Fig. 1. Exhaled gas detection system based on DFB laser

Fig. 2. 2f signal simulation for CO2 and water vapor

Fig. 3. Variation of 2f signal peak height with modulation amplitude at different pressures

Fig. 4. Variations of 2f signal peak height with (a) modulation phase and (b) modulation frequency

Fig. 5. Relation between 2f signal peak height and volume fraction of CO2

Fig. 6. (a) Fitted relation between 2f signal peak height and volume fraction of CO2; (b) partial enlarged detail

Fig. 7. (a) Relation between 2f signal peak height and volume fraction of water vapor; (b) partial enlarged detail

Fig. 8. 2f signals of exhaled CO2 and water vapor obtained by experimental measurement

Fig. 9. Variations of volume fraction of CO2 during respiration of two volunteers. (a) The first volunteer; (b) the second volunteer

Fig. 10. Variation of volume fraction of water vapor during respiration of the first volunteer

Fig. 11. (a) Distribution of CO2volume fraction deviation with measurement time; (b) frequency distribution histogram of CO2 volume fraction deviation and Gaussian lineshape fitting

Fig. 12. Allan variance of measurement system