Gas detection technology has developed rapidly in recent decades. To address factors such as the complexity of practical environments, the variety of detection objects, and the interference between gases, we focus on multi-component gas measurement technology in response to the increasing demand for accuracy and application breadth in gas detection. In particular, effective and accurate detection of multi-component gases plays a critical role in safety warning and fault diagnosis within the fields of environmental protection, biomedicine, and industrial production. However, using a detection method based solely on the simple superposition of single-component gases leads to increased measurement costs and limitations in application fields. Therefore, mastering key technologies for multi-component gas detection holds significant practical value.

The tunable diode laser absorption spectroscopy (TDLAS) technology, based on wavelength modulation, enables highly sensitive detection of absorption intensity. By applying the Beer?Lambert law, we can invert the concentration of each component gas based on its signal intensity. This study introduces the combination of TDLAS technology with frequency division multiplexing (FDM) and time division multiplexing (TDM) technologies. The core of FDM measurement involves demodulating high-frequency modulated signals at different frequencies to obtain the laser signals corresponding to each gas component. The TDM technology implements timing switching by changing the laser drive current, allowing for the detection of gases at the corresponding timing. The absorption spectra for CO₂, C₂H₂, CH₄, and H₂O used for detection are 1579.57, 1530.37, 1653.72, and 1392.53 nm, respectively. Experimental simulations demonstrate that the absorption spectra of each gas meet detection requirements while avoiding interference from other gases. We build a multi-component gas measurement system based on frequency-time division multiplexing (F-TDM) technology, consisting of a light source module, sensing module, demodulation module, and signal processing module. A self-designed driver circuit generates low-frequency waveforms and high-frequency sinusoidal signals with corresponding timings to control the current and temperature of the lasers, adjusting the output wavelength for each detected gas. The laser beam interacts with the gas mixture in the chamber, and the resulting signals are received by the detector and demodulated to obtain the 2f and R channel signals for the corresponding gases and data acquisition.

To verify the validity of the F-TDM detection system and conduct performance analysis, we perform subsequent detection experiments. First, FDM measurement experiments are carried out for two groups of mixed gases, CO₂ and C₂H₂, CH₄ and H₂O, respectively, validating the FDM detection component of the system (Figs. 4 and 5). Continuous FDM detection is continued for 30 min, resulting in relative standard deviations of the peak 2f signals for CO₂, C₂H₂, CH₄, and H₂O of 1.22%, 2.23%, 2.35%, and 1.91%, respectively (Figs. 6 and 7). In the second step, TDM measurement experiments are performed for the two groups of mixed gases, CO₂ and CH₄, H₂O and C₂H₂, to validate the TDM detection component (Figs. 8 and 9). Continuous TDM detection for 30 min yields relative standard deviations of the peak R-channel signals for CO₂, C₂H₂, CH₄, and H₂O of 0.98%, 1.93%, 0.92%, and 1.23%, respectively (Figs. 10 and 11). Finally, by fitting the signals of the multi-component gases in the F-TDM measurement (Fig. 12), we obtain signal-to-noise ratios of the R-channel signals for CO₂, C₂H₂, CH₄, and H₂O of 228.86, 222.74, 236.31, and 198.57, respectively, leading to detection limits of 0.39% for CO₂, 0.67% for C₂H₂ and 3.81×10^-6 for CH₄. The four gas mixtures are continuously detected by F-TDM for 150 min, resulting in relative standard deviations of volume fractions for CO₂, C₂H₂, and CH₄ of 1.89%, 2.85%, and 2.75%, respectively, while the peak R-channel signal for H₂O has a relative standard deviation of 2.61% (Fig. 13). These results indicate that the detection of the four gases remains stable and accurate throughout the extended F-TDM detection period.

We propose a detection system for multi-component gases based on F-TDM and TDLAS technologies, focusing on four gas mixtures: CO₂, C₂H₂, CH₄, and H₂O. The laser signals at each wavelength undergo modulation and demodulation at different frequencies, and the timing switching in TDM measurement is implemented. The feasibility of the two multiplexed detection sections is verified. The relative standard deviations for the four gases obtained through continuous F-TDM detection for 150 min are 2.26%, 3.11%, 2.43%, and 2.61%, demonstrating the effectiveness and reliability of applying F-TDM technology to TDLAS with high detection accuracy. By combining FDM and TDM technologies to measure four-component gas mixtures, we avoid issues caused by detector overload and over-reliance on modulation signals compared with using FDM alone, while improving detection speed and system stability compared to using TDM alone. This study provides a system scheme for F-TDM in wavelength modulation spectroscopy technology, verifying its validity and reliability. We achieve in-depth detection of mixed gases by selecting the applicable multiplexing detection technology, and the experimental results provide a new means for further research on multi-component gas detection. The scheme can be extended to the detection of additional multi-component gases, providing an efficient, safe, fast, and stable detection method for industrial production, environmental protection monitoring, and other fields.