere 200, resulting in changes in the interference of the optical signal output from the detection optical fiber 400. The data of the carbon dioxide concentration in the gas to be detected can be obtained by analyzing the interference of the optical signal output by the detection optical fiber 400.

[0033] The carbon dioxide sensor in this application can be applied to fields such as smart manufacturing, smart home, smart building, smart campus and smart agriculture.

[0034] In a possible embodiment, the hollow microspheres 200 are formed by performing multiple discharge treatments on a hollow core optical fiber.

[0035] For example, in the manufacturing process of the hollow microsphere 200, a hollow core fiber of the same material is firstly arranged at the end of the detection optical fiber 400, and the hollow core fiber has an interference cavity 210 inside. After the hollow core fiber is subjected to discharge treatment, the side wall of the hollow core fiber will be softened at high temperature, thereby expanding the interference cavity 210. After repeated discharge treatment, the interference cavity 210 will be expanded to a thickness of only a few microns on the side wall. This extremely thin hollow spherical structure is very sensitive to external pressure and therefore has a high sensitivity.

[0036] In a possible embodiment, the hollow core optical fiber is subjected to multiple discharge treatments to form a closed hollow spherical structure, and a micro-sphere gap 220 is formed on the closed hollow spherical structure using a focused femtosecond laser.

[0037] For example, the hollow microsphere 200 formed after the discharge treatment is a closed structure. In order to further improve the sensitivity, a microsphere seam 220 can be formed on the hollow microsphere 200 by laser etching. The hollow microsphere 200 can be formed into an open structure through the microsphere seam 220. This open structure can make the air pressure inside and outside the hollow microsphere 200 equal (the gas-sensitive film 300 allows gas to pass through), so the hollow microsphere 200 will only deform when the pressure generated by the gas-sensitive film 300 changes. Due to the existence of the microsphere gap 220, the pressure generated by the gas sensitive film 300 will not cause the hollow microsphere 200 to deform in the same way in all directions, that is, the hollow microsphere 200 will become longer in the axis parallel to the microsphere gap 220, and shorten in the axis perpendicular to the microsphere gap 220. This uneven deformation will increase the deformation amount, thereby improving the sensitivity of the hollow microsphere 200 to pressure changes. Under the dual effects of the micron-sized hollow microsphere 200 and the microsphere gap 220, the sensitivity of the carbon dioxide sensor in this application reaches the ppb level.

[0038] In a possible embodiment, the gas-sensitive film 300 is formed by covering the outer surface of the hollow microsphere 200 with nanomaterials using electrospinning technology, a pulling method, or a dripping method.

[0039] For example, the nanomaterial may be ZnO or a polymer material, and the thickness of the nanomaterial covering the outer surface of the hollow microsphere 200 is about 3-10 μm.

[0040] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0041] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A fiber-based Fabry-Perot interferometer carbon dioxide sensor, characterized in that: include: Photoacoustic Pool(100); A hollow microsphere (200) is located inside the photoacoustic cell (100), and the hollow microsphere (200) is a hollow spherical structure made of a hollow core optical fiber; A microsphere seam (220) is arranged on the hollow microsphere (200); A gas-sensitive film (300) covering the outer surface of the hollow microsphere (200); A detection optical fiber (400) has one end extending into the photoacoustic cell (100) and connected to the outer surface of the hollow microsphere (200).

2. The optical fiber Fabry-Perot interferometer carbon dioxide sensor according to claim 1, characterized in that: The photoacoustic cell (100) has an air inlet (110) and an air outlet (120).

3. The optical fiber Fabry-Perot interferometer carbon dioxide sensor according to claim 1, characterized in that: The hollow microspheres (200) are formed by subjecting the hollow core optical fiber to multiple discharge treatments.

4. The optical fiber Fabry-Perot interferometer carbon dioxide sensor according to claim 3, characterized in that: The hollow core optical fiber forms a closed hollow spherical structure after multiple discharge treatments, and the microsphere gap (220) is formed on the closed hollow spherical structure by using a focused femtosecond laser.

5. The optical fiber Fabry-Perot interferometer carbon dioxide sensor according to claim 1, characterized in that: The gas-sensitive film (300) is formed by covering the outer surface of the hollow microsphere (200) with nanomaterials using electrostatic spinning technology, a pulling method or a dripping method.

6. The optical fiber Fabry-Perot interferometer carbon dioxide sensor according to claim 5, characterized in that: The nano material is ZnO or a polymer material.

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