A nano-fiber gas detection device and method based on TDLAS technology

Abstract

The present invention discloses a nano-fiber gas detection device and method based on TDLAS technology, belonging to the field of gas detection technology. Aiming at the technical problem that the laser power required by the existing gas detection device is too high and not convenient for miniaturization, the present invention provides a miniaturized gas detection device based on TDLAS and nano-fiber technology, which realizes nanowatt-level weak light methane detection by using modulation and demodulation technology. The method is of great significance for atmospheric composition analysis, environmental monitoring and extraterrestrial gas detection.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas detection, and in particular relates to a nano-optical fiber gas detection device and method based on TDLAS technology. Background Art

[0002] Under the traditional tunable diode laser absorption spectroscopy (TDLAS) technology, gas component detection usually requires a laser with a power of more than milliwatts to scan an independent gas absorption line and perform resonance absorption detection on gas molecules. This measurement method was proposed by Hinkley and Reid and is currently the most commonly used technology for detecting trace gases in the atmosphere.

[0003] Nanofibers have attracted attention in the field of gas detection in recent years due to their strong binding characteristics of the evanescent field and their ultra-low power requirements for gas detection, becoming one of the research focuses of cutting-edge gas detection technologies. Nanofibers refer to standard single-mode optical fibers with a diameter of 125 μm that are tapered to have a centimeter-level length and a sub-micron diameter. Since the diameter of a nanofiber is smaller than the wavelength of the waveguide light, the waveguide light propagating in the nanofiber is strongly bound to the surface of the fiber to form an evanescent field. Its high field density distribution effectively increases the coupling rate between light and gas molecules, enabling it to achieve resonant absorption detection of gas molecules at ultra-low optical power. Summary of the invention

[0004] In order to solve the technical problem that the laser power required by existing gas detection devices is too high and not convenient for miniaturization, the present invention provides a miniaturized gas detection device based on TDLAS and nano-optical fiber technology, which uses modulation and demodulation technology to achieve nanowatt-level weak light methane detection. This method is of great significance for atmospheric composition analysis, environmental monitoring and extraterrestrial gas detection.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A nano-fiber gas detection device and method based on TDLAS technology, comprising a DFB laser, a fiber isolator, a fiber attenuator, a gas pool, a gas inlet, a nano-fiber, an avalanche detector, a gas outlet, a signal control acquisition card, an industrial computer, and a DFB laser controller;

[0007] The DFB laser, optical fiber isolator, optical fiber attenuator and avalanche detector are respectively provided with input ends and output ends, and are connected in sequence through optical fibers; the optical fiber between the optical fiber attenuator and the avalanche detector is passed through a gas pool; a gas inlet is provided on the top of the gas pool, and a gas outlet is provided on the bottom; methane gas flows into the gas pool from the gas inlet and flows out from the gas outlet to maintain the air pressure balance inside and outside the pool; a signal control acquisition card sends a second-order modulation signal to modulate the DFB laser controller, and the DFB laser controller outputs a modulation current to the DFB laser to realize light modulation of the DFB laser output; the signal control acquisition card collects the optical signal detected by the avalanche detector on the other side and demodulates it to obtain its second-order differential signal; an industrial computer is connected to the signal control acquisition card for processing and display of gas detection device control and signal acquisition.

[0008] Furthermore, the optical fiber between the optical fiber attenuator and the avalanche detector is a nano optical fiber, and the diameter of the nano optical fiber cone region is on the order of hundreds of nanometers and the length is 1-10 mm.

[0009] Furthermore, the gas in the gas pool is suitable for atomic vapor or various gas molecular components having a resonance absorption energy level.

[0010] Furthermore, the gas pool adopts a dual-port design of a gas inlet and a gas outlet, so that the gas in the gas pool and the outside gas are rapidly exchanged to reach a balanced state.

[0011] Furthermore, the signal control acquisition card modulates the DFB laser controller to achieve optical modulation of the DFB laser. The signal control acquisition card demodulates the modulated signal detected by the avalanche detector to obtain the second-order differential signal of gas resonance absorption, thereby enhancing the signal-to-noise ratio of the gas absorption signal and improving the sensitivity of gas detection.

[0012] Furthermore, the electronic part of the laser light source adopts a DFB laser with a butterfly package, an industrial computer and a signal control acquisition card with field operation functions, and the optical parts are all connected by optical fiber. The gas detection device can be miniaturized and has strong anti-vibration and anti-interference capabilities, making it suitable for field operations and UAV mounting.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] The present invention is based on tunable diode laser absorption spectroscopy (TDLAS) technology, combined with the strong binding characteristics of the evanescent field of nano-fiber, to achieve nanowatt-level weak light methane gas detection. The optical part of the gas detection device is all connected by optical fiber, and the electronic device part is all miniaturized, which solves the technical problem that the laser power required by the existing gas detection device is too high and not convenient for miniaturization. It is of great significance in special and important fields such as atmospheric composition analysis, environmental monitoring and extraterrestrial gas detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the device structure of the present invention;

[0016] Figure 2 (a) is a schematic diagram of the structure and waveguide light field of the nanofiber cone region; (b) standard diameter 125μm fiber imaging; (c) scanning electron microscope imaging of the nanofiber;

[0017] Figure 3 It is a 500nm diameter nanofiber, the resonance absorption spectrum signal of methane gas;

[0018] Figure 4 It is the amplitude voltage of the second-order differential signal of methane gas resonance absorption under different detection light powers.

[0019] 1. DFB laser; 2. Fiber isolator; 3. Fiber attenuator; 4. Gas pool; 5. Gas inlet; 6. Nano fiber; 7. Avalanche detector; 8. Gas outlet; 9. Signal control acquisition card; 10. Industrial computer; 11. DFB laser controller; DETAILED DESCRIPTION

[0020] Example 1

[0021] A nano-fiber gas detection device and method based on TDLAS technology, such as Figure 1 As shown, it includes a DFB laser 1 (also called a distributed laser), an optical fiber isolator 2, an optical fiber attenuator 3, a gas pool 4, a gas inlet 5, a nano-optical fiber 6, an avalanche detector 7, a gas outlet 8, a signal control acquisition card 9, an industrial computer 10, and a DFB laser controller 11;

[0022] The schematic diagram of the nanofiber 6 structure and waveguide light field distribution is shown in Figure 2 As shown in (a), the scanning electron microscope imaging of the standard optical fiber with an un-tapered diameter of 125 μm and the nano-optical fiber 6 are shown in Figure 2. Figure 2The electron beam acceleration voltage of the scanning electron microscope is 5KV, the magnification is 50000 times, the actual measured diameter of the nanofiber is 507nm, and the length of the cone region is about 5mm, which is consistent with the designed diameter of the nanofiber of 500nm.

[0023] The output end of the DFB laser is connected to the input end of the fiber isolator through an optical fiber. The fiber isolator is used to isolate the feedback light of the fiber end face at the fiber connection to avoid interference with the laser mode of the DFB laser. The output end of the fiber isolator 2 is connected to the input end of the fiber attenuator 3 through an optical fiber to attenuate the optical power of the detection light output by the DFB laser 1. The nano-fiber 6 is installed in the gas pool 4 through a bracket, and the input end of the nano-fiber 6 is connected to the output end of the fiber attenuator 3 through an optical fiber. Methane gas flows into the gas pool 4 from the gas inlet 5 and flows out from the gas outlet 8 to maintain the air pressure balance inside and outside the pool. The output end of the nano-fiber 6 is connected to the input end of the avalanche detector 7 through an optical fiber, and the detection light in the nano-fiber 6 is introduced into the avalanche detector 7. The obtained methane gas absorption signal is sent to the signal control acquisition card 9. The signal control acquisition card 9 sends out a second-order modulation signal to modulate the DFB laser controller 11, and the DFB laser controller 11 outputs a modulation current to the DFB laser 1 to realize the light modulation output by the DFB laser 1. The signal control acquisition card 9 collects the light signal detected by the avalanche detector 7 and demodulates it to obtain its second-order differential signal. The industrial computer 10 is connected to the signal control acquisition card 9 for processing and displaying the gas detection device control and signal acquisition.

[0024] When the diameter of the nanofiber is 500nm, the measured methane resonance absorption spectrum is as follows: Figure 3 As shown, the resonance absorption ratio of the detection light by methane gas with a concentration of 30% is 9.2%.

[0025] When the diameter of the nanofiber is 500nm, the amplitude of the second-order differential signal of methane gas resonance absorption under different detection light powers is as follows: Figure 4 As shown in the figure, the signal amplitude is linearly related to the optical power. The lowest incident power measured by the device is 9nW, which proves the feasibility of nano-optical fiber to detect methane gas under nanowatt-level weak light conditions.

[0026] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A nano-fiber gas detection device based on TDLAS technology, characterized in that: It includes a DFB laser (1), an optical fiber isolator (2), an optical fiber attenuator (3), a gas pool (4), a gas inlet (5), a nano optical fiber (6), an avalanche detector (7), a gas outlet (8), a signal control acquisition card (9), an industrial computer (10), and a DFB laser controller (11); The DFB laser (1), the optical fiber isolator (2), the optical fiber attenuator (3) and the avalanche detector (7) are respectively provided with an input end and an output end, and are sequentially connected through optical fibers; the optical fiber between the optical fiber attenuator (3) and the avalanche detector (7) is inserted into a gas pool (4); the gas pool (4) is provided with a gas inlet (5) at the top and a gas outlet (8) at the bottom; methane gas flows into the gas pool (4) from the gas inlet (5) and flows out from the gas outlet (8) to maintain a gas pressure balance inside and outside the pool The signal control acquisition card (9) sends a second-order modulation signal to modulate the DFB laser controller (11), and the DFB laser controller (11) outputs a modulation current to the DFB laser (1), thereby realizing light modulation of the DFB laser (1). The signal control acquisition card (9) collects the light signal detected by the avalanche detector (7) and demodulates it to obtain its second-order differential signal. The industrial computer (10) is connected to the signal control acquisition card (9) for controlling the gas detection device and processing and displaying the signal acquisition.

2. The nano-fiber gas detection device based on TDLAS technology according to claim 1 is characterized in that: The optical fiber between the optical fiber attenuator (3) and the avalanche detector (7) is a nano optical fiber (6), and the cone region diameter of the nano optical fiber (6) is in the order of hundreds of nanometers and the length is 1-10 mm.

3. The nano-fiber gas detection device based on TDLAS technology according to claim 1 is characterized in that: The gas in the gas pool (4) is suitable for atomic vapor or various gas molecular components having a resonance absorption energy level.

4. The nano-fiber gas detection device based on TDLAS technology according to claim 1 is characterized in that: The electronic part of the laser light source adopts a butterfly-packaged DFB laser (1), an industrial computer (10) with field operation function and a signal control acquisition card (9), and the optical part is all connected by optical fiber.

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