Single optical fiber type multi-reflection enhanced photoacoustic gas sensor and detection method thereof

Abstract

The invention discloses a single optical fiber type multiple reflection enhanced photoacoustic gas sensor and a detection method thereof. The sensor comprises a single-mode optical fiber, a 3D printing type shell, a spherical multi-reflection cavity, a diaphragm unit, a cantilever beam sound wave sensing unit and an air hole. The optical fiber end face of a traditional single-optical-fiber type photoacoustic gas sensor must be flush with the end face of a sound wave sensing unit, so that multiple reflections cannot be realized to further improve the gas detection sensitivity; according to the invention, the problem that a traditional single-fiber photoacoustic gas sensor cannot improve the gas detection sensitivity through a multi-reflection mode is solved, and high sensitivity and high stability of the cantilever beam sound wave sensing unit are maintained. The single optical fiber type multiple reflection enhanced photoacoustic gas sensor is good in stability, simple in structure, high in sensitivity, good in signal-to-noise ratio and low in detection limit. The invention provides a new thought for a high-sensitivity single-optical-fiber long-distance telemetering type photoacoustic sensor, and has a huge application prospect in the field of photoacoustic spectroscopy.

Description

Technical Field

[0001] This invention belongs to the field of photoacoustic spectroscopy and trace gas detection technology, and relates to a single-fiber type multiple reflection enhanced photoacoustic gas sensor and its detection method. Background Technology

[0002] Laser photoacoustic spectroscopy gas sensors based on optical detection technology are a highly selective, highly sensitive, and background-free method for measuring trace gases, and have been successfully applied in fields such as environmental pollution, aerospace, and medical diagnostics. In recent years, non-resonant photoacoustic spectroscopy sensors, due to their small size, can achieve long-distance in-situ telemetry of trace gases, making them not only convenient to carry but also capable of real-time and rapid monitoring of trace gas concentration changes. Traditional non-resonant photoacoustic spectroscopy sensors all use one optical fiber to excite the gas and another optical fiber to detect the photoacoustic signal. The presence of two optical fibers occupies too much space, therefore, the literature Z.Gong,G.Wu,K.Chen,M.Guo,J.Ma,H.Li,F.Ma,L.Mei,W.Peng,Q.Yu,Fiber-tip gas transducer based on all-optical photoacousticspectroscopy,Journal of Lightwave Technology,2022,40(15),5300-5306. A single-fiber photoacoustic gas sensor was designed, significantly reducing its size. However, the sensor's absorption optical path is too short, resulting in poor performance. The magnitude of the photoacoustic signal is positively correlated with the absorption optical path, making increasing the absorption optical path of the single-fiber photoacoustic gas sensor a challenge. Another effective method to increase the gas absorption optical path is to design the optical path to cause multiple reflections of light, thereby increasing the interaction between light and gas. However, in traditional single-fiber photoacoustic gas sensors, the fiber end face must be flush with the end face of the acoustic wave sensing unit; therefore, traditional single-fiber photoacoustic gas sensors cannot achieve a multi-reflection optical path.

[0003] In summary, designing a single-fiber photoacoustic spectroscopy gas sensor that undergoes multiple reflections in a small space has significant application value for high-sensitivity, long-distance, real-time, in-situ monitoring of trace gases. Summary of the Invention

[0004] To address the aforementioned problems, this invention proposes a single-fiber multiple reflection enhanced photoacoustic gas sensor and its detection method. This gas sensor has a small overall size, solves the problem of low sensitivity in traditional single-fiber photoacoustic gas sensors, and can perform high-sensitivity, long-distance, real-time, in-situ monitoring of trace gases, showing great promise for applications in the field of photoacoustic spectroscopy.

[0005] The technical solution of the present invention:

[0006] A single-fiber multiple reflection enhanced photoacoustic gas sensor, the main structure of which includes a 3D printed shell on the left and a 3D printed shell on the right, with a high reflectivity diaphragm unit disposed between the two, and small holes opened on the high reflectivity diaphragm unit.

[0007] The interior of the 3D-printed shell on the left is a spherical multi-reflection cavity with a gold film deposited on its inner wall; the end of the spherical multi-reflection cavity is a high-reflectivity diaphragm unit.

[0008] The 3D-printed shell on the right has a hollow cavity inside, with an inclined cantilever beam acoustic wave sensing unit placed at its end.

[0009] A single-mode fiber is inserted into a spherical multiple reflection cavity, with an inclined angle between its end face and the horizontal plane, so that the reflected excitation light is reflected the most times in the spherical multiple reflection cavity.

[0010] The end face of the single-mode fiber is flush with the end face of the cantilever beam acoustic wave sensing unit, and the distance between them is controlled between 1mm and 1.76mm. This design allows the transmitted light to be used for two-beam interference between the single-mode fiber and the cantilever beam acoustic wave sensing unit. Furthermore, the photoacoustic signal generated in the cavity corresponding to the 3D printed housing on the right will be superimposed with the photoacoustic signal generated by multiple reflections, thereby further improving the sensitivity of gas detection.

[0011] The radius of the spherical multiple reflection cavity is 2mm, and the vent is opened at its 1 / 2 position. The advantage of this design is that when the excitation light is reflected in the reflection cavity, it will not be transmitted into the free space, and the final effect of up to 5 reflections can be achieved.

[0012] The 3D printed shell on the left and the 3D printed shell on the right are connected by threads.

[0013] The high-reflectivity film unit is a film unit with a reflectivity of 80%.

[0014] The tilt angle between the end face of the single-mode fiber and the horizontal plane is 30°.

[0015] The 3D printed shell and internal structure are both manufactured using photosensitive resin (density = 1.3 g / cm³) through 3D printing technology, with a manufacturing precision of 0.05-0.1 mm.

[0016] A gas detection method using a single-fiber multiple reflection enhanced photoacoustic gas sensor is disclosed. The excitation beam emitted from the single-mode fiber passes through a high-reflectivity diaphragm unit, and the reflected light undergoes multiple reflections within a spherical multiple reflection cavity in a 3D-printed shell on the left. This results in a photoacoustic effect with the gas, and the photoacoustic signal is transmitted to a cantilever beam acoustic wave sensing unit through a small hole in the high-reflectivity diaphragm unit. The transmitted light is used to generate a photoacoustic effect with the gas in the hollow cavity, and also to generate a two-beam interference between the single-mode fiber and the cantilever beam acoustic wave sensing unit. The vibration change of the cantilever beam acoustic wave sensing unit is then fed back to a computer, thereby calculating the concentration of the gas to be measured.

[0017] The beneficial effects of this invention are as follows: This invention provides a single-fiber multiple reflection enhanced photoacoustic gas sensor and its detection method. This gas sensor has a small overall size, solving the problem of low sensitivity caused by the short absorption optical path of traditional single-fiber photoacoustic gas sensors. The design of the two cavities in this sensor allows the photoacoustic signals generated by each cavity to be superimposed, further increasing the sensitivity of gas detection. This single-fiber multiple reflection enhanced photoacoustic gas sensor has good stability, simple structure, low sensitivity, good signal-to-noise ratio, and low detection limit. This invention provides a new approach for long-distance telemetry photoacoustic sensors and has great application prospects in the field of photoacoustic spectroscopy. Attached Figure Description

[0018] Figure 1 This invention relates to a single-fiber type multiple reflection enhanced photoacoustic gas sensor.

[0019] In the diagram: 1 Single-mode fiber; 2 Left 3D printed housing; 3 Spherical cavity with multiple reflections; 4 High-reflectivity diaphragm unit; 5 Right 3D printed housing; 6 Cantilever beam acoustic wave sensing unit; 7 Small hole; 8 Air hole; 9 Tilt angle. Detailed Implementation

[0020] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and technical solutions.

[0021] Figure 1 This is a schematic diagram of a single-fiber, multiple-reflection enhanced photoacoustic gas sensor according to the present invention. Figure 1As shown, the single-fiber multiple reflection enhanced photoacoustic gas sensor provided in this embodiment of the invention includes a single-mode fiber 1, a 3D-printed housing 2 on the left, a spherical multiple reflection cavity 3, a high-reflectivity diaphragm unit 4, a 3D-printed housing 5 on the right, a cantilever beam acoustic wave sensing unit 6, a small hole 7, an air vent 8, and a tilt angle 9. The gas to be measured enters the spherical multiple reflection cavity 3 through the air vent 6. The excitation beam emitted by the single-mode fiber 1 passes through the diaphragm unit 4 with a reflectivity of 80%, and then interacts with the gas to produce a photoacoustic effect. The photoacoustic signal is transmitted to the cantilever beam acoustic wave sensing unit through the small hole 7 of the high-reflectivity diaphragm unit 4. The transmitted light is used on one hand to produce a photoacoustic effect with the gas in the hollow cavity, and on the other hand, it is used to generate a two-beam interference between the single-mode fiber 1 and the cantilever beam acoustic wave sensing unit 6. The vibration change of the cantilever beam acoustic wave sensing unit is fed back to the computer, thereby calculating the concentration of the gas to be measured.

[0022] Experimental Example 1:

[0023] Traditional single-fiber photoacoustic gas sensors can be found in the literature Z.Gong, G.Wu, K.Chen, M.Guo, J.Ma, H.Li, F.Ma, L.Mei, W.Peng, Q.Yu, Fiber-tip gas transducer based on all-optical photoacoustic spectroscopy, Journal of Lightwave Technology, 2022, 40(15), 5300-5306. Since its FP cavity length does not exceed 1.5mm, the gas absorption optical path does not exceed 3mm, and the normalized equivalent noise figure for methane gas detection is 4.57×10⁻⁶. -7 cm -1 WHz -1 / 2 .

[0024] Experimental Example 2:

[0025] The optimized single-fiber multiple reflection enhanced photoacoustic gas sensor has a gas absorption optical path length close to 15 mm, which is 5 times that of the single-fiber photoacoustic gas sensor. Therefore, the normalized equivalent noise figure of the optimized single-fiber multiple reflection enhanced photoacoustic gas sensor for methane is approximately 9.14 × 10⁻⁶. -8 cm -1 WHz -1 / 2 .

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A single-fiber multi-reflection enhanced photoacoustic gas sensor, It is characterized in that The main structure of the single-fiber multiple-reflection enhanced photoacoustic gas sensor includes a 3D printed shell on the left and a 3D printed shell on the right, with a high-reflectivity diaphragm unit arranged between the two, and a small hole is opened on the high-reflectivity diaphragm unit; The interior of the 3D printed shell on the left is a spherical multiple reflection cavity with a gold film evaporated on its inner wall; the end of the spherical multiple reflection cavity is a high reflectivity diaphragm unit; The interior of the 3D printed shell on the right is a hollow cavity, and a tilted cantilever beam acoustic wave sensor unit is placed at its end; The single-mode optical fiber extends into the spherical multiple-reflection cavity, and there is an inclination angle between the end face of the optical fiber and the horizontal plane, so that the reflected excitation light is reflected the most times in the spherical multiple-reflection cavity.

2. The single-fiber multiple-reflection enhanced photoacoustic gas sensor according to claim 1, It is characterized in that The end face of the single-mode optical fiber is flush with the end face of the cantilever beam acoustic wave sensor unit, and the distance between the two is controlled between 1 mm and 1.76 mm.

3. The single-fiber multi-reflection enhanced photoacoustic gas sensor according to claim 1, It is characterized in that The radius of the spherical multiple reflection cavity is 2 mm, and the air hole is opened at the 1 / 2 position thereof.

4. The single-fiber multi-reflection enhanced photoacoustic gas sensor according to claim 1, It is characterized in that The 3D printed housing on the left and the 3D printed housing on the right are connected by threads.

5. The single-fiber multi-reflection enhanced photoacoustic gas sensor according to claim 1, It is characterized in that The high reflectivity diaphragm unit is a diaphragm unit with a reflectivity of 80%.

6. The single-fiber multi-reflection enhanced photoacoustic gas sensor according to claim 1, It is characterized in that The tilt angle between the single-mode optical fiber end face and the horizontal plane is 30°.

7. A method for gas detection using single-fiber multi-reflection enhanced photoacoustic gas sensing, It is characterized in that After the excitation light beam emitted by the single-mode optical fiber passes through the high-reflectivity diaphragm unit, the reflected light forms multiple reflections in the spherical multiple-reflection cavity in the 3D-printed shell on the left, and then produces photoacoustic effect with the gas and transmits the photoacoustic signal to the cantilever beam acoustic wave sensor unit through the small holes of the high-reflectivity diaphragm unit. On the one hand, the transmitted light is used to produce photoacoustic effect with the gas in the hollow cavity, and on the other hand, it is used to produce double-beam interference between the single-mode optical fiber and the cantilever beam acoustic wave sensor unit to sense the vibration change of the cantilever beam acoustic wave sensor unit, and then infer the concentration of the gas to be measured.

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