A high-precision laser absorption spectrum wavelength calibration system for multi-component gas detection

Abstract

This application provides a high-precision laser absorption spectrum wavelength calibration system for multi-component gas detection, comprising: a laser emitting module including multiple lasers; an optical path switching module, wherein the collimator output of each laser is connected to the input of a MEMS optical switch; a mixing reference chamber module, including a sealed chamber with an entrance window at one end and an exit window at the other end, the entrance window being coupled to the output of the MEMS optical switch, and the mixing reference chamber module including a temperature sensor and a pressure sensor; a photoelectric detection module, located directly behind the exit window, for detecting the intensity of transmitted laser light after passing through the chamber; a signal processing module for processing the transmitted laser light intensity, including a temperature and pressure correction unit; and a control module, connected to the laser emitting module, the optical path switching module, and the signal processing module respectively, forming a closed-loop calibration system. This application can achieve high-precision, rapid, and low-cost calibration of laser wavelengths in multi-component gas detection scenarios.

Description

Technical Field

[0001] This application relates to the field of laser spectral detection and wavelength calibration, specifically to a high-precision laser absorption spectral wavelength calibration system for multi-component gas detection. Background Technology

[0002] In the field of multi-component gas detection, tunable semiconductor laser spectroscopy is widely used due to its advantages such as high sensitivity, high selectivity, and fast response speed. The core principle of this technology is to use the differences in characteristic absorption spectral lines of different gas components to achieve component identification and concentration detection. The accuracy of the laser output wavelength directly determines the reliability of the detection results. If the laser wavelength is off, it may lead to an inability to accurately match the characteristic absorption spectral lines of the target gas, resulting in detection errors or even misjudgments.

[0003] To ensure laser wavelength accuracy, existing technologies typically employ a one-to-one calibration scheme of "single-component reference gas cell + single laser." This means that for each laser to be calibrated, a reference gas cell filled with a single standard gas (such as methane or carbon dioxide only) is configured, and calibration is achieved by detecting characteristic absorption peaks through wavelength scanning. Alternatively, some schemes use a shared single-component reference gas cell across multiple lasers, switching the optical path via a mechanical shutter; however, this suffers from low switching efficiency.

[0004] Analysis reveals the following significant shortcomings in existing technologies: Low system integration and high cost: For the multiple lasers required for multi-component gas detection, if one-to-one single-component reference gas cell calibration is used, a reference gas cell and matching optical path adjustment components with the same number of lasers are required, resulting in a large system size and a large number of parts, which greatly increases the manufacturing cost and installation and debugging difficulty of the equipment. Low optical path switching efficiency and long calibration time: When using a mechanical shutter to switch the optical path between multiple lasers and the reference gas cell, the action response time of the mechanical structure is usually more than 100ms, and optical path offset is easily generated during the switching process, requiring additional optical path calibration, which makes the overall calibration process time-consuming and difficult to meet the rapid calibration requirements in multi-component detection scenarios. The calibration accuracy is greatly affected by environmental interference: In the existing schemes, the reference gas chamber is not equipped with a precise temperature and pressure control module. The center wavelength of the gas characteristic absorption spectrum will shift slightly with the change of temperature and pressure (for example, the center wavelength of the carbon dioxide characteristic absorption line shifts by about 0.0001nm for every 1°C change in temperature). Uncorrected temperature and pressure fluctuations will directly introduce calibration errors and reduce the accuracy of wavelength calibration. Poor compatibility and high difficulty in expansion: If a new gas component needs to be detected, the existing single-component reference gas cell scheme needs to add a corresponding reference gas cell and optical path, which requires a large modification to the original system structure, has poor scalability, and cannot flexibly adapt to the dynamic adjustment of multi-component detection needs. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of this application is to provide a high-precision laser absorption spectral wavelength calibration system for multi-component gas detection.

[0006] This application provides a high-precision laser absorption spectroscopy wavelength calibration system for multi-component gas detection, comprising: The laser emitting module includes multiple lasers, each laser having a wavelength tuning range covering at least one characteristic absorption line of the corresponding gas component; The optical path switching module uses a MEMS optical switch, with the collimator output of each laser connected to the corresponding input of the MEMS optical switch. The hybrid reference gas chamber module includes a sealed gas chamber with an entrance window at one end and an exit window at the other end. The gas chamber is filled with a mixed standard gas. The entrance window is coupled to the output end of the MEMS optical switch. The hybrid reference gas chamber module is equipped with a temperature sensor and a pressure sensor. The photoelectric detection module is located directly behind the exit window and is used to detect the intensity of the transmitted laser light after passing through the gas chamber. The signal processing module, connected to the photoelectric detection module, is used to process the intensity of transmitted laser light. It includes a temperature and pressure correction unit connected to a temperature sensor and a pressure sensor, which is used to correct the wavelength corresponding to the characteristic absorption peak based on temperature and pressure data. The control module is connected to the laser emission module, the optical path switching module, and the signal processing module respectively, forming a closed-loop calibration system.

[0007] Optionally, the parallelism error of the laser beams after collimation of multiple lasers is ≤0.1mrad.

[0008] Optionally, the coaxiality of the input end of the MEMS optical switch and the collimator is calibrated by a three-dimensional adjustment frame, with a coaxiality error ≤0.2mm.

[0009] Optionally, the output end of the MEMS optical switch is coupled to the incident window via a quartz optical fiber, and the optical fiber connector is an FC / APC connector.

[0010] Optionally, the MEMS optical switch has a calibration terminal that is connected to a standard laser wavelength meter.

[0011] Optionally, the pressure sensor is embedded inside the air chamber, the air chamber is wrapped with an insulation sleeve, and the temperature sensor and heating element are embedded inside the insulation sleeve.

[0012] Optionally, the incident window of the hybrid reference gas chamber module is coupled to the optical fiber at the output end of the optical path switching module through a focusing lens to ensure that the laser beam is focused on the central region of the gas chamber.

[0013] Optionally, the photoelectric detection module includes: A photodetector, fixed directly behind the exit window, is used to receive the transmitted laser light after it passes through the gas chamber and convert the light intensity signal into an electrical signal. A preamplifier, connected to the photodetector, is used to amplify the electrical signal to a range that can be collected.

[0014] Optionally, the signal processing module further includes: A lock-in amplifier, whose input terminal is connected to the output terminal of the preamplifier of the photoelectric detection module, and whose reference signal input terminal is connected to the synchronization signal output terminal of the control module, is used to suppress ambient light noise and extract effective light intensity signals. The data acquisition card, whose input terminal is connected to the output terminal of the lock-in amplifier, is used to convert the effective light intensity signal into a digital light intensity signal.

[0015] Optionally, the control module includes: The scanning control unit is used to output the laser drive current, control the continuous scanning of the laser wavelength, and record the correspondence between the drive current and the scanning time in real time. The switching control unit is used to output the MEMS optical switch switching signal and output a synchronization signal to the lock-in amplifier after the switching is completed; The data processing unit is used to obtain the correspondence between light intensity and driving current based on the correspondence between digital light intensity signal, driving current and scanning time, locate the center wavelength of light intensity valley based on the correspondence between light intensity and driving current, and obtain the accurate wavelength value by combining the data from the temperature and pressure correction unit. The current calibration unit has built-in current-wavelength calibration curves for each laser. It determines the corresponding drive current value based on the target absorption peak wavelength and outputs a correction signal to the laser emission module.

[0016] The high-precision laser absorption spectrum wavelength calibration system for multi-component gas detection provided in this application adopts a multi-component mixed reference gas chamber, in which multiple lasers share a single reference gas chamber for calibration. The mixed gas composition can be flexibly adjusted according to detection requirements, and it has the advantages of high integration, low manufacturing cost, and strong scalability. The MEMS optical switch, combined with direct light intensity detection, improves the efficiency and stability of optical path switching and shortens the overall calibration time. Temperature and pressure correction simplifies the calibration process and eliminates environmental interference, thereby achieving high-precision, fast, and low-cost calibration of laser wavelengths in multi-component gas detection scenarios.

[0017] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0018] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a high-precision laser absorption spectroscopy wavelength calibration system for multi-component gas detection according to an exemplary embodiment. Detailed Implementation

[0019] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0020] In existing technologies related to laser spectral wavelength calibration systems for multi-component gas detection, multi-laser calibration requires the configuration of multiple single-component reference gas chambers, resulting in low system integration and high manufacturing costs. The use of mechanical shutters for switching optical paths suffers from slow response and susceptibility to misalignment. Furthermore, fluctuations in environmental temperature and pressure lead to a decrease in calibration accuracy. In addition, existing solutions require significant modifications to the system structure when adding new detectable components. To address these issues, this application provides a high-precision laser absorption spectral wavelength calibration system for multi-component gas detection, thereby resolving the aforementioned problems.

[0021] Reference Figure 1 As shown, a high-precision laser absorption spectroscopy wavelength calibration system for multi-component gas detection in one embodiment of this application includes six core components: a laser emission module, an optical path switching module, a mixed reference gas cell module, a photoelectric detection module, a signal processing module, and a control module. The laser emission module includes multiple lasers, each with a wavelength tuning range covering at least one characteristic absorption line of the corresponding gas component. The optical path switching module uses a MEMS optical switch, with the collimator output of each laser connected to the input of the MEMS optical switch. The mixed reference gas cell module includes a sealed gas cell with an entrance window at one end and an exit window at the other end. The gas chamber is filled with a mixed standard gas. The incident window is coupled to the output of the MEMS optical switch. The mixed reference gas chamber module is equipped with a temperature sensor and a pressure sensor. The photoelectric detection module is located directly behind the exit window and is used to detect the intensity of the transmitted laser light after passing through the gas chamber. The signal processing module is connected to the photoelectric detection module and is used to process the intensity of the transmitted laser light. It includes a temperature and pressure correction unit connected to the temperature sensor and the pressure sensor, which is used to correct the wavelength corresponding to the characteristic absorption peak according to the temperature and pressure data. The control module is connected to the laser emission module, the optical path switching module and the signal processing module respectively to form a closed-loop calibration system.

[0022] Specifically, the temperature and pressure correction unit can be an independent microprocessor / firmware integrated in the signal processing module, or it can be a software algorithm module in the control module. In this embodiment, it is logically attributed to the signal processing module to output correction data in real time for the control module to call.

[0023] The control module provides drive current to the laser emitting module, provides optical switching signals to the optical path switching module, and calibrates the laser wavelength of the laser in the laser emitting module by receiving digital light intensity signals from the signal processing module.

[0024] The laser absorption spectrum wavelength calibration system in this application embodiment is applied to multi-component gas detection scenarios, and is particularly suitable for multi-component gas detection equipment based on tunable semiconductor laser absorption spectroscopy technology. Each part is connected by optical path coupling or circuit to form a closed-loop calibration system to perform high-precision calibration of the output wavelength of multiple lasers.

[0025] The calibration system provided in this application, which allows multiple lasers to share a single multi-component hybrid reference gas chamber and employs a MEMS optical switch for rapid optical path switching, enables multiple lasers to complete calibration by sharing a single multi-component hybrid reference gas chamber. The use of a MEMS optical switch improves the efficiency and stability of optical path switching and shortens the overall calibration time. By adding a high-precision temperature and pressure monitoring and correction module to the reference gas chamber, the accuracy of wavelength calibration is improved. The flexible configuration of the components in the hybrid reference gas chamber enhances the system's adaptability and scalability for multi-component detection scenarios, effectively solving the problems of low integration, high cost, slow switching, insufficient accuracy, and poor scalability in existing solutions.

[0026] If the parallelism of the beams from multiple lasers differs significantly, it may affect the optical path alignment during MEMS optical switch switching, reducing system stability. In some specific embodiments of this application, the parallelism error of the laser beams after collimation from multiple lasers is ≤0.1 mrad.

[0027] For example, the laser emission module includes six tunable semiconductor lasers, each designed to correspond to the characteristic absorption spectra of six target gas components: acetylene (C2H2), ethylene (C2H4), ethane (C2H6), methane (CH4), carbon monoxide (CO), and carbon dioxide (CO2). The wavelength tuning range of each laser covers at least one characteristic absorption line of the corresponding gas component; for example, the methane laser's tuning range covers the characteristic absorption line near 1653.7 nm. The outputs of all six lasers are collimated using fiber optic collimators, and the parallelism error of the collimated laser beam is ≤0.1 mrad.

[0028] It should be noted that the above six target gas components are an exemplary application in trace gas detection. In other embodiments, the types of target gas components may be expanded from one to multiple.

[0029] The embodiments described above in this application improve the collimation of the laser beam, ensuring that the beams output by each laser are uniformly focused in the gas cell, thereby improving the signal-to-noise ratio of the absorbed signal. At the same time, they ensure the consistency of the optical path when switching between different lasers, reduce calibration errors caused by optical path offset, and enhance the overall stability and calibration accuracy of the system.

[0030] To avoid misalignment between the input end of the optical switch and the output end of the laser, which would lead to high optical path loss and unstable signal, in some specific embodiments of this application, the coaxiality between the input end of the MEMS optical switch and the collimator is calibrated by a three-dimensional adjustment frame, with a coaxiality error ≤0.2mm.

[0031] The embodiments described above in this application improve optical path alignment accuracy and reduce optical path transmission loss through calibration, which is beneficial for achieving fast and stable optical path switching, avoiding calibration failures or errors caused by optical path offset, and improving system reliability.

[0032] To further improve the stability of optical path transmission, in some specific embodiments of this application, the output end of the MEMS optical switch is coupled to the incident window through a quartz optical fiber, and the optical fiber connector adopts an FC / APC connector.

[0033] The embodiments described above employ a stable and reliable optical fiber connection method. The FC / APC connector has low reflection characteristics, which can reduce echo interference, thereby further improving detection accuracy and enhancing the long-term stability of the system.

[0034] To improve the stability and repeatability of the system during long-term operation, in some specific embodiments of this application, the MEMS optical switch has a calibration end, which is connected to a standard laser wavelength meter.

[0035] For example, the optical path switching module uses an 8-port MEMS optical switch, which includes 6 input terminals, 1 output terminal, and 1 calibration terminal. The 6 input terminals are respectively connected to the collimator output terminals of the 6 lasers in the laser emission module via flange fixing. The coaxiality between the input terminals and the collimators is calibrated by a three-dimensional adjustment frame, and the coaxiality error is ≤0.2mm. The output terminal of the MEMS optical switch is coupled to the incident window of the hybrid reference gas cell module via a quartz optical fiber. The fiber connector adopts an FC / APC low-loss connector with an insertion loss ≤0.3dB. The calibration terminal is connected to a standard laser wavelength meter for periodically calibrating the optical path transmission accuracy of the MEMS optical switch.

[0036] The embodiments described above in this application ensure the optical path transmission accuracy by periodically calibrating the MEMS optical switch using a standard laser wavelength meter, thus avoiding the problem of system performance degradation over time due to the lack of a periodic calibration mechanism.

[0037] In some specific embodiments of this application, the pressure sensor is embedded inside the air chamber, the air chamber is wrapped with an insulation sleeve, and the temperature sensor and heating element are embedded inside the insulation sleeve.

[0038] To improve the accuracy of light intensity detection and more accurately locate the absorption peak, in some specific embodiments of this application, the incident window of the hybrid reference gas cell module is coupled to the optical fiber at the output end of the optical path switching module through a focusing lens to ensure that the laser beam is focused on the central region of the gas cell.

[0039] For example, the mixed reference gas chamber module is a sealed quartz gas chamber with an entrance window at one end and an exit window at the other end. The chamber is 100mm long, and its inner wall is polished to reduce light reflection interference. The chamber is filled with a mixed standard gas of acetylene, ethylene, ethane, methane, carbon monoxide, and carbon dioxide, with each component having a concentration of 1% (volume fraction) and a gas purity ≥99.999%. The chamber is externally wrapped with an insulation sleeve, inside which a heating element and a temperature sensor are embedded. A pressure sensor is embedded inside the chamber, with measurement accuracies of ±0.05℃ and ±0.001MPa, respectively. The optical fiber at the entrance window of the chamber and the output of the optical path switching module is coupled through a focusing lens with a focal length of 20mm to ensure that the laser beam is focused on the central region of the chamber. During installation, the focusing lens must be installed so that its central optical axis is on the central axis of the chamber.

[0040] To improve system integration and reduce the impact of external factors on calibration, in a further embodiment, the hybrid reference gas chamber module adopts an integrated structure of a sealed gas chamber and a temperature and pressure control unit. The entrance and exit windows of the sealed gas chamber are both made of calcium fluoride (transmittance ≥95%, applicable wavelength range 200nm-5000nm). The windows are sealed to the gas chamber body by welding, with a leakage rate ≤1×10⁻⁶. -9 Pa·m³ / s; The temperature and pressure control unit includes an insulation jacket, a heating element, a temperature sensor, a pressure sensor, and a temperature control chip. The insulation jacket is made of polyurethane insulation material with a thickness of 10mm. The heating element has a power of 5W. The temperature control chip uses a PID control algorithm to stabilize the gas chamber temperature within the range of 25℃±0.1℃. The pressure sensor is a piezoresistive type sensor with a pressure measurement range of 0.05-0.15MPa and a data update frequency of 10Hz. The outer side of the gas chamber exit window is equipped with an anti-reflective coating with a reflectivity ≤0.5% to reduce light intensity loss and improve detection accuracy.

[0041] The aforementioned multi-component mixed reference gas chamber design enables multiple (e.g., 6) lasers to share a single reference gas chamber for calibration, eliminating the need for a separate single-component gas chamber for each laser. This solves the technical problems of low system integration, numerous components, high manufacturing costs, and difficult installation and debugging caused by the existing "single-component gas chamber + single laser" mode. At the same time, the mixed gas composition can be flexibly adjusted according to detection requirements, and adding a new component only requires replacing the gas inside the chamber, thus solving the problem of poor scalability of the existing solution.

[0042] To further simplify the system structure and improve the system response speed and detection accuracy, in some specific embodiments of this application, the photoelectric detection module includes a photodetector and a preamplifier. The photodetector is fixed directly behind the exit window and is used to receive the transmitted laser after passing through the gas chamber and convert the light intensity signal into an electrical signal. The preamplifier is connected to the photodetector and is used to amplify the electrical signal to a range that can be collected.

[0043] For example, a high-sensitivity photodetector is fixed behind the emission window of the hybrid reference gas chamber module by a bracket, at a distance of 25mm from the emission window. It is used to receive the transmitted laser light after passing through the reference gas chamber and convert the light intensity signal into an electrical signal. The response wavelength range of the photodetector covers the output wavelength of 6 lasers, with a peak responsivity ≥0.8A / W and a dark current ≤1nA. The preamplifier is connected to the photodetector through a shielded wire, and the amplification factor can be adjusted in the range of 100-1000 times. The output impedance is 50Ω, which is used to amplify the weak electrical signal to a range that can be collected.

[0044] In multi-component gas detection, some existing technologies employ photoacoustic spectroscopy, which requires converting light intensity signals into acoustic signals for detection. While this ensures detection accuracy, it introduces additional acoustic noise and makes the system relatively cumbersome. The embodiments of this application employ direct absorption spectroscopy, achieving direct light intensity detection through a photodetector, thus eliminating the photoacoustic conversion step.

[0045] In the embodiments described above, the MEMS optical switch and direct light intensity detection technology achieve a switching response time of ≤1ms, significantly improving optical path switching efficiency compared to mechanical shutters (≥100ms). Combined with direct light intensity detection, the photoacoustic conversion step in existing technologies is eliminated, reducing the total multi-laser cycle calibration time to ≤8s. This solves the problems of low optical path switching efficiency and long calibration time in existing technologies. Furthermore, the MEMS optical switch is fixed by a flange and calibrated using a three-dimensional adjustment frame, resulting in a coaxiality error of ≤0.2mm. The switching process is free of optical path offset, avoiding additional optical path calibration steps and improving calibration stability.

[0046] Ambient light noise and circuit noise may interfere with the light intensity signal, making it impossible to extract the effective signal and affecting the calibration accuracy. In some specific embodiments of this application, the signal processing module also includes a lock-in amplifier and a data acquisition card. The input terminal of the lock-in amplifier is connected to the output terminal of the preamplifier of the photoelectric detection module, and the reference signal input terminal is connected to the synchronization signal output terminal of the control module, which is used to suppress ambient light noise and extract the effective light intensity signal. The input terminal of the data acquisition card is connected to the output terminal of the lock-in amplifier, which is used to convert the effective light intensity signal (analog electrical signal) into a digital light intensity signal.

[0047] For example, the data acquisition card uses a 16-bit AD converter with a sampling rate of ≥100kHz; the temperature and pressure correction unit is connected to the temperature sensor and pressure sensor of the mixed reference gas chamber module via a 485 bus.

[0048] Traditional systems rely on manual operation or offline calibration, resulting in low efficiency and poor accuracy. To achieve a fully automated calibration process, in some specific embodiments of this application, the control module includes a scanning control unit, a switching control unit, a data processing unit, and a current calibration unit. Specifically: the scanning control unit outputs the laser drive current, controls the continuous scanning of the laser wavelength, and records the correspondence between the drive current and the scanning time in real time; the switching control unit outputs a MEMS optical switch switching signal and, after switching, outputs a synchronization signal to the lock-in amplifier; the data processing unit obtains the correspondence between light intensity and drive current based on the digital light intensity signal and the correspondence between drive current and scanning time, locates the center wavelength of the light intensity valley based on the correspondence between light intensity and drive current, and obtains a precise wavelength value by combining data from the temperature and pressure correction unit; the current calibration unit has built-in current-wavelength calibration curves for each laser, determines the corresponding drive current value based on the target absorption peak wavelength, and outputs a correction signal to the laser emission module. Specifically, the laser emission module includes multiple lasers and corresponding laser drive circuits, and the current calibration unit outputs a correction signal to the laser drive circuits.

[0049] For example, the control module is an embedded controller (using an ARM Cortex-A9 processor with a main frequency of 1GHz), which is connected to the six lasers of the laser emission module and the MEMS optical switch of the optical path switching module through GPIO interfaces, respectively, to output the laser drive current (adjustable range 0-200mA, accuracy 0.1mA) and the MEMS optical switch switching signal (switching response time ≤1ms); it is connected to the data acquisition card of the signal processing module through a PCIe interface to receive digital light intensity signals; it has a built-in HITRAN standard spectral line database to store the standard wavelength data of the characteristic absorption peaks of the six gas components, and integrates a current-wavelength correspondence model to determine the target bias current based on the absorption peak position.

[0050] The scanning control unit uses a DAC converter to output a sawtooth wave drive signal to control the continuous scanning of the laser wavelength. The scanning range is 0.5nm, and the scanning rate can be adjusted within the range of 0.01-0.1nm / ms. Simultaneously, it records the correspondence between the drive current and the scanning time in real time. The switching control unit outputs a TTL level signal to control the port switching of the MEMS optical switch. The switching sequence refers to the order in which the MEMS optical switch sequentially turns on each laser, allowing lasers of different wavelengths to enter the mixed reference gas cell for calibration. The switching sequence can be preset by the host computer software. After switching, a synchronization signal is output to the lock-in amplifier. The data processing unit uses a wavelet transform algorithm to filter the acquired light intensity signal and a Lorentz fitting algorithm to locate the center wavelength of the light intensity valley (corresponding to the absorption peak). Combined with data from the temperature and pressure correction unit, a precise wavelength value is obtained. The current calibration unit has built-in current-wavelength calibration curves for each laser. Based on the target absorption peak wavelength, it queries the corresponding drive current value and outputs a correction signal to the laser drive circuit.

[0051] The embodiments described above employ temperature and pressure correction combined with current-wavelength correlation model technology. By using PID temperature control to maintain the ambient temperature difference within ±0.1℃, and combining real-time data from the pressure sensor to correct the absorption peak wavelength, the calibration accuracy problem caused by environmental temperature and pressure fluctuations is solved. The control module has a built-in current-wavelength correspondence model, which can directly locate the bias current corresponding to the absorption peak from the light intensity-current curve without the need for additional wavelength measurement equipment, thus solving the cumbersome problem of offline calibration of the current-wavelength relationship in the prior art.

[0052] The core principle of the above embodiments of this application is as follows: using the characteristic absorption spectra of multiple (e.g., 6) gas components in the mixed reference gas chamber as a "wavelength scale", a MEMS optical switch is used to realize the rapid optical path switching between multiple lasers and a single mixed gas chamber, a photodetector is used to directly detect the changes in transmitted light intensity, and the position of the characteristic absorption peak is accurately located by the light intensity valley value; combined with the linear correlation between the laser driving current and the wavelength, the driving current corresponding to the absorption peak is directly extracted from the light intensity-current curve as the bias current, eliminating the photoacoustic signal conversion link and simplifying the calibration process; environmental interference is eliminated by temperature and pressure correction, and finally, high-precision determination of the bias current of each laser and wavelength calibration are achieved.

[0053] The system in the above embodiments of this application has the following connection relationship between modules: laser emitting module (e.g., 6 lasers) → optical path switching module (MEMS optical switch) → hybrid reference gas chamber module (sealed gas chamber with temperature and pressure sensor) → photoelectric detection module (photodetector + preamplifier) ​​→ signal processing module (lock-in amplifier + data acquisition card + temperature and pressure correction unit) → control module (embedded controller). The control module is connected to the laser emitting module and the optical path switching module through reverse feedback to form a closed-loop system. The MEMS optical switch is additionally connected to a standard laser wavelength meter as a calibration terminal.

[0054] Taking six lasers as an example, the calibration system operates based on a closed-loop process of "optical path switching - wavelength scanning - light intensity signal detection - peak current determination". Combining the fast switching characteristics of MEMS optical switches with the simplicity of direct light intensity detection, it achieves sequential high-precision wavelength calibration and bias current determination for the six lasers. The specific working process is as follows: (1) System initialization: After the control module starts, it first heats the temperature of the mixed reference gas chamber to 25°C and stabilizes it through the temperature and pressure control unit, and maintains the pressure at 0.1MPa. At the same time, it calls the standard laser wavelength meter through the calibration terminal of the MEMS optical switch to perform a self-check on the optical path switching accuracy of the six input and output terminals of the optical switch, ensuring that the transmission error is ≤0.001nm. The control module retrieves the standard characteristic absorption peak wavelengths of the six gas components from the HITRAN database (such as acetylene 1530.36nm, ethylene 1620.4nm, etc.), and performs preliminary correction through the temperature and pressure correction unit according to the current temperature and pressure data of the gas chamber to obtain the corrected standard target wavelengths λ1-λ6. At the same time, it loads the preset current-wavelength calibration initial curves of each laser.

[0055] (2) Optical path switching and wavelength scanning: The control module controls the MEMS optical switch to switch to the input terminal corresponding to the first laser (such as a methane laser) by switching the output signal of the control unit, so that the output optical path of the methane laser is connected to the mixed reference gas cell; then the scanning control unit outputs a sawtooth wave drive signal to control the driving current of the methane laser to be linearly adjusted from 100mA to 150mA, so as to realize continuous scanning of the laser wavelength in the range of 1653.5-1654.0nm, the scanning rate is set to 0.05nm / ms, and the driving current value I at each moment is recorded in real time. x The correspondence between the time and the scan time t.

[0056] (3) Acquisition and processing of light intensity signal: When the scanning wavelength matches the characteristic absorption peak wavelength of methane in the mixed reference gas chamber, the laser energy is absorbed by the methane molecules, and the transmitted light intensity is significantly reduced to form a light intensity valley. The transmitted light is received by the photodetector of the photoelectric detection module and converted into a weak electrical signal proportional to the light intensity. After being amplified 500 times by the preamplifier, it is transmitted to the lock-in amplifier. The lock-in amplifier uses the synchronization signal output by the control module as a reference, suppresses ambient light and circuit noise, and transmits the extracted effective light intensity signal to the data acquisition card. After being converted into a digital signal, it is uploaded to the data processing unit of the control module.

[0057] (4) Absorption peak location and bias current determination: The data processing unit performs wavelet filtering on the digital light intensity signal to remove high-frequency noise, and then plots the "light intensity-scanning time" curve. Combined with the "current-time" relationship recorded by the scanning control unit, the "light intensity-driving current" curve is obtained. The Lorentz fitting algorithm is used to fit the light intensity valley value in the curve to locate the driving current I corresponding to the valley value. m1 Simultaneously calculate the measured wavelength λ corresponding to this valley value. m1 ; will λ m1 Compared with the corrected standard target wavelength λ1, if the wavelength deviation Δλ1=|λ m1 If -λ1|≤0.002nm, then I can be directly applied. m1 The bias current after calibration of the laser is determined; if Δλ1 > 0.002 nm, the current correction ΔI1 is calculated based on the current-wavelength calibration curve, and the drive current is adjusted to I. m1 After +ΔI1, the scanning process is repeated, that is, the same laser is scanned and calibrated multiple times until the wavelength deviation meets the requirements, and finally the calibrated bias current is determined and stored.

[0058] (5) Multi-laser cyclic calibration: After the bias current of the methane laser is determined, the control module controls the MEMS optical switch to switch sequentially to the input terminals corresponding to the second (ethane), third (ethylene)...sixth (carbon dioxide) lasers, repeating the process of steps (2)-(4) to complete the wavelength scanning, absorption peak positioning and bias current determination of the six lasers respectively; the entire cyclic calibration process takes ≤8s, and there is no need to readjust the optical path during the switching process. The bias current of each laser after calibration is automatically stored in the register of the control module for use during detection. The final calibration accuracy of the system in the above embodiment of this application is ±0.001nm.

[0059] The embodiments described above in this application achieve high-precision, fast, and low-cost calibration of laser wavelengths in multi-component gas detection scenarios through the synergistic effect of a multi-component mixed reference gas chamber, MEMS optical switch, direct light intensity detection, and temperature and pressure correction. This overcomes the combined problems of low integration, slow calibration, insufficient accuracy, poor scalability, and high cost of existing technologies.

[0060] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0061] The following examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.

[0062] By building a hardware system and providing supporting control software, as well as parameter matching and coordinated control of each module, the calibration system in the above embodiments of this application can be applied to different application scenarios.

[0063] Application Example 1: High-precision calibration scenario in the laboratory This application example is used by a metrology and testing institution to perform traceability-level calibration of the laser in a multi-component gas analyzer, requiring a wavelength calibration accuracy of ±0.001nm and a cycle calibration time of ≤10s.

[0064] Hardware selection and setup: Laser emission module: Six distributed feedback (DFB) tunable semiconductor lasers are selected, each matched to a characteristic wavelength of a gas (such as C2H2: 1530.36nm, CH4: 1653.7nm, CO2: 1570nm, etc.), with a wavelength tuning accuracy of ±0.0005nm. Optical path switching module: An 8-port MEMS optical switch (model: AGILTRON MEMS-8×1) is selected, with insertion loss ≤0.2dB and switching response time of 0.8ms. The calibration end is connected to a high-precision laser wavelength meter (model: Bristol 621A, accuracy ±0.0001nm). Mixed reference gas chamber module: A custom 100mm long quartz gas chamber is filled with 1% (volume fraction) of 6-component mixed standard gas (purity 99.999%). The temperature and pressure sensors used are PT1000 (accuracy ±0.02℃) and Keller PA-21Y (accuracy ±0.0005MPa), and the temperature control accuracy is ±0.05℃. Photodetector module: InGaAs photodetector (model: Thorlabs PDA10CS-EC, responsivity 1.0A / W, dark current 0.5nA) is selected, and low-noise preamplifier (model: Stanford SR560, amplification factor 1000x) is selected. Control module: ARM Cortex-A9 embedded controller (model: NVIDIA Jetson TK1) is selected, and LabVIEW-based control software is developed to match it, integrating HITRAN 2020 database and Gauss-Lorentz fitting algorithm.

[0065] Implementation process: System initialization: After startup, stabilize the gas chamber temperature at 25.00℃±0.05℃ and the pressure at 0.1000MPa±0.0005MPa. Calibrate the transmission accuracy of the MEMS optical switch using a wavelength meter to ensure that the error is ≤0.0005nm. Cyclic calibration: The MEMS optical switch is controlled to switch to each laser in sequence. Each laser scans at a rate of 0.02nm / ms. After collecting the light intensity signal, the absorption peak is located by double Gaussian fitting. The wavelength is corrected by combining temperature and pressure data. When the deviation is >0.001nm, the current is adjusted and the scan is repeated. Results output: After calibration, the bias current of each laser is stored (e.g., the current of the methane laser after calibration is 125.3mA), and a calibration report is generated. The entire process takes 7.2s, and the wavelength calibration accuracy is ±0.0008nm.

[0066] Application Example 2: Rapid Calibration Scenarios in Industrial Fields This application example is used for the on-site periodic calibration of multi-component gas online monitoring equipment in a chemical industrial park. It is required to be able to withstand industrial environmental interference, with a single calibration time of ≤5s and a calibration accuracy of ±0.002nm.

[0067] Hardware selection and setup: Laser emission module: Uses an industrial-grade DFB laser (model: Sacher Lasertechnik TEC-100) with a wide operating temperature range (-20℃~60℃). Optical path switching module: An industrial-grade 8-port MEMS optical switch (model: NeoPhotonics MX100) with IP65 protection rating and a switching response time of 0.5ms is selected; Hybrid reference chamber module: The chamber is made of stainless steel (80mm in length), with an internal shockproof structure. The temperature and pressure sensors are industrial grade models (temperature accuracy ±0.1℃, pressure accuracy ±0.001MPa). Photoelectric detection module: An anti-interference photoelectric detector (model: Hamamatsu H10721-01) is selected, with a built-in electromagnetic shielding layer and a preamplifier with a fixed amplification factor of 500 times; Control module: An industrial-grade embedded controller (model: Advantech ARK-2120) is selected, equipped with a real-time operating system, and the simplified fitting algorithm is Lorentz single-peak fitting.

[0068] Implementation process: Environmental adaptability: The system is connected to a 24V DC power supply on site, and the temperature of the air chamber is stabilized at 25℃±0.1℃ through the insulation jacket, and the pressure is automatically compensated to the standard atmospheric pressure; Rapid calibration: The “pre-scan + fine scan” mode is adopted. First, a coarse scan is performed at a rate of 0.1nm / ms to locate the approximate range of the absorption peak, and then a fine scan is performed at a rate of 0.03nm / ms. The MEMS optical switch switching interval is 0.5ms. Data upload: After calibration, the bias current of each laser is written into the monitoring device register, and the calibration record is uploaded via 4G module. The whole process takes 4.5 seconds, and the calibration accuracy is ±0.0015nm under the electromagnetic interference environment on site.

[0069] Application Example 3: Calibration Scenario for Portable Testing Equipment This application example is used for the factory calibration of a portable multi-component gas detector. The system is required to be small in size (≤300mm×200mm×100mm), lightweight (≤2kg), and have a calibration accuracy of ±0.002nm.

[0070] Hardware selection and setup: Laser emission module: A miniaturized DFB laser (model: Thorlabs DL100, size 14mm×14mm×4mm) is selected. Optical path switching module: A miniature 8-port MEMS optical switch (model: Fujitsu FMSW-81, size 20mm×15mm×5mm) is selected. Hybrid reference chamber module: Uses a miniature quartz chamber (50mm in length, 10mm in outer diameter) and integrates a miniature temperature and pressure sensor (model: Bosch BME280). Photoelectric detection module: A miniature photoelectric detector (model: Excelitas XC1266, size 5mm×5mm) is selected and integrated with the preamplifier. Control module: A miniature embedded controller (model: Raspberry Pi Pico, 133MHz) was selected, and the control program was optimized, retaining only the core calibration algorithm.

[0071] Implementation process: Miniaturized integration: Each module is integrated and fixed via a PCB board, with a total weight of 1.8kg. It is powered by a 5V lithium battery and has a standby time of ≥4 hours. Simplified calibration: Preset the scanning range of each laser (e.g., fix the acetylene laser at 1530.3~1530.4nm), shorten the scanning time, and use a fast Lorentz fitting algorithm; Batch calibration: Connect to a computer via USB interface to calibrate up to 10 portable devices at a time. The calibration time for a single device is 6 seconds, with a calibration accuracy of ±0.0018nm, meeting factory calibration requirements.

[0072] In the description of the embodiments of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0073] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0074] In the description of the embodiments in this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0075] The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or devices.

[0076] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A high-precision laser absorption spectroscopy wavelength calibration system for multi-component gas detection, characterized in that, include: The laser emitting module includes multiple lasers, each laser having a wavelength tuning range covering at least one characteristic absorption line of the corresponding gas component; The optical path switching module uses a MEMS optical switch, with the collimator output of each laser connected to the corresponding input of the MEMS optical switch. The hybrid reference gas chamber module includes a sealed gas chamber with an entrance window at one end and an exit window at the other end. The gas chamber is filled with a mixed standard gas. The entrance window is coupled to the output end of the MEMS optical switch. The hybrid reference gas chamber module is equipped with a temperature sensor and a pressure sensor. The photoelectric detection module is located directly behind the exit window and is used to detect the intensity of the transmitted laser light after passing through the gas chamber. The signal processing module, connected to the photoelectric detection module, is used to process the intensity of transmitted laser light. It includes a temperature and pressure correction unit connected to a temperature sensor and a pressure sensor, which is used to correct the wavelength corresponding to the characteristic absorption peak based on temperature and pressure data. The control module is connected to the laser emission module, the optical path switching module, and the signal processing module respectively, forming a closed-loop calibration system.

2. The system according to claim 1, characterized in that, The parallelism error of the laser beam after collimation of multiple lasers is ≤0.1mrad.

3. The system according to claim 1, characterized in that, The coaxiality of the input end of the MEMS optical switch and the collimator is calibrated by a three-dimensional adjustment frame, and the coaxiality error is ≤0.2mm.

4. The system according to claim 1, characterized in that, The output end of the MEMS optical switch is coupled to the incident window via a quartz optical fiber, and the optical fiber connector is an FC / APC connector.

5. The system according to claim 1, characterized in that, The MEMS optical switch has a calibration terminal, which is connected to a standard laser wavelength meter.

6. The system according to claim 1, characterized in that, The pressure sensor is embedded inside the air chamber, the air chamber is wrapped with an insulation sleeve, and the temperature sensor and heating element are embedded inside the insulation sleeve.

7. The system according to claim 1, characterized in that, The incident window of the hybrid reference gas chamber module is coupled to the optical fiber at the output end of the optical path switching module through a focusing lens to ensure that the laser beam is focused on the central region of the gas chamber.

8. The system according to claim 1, characterized in that, The photoelectric detection module includes: A photodetector, fixed directly behind the exit window, is used to receive the transmitted laser light after it passes through the gas chamber and convert the light intensity signal into an electrical signal. A preamplifier, connected to the photodetector, is used to amplify the electrical signal to a range that can be collected.

9. The system according to claim 8, characterized in that, The signal processing module further includes: A lock-in amplifier, whose input terminal is connected to the output terminal of the preamplifier of the photoelectric detection module, and whose reference signal input terminal is connected to the synchronization signal output terminal of the control module, is used to suppress ambient light noise and extract effective light intensity signals. The data acquisition card, whose input terminal is connected to the output terminal of the lock-in amplifier, is used to convert the effective light intensity signal into a digital light intensity signal.

10. The system according to claim 9, characterized in that, The control module includes: The scanning control unit is used to output the laser drive current, control the continuous scanning of the laser wavelength, and record the correspondence between the drive current and the scanning time in real time. The switching control unit is used to output the MEMS optical switch switching signal and output a synchronization signal to the lock-in amplifier after the switching is completed; The data processing unit is used to obtain the correspondence between light intensity and driving current based on the correspondence between digital light intensity signal, driving current and scanning time, locate the center wavelength of light intensity valley based on the correspondence between light intensity and driving current, and obtain the accurate wavelength value by combining the data from the temperature and pressure correction unit. The current calibration unit has built-in current-wavelength calibration curves for each laser. It determines the corresponding drive current value based on the target absorption peak wavelength and outputs a correction signal to the laser emission module.

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