Dual optical path photo-thermal gas detection device

Abstract

The application relates to the technical field of gas detection, in particular to a double-light-path light-heat gas detection device which comprises a detection light source, a fiber splitter, a first coupler, a first gas chamber, a hollow-core optical fiber, a dichroic mirror, a pump light source, a second coupler, a reference optical fiber, a second gas chamber, a fiber combiner and a light detector. In the application, the hollow-core optical fiber is a glass tube, the hollow-core optical fiber is internally provided with metal oxide particles, and the hollow-core optical fiber is externally coated with a metal oxide layer. The application utilizes the metal oxide particles and the metal oxide layer to enhance the absorption of infrared rays by the gas, more changes the refractive index of the gas in the hollow-core optical fiber, more changes the optical path of the hollow-core optical fiber, and improves the sensitivity of gas detection.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of gas detection, and particularly relates to a dual-optical-path photothermal gas detection device. BACKGROUND

[0002] Accurate and high-sensitivity detection of gas types and gas concentrations is an important technology in the fields of safety production, environmental monitoring, industrial control, and is related to multiple technical fields such as petroleum and chemical production, human food safety detection, disease medical diagnosis, and national public security. For example, detection of gases such as formaldehyde, methane, carbon monoxide, and nitrogen oxide is related to people's life and safety production in coal mines.

[0003] There are various gas detection technologies based on different principles in the prior art, such as gas sensors based on changes in the conductive properties of metal oxide semiconductors, surface plasmon resonance gas sensors based on changes in the refractive index of gases, gas sensors based on changes in electrochemical properties, and gas sensors based on infrared absorption spectra.

[0004] Among the above sensors, gas sensors based on gas infrared absorption spectra have the advantages of strong selectivity and fast response, so gas sensors based on gas infrared absorption spectra have good development prospects relative to gas type gas sensors.

[0005] In gas sensors based on gas infrared absorption spectra, the gas is arranged in a gas chamber, and the type and concentration of the gas in the gas chamber are determined by measuring the transmission spectrum of the laser passing through the gas chamber. In such a design, because the beam cross-sectional area of the laser is small, the absorption of the gas to the laser is weak, resulting in low sensitivity of gas concentration detection. In recent years, researchers have proposed gas detectors based on photothermal effects, that is, the gas generates heat after absorbing infrared light, changes the temperature of the gas, and thus changes the refractive index of the gas. Ultimately, the type and concentration of the gas are determined by the response caused by the refractive index. For example, the paper Mid-infrared fiber-optic photothermal interferometry, Optics Letter Vol. 42, No. 18, pp. 3718, 2017 proposes to arrange nitrous oxide in a hollow optical fiber, use nitrous oxide to absorb infrared light, cause changes in the refractive index and optical path, and use the principle of a Mach-Zehnder interferometer to realize gas detection. In this design, the light field in the hollow optical fiber is weak, and the absorption of nitrous oxide to infrared light is weak, resulting in low sensitivity of gas detection. Improving the absorption of infrared light by the gas is of great significance to providing the sensitivity of gas detection. SUMMARY

[0006] To solve the above problems, the application provides a dual optical path light-heat gas detection device, which comprises a detection light source, a fiber splitter, a first coupler, a first gas chamber, a hollow core fiber, a dichroic mirror, a pump light source, a second coupler, a reference fiber, a second gas chamber, a fiber combiner and a light detector.

[0007] The application sets the metal oxide particles in the hollow core fiber and sets the metal oxide layer outside the hollow core fiber, and the metal oxide layer outside the hollow core fiber serves as the reflection layer of infrared light and gathers stronger light field at the metal oxide particles.

[0008] Further, the reference fiber is a single-mode fiber.

[0009] Further, the detection light source is a quantum cascade laser.

[0010] Further, the detection light source emits mid-infrared laser.

[0011] Further, the length of the hollow core fiber is greater than 10 cm.

[0012] Further, the inner hole diameter of the glass tube is greater than 100 microns and less than 300 microns.

[0013] Further, the inner diameter of the glass tube is small in the middle part and large at the two ends.

[0014] Further, the splitting ratio of the fiber splitter is 95:1.

[0015] Further, the material of the metal oxide particles is titanium dioxide, zinc oxide, tin oxide, indium oxide or ITO.

[0016] Further, the size of the metal oxide particles is less than 100 nanometers.

[0017] The beneficial effects of the present application are as follows:

[0018] (1) The present application sets metal oxide particles in the hollow core optical fiber and sets a metal oxide layer outside the hollow core optical fiber. The metal oxide layer outside the hollow core optical fiber serves as a reflection layer for infrared light, and a stronger light field is gathered at the metal oxide particles. Under the excitation of this light field, the metal oxide particles produce surface plasmon resonance, which not only produces a strong light field near the metal oxide particles, but also scatters the pump laser, resulting in the formation of a strong light field inside the hollow core optical fiber, enhancing the absorption of infrared light by the gas, and more changing the refractive index of the gas in the hollow core optical fiber, thereby more changing the optical path of the hollow core optical fiber, and improving the sensitivity of gas detection.

[0019] (2) The present application uses a glass tube with uneven thickness as the hollow core optical fiber. Specifically, the inner diameter of the glass tube is small in the middle part, and the inner diameter of the glass tube is large at both ends. On the one hand, this facilitates the coupling of the probe laser and the pump laser into the glass tube. On the other hand, a high concentration of gas is formed in the middle part of the glass tube, enhancing the absorption of the pump laser by the gas. In addition, the thinner middle part of the glass tube is conducive to the gathering of pump light, forming a stronger pump light field and enhancing the absorption of the pump laser by the gas, which all improve the sensitivity of gas detection.

[0020] In summary, the present application has good application prospects in the field of dual optical path photo-thermal gas detection.

[0021] The present application will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is a schematic diagram of a dual optical path photo-thermal gas detection device.

[0023] Figure 2 is a schematic diagram of the propagation path of the gas to be detected, the probe laser and the pump laser in the hollow core optical fiber.

[0024] Figure 3 is a schematic diagram of the hollow core optical fiber.

[0025] Figure 4 is a schematic diagram of a hollow core optical fiber.

[0026] In the figure: 1, probe light source; 2, optical fiber splitter; 3, first coupler; 4, first gas chamber; 5, hollow core optical fiber; 6, dichroic mirror; 7, pump light source; 8, second coupler; 9, reference optical fiber; 10, second gas chamber; 11, optical fiber combiner; 12, optical detector; 41, gas inlet; 51, glass tube; 52, metal oxide particles; 53, metal oxide layer. DETAILED DESCRIPTION

[0027] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments.

[0028] This invention provides a dual-path photothermal gas detection device, such as... Figure 1 As shown, the system includes a detection light source 1, an optical fiber splitter 2, a first coupler 3, a first gas chamber 4, a hollow-core optical fiber 5, a dichroic mirror 6, a pump light source 7, a second coupler 8, a reference optical fiber 9, a second gas chamber 10, an optical fiber combiner 11, and a photodetector 12. The detection light source 1 is a quantum cascade laser. The emission spectrum of the quantum cascade laser is in the mid-infrared and far-infrared bands. In this invention, a quantum cascade laser is used to emit broadband laser light, with the emitted wavelength range including at least 1500 nm to 1600 nm of mid-infrared laser light. The broadband laser light emitted by the quantum cascade laser is split using the optical fiber splitter 2. In this invention, the optical fiber splitter 2 is a fused biconical taper optical fiber splitter, which distributes the optical energy transmitted in one optical fiber to two optical fibers according to a predetermined ratio. After passing through the fiber optic splitter 2, the light is divided into two paths: one path passes through the first coupler 3, through the side wall of the first gas chamber 4, enters the first gas chamber 4, and couples into the hollow fiber 5. After transmission within the hollow fiber 5, it exits from the other end of the hollow fiber 5, is reflected by the dichroic mirror 6, passes through the second coupler 8, and enters the conducting fiber, then enters the fiber combiner 11; the other path passes through the reference fiber 9 located in the second gas chamber 10 and also enters the fiber combiner 11. The reference fiber 9 is a single-mode fiber. The gas to be tested is placed inside the first gas chamber 4. The gas to be tested can absorb light of infrared wavelengths. For example, the gas to be tested can be carbon monoxide, nitrous oxide, methane, etc. The output end of the fiber combiner 11 is connected to a photodetector 12, which detects the spectrum of the emitted light. One end of the hollow fiber 5 is connected to the first gas chamber 4, which has an air inlet 41. Under the action of an air pump or other external force, the gas to be tested in the first gas chamber 4 can enter the hollow fiber 5. Pump source 7 emits a pump laser. The wavelength of the pump laser is different from that of the probe laser. The gas to be tested absorbs the pump laser but not the probe laser. In other words, the wavelength of the pump laser is in the infrared absorption band of the gas, while the wavelength of the probe laser is not in the infrared absorption band of the gas to be tested. For example, when probing nitrous oxide gas, the wavelength of the pump laser is 4.46 micrometers. The pump laser passes through dichroic mirror 6 and enters the other end of hollow fiber 5, i.e., from... Figure 1 Transmission occurs from the right side of the hollow fiber 5 to the left side of the hollow fiber 5.

[0029] To more clearly illustrate the transmission of the gas under test, the probe laser, and the pump laser, this invention provides a schematic diagram of their transmission. For example... Figure 2As shown, there are three paths in the hollow core optical fiber 5: the to-be-detected gas is transmitted from the left side of the hollow core optical fiber 5 to the right side of the hollow core optical fiber 5; the probe laser is transmitted from the left side of the hollow core optical fiber 5 to the right side of the hollow core optical fiber 5; and the pump laser is transmitted from the right side of the hollow core optical fiber 5 to the left side of the hollow core optical fiber 5.

[0030] In Figure 1 the probe laser is split into two paths after the optical fiber splitter 2, the optical paths of the two paths are different, a phase difference is generated between the two paths, and the spectrum detected by the optical detector 12 is affected, the detected spectrum reflects the refractive index change of the to-be-detected gas in the hollow core optical fiber 5, and further reflects the temperature change of the to-be-detected gas, and further reflects the type and concentration of the to-be-detected gas.

[0031] The hollow core optical fiber 5 is a glass tube 51, the length of the glass tube 51 is greater than 10 cm and less than 50 cm, the inner hole diameter of the glass tube 51 is greater than 100 microns and less than 300 microns. Figure 3 As shown, the hollow core optical fiber 5 is internally provided with metal oxide particles 52, and the hollow core optical fiber 5 is externally coated with a metal oxide layer 53. The material of the metal oxide particles 52 is titanium dioxide, zinc oxide, tin oxide, indium oxide or ITO. The size of the metal oxide particles 52 is less than 100 nanometers, and the size of the metal oxide particles 52 should not be too large, otherwise the absorption loss of the probe laser will be excessively increased. In the present application, the metal oxide particles 52 are arranged to increase the loss of the probe laser at the hollow core optical fiber 5, and therefore, the splitting ratio of the optical fiber splitter 2 is 95:1, and stronger laser needs to pass through the hollow core optical fiber 5 path.

[0032] In the present application, the metal oxide particles 52 are arranged in the hollow core optical fiber 5, and the metal oxide layer 53 is arranged outside the hollow core optical fiber 5, the metal oxide layer 53 outside the hollow core optical fiber 5 serves as a reflection layer of infrared light, and a stronger light field is gathered at the metal oxide particles 52. Under the excitation of the light field, the metal oxide particles 52 generate surface plasmon resonance, not only a strong light field is generated near the metal oxide particles 52, but also the pump laser is scattered, so that a strong light field is formed in the hollow core optical fiber 5, the absorption of infrared light by the to-be-detected gas is enhanced, the temperature of the to-be-detected gas is changed more, the refractive index of the gas in the hollow core optical fiber 5 is changed more, and thus the optical path of the hollow core optical fiber 5 is changed more, and the sensitivity of gas detection is improved.

[0033] Preferably, a glass tube 51 with a non-uniform inner diameter is used to replace a glass tube 51 with a uniform inner diameter, and specifically, as shown in Figure 4As shown, in the middle part of the glass tube 51, the inner diameter of the glass tube 51 is set to be small; in the two ends of the glass tube 51, the inner diameter of the glass tube 51 is set to be large. On the one hand, due to the large inner diameter of the two ends, it is convenient for the probe laser and the pump laser to be coupled into the glass tube 51; on the other hand, due to the small inner diameter of the middle part, the gas concentration in the middle part of the glass tube 51 is large, that is, a high-concentration gas is formed in the middle part of the glass tube 51, and the absorption of the pump laser by the gas is enhanced; on the other hand, the thin middle part of the glass tube 51 is beneficial to the aggregation of the pump light, and a stronger pump light field is formed, and these parts are also the areas with large gas concentration to be measured, which enhances the absorption of the pump laser by the gas, and the above aspects all improve the sensitivity of gas detection.

[0034] In summary, the present application provides a double optical path light-thermal gas detection device, metal oxide particles 52 are arranged in the hollow core optical fiber 5, and a metal oxide layer 53 is arranged outside the hollow core optical fiber 5, the metal oxide layer 53 outside the hollow core optical fiber 5 serves as a reflection layer of infrared light, and a stronger light field is gathered at the metal oxide particles 52. Under the excitation of this light field, the metal oxide particles 52 produce surface plasmon resonance, not only a strong light field is generated near the metal oxide particles 52, but also the pump laser is scattered, resulting in the formation of a strong light field inside the hollow core optical fiber 5, the absorption of the gas to the infrared light is enhanced, the refractive index of the gas in the hollow core optical fiber 5 is changed more, and thus the optical path of the hollow core optical fiber 5 is changed more, and the sensitivity of gas detection is improved. The core technical scheme of the present application is effective for gas and liquid detection with infrared absorption characteristics, and thus has good application prospect in the field of gas and liquid detection.

[0035] The above only describes the preferred embodiments of the present application and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A dual-path photothermal gas detection device, characterized in that, The system includes a detection light source, an optical fiber splitter, a first coupler, a first gas chamber, a hollow-core optical fiber, a dichroic mirror, a pump light source, a second coupler, a reference optical fiber, a second gas chamber, an optical fiber combiner, and a photodetector. The detection light source emits broadband laser light, which, after passing through the optical fiber splitter, passes through the first coupler, through the first gas chamber, enters the hollow-core optical fiber, exits from the other end of the hollow-core optical fiber, passes through the dichroic mirror and the second coupler, and enters the optical fiber combiner; the other path passes through the reference optical fiber located in the second gas chamber and also enters the optical fiber combiner. The output end of the optical fiber combiner is connected to the photodetector. One end of the hollow-core optical fiber is connected to the first gas chamber, which has an air inlet. The pump light source emits pump laser light, which, after passing through the dichroic mirror, enters the other end of the hollow-core optical fiber. The hollow-core optical fiber is a glass tube containing metal oxide particles and is coated with a metal oxide layer.

2. The dual-optical-path photothermal gas detection device as described in claim 1, characterized in that: The reference fiber is a single-mode fiber.

3. The dual-optical-path photothermal gas detection device as described in claim 1, characterized in that: The detection light source is a quantum cascade laser.

4. The dual-optical-path photothermal gas detection device as described in claim 3, characterized in that: The detection light source emits mid-infrared laser light.

5. The dual-optical-path photothermal gas detection device as described in claim 1, characterized in that: The length of the hollow optical fiber is greater than 10 centimeters.

6. The dual-optical-path photothermal gas detection device as described in claim 1, characterized in that: The inner diameter of the glass tube is greater than 100 micrometers and less than 300 micrometers.

7. The dual-optical-path photothermal gas detection device as described in claim 1, characterized in that: The inner diameter of the glass tube is small in the middle and large at both ends.

8. The dual-optical-path photothermal gas detection device as described in claim 1, characterized in that: The splitting ratio of the optical fiber splitter is 95:

1.

9. The dual-path photothermal gas detection device as described in any one of claims 1-8, characterized in that: The metal oxide particles are made of titanium dioxide, zinc oxide, tin oxide, indium oxide, or ITO.

10. The dual-optical-path photothermal gas detection device as described in claim 8, characterized in that: The size of the metal oxide particles is less than 100 nanometers.

Images