Fig. 1. Processing flow chart of PLS algorithm

Fig. 2. Absorption spectral lines of alkane gas near 1680 nm

Fig. 3. Schematic diagram of experimental device

Fig. 4. Current-wavelength tuning curve of DFB laser

Fig. 5. Absorption signal of C₃H₈ and C₄H₁₀. (a) Direct absorption signal of C₃H₈; (b)2f signal of C₃H₈; (c) direct absorption signal of C₄H₁₀; (d)2f signal of C₄H₁₀

Fig. 6. Inversion results. (a) C₃H₈,_{correlation; (b) C4H10, correlation; (c) C3H8,inversion error; (d) C4H10,inversion error}

Fig. 7. Absorption signal of C₃H₈ and C₄H₁₀ mixture. (a) 2f signal; (b) absorbance signal

Fig. 8. Inversion of low volume fraction mixture of C₃H₈ and C₄H₁₀. (a) Inversion volume fraction of C₃H₈; (b) inversion volume fraction of C₄H₁₀; (c) inversion error of C₃H₈; (d) inversion error of of C₄H₁₀

Fig. 9. Inversion of high volume fraction mixture of C₃H₈ and C₄H₁₀._{(a) Inversion volume fraction of C3H8; (b) inversion volume fraction of C4H10; (c) inversion error of C3H8; (d) inversion error of C4H10}

Fig. 10. Continuous inversion of C₃H₈ and C₄H₁₀ in low volume fraction group. (a) C₃H₈; (b) C₄H₁₀

Fig. 11. Continuous inversion of C₃H₈ and C₄H₁₀ in high volume fraction group. (a) C₃H₈; (b) C₄H₁₀