Fig. 1. Schematic diagram of dual-beam feedback self-mixing interference system model

Fig. 2. Relationship curve between amplitude of self-mixing interference signal and external cavity length Lext1

Fig. 3. Simulation diagram of self-mixing interference signal with single-beam feedback and dual-beam feedback

Fig. 4. Schematic diagram of dual-beam feedback self-mixing interference experimental system using randomly polarized He-Ne laser

Fig. 5. Relationship curve between amplitude of self-mixing interference signal and external cavity length Lext1

Fig. 6. Comparison of self-mixing interference signals with single-beam feedback and double-beam feedback. (a) Single-beam feedback; (b) dual-beam feedback when Lext1=50.50μm; (c) dual-beam feedback when Lext1=50.55μm; (d) dual-beam feedback when Lext1=50.60μm

Fig. 7. Spectra of self-mixing interference signals with single-beam feedback and double-beam feedback. (a) Single-beam feedback; (b) dual-beam feedback when Lext1=50.50μm; (c) dual-beam feedback when Lext1=50.55μm; (d) dual-beam feedback when Lext1=50.60μm

Fig. 8. Schematic diagram of dual-beam feedback self-mixing interference experimental system for dual-polarization differential detection

Fig. 9. Self-mixing interference signal for dual-polarization differential detection. (a) Self-mixing interference signal with single-beam feedback; (b) Dual-beam feedback self-mixing interference signal when Lext1=50.45μm

Fig. 10. Spectra of self-mixing interference signal for dual-polarization differential detection. (a) Spectrum of S-polarized light interference signal with single-beam feedback; (b) spectrum of P-polarized light interference signal with single-beam feedback; (c) spectrum of dual-polarization differential signal with single-beam feedback; (d) spectrum of S-polarized light interference signal with dual-beam feedback; (e) spectrum of P-polarized light interference signal with dual-beam feedback; (f) spectrum of dual-polarization differential signal with dual-beam feedback

Fig. 11. Variation curves of external cavity length caused by flat crystal rotation