GaSb single-frequency laser and dual-wavelength differential multi-gas trace detection system and method based on GaSb single-frequency laser

Abstract

This application provides a GaSb single-frequency laser and a dual-wavelength differential multi-gas trace detection system and method based on the GaSb single-frequency laser, belonging to the field of gas detection. It solves the problems of insufficient sensitivity, slow response, susceptibility to environmental interference, and lack of domestically produced core light sources in existing gas detection instruments. The system uses a 1950nm high-power GaSb single-frequency laser as the core light source, adopts a WMS-2f wavelength modulation detection scheme to eliminate low-frequency 1 / f noise, and uses a dual-wavelength differential absorption scheme to achieve rapid switching between the two wavelengths through the unique temperature-tunable characteristics of the GaSb single-frequency laser. Together, these three elements constitute the complete technical solution for achieving ppb-level trace gas detection in this application. This application can perform in-situ, online, and high-precision concentration measurement of the characteristic absorption lines of various gas molecules in industrial processes, new energy equipment, life sciences, and environmental monitoring at the ppb level.

Description

Technical Field

[0001] This application relates to the field of gas detection technology, and in particular to a GaSb single-frequency laser and a dual-wavelength differential multi-gas trace detection system and method based on the GaSb single-frequency laser. Background Technology

[0002] Trace gas detection is a common key technology in industrial process control, safety early warning, environmental monitoring, and life science research. In the field of new energy battery manufacturing, real-time online monitoring of ppb-level H2O is required in the electrode drying process before cell packaging and in the sealing and leak detection after liquid injection. Excessive residual moisture is a major cause of battery bulging, internal short circuits, and thermal runaway. In the field of hydrogen energy equipment, fuel cell stacks require H2O content in hydrogen to be below 5 ppm (ISO 14687 standard), otherwise it will cause proton exchange membrane poisoning. In the field of semiconductor wafer manufacturing, ppb-level H2O in the process cavity can significantly reduce device yield. ppb represents parts per billion, and ppm represents parts per million. ppb-level H2O refers to the trace moisture content in a gas / high-purity medium, indicating that the water vapor content in the system is controlled at the part per billion level, representing an extremely dry, ultra-high-purity anhydrous environment, which is a core quality control indicator for semiconductors, optoelectronic devices, and vacuum processes.

[0003] However, existing gas detection methods have the following shortcomings:

[0004] (1) Traditional methods such as electrochemical sensors, dew point meters, and gas chromatography have slow response speeds (minutes), require sampling pipelines, and have high maintenance costs, which cannot meet the millisecond-level cycle time requirements of GWh-level production lines;

[0005] (2) Although the tunable diode laser absorption spectroscopy (TDLAS) system based on the 1550nm band has been commercialized, the characteristic absorption intensity of H2O and CO2 gas molecules is weak in the 1550nm band, making it difficult to achieve ppb-level detection sensitivity.

[0006] (3) The 2μm band (especially the 1950nm band) contains strong characteristic absorption spectra of gas molecules such as H2O and CO2. Theoretically, the detection sensitivity can be improved by 1 to 2 orders of magnitude compared with the 1550nm band. However, commercial laser sources in this band are scarce at present, and China is highly dependent on imports. Moreover, the power is generally low (mostly in the tens of milliwatts range), which makes it difficult to support trace detection with long optical path and high signal-to-noise ratio.

[0007] (4) Conventional single-wavelength absorption spectroscopy detection is susceptible to laser intensity drift, optical path contamination, low-frequency environmental disturbances and background noise interference. The frequency drift of the single-frequency laser will also be directly converted into concentration measurement error, resulting in insufficient long-term stability of the system.

[0008] (5) Existing TDLAS systems mostly use free space optical paths, which are large in structure and sensitive to vibration, making them difficult to adapt to the harsh working conditions in industrial sites. Summary of the Invention

[0009] To address the issues of insufficient sensitivity, slow response, susceptibility to environmental interference, and lack of domestically produced core light sources in existing gas detection instruments, this application proposes a GaSb single-frequency laser and a dual-wavelength differential multi-gas trace detection system and method based on the GaSb single-frequency laser. Using a 1950nm high-power single-frequency GaSb laser as the core light source, and employing a wavelength modulation spectroscopy (WMS) and dual-wavelength differential detection scheme, the fully fiber-optic integrated multi-gas trace detection system achieves ppb-level sensitivity, millisecond-level response, and strong anti-interference capabilities.

[0010] The technical solution adopted in this application is: a GaSb single-frequency laser, which is composed of a GaSb quantum well FP gain chip, an input fiber lens, a fiber Bragg grating, a polarization-maintaining fiber magneto-optical isolator, an output fiber lens, and a GaSb tapered amplifier connected in series, wherein the fiber Bragg grating is set in the polarization-maintaining single-mode fiber.

[0011] The laser emitted from the front end of the GaSb quantum well FP gain chip is collimated and coupled into the polarization-maintaining single-mode fiber via the input fiber lens. The light propagating in the polarization-maintaining single-mode fiber reaches the fiber Bragg grating, which reflects the light of a specific wavelength back to the GaSb quantum well FP gain chip, forming an external cavity feedback loop that forces the GaSb quantum well FP gain chip to oscillate stably in a single longitudinal mode. The single-frequency seed light output from the transmission direction of the fiber Bragg grating is suppressed by the polarization-maintaining fiber magneto-optical isolator and then passes through the polarization-maintaining single-mode fiber to the output fiber lens. The output fiber lens performs mode collimation and focusing control on the output beam, so that the beam is coupled into the input end of the GaSb tapered amplifier with appropriate mode field matching parameters. The GaSb tapered amplifier amplifies the single-frequency seed light in a single pass, and outputs a high-power single-frequency laser from the output end of the GaSb tapered amplifier.

[0012] Furthermore, the GaSb quantum well FP gain chip operates at wavelengths ranging from 1800nm ​​to 2300nm. The front face of the GaSb quantum well FP gain chip is coated with an antireflection film to establish external cavity oscillation under fiber Bragg grating feedback. The rear face of the GaSb quantum well FP gain chip is coated with a high-reflection film to serve as a single-sided mirror of the external cavity.

[0013] Furthermore, a fiber Bragg grating with a center wavelength of 1950nm, a reflectivity of 10%~30%, and a bandwidth of ≤0.5nm is arranged in the polarization-maintaining single-mode fiber.

[0014] Furthermore, the GaSb tapered amplifier uses a GaSb quantum well tapered amplifier chip with an operating wavelength covering 1800nm~2300nm, and both ends of the GaSb quantum well tapered amplifier chip are coated with antireflection films.

[0015] A dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser includes:

[0016] Laser source module: including the aforementioned GaSb single-frequency laser, used to output single-frequency laser;

[0017] Signal modulation module: used to apply a modulation signal to the injected current of the laser source module and periodically switch the operating temperature of the laser source module, and to perform dual-wavelength differential between the absorption line wavelength of the gas molecules to be measured and the reference wavelength;

[0018] Gas sensing module: used to convert the single-frequency laser output from the laser source module into a laser signal that combines the molecules of the gas to be measured and a reference light signal for output;

[0019] Photoelectric detection module: used to detect the laser signal and reference light signal that are combined with the gas molecules to be measured, output differential photocurrent and transmit it to the data acquisition and processing module;

[0020] Data acquisition and processing module: used to demodulate differential photocurrent and perform gas concentration inversion.

[0021] Furthermore, the laser source module also includes a first TEC temperature control module, a second TEC temperature control module, and a laser driving current source. The first TEC temperature control module is used to regulate the operating temperature of the GaSb tapered amplifier in real time, the second TEC temperature control module is used to regulate the operating temperature of the GaSb quantum well FP gain chip in real time, and the laser driving current source is used to provide stable bias current and modulation current to the GaSb quantum well FP gain chip and the GaSb tapered amplifier.

[0022] Furthermore, the signal modulation module includes a laser drive current modulation unit and a temperature control unit. These are used to apply a high-frequency sinusoidal modulation signal to the injected current of the laser source module and superimpose a low-frequency sawtooth scanning signal to achieve wavelength modulation spectral operation. Simultaneously, the temperature control unit periodically switches the operating temperature of the laser source module to switch the laser wavelength, thus achieving wavelength switching at the absorption line. and reference wavelength Two-wavelength differential is performed between them.

[0023] Furthermore, the gas sensing module includes a beam splitter, a reference optical path, and a sample optical path. A gas absorption cell is provided in the sample optical path, with a gas inlet at the bottom and a gas outlet at the top. The photoelectric detection module includes a reference detector and a sample detector.

[0024] The single-frequency laser output from the laser source module is split into probe light and reference light by a beam splitter. The reference light is directly input to the reference detector, and the probe light is input to the sample detector after passing through the gas absorption cell.

[0025] The reference detector and sample detector use extended wavelength InGaAs photodetectors to detect the laser signal and reference light signal after passing through the gas absorption cell, and output differential photocurrent.

[0026] Furthermore, the data acquisition and processing module includes a data acquisition card, a lock-in amplifier, and an industrial computer. The industrial computer integrates a dual-wavelength differential operation module and a concentration inversion module, used to perform second harmonic demodulation on the output signal of the photoelectric detection module to obtain a 2f signal proportional to the gas concentration; and to perform second harmonic demodulation on the absorption line wavelength. and reference wavelength The gas concentration is retrieved by subtracting the 2f signal from the 2f signal and eliminating common-mode interference.

[0027] A dual-wavelength differential multi-gas trace detection method based on GaSb single-frequency laser, employing the aforementioned dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser, includes the following steps:

[0028] S1: The laser source module outputs the required single-frequency laser. A high-frequency sinusoidal modulation signal and a low-frequency sawtooth scanning signal are applied to the injected current of the laser source module via the signal modulation module, causing the laser center wavelength to surround the absorption line wavelength of the gas molecules being measured. It produces periodic small-amplitude modulation;

[0029] S2: After the laser is collimated by the optical fiber, it is split into two paths by the beam splitter: one path enters the gas absorption cell containing the gas to be measured, and the other path goes directly to the reference detector reference optical path for normalizing the light intensity drift.

[0030] S3: After passing through the gas absorption cell, the laser is selectively absorbed by the molecules of the gas to be measured, carrying gas concentration information, which is then converted into an electrical signal by the sample detector;

[0031] S4: The data acquisition and processing module performs digital phase-locking on the output signal of the sample detector and demodulates the 2f signal at twice the modulation frequency. ;

[0032] S5: The system periodically switches the operating temperature of the laser source module, causing the laser center wavelength to change from the absorption line wavelength. Switch to a nearby non-absorption reference wavelength , The reference wavelength is obtained. 2f reference signal below ;

[0033] S6: Absorption line wavelength and reference wavelength The difference between the 2f signals at the two wavelengths is used to obtain the net second harmonic signal caused only by the absorption of the gas molecules being measured.

[0034] S7: Based on the pre-calibrated concentration-2f signal relationship curve, the gas concentration value is obtained by inversion and output.

[0035] The advantages of this application over the prior art are as follows:

[0036] (1) Detection sensitivity is significantly improved:

[0037] This application employs a 1950nm wavelength laser, which precisely corresponds to the strong characteristic absorption lines of gas molecules such as H2O and CO2. Combined with a high-power (>1W) light source and a long-path, multiple-reflection gas absorption cell, the detection limit is pushed to the ppb level, which is 1 to 2 orders of magnitude higher than the existing 1550nm wavelength TDLAS system. This meets the urgent needs of high-end scenarios such as new energy manufacturing and semiconductor processes for trace gas analysis.

[0038] (2) Excellent anti-interference ability:

[0039] The dual-wavelength differential absorption detection scheme effectively cancels common-mode interference such as laser power drift, optical window contamination, detector response changes, and ambient temperature disturbances; WMS-2f phase-locked demodulation shifts the measurement signal to the high-frequency domain, avoiding low-frequency 1 / f noise (flicker noise), and baseline drift is controlled within ±2% / 72h, resulting in excellent long-term system stability.

[0040] (3) Fast response speed, supports online detection:

[0041] The spectral detection method itself is a direct optical response, without any delay steps such as sampling and enrichment. Combined with the rapid gas replacement design in the gas absorption cell, the system response time is <1s, which is 2 to 3 orders of magnitude better than traditional offline methods such as chromatography and dew point meters. It can meet the millisecond-level cycle time requirements of GWh-level battery production lines.

[0042] (4) The system has a compact structure and is suitable for industrial sites:

[0043] The light source and signal link are fully integrated with fiber optics, making it resistant to vibration and impact; the modular design of the whole machine facilitates installation and maintenance, and can be directly embedded into existing industrial equipment or production lines.

[0044] (5) Multi-gas compatible platform architecture:

[0045] By replacing the laser source module, the characteristic absorption lines of various gas molecules such as H2O, CO2, CH4, HF, N2O, and CO in the 1800~2300nm wavelength range can be covered, which has good scalability and forms a general gas analysis and measurement platform.

[0046] (6) Localization of core components:

[0047] The core laser source module of this application adopts a self-developed 1950nm GaSb single-frequency laser, breaking through the bottleneck of long-term reliance on imports for the core source of high-end laser spectrometers. Attached Figure Description

[0048] The following description, in conjunction with the accompanying drawings, further illustrates this application:

[0049] Figure 1 This is a schematic diagram of the optical path structure of a 1950nm GaSb single-frequency laser source module provided in an embodiment of this application.

[0050] Figure 2 This is a schematic diagram of the overall structure of the gas trace detection system provided in the embodiments of this application;

[0051] Figure 3 This is a schematic diagram of the dual-wavelength differential absorption detection principle provided in the embodiments of this application. In the figure, (3a) represents the absorption line wavelength. and reference wavelength The positional relationship on both sides of the absorption line, (3b) indicates the wavelength of the absorption line. and reference wavelength A schematic diagram of the difference between the 2f signals, i.e., the net absorbed signal;

[0052] Figure 4 This is a schematic diagram illustrating the principle of WMS-2f wavelength modulation spectrum signal generation and demodulation.

[0053] Figure 5 The system timing control diagram is shown in the figure. (5a) is the high-frequency sinusoidal modulation signal, (5b) is the low-frequency sawtooth scanning signal, and (5c) is the dual-wavelength switching signal.

[0054] Figure 6 This is a schematic diagram of a multi-reflection gas absorption cell (Herriott type);

[0055] In the diagram: 100 is the laser source module, 200 is the signal modulation module, 300 is the gas sensing module, 400 is the photoelectric detection module, 500 is the data acquisition and processing module, 600 is the host computer, 101 is the GaSb quantum well FP gain chip, 102 is the input fiber optic lens, 103 is the fiber Bragg grating, 104 is the polarization-maintaining fiber magneto-optic isolator, 105 is the output fiber optic lens, 106 is the GaSb tapered amplifier, 107 is the first TEC temperature control module, 108 is the second TEC temperature control module, and 10... 9 is the laser driving current source, 201 is the laser driving current modulation unit, 202 is the temperature control unit, 301 is the beam splitter, 302 is the gas absorption cell, 3021 is the first concave mirror, 3022 is the second concave mirror, 303 is the gas inlet, 304 is the gas outlet, 305 is the filter, 306 is the mass flow controller, 401 is the reference detector, 402 is the sample detector, 501 is the data acquisition card, 502 is the lock-in amplifier, 503 is the dual-wavelength differential operation module, and 504 is the concentration inversion module. Detailed Implementation

[0056] like Figures 1 to 6 As shown, this application provides a GaSb single-frequency laser, which adopts a MOPA (Master Oscillator Power Amplifier) ​​architecture and is composed of a GaSb quantum well FP gain chip 101, an input fiber lens 102, a fiber Bragg grating 103 (FBG), a polarization-maintaining fiber magneto-optical isolator 104 (PM-ISO), an output fiber lens 105, and a GaSb tapered amplifier 106 connected in series.

[0057] The fiber Bragg grating 103 and the GaSb quantum well FP gain chip 101 form an external cavity feedback loop, outputting a single-frequency laser with a wavelength of 1950nm, power greater than 1W, and a side-mode rejection ratio (SMSR) greater than 40dB. The GaSb quantum well FP gain chip 101 provides gain in the 1950nm band and serves as the gain medium for external cavity feedback; the fiber Bragg grating 103 provides wavelength-selective external cavity feedback, locking the GaSb quantum well FP gain chip 101 into single-longitudinal-mode operation, outputting a single-frequency 1950nm laser with a power >10mW.

[0058] The input fiber lens 102 efficiently couples the emitted light from the GaSb quantum well FP gain chip 101 into the polarization-maintaining single-mode fiber. The polarization-maintaining fiber magneto-optical isolator 104 is used to suppress the backlight of the subsequent amplifier from disturbing the single-frequency seed light and ensure single-frequency stability. The output fiber lens 105 is used to collimate the single-frequency laser in the fiber and efficiently couple it into the input end of the GaSb tapered amplifier 106. The GaSb tapered amplifier 106 is used to amplify the single-frequency seed light with high power to achieve a power output of >1W.

[0059] Laser emitted from the front end of the GaSb quantum well FP gain chip 101 is collimated and coupled into a polarization-maintaining single-mode fiber via an input fiber lens 102. The light propagating in the polarization-maintaining single-mode fiber reaches a fiber Bragg grating 103, which reflects light of a specific wavelength (1950nm) back to the GaSb quantum well FP gain chip 101, forming an external cavity feedback loop that forces the GaSb quantum well FP gain chip 101 to oscillate stably in a single longitudinal mode (single frequency). The fiber Bragg grating 103 outputs a single-frequency seed light (power >10mW) in the transmission direction, which is then magneto-optically transmitted through the polarization-maintaining fiber. Isolator 104 suppresses back reflection and ensures the stability of single-frequency seed light. After passing through polarization-maintaining fiber magneto-optical isolator 104, the single-frequency seed light reaches the output fiber lens 105 through polarization-maintaining single-mode fiber. The output fiber lens 105 can perform mode collimation and focusing control on the fiber output beam, so that the beam is coupled into the input end (small port) of GaSb tapered amplifier 106 with appropriate mode field matching parameters. GaSb tapered amplifier 106 amplifies the single-frequency seed light once and outputs high-power single-frequency laser from the output end (large port) of GaSb tapered amplifier 106, with an output power >1W.

[0060] The GaSb quantum well FP gain chip 101 operates in the 2μm band (referring to a center wavelength of approximately 2μm, covering the near-infrared band from 1800nm ​​to 2300nm (i.e., 1.8μm to 2.3μm)). The front face of the GaSb quantum well FP gain chip 101 is coated with an antireflection (AR) film to establish external cavity oscillations under the feedback of the fiber Bragg grating 103; the rear face of the GaSb quantum well FP gain chip 101 is coated with a high reflectivity (HR) film, serving as a single-sided mirror for the external cavity.

[0061] The input fiber lens 102 is an aspherical fiber lens (numerical aperture NA matched to the chip divergence angle), with a target coupling efficiency of ≥60%. A fiber Bragg grating 103 with a center wavelength of 1950nm, a reflectivity of approximately 10%~30%, and a bandwidth ≤0.5nm is arranged in the polarization-maintaining single-mode fiber. The external cavity efficiency and single-frequency stability are optimized by adjusting the reflectivity of the fiber Bragg grating 103. This allows for a single-frequency laser power target >10mW and a side-mode suppression ratio (SMSR) >40dB.

[0062] The polarization-maintaining fiber magneto-optical isolator 104 has an isolation of ≥30dB and an insertion loss of ≤1dB. The slow axis of the polarization-maintaining fiber magneto-optical isolator 104 is aligned with the polarization-maintaining axis of the entire fiber optic link, ensuring polarization state preservation and isolation effectiveness.

[0063] The GaSb cone amplifier 106 uses a GaSb quantum well cone amplifier chip (SOA / TA) with an operating wavelength coverage of 1800nm~2300nm. Both ends of the GaSb quantum well cone amplifier chip are coated with AR films to suppress self-oscillation and ensure stable MOPA amplification under single-frequency seed light injection conditions. The drive current is set according to the saturated output power characteristics, with a target output power >1W (continuous wave CW mode). The GaSb quantum well cone amplifier chip is mounted on a high-precision temperature-controlled heat sink (temperature stability ±0.1℃) to maintain stable peak gain wavelength.

[0064] The GaSb single-frequency laser of this application has the following advantages:

[0065] External cavity structure: External cavity feedback is achieved by using fiber optic lens + FBG, which has the advantages of compact structure, high stability and easy fiber integration compared to free space external cavity;

[0066] Both ends of the optical fiber are integrated with optical fiber lenses: the input optical fiber lens 102 realizes efficient coupling of light output from the chip, and the output optical fiber lens 105 realizes efficient injection of single-frequency seed light into the GaSb tapered amplifier 106, thus solving the problem of mode field mismatch between semiconductor chip and optical fiber.

[0067] Fiber-optic integrated magneto-optical isolator: achieves full fiber isolation between the seed source and the amplifier, avoiding interference from stray reflected light on single-frequency operation;

[0068] GaSb material system: GaSb quantum well material is selected for the 1950nm band, which has a higher gain in the 1950nm band compared with the InP system;

[0069] The master oscillator power amplifier (MOPA) architecture decouples the seed source from the amplifier. The seed source independently ensures frequency purity and stability, while the amplifier independently optimizes power, overcoming the inherent contradiction of high power and single frequency in a single chip.

[0070] This application also provides a dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser, including a laser source module 100, a signal modulation module 200, a gas sensing module 300, a photoelectric detection module 400, a data acquisition and processing module 500, and a host computer 600. The laser source module 100 is used to output a single-frequency laser, and the signal modulation module 200 is used to apply a modulation signal to the injected current of the laser source module 100 and periodically switch the operating temperature of the laser source module 100 to control the wavelength switching (wide wavelength variation) of the GaSb single-frequency laser. A dual-wavelength differential is performed between the absorption line wavelength and the reference wavelength. The single-frequency laser output from the laser source module 100 enters the gas sensing module 300. The gas sensing module 300 converts the single-frequency laser into a laser signal that combines with the gas molecules to be measured and a reference light signal for output. The photoelectric detection module 400 detects the laser signal and the reference light signal that combine with the gas molecules to be measured, outputs a differential photocurrent, and transmits it to the data acquisition and processing module 500. The data acquisition and processing module 500 demodulates the differential photocurrent and performs gas concentration inversion. The host computer 600 displays the relevant data and curves.

[0071] The laser source module 100 includes a GaSb single-frequency laser, a first TEC temperature control module 107, a second TEC temperature control module 108, and a laser driving current source 109. The first TEC temperature control module 107 is used to adjust the operating temperature of the GaSb tapered amplifier 106 in real time (which can change the wavelength of the laser within a small range). The second TEC temperature control module 108 is used to adjust the operating temperature of the GaSb quantum well FP gain chip 101 in real time (which can change the wavelength of the laser within a small range). The laser driving current source 109 is used to provide stable bias current and modulation current to the GaSb quantum well FP gain chip 101 and the GaSb tapered amplifier 106.

[0072] The GaSb single-frequency laser of this application adopts an all-fiber integrated structure. Compared with existing commercial 1550nm lasers and InP system lasers, the laser source module 100 of this application has the following irreplaceable advantages:

[0073] The 2μm operating wavelength band precisely covers the strong characteristic absorption lines of H2O gas molecules (around 1.87μm) and CO2 gas molecules (around 2.0μm), with an absorption cross-section that is 1 to 2 orders of magnitude higher than that of the 1550nm band, directly resulting in an order of magnitude increase in detection sensitivity.

[0074] With an output power greater than 1W, it supports long optical path multiple reflection cells (equivalent optical path of tens of meters), further improving the signal-to-noise ratio;

[0075] The side-mode suppression ratio (SMSR) is greater than 40 dB, and the narrow linewidth at a single frequency ensures the absorption spectral resolution, which is a prerequisite for achieving ppb-level detection.

[0076] With its fully fiber-optic integration, it naturally possesses vibration and shock resistance characteristics, making it suitable for harsh working conditions in industrial environments.

[0077] Furthermore, by replacing the GaSb quantum well FP gain chip 101 or adjusting the operating temperature, the output wavelength of the laser source module 100 can be flexibly adjusted within a wide wavelength range of 1800nm~2300nm, covering the characteristic absorption lines of various gases such as H2O, CO2, CH4, HF, N2O, and CO. The system architecture remains unchanged; only the laser needs to be updated to achieve the detection of different gases, demonstrating excellent platform scalability.

[0078] The signal modulation module 200 includes a laser drive current modulation unit 201 and a temperature control unit 202, used to apply a high-frequency sinusoidal modulation signal (frequency) to the injected current of the laser source module 100. =10~100kHz), superimposed low-frequency sawtooth scanning signal (frequency) =10~100Hz), realizing wavelength modulation spectrum (WMS) operation mode; at the same time, the operating temperature of the laser source module 100 can be periodically switched (switching period is 0.1~10s) by the temperature control unit 202, at the absorption line wavelength. and reference wavelength Two-wavelength differential is performed between them.

[0079] This application applies high-frequency sinusoidal modulation to the injection current of a GaSb single-frequency laser. When the laser passes through the gas absorption cell 302, the absorption signal is modulated to the high-frequency domain and then transmitted through the lock-in amplifier 502. The second harmonic signal (2f signal) is obtained by demodulation at the frequency. The WMS-2f method shifts the measurement signal to a higher frequency band, effectively avoiding low-frequency 1 / f noise interference; the peak value of the second harmonic is proportional to the gas concentration and is not sensitive to laser baseline drift, which significantly improves the detection accuracy.

[0080] The gas sensing module 300 includes a beam splitter 301, a gas absorption cell 302, a reference optical path, and a sample optical path. The gas absorption cell 302 is located in the sample optical path and is a long-path, multiple-reflection cell (typically with ≥30 reflections and an equivalent optical path of not less than 10m). A first concave mirror 3021 and a second concave mirror 3022 are installed in the gas absorption cell 302 to achieve multiple reflections of the laser. A gas inlet 303 is located at the bottom of the gas absorption cell 302, and a gas outlet 304 is located at the top of the gas absorption cell 302. A filter 305 is installed in the gas inlet 303. After being filtered and dust-removed, the gas enters the gas absorption cell 302 and interacts with the laser. A mass flow controller 306 is installed in the gas outlet 304.

[0081] The photoelectric detection module 400 includes a reference detector 401 and a sample detector 402. The single-frequency laser output from the laser source module 100 is split into a probe beam and a reference beam after passing through the beam splitter 301. The reference beam is directly input to the reference detector 401, and the probe beam is input to the sample detector 402 after passing through the gas absorption cell 302. The reference detector 401 and the sample detector 402 use an extended wavelength InGaAs photodetector (response band 1000nm~2300nm) to detect the laser signal and the reference beam signal after passing through the gas absorption cell 302 and output a differential photocurrent.

[0082] The data acquisition and processing module 500 includes a data acquisition card 501, a lock-in amplifier 502, and an industrial control computer. The industrial control computer integrates a dual-wavelength differential operation module 503 and a concentration inversion module 504, used to demodulate the second harmonic (2f) signal from the output signal of the photoelectric detection module 400 to obtain a second harmonic signal (WMS-2f) proportional to the gas concentration; and to perform second harmonic demodulation on the absorption line wavelength. and reference wavelength The difference between the 2f signals is used to eliminate common-mode interference, invert the gas concentration, and display it on the host computer 600.

[0083] This application utilizes the characteristic that the operating wavelength of a GaSb single-frequency laser can be precisely switched through temperature adjustment, periodically changing the laser center wavelength to the absorption line wavelength. (e.g., the characteristic absorption line of H2O gas molecules at 1950.10 nm) and adjacent reference wavelengths Switching between wavelengths (e.g., 1950.80nm, where there is no absorption by the gas molecules being measured) and wavelength intervals. 2f signals were acquired at both wavelengths. and The net absorption signal is obtained by subtracting the two. This method has the following unique advantages:

[0084] Common-mode interference, such as laser output power fluctuations, optical window contamination, and photodetector response drift, occurs in... and They are approximately equal at wavelength and are completely canceled out in difference operations;

[0085] The optical path thermal drift caused by changes in ambient temperature is a slowly varying signal, which can be regarded as a constant within the two wavelength switching cycles and is also canceled out by the differential.

[0086] Absorption line wavelength With reference wavelength The wavelength difference is extremely small (≤1nm), and the transmittance and reflectance of the optical element for the two wavelengths are almost identical, ensuring the effectiveness of common-mode suppression;

[0087] Reference wavelength While there may be no absorption by the target gas molecules, weak absorption by other gases may exist. This can be addressed by appropriately selecting the reference wavelength. The location can further reduce background gas cross-interference.

[0088] In this application's system, key links such as the laser source, fiber optic beam splitter, fiber optic isolation, and signal detection all utilize polarization-maintaining single-mode fiber connections, with a free-space optical path used only at the gas absorption cell 302. The entire system has a compact structure, can be modularly integrated, and is easy to deploy and maintain in industrial settings.

[0089] This application also provides a dual-wavelength differential multi-gas trace detection method based on GaSb single-frequency laser. Based on the above system structure, the method includes the following steps:

[0090] S1: The laser source module 100 outputs a single-frequency laser with a center wavelength of 1950nm and a power greater than 1W. A high-frequency sinusoidal modulation signal and a low-frequency sawtooth scanning signal are applied to the injected current of the laser source module 100 via the signal modulation module 200, causing the laser center wavelength to surround the absorption line wavelength of the gas molecules being measured. It produces periodic small-amplitude modulation;

[0091] S2: After the laser is collimated by the optical fiber, it is split into two paths by the beam splitter 301: one path enters the gas absorption cell 302 containing the gas to be measured (sample optical path), and the other path goes directly to the reference detector 401 (reference optical path) for normalizing the light intensity drift.

[0092] S3: After passing through the gas absorption cell 302, the laser is selectively absorbed by the molecules of the gas to be tested, carrying the gas concentration information, which is then converted into an electrical signal by the sample detector 402.

[0093] S4: The data acquisition and processing module 500 performs digital phase-locking on the output signal of the sample detector 402 and demodulates the 2f signal at twice the modulation frequency. The peak value of this signal is proportional to the gas concentration and is not affected by baseline drift.

[0094] S5: The system periodically switches the operating temperature of the laser source module 100, causing the laser center wavelength to change from the absorption line wavelength. Switch to a nearby non-absorption reference wavelength ( Repeat the above detection process to obtain the reference wavelength. 2f reference signal below ;

[0095] Specifically, the operating temperature of the laser source module 100 is adjusted to... This makes the laser wavelength located at Simultaneously, a high-frequency sinusoidal current modulation signal and a low-frequency sawtooth scanning signal are applied to acquire the 2f signal of the sample optical path. Then switch the operating temperature of the laser source module 100 to... This switches the laser wavelength to Acquire the 2f signal of the reference optical path. ;

[0096] S6: Absorption line wavelength and reference wavelength The difference between the 2f signals at the two wavelengths yields the net 2f signal caused solely by absorption by the gas molecules being measured. It effectively eliminates common-mode interference caused by laser power fluctuations, optical component contamination, window deposition, and changes in ambient temperature.

[0097] S7: Based on the pre-calibrated concentration-2f signal relationship curve, the gas concentration value is obtained by inversion and output to the host computer 600 for display.

[0098] The present application will be further described below with reference to specific embodiments.

[0099] Example 1: A ppb-level trace detection system for H2O gas

[0100] 1. Implementation plan for laser source module 100:

[0101] The 1950nm GaSb single-frequency laser source module is integrated according to the following structure:

[0102] The GaSb quantum well FP gain chip 101 is selected, with an anti-reflection (AR) coating on the front side and a high reflectance (HR) coating on the back side, and the working center wavelength covers 1950nm.

[0103] The light emitted from the front end of the GaSb quantum well FP gain chip 101 is coupled into the polarization-maintaining single-mode fiber via the input fiber lens 102 (numerical aperture NA is matched with the chip divergence angle), with a target coupling efficiency ≥60%.

[0104] A fiber Bragg grating 103 with a center wavelength of 1950.10 nm, a reflectivity of 20%, and a bandwidth of 0.3 nm is integrated in a polarization-maintaining single-mode fiber to provide wavelength-selective external cavity feedback to the GaSb quantum well FP gain chip 101, forcing the GaSb quantum well FP gain chip 101 to oscillate stably in a single longitudinal mode.

[0105] The single-frequency laser (power > 10mW, SMSR > 40dB) transmitted from the fiber Bragg grating 103 is suppressed for back reflection by the polarization-maintaining fiber magneto-optical isolator 104 (isolation ≥ 30dB, insertion loss ≤ 1dB).

[0106] The output of the polarization-maintaining fiber magneto-optical isolator 104 is collimated and focused by the output fiber lens 105, injecting single-frequency seed light into the small port of the GaSb tapered amplifier 106, with a target injection efficiency ≥50%.

[0107] The GaSb cone amplifier 106 has AR film coated on both ends. The drive current is set according to the saturation characteristics, and the continuous wave (CW) output power is >1W. It is mounted on a high-precision temperature-controlled heat sink with a temperature stability of ±0.1℃.

[0108] 2. Signal modulation implementation scheme:

[0109] The function generator in the laser drive current modulation unit 201 generates the following composite signal:

[0110] Low-frequency sawtooth scanning signal: frequency =50Hz, used to scan the laser wavelength covering the characteristic absorption line of H2O gas molecules (around 1950.10nm, linewidth about 0.02nm).

[0111] High-frequency sinusoidal modulation signal: frequency =20kHz, the modulation depth corresponds to a wavelength change of approximately 0.04nm (approximately twice the full width at half maximum of the characteristic absorption line of H2O gas molecules), used for WMS-2f detection;

[0112] Low-frequency dual-wavelength switching signal: The operating temperature of the GaSb single-frequency laser is controlled by the temperature control unit 202, at 25℃ (corresponding to...). =1950.10nm, the strong characteristic absorption line of H2O gas molecules) and 28℃ (corresponding to The wavelength (1950.80nm, without characteristic absorption of H2O gas molecules) switches periodically between these wavelengths, with a switching period of 1 second.

[0113] 3. Implementation plan for gas sensing module 300:

[0114] The gas absorption cell 302 is a long-path cell with multiple reflections (such as a Herriott cell or a White cell), with a cavity length of 0.3m and an actual equivalent optical path of 20m. The gas absorption cell 302 has wedge-shaped anti-reflection windows at both ends. Gas enters the cavity from the bottom gas inlet 303, passes through a 0.2μm filter 305, and exits from the top gas outlet 304. The sample gas path is equipped with a mass flow controller 306, with a typical sampling flow rate of 1 SLPM (Standard Liters Per Minute). The reference optical path bypasses the gas absorption cell 302 and goes directly to the reference detector 401.

[0115] 4. Detection and Data Processing Implementation Plan:

[0116] The sample optical path and reference optical path are detected by extended wavelength InGaAs photodetectors, and the signals enter the data acquisition card 501 (sampling rate ≥ 500 kS / s, resolution 16 bits). The lock-in amplifier 502 software running in the industrial control computer is in 2... The output signal of sample detector 402 is digitally demodulated at a frequency of 40kHz to obtain the 2f signal. and Perform difference operation The H2O gas concentration can be retrieved by pre-calibrating the curve.

[0117] Under the above implementation scheme, the system performance is as follows: H2O gas detection limit (LOD) <10ppb H2O (3σ criterion); linear dynamic range 10ppb~1000ppm; response time <1s (depending on the gas replacement process of gas absorption cell 302); baseline drift <2% / 72h; operating temperature range 5~50℃; total power consumption <50W.

[0118] Example 2: Online detection system for CO2 gas

[0119] The center wavelength of the fiber Bragg grating 103 in Example 1 was adjusted to 1997.20 nm (the strong absorption line characteristic of CO2 gas molecules), and the operating temperature of the GaSb quantum well FP gain chip 101 was adjusted to the corresponding wavelength. The rest of the structure was the same as in Example 1. The dual-wavelength switching was set to... =1997.20nm (characteristic strong absorption line of CO2 gas molecules) =1996.50nm (characteristic absorption of CO2 gas molecules). Under this implementation scheme, the CO2 gas detection limit is <50ppb and the response time is <1s, which can meet the needs of CO2 trace monitoring at the fuel cell inlet and measurement of atmospheric CO2 background concentration.

[0120] Example 3: Multi-gas sequential detection extended scheme

[0121] Multiple laser source modules 100 with different center wavelengths (e.g., 1950nm for H2O gas molecules, 1997nm for CO2 gas molecules, 2004nm for N2O gas molecules, etc.) are integrated on the same system platform. Each source is switched to a shared gas absorption cell 302 and detection channel via a 1×N fiber optic switch, enabling sequential measurement of multiple gases. The system architecture, modulation scheme, and differential processing are exactly the same as in the single-gas implementation. Only the wavelength switching timing and calibration curve need to be configured in the software to achieve multi-component trace analysis.

[0122] The above embodiments can be applied to online trace detection of H2O or CO2 gas in the electrode drying and liquid injection sealing stages of lithium-ion battery or fuel cell production lines. They can also be applied to real-time monitoring of trace H2O or CO2 components in hydrogen at hydrogen refueling stations or fuel cell inlets. Furthermore, they can be applied to in-situ online monitoring of H2O gas within semiconductor wafer manufacturing process chambers.

[0123] This application proposes using a 1950nm high-power GaSb single-frequency laser as the core light source, which solves the need for high-sensitivity detection with strong absorption band, high power, and narrow linewidth laser.

[0124] The WMS-2f wavelength modulation detection scheme eliminates low-frequency 1 / f noise and improves detection accuracy.

[0125] The dual-wavelength differential absorption scheme achieves dual-wavelength operation through the unique temperature-tunable characteristics of GaSb single-frequency lasers. Rapid switching effectively cancels out common-mode interference, which is the core difference between this application and all existing TDLAS systems and photothermal interferometry systems;

[0126] These three elements together constitute the complete technical solution for achieving ppb-level trace gas detection in this application.

[0127] This application enables in-situ, online, and high-precision concentration measurement of characteristic absorption lines of various gas molecules such as H2O, CO2, CH4, HF, and N2O at the ppb (parts per billion) level in fields such as industrial processes, new energy equipment, life sciences, and environmental monitoring. It is applicable to scenarios such as online quality inspection of lithium-ion battery and fuel cell production lines, purity monitoring of hydrogen energy equipment, gas analysis in semiconductor process chambers, atmospheric environment remote sensing, and medical breath diagnosis.

[0128] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A GaSb single-frequency laser, characterized in that: It consists of a GaSb quantum well FP gain chip, an input fiber lens, a fiber Bragg grating, a polarization-maintaining fiber magneto-optical isolator, an output fiber lens, and a GaSb tapered amplifier connected in series, wherein the fiber Bragg grating is set in the polarization-maintaining single-mode fiber; The laser emitted from the front end of the GaSb quantum well FP gain chip is collimated and coupled into the polarization-maintaining single-mode fiber through the input fiber lens. The light propagating in the polarization-maintaining single-mode fiber reaches the fiber Bragg grating, which reflects the light of a specific wavelength back to the GaSb quantum well FP gain chip, forming an external cavity feedback loop that forces the GaSb quantum well FP gain chip to oscillate stably in a single longitudinal mode. The single-frequency seed light output from the transmission direction of the fiber Bragg grating is suppressed by the polarization-maintaining fiber magneto-optical isolator and then passes through the polarization-maintaining single-mode fiber to the output fiber lens. The output fiber lens performs mode collimation and focusing control on the output beam, so that the beam is coupled into the input end of the GaSb tapered amplifier with appropriate mode field matching parameters. The GaSb tapered amplifier amplifies the single-frequency seed light in a single pass and outputs a high-power single-frequency laser from the output end of the GaSb tapered amplifier.

2. A GaSb single-frequency laser according to claim 1, characterized in that: The GaSb quantum well FP gain chip operates at wavelengths ranging from 1800nm ​​to 2300nm. The front face of the GaSb quantum well FP gain chip is coated with an antireflection film to establish external cavity oscillation under fiber Bragg grating feedback. The rear face of the GaSb quantum well FP gain chip is coated with a high-reflection film to serve as a single-sided mirror of the external cavity.

3. A GaSb single-frequency laser according to claim 1, characterized in that: A fiber Bragg grating with a center wavelength of 1950nm, a reflectivity of 10%~30%, and a bandwidth of ≤0.5nm is arranged in a polarization-maintaining single-mode fiber.

4. A GaSb single-frequency laser according to claim 1, characterized in that: The GaSb tapered amplifier uses a GaSb quantum well tapered amplifier chip with an operating wavelength covering 1800nm~2300nm. Both ends of the GaSb quantum well tapered amplifier chip are coated with antireflection films.

5. A dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser, characterized in that: include: Laser source module: includes a GaSb single-frequency laser as described in any one of claims 1-4, for outputting single-frequency laser; Signal modulation module: used to apply a modulation signal to the injected current of the laser source module and periodically switch the operating temperature of the laser source module, and to perform dual-wavelength differential between the absorption line wavelength of the gas molecules to be measured and the reference wavelength; Gas sensing module: used to convert the single-frequency laser output from the laser source module into a laser signal that combines the molecules of the gas to be measured and a reference light signal for output; Photoelectric detection module: used to detect the laser signal and reference light signal that are combined with the gas molecules to be measured, output differential photocurrent and transmit it to the data acquisition and processing module; Data acquisition and processing module: used to demodulate differential photocurrent and perform gas concentration inversion.

6. The dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser according to claim 5, characterized in that: The laser source module also includes a first TEC temperature control module, a second TEC temperature control module, and a laser driving current source. The first TEC temperature control module is used to regulate the operating temperature of the GaSb tapered amplifier in real time, the second TEC temperature control module is used to regulate the operating temperature of the GaSb quantum well FP gain chip in real time, and the laser driving current source is used to provide stable bias current and modulation current to the GaSb quantum well FP gain chip and the GaSb tapered amplifier.

7. The dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser according to claim 5, characterized in that: The signal modulation module includes a laser drive current modulation unit and a temperature control unit. It applies a high-frequency sinusoidal modulation signal to the injected current of the laser source module and superimposes a low-frequency sawtooth scanning signal to achieve wavelength modulation spectral operation. Simultaneously, the temperature control unit periodically switches the operating temperature of the laser source module to switch the laser wavelength, thus controlling the wavelength at the absorption line. and reference wavelength Two-wavelength differential is performed between them.

8. The dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser according to claim 7, characterized in that: The gas sensing module includes a beam splitter, a reference optical path, and a sample optical path. A gas absorption cell is provided in the sample optical path, with a gas inlet at the bottom and a gas outlet at the top. The photoelectric detection module includes a reference detector and a sample detector. The single-frequency laser output from the laser source module is split into probe light and reference light by a beam splitter. The reference light is directly input to the reference detector, and the probe light is input to the sample detector after passing through the gas absorption cell. The reference detector and sample detector use extended wavelength InGaAs photodetectors to detect the laser signal and reference light signal after passing through the gas absorption cell, and output differential photocurrent.

9. The dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser according to claim 8, characterized in that: The data acquisition and processing module includes a data acquisition card, a lock-in amplifier, and an industrial computer. The industrial computer integrates a dual-wavelength differential operation module and a concentration inversion module, used to perform second-harmonic demodulation on the output signal of the photoelectric detection module to obtain a 2f signal proportional to the gas concentration; and to process the absorption line wavelength... and reference wavelength The gas concentration is retrieved by subtracting the 2f signal from the 2f signal and eliminating common-mode interference.

10. A dual-wavelength differential multi-gas trace detection method based on GaSb single-frequency laser, characterized in that: The dual-wavelength differential multi-gas trace detection system based on GaSb single-frequency laser as described in any one of claims 5-9 includes the following steps: S1: The laser source module outputs the required single-frequency laser. A high-frequency sinusoidal modulation signal and a low-frequency sawtooth scanning signal are applied to the injected current of the laser source module via the signal modulation module, causing the laser center wavelength to surround the absorption line wavelength of the gas molecules being measured. It produces periodic small-amplitude modulation; S2: After the laser is collimated by the optical fiber, it is split into two paths by the beam splitter: one path enters the gas absorption cell containing the gas to be measured, and the other path goes directly to the reference detector reference optical path for normalizing the light intensity drift. S3: After passing through the gas absorption cell, the laser is selectively absorbed by the molecules of the gas to be measured, carrying gas concentration information, which is then converted into an electrical signal by the sample detector; S4: The data acquisition and processing module performs digital phase-locking on the output signal of the sample detector and demodulates the 2f signal at twice the modulation frequency. ; S5: The system periodically switches the operating temperature of the laser source module, causing the laser center wavelength to change from the absorption line wavelength. Switch to a nearby non-absorption reference wavelength , The reference wavelength is obtained. 2f reference signal below ; S6: Absorption line wavelength and reference wavelength The difference between the 2f signals at the two wavelengths is used to obtain the net second harmonic signal caused only by the absorption of the gas molecules being measured. S7: Based on the pre-calibrated concentration-2f signal relationship curve, the gas concentration value is obtained by inversion and output.

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