Fig. 1. Schematic of FRS

Fig. 2. Simulation results of Spectraplot database of O₂ absorption

Fig. 3. Experimental setup for O₂ sensor based on FRS

Fig. 4. Measurement results of magnetic field strength. (a) Distribution of axial magnetic field strength of Herriott multi-cell; (b) variation of central magnetic field strength of Herriott multi-cell with excitation current

Fig. 5. Measurement results of solenoid magnetic field strength for 12 h

Fig. 6. Relation between laser intensity signal and offset angle

Fig. 7. Measurement results of optimal offset angle. (a) Relation between detector noise and offset angle; (b) relation between SNR and offset angle

Fig. 8. Optimal modulation amplitude of O₂ sensor based on FRS

Fig. 9. FRS-2f signals under different magnetic field strengths. (a) FRS-2f signal at different excitation currents; (b) variation of peak-to-peak value of FRS-2f signal with excitation current

Fig. 10. Spectra of O₂ at different volume ratios. (a) Direct absorption spectra; (b) FRS-2f spectra

Fig. 11. Calibration of O₂ volume ratio and Faraday rotation spectrum signal

Fig. 12. Performance evaluation of O₂ sensor based on FRS. (a) Time series of O₂ for 1 h; (b) histogram plot of Gaussian statistics; (c) Allan deviation