Gas measurement system based on wavelength modulation technology

Abstract

The utility model discloses a gas measuring system based on wavelength modulation technology, which relates to the technical field of trace gas detection of absorption spectrum technology and comprises a light source module, a modulation and phase locking module, an optical cavity module, a signal processing module and a feedback module. The light source module generates laser which is incident to the optical cavity module. In the modulation and phase locking module, a signal generation unit generates low-frequency triangular waves, a phase locking amplification unit generates high-frequency sine waves and realizes a phase locking function, an addition unit superposes the low-frequency triangular waves and the high-frequency sine waves, and a white noise generation unit generates white noise signals with adjustable power. And the superposed signal and the white noise signal are respectively injected into the light source module for laser modulation. The signal processing module receives emergent light of the optical cavity module and controls and adjusts white noise power through the feedback module. The signal processing module further receives output laser of the light source module and controls and adjusts the laser wavelength to be stabilized to a preset value through the feedback module. The utility model aims to provide hardware support for solving the problems of interference noise and insufficient wavelength stability in the prior art.

Description

Technical Field

[0001] This utility model relates to the field of trace gas detection technology using absorption spectroscopy, and in particular to a gas measurement system based on wavelength modulation technology. Background Technology

[0002] Laser absorption spectroscopy is widely used in gas analysis, environmental monitoring, and industrial process control. Its core principle involves irradiating the sample with a laser source and measuring the characteristic spectral lines absorbed by the laser in the sample to obtain the concentration, composition, and other physicochemical properties of the substance. However, in practical applications, laser absorption spectroscopy often faces two key problems: interference noise and the stability of the laser wavelength. These factors severely affect its measurement accuracy and reliability.

[0003] First, interference noise is a common source of interference in laser absorption spectroscopy, especially in high-sensitivity gas detection, where its impact on the signal is particularly significant. While traditional methods improve the signal-to-noise ratio by increasing light source power or modifying the detection system, these methods often come with high costs and increased system complexity, making it difficult to meet the requirements of high precision and efficiency. Therefore, effectively reducing interference noise and improving signal quality has become the core issue in achieving high-precision laser absorption spectroscopy.

[0004] Secondly, the stability of the laser wavelength directly affects the accuracy of the absorption spectrum. The output wavelength of a laser is affected by various factors such as ambient temperature and current driving, which may cause wavelength drift and thus affect the results of spectral analysis. Although existing technologies have proposed maintaining the stability of the laser wavelength through temperature control and current adjustment, these methods often have long response times and limited adjustment accuracy, making it difficult to ensure that the laser remains at the preset wavelength during long-term operation, thereby limiting the accuracy and reliability of the laser absorption spectroscopy system. Utility Model Content

[0005] In order to overcome the defects in the prior art, this utility model provides a gas measurement system based on wavelength modulation technology, which aims to provide hardware support for solving the problems of interference noise and insufficient wavelength stability in the prior art.

[0006] To achieve the above objectives, the present invention adopts the following technical solution, including:

[0007] A gas measurement system based on wavelength modulation technology includes a light source module, a modulation and phase-locked loop module, an optical cavity module, a signal processing module, and a feedback module;

[0008] The light source module is used to generate laser light and direct it to the optical cavity module;

[0009] The modulation and phase-locked module includes a signal generation unit, a phase-locked amplifier unit, an adder unit, and a white noise generation unit. The signal generation unit generates a low-frequency triangular wave. The phase-locked amplifier unit generates a high-frequency sine wave and performs phase-locking. The adder unit superimposes the low-frequency triangular wave and the high-frequency sine wave. The white noise generation unit generates a white noise signal with adjustable power. The adder unit and the white noise generation unit inject the superimposed signal and the white noise signal, respectively, into the light source module for laser modulation.

[0010] The signal processing module is used to receive the emitted light from the optical cavity module and generate a second feedback signal to the feedback module; the feedback module is used to control the white noise generator and adjust the white noise power according to the second feedback signal.

[0011] Preferably, the signal processing module is further configured to acquire the output laser light from the light source module and generate a first feedback signal for the feedback module; the feedback module is configured to control the light source module according to the first feedback signal to generate wavelength-stable laser light.

[0012] Preferably, the light source module includes: a laser, a beam splitter, a collimating lens, an aperture, a laser driver module, and a laser temperature control module;

[0013] The beam splitter is used to split the laser emitted by the laser; the collimating lens is used to collimate one of the beams after it is split by the beam splitter, so that the diverging light becomes parallel light; the aperture is used to filter out the stray light at the edge of the parallel light output by the collimating lens, and to incident the parallel light after the stray light is filtered out onto the optical cavity module.

[0014] The laser driver module is used to control the drive current of the laser; the laser temperature control module is used to control the temperature of the laser.

[0015] The addition unit and the white noise generation unit are respectively connected to the laser driving module, and inject the superimposed signal and the white noise signal into the laser driving module for laser modulation.

[0016] Preferably, the signal processing module includes a wavelength meter and a computer;

[0017] The wavelength meter is used to collect the other beam of light after the beam splitter splits the beam and measure the wavelength. The wavelength meter is connected to the computer and sends the measurement results to the computer. The computer generates a first feedback signal to the feedback module based on the wavelength of the light emitted from the light source module. The feedback module controls the laser drive module and the laser temperature control module based on the first feedback signal to adjust the laser drive current and temperature until the laser wavelength stabilizes to a preset value.

[0018] Preferably, the laser is a mid-infrared quantum cascade laser.

[0019] Preferably, the optical cavity module includes: a cavity, a first high-reflection mirror, a second high-reflection mirror, a filter, and a focusing lens;

[0020] The first and second high-reflection mirrors are located at both ends of the cavity, causing the incident light to undergo multiple reflections within the cavity. After multiple reflections within the cavity, the light exits to a filter, which is used to filter out excess wavelengths of broadband light and ambient light. The light filtered by the filter then exits to a focusing lens, which is used to focus the exiting light and shoot it out.

[0021] Preferably, the signal processing module includes a photomultiplier tube and a computer;

[0022] The light, focused by the focusing lens, is emitted to the photomultiplier tube, which is used to perform photoelectric conversion on the emitted light. The photomultiplier tube is connected to a computer and sends the photoelectric converted signal to the computer. The computer obtains the signal-to-noise ratio of the second harmonic based on the emitted light from the optical cavity module and generates a second feedback signal for the feedback module.

[0023] Preferably, the optical cavity module further includes: a pressure gauge, a flow meter, and an air pump;

[0024] The pressure gauge is installed on the cavity to monitor the pressure inside the cavity in real time; the air pump is connected to the cavity through a gas pipeline and is used to draw the sampling gas into the cavity; the flow meter is installed on the gas pipeline to monitor the gas flow rate in real time and control the pumping speed of the air pump.

[0025] Preferably, each unit of the modulation and phase-locked module is integrated on a single FPGA circuit board.

[0026] Preferably, the computer includes a processor and a display.

[0027] The advantages of this utility model are:

[0028] (1) This invention reduces interference noise in the output spectrum of the optical cavity by injecting white noise into the modulation current (driving current) of the laser. At the same time, a high-frequency sine wave is added by using wavelength modulation technology to suppress the influence of background noise.

[0029] (2) The present invention injects white noise into the laser to effectively suppress interference noise. The principle is that when the driving current of the laser is disturbed by white noise, the linewidth of the output laser will be widened and its coherence will be weakened. Therefore, even if the light incident on the resonant cavity undergoes multiple back-and-forth reflections and the back-and-forth beams overlap, no serious interference effect will be produced.

[0030] (3) This utility model receives the emitted light from the optical cavity module through the signal processing module, can detect the signal-to-noise ratio of the second harmonic, and generate a second feedback signal. The feedback module controls the white noise generator according to the second feedback signal to adjust the white noise power. This utility model provides hardware support for the automatic adjustment of white noise power.

[0031] (4) The present invention has a simple structure, which can avoid interference noise and background noise from interfering with the measurement results and effectively improve the sensitivity and detection limit of the measurement system.

[0032] (5) This utility model splits the light emitted by the laser into two beams. One beam enters the optical cavity, and the other beam enters the wavelength meter for real-time wavelength monitoring. The wavelength meter inputs the measurement result into the signal processing module. The signal processing module generates a first feedback signal to the feedback module. The feedback module controls the laser driving module and the laser temperature control module according to the first feedback signal to adjust the laser driving current and temperature until the laser wavelength stabilizes to the preset value. This utility model provides hardware support for the automatic adjustment of laser wavelength.

[0033] (6) This invention provides a gas measurement system based on wavelength modulation technology, aiming to provide hardware support for solving the problems of interference noise and insufficient wavelength stability in existing technologies. Specifically, this invention effectively reduces interference noise by applying white noise modulation to the light source, and simultaneously improves the signal-to-noise ratio of the signal by detecting the signal-to-noise ratio of the second harmonic and automatically adjusting the white noise power in real time. In addition, this invention also combines a wavelength meter to detect the laser output wavelength in real time, and ensures that the laser is stable within the preset wavelength range by automatically adjusting the laser's driving current and temperature. The innovation of this invention lies in the fact that through a precise feedback adjustment mechanism, it not only improves the wavelength stability of the laser, but also effectively reduces interference noise, thereby significantly improving the accuracy and reliability of laser absorption spectroscopy analysis. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a gas measurement system based on wavelength modulation technology according to this utility model.

[0035] Explanation of reference numerals in the attached figures:

[0036] 1-Laser temperature control module, 2-Laser, 3-Beam splitter, 4-Wavemeter, 5-Collimating lens, 6-Aperture, 7-Cavity, 8-High-reflection mirror No. 1, 9-High-reflection mirror No. 2, 10-Filter, 11-Focusing lens, 12-Photomultiplier tube, 13-Pressure gauge, 14-Flow meter, 15-Air pump, 16-Computer, 17-Feedback circuit, 18-Modulation and phase-locked loop module, 19-Laser driver module. Detailed Implementation

[0037] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.

[0038] Depend on Figure 1 As shown, a gas measurement system based on wavelength modulation technology includes a light source module, a modulation and phase-locked loop module 18, an optical cavity module, a signal processing module, and a feedback module.

[0039] The light source module includes: laser 2, beam splitter 3, collimating lens 5, aperture 6, laser driver module 19, and laser temperature control module 1.

[0040] In this system, beam splitter 3 is used to split the laser emitted by laser 2. Collimating lens 5 is used to collimate one of the beams after splitting by beam splitter 3, turning the diverging light into parallel light. Aperture 6 is used to filter out stray light from the edges of the parallel light output by collimating lens 5, and to direct the filtered parallel light into the optical cavity module. Laser driver module 19 is used to control the driving current of laser 2. Laser temperature control module 1 is used to control the temperature of laser 2. The temperature and driving current of laser 2 directly affect the output performance of the light source, therefore, a highly stable driver module and temperature control module are required, specifically including a current control circuit and a temperature control circuit. In this embodiment, laser 2 is an infrared quantum cascade laser (QCL).

[0041] The modulation and phase-locked module 18 includes: a signal generation unit, a phase-locked amplifier unit, an adder unit, and a white noise generation unit.

[0042] The system includes a signal generation unit for generating a low-frequency triangular wave and a phase-locked amplifier unit for generating a high-frequency sine wave and implementing phase-locking functionality. The outputs of both the signal generation unit and the phase-locked amplifier unit are connected to the input of the adder unit, whose output is connected to the input of the laser driver module 19. The adder unit superimposes the low-frequency triangular wave generated by the signal generation unit and the high-frequency sine wave generated by the phase-locked amplifier unit, and injects the superimposed signal into the laser driver module 19 for laser modulation. The output of the white noise generation unit is connected to the input of the laser driver module 19. The white noise generation unit generates a white noise signal with adjustable power and injects it into the laser driver module 19 for laser modulation.

[0043] In this embodiment, each unit of the modulation and phase-locked module 18 is integrated on an FPGA circuit board.

[0044] The optical cavity module includes: cavity 7, high-reflection mirror 1 8, high-reflection mirror 2 9, filter 10, focusing lens 11, pressure gauge 13, flow meter 14, and air pump 15.

[0045] In this design, high-reflection mirrors 8 and 9 are located at both ends of cavity 7, causing the incident light to undergo multiple reflections within cavity 7. The light, after multiple reflections within cavity 7, exits to filter 10, which filters out excess wavelengths of broadband light and ambient light. The light filtered by filter 10 then exits to focusing lens 11, which focuses and ejects the exiting light. A pressure gauge 13 is mounted on cavity 7 to monitor the pressure within cavity 7 in real time. An air pump 15 is connected to cavity 7 via a gas pipeline and is used to pump sampling gas into cavity 7. A flow meter 14 is mounted on the gas pipeline to monitor the gas flow rate in real time and control the pumping speed of air pump 15. In this embodiment, cavity 7 is made of Teflon.

[0046] The signal processing module includes a wavelength meter 4, a photomultiplier tube 12, and a computer 16.

[0047] The wavelength meter 4 is used to collect the other beam of light after it has been split by the beam splitter 3 and measure its wavelength. The wavelength meter 4 is connected to the computer 16 and sends the measurement results to the computer 16. The computer 16 is used to output a first feedback signal based on the measurement results of the wavelength meter 4 and send the first feedback signal to the feedback module.

[0048] The light focused by the focusing lens 11 is emitted to the photomultiplier tube 12, which performs photoelectric conversion on the emitted light. The photomultiplier tube 12 is connected to the computer 16, and sends the photoelectric converted signal to the computer 16. The computer 16 is also used to obtain the signal-to-noise ratio of the second harmonic based on the detection signal of the photomultiplier tube 12, and outputs a second feedback signal, which is then sent to the feedback module.

[0049] The computer 16 includes a processor and a display. The processor processes signals; the display shows the signals.

[0050] The feedback module includes a feedback circuit 17. The feedback circuit 17 is connected to the modulation and phase-locked loop module 18. The feedback circuit 17 controls the white noise generator according to the second feedback signal, adjusting the white noise power. The feedback circuit 17 also controls the laser drive module 19 and the laser temperature control module 1 according to the first feedback signal, adjusting the drive current and temperature of the laser 2 until the laser wavelength stabilizes at a preset value.

[0051] Except for this embodiment Figure 1 As shown, the feedback circuit 17 can also be integrated with the modulation and phase-locked module 18 on a single FPGA board.

[0052] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A gas measurement system based on wavelength modulation technology, characterized in that, It includes a light source module, a modulation and phase-locked loop module (18), an optical cavity module, a signal processing module, and a feedback module; The light source module is used to generate laser light and direct it to the optical cavity module; The modulation and phase-locked module (18) includes a signal generation unit, a phase-locked amplifier unit, an adder unit, and a white noise generation unit; the signal generation unit is used to generate a low-frequency triangular wave; the phase-locked amplifier unit is used to generate a high-frequency sine wave and realize the phase-locking function; the adder unit is used to superimpose the low-frequency triangular wave and the high-frequency sine wave; the white noise generation unit is used to generate a white noise signal with adjustable power; the adder unit and the white noise generation unit respectively inject the superimposed signal and the white noise signal into the light source module for laser modulation; The signal processing module is used to receive the emitted light from the optical cavity module and generate a second feedback signal to the feedback module; the feedback module is used to control the white noise generator and adjust the white noise power according to the second feedback signal.

2. The gas measurement system based on wavelength modulation technology according to claim 1, characterized in that, The signal processing module is also used to acquire the output laser light from the light source module and generate a first feedback signal to the feedback module; the feedback module is used to control the light source module according to the first feedback signal to generate laser light with a stable wavelength.

3. A gas measurement system based on wavelength modulation technology according to claim 2, characterized in that, The light source module includes: a laser (2), a beam splitter (3), a collimating lens (5), an aperture (6), a laser driving module (19), and a laser temperature control module (1); The beam splitter (3) is used to split the laser emitted by the laser (2); the collimating lens (5) is used to collimate one of the beams after it is split by the beam splitter (3), so that the diverging light becomes parallel light; the aperture (6) is used to filter out the edge stray light of the parallel light output by the collimating lens (5), and to incident the parallel light after the stray light is filtered out onto the optical cavity module. The laser driving module (19) is used to control the driving current of the laser (2); the laser temperature control module (1) is used to control the temperature of the laser (2); The addition unit and the white noise generation unit are respectively connected to the laser driving module (19) to inject the superimposed signal and the white noise signal into the laser driving module (19) for laser modulation.

4. A gas measurement system based on wavelength modulation technology according to claim 3, characterized in that, The signal processing module includes a wavelength meter (4) and a computer (16); The wavelength meter (4) is used to collect another beam of light after the beam splitter (3) splits the beam and measure the wavelength. The wavelength meter (4) is connected to the computer (16) and sends the measurement result to the computer (16). The computer (16) generates a first feedback signal to the feedback module according to the wavelength of the light emitted from the light source module. The feedback module controls the laser drive module (19) and the laser temperature control module (1) according to the first feedback signal to adjust the drive current and temperature of the laser (2) until the laser wavelength stabilizes to the preset value.

5. A gas measurement system based on wavelength modulation technology according to claim 3, characterized in that, The laser (2) is a mid-infrared quantum cascade laser.

6. A gas measurement system based on wavelength modulation technology according to claim 1, characterized in that, The optical cavity module includes: cavity (7), first high-reflection mirror (8), second high-reflection mirror (9), filter (10), and focusing lens (11); The first high-reflection mirror (8) and the second high-reflection mirror (9) are located at both ends of the cavity (7), causing the incident light to undergo multiple reflections within the cavity (7). After multiple reflections within the cavity (7), the light exits to the filter (10), which is used to filter out excess wavelengths of broadband light and ambient light. The light filtered by the filter (10) exits to the focusing lens (11), which is used to focus the exiting light and shoot it out.

7. A gas measurement system based on wavelength modulation technology according to claim 6, characterized in that, The signal processing module includes a photomultiplier tube (12) and a computer (16); The light focused by the focusing lens (11) is emitted to the photomultiplier tube (12), which is used to perform photoelectric conversion on the emitted light. The photomultiplier tube (12) is connected to the computer (16) and sends the photoelectric converted signal to the computer (16). The computer (16) obtains the signal-to-noise ratio of the second harmonic based on the emitted light from the optical cavity module and generates a second feedback signal to the feedback module.

8. A gas measurement system based on wavelength modulation technology according to claim 6, characterized in that, The optical cavity module also includes: a pressure gauge (13), a flow meter (14), and an air pump (15); The pressure gauge (13) is installed on the cavity (7) and is used to monitor the pressure inside the cavity (7) in real time; the air pump (15) is connected to the cavity (7) through a gas pipeline and is used to draw the sampling gas into the cavity (7); the flow meter (14) is installed on the gas pipeline and is used to monitor the gas flow rate in real time and control the pumping speed of the air pump (15).

9. A gas measurement system based on wavelength modulation technology according to claim 1, characterized in that, The various units of the modulation and phase-locked module (18) are integrated on a single FPGA circuit board.

10. A gas measurement system based on wavelength modulation technology according to claim 4 or 7, characterized in that, The computer (16) includes a processor and a display.

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