Fig. 1. Chaotic waveforms and attractors of coupled laser system. (a) Laser 1; (b) laser 2

Fig. 2. Chaotic waveforms of two lasers when phase conjugation feedback is applied to laser 1. (a) Laser 1; (b) laser 2

Fig. 3. Numerical relationship between chaotic frequency increase and feedback level

Fig. 4. Gain

Fig. 5. Carrier loss rate of laser 1 without phase conjugation feedback

Fig. 6. Gain of laser 1 with phase conjugation feedback

Fig. 7. Carrier loss rate of laser 1 with phase conjugation feedback

Fig. 8. Influence of delay on frequency increase

Fig. 9. Numerical relationship between chaotic frequency increase and feedback level when phase conjugation feedback is applied to laser 2

Fig. 10. Effect of feedback level on frequency increase

Fig. 11. Spectra of lasers before increasing frequency. (a) Laser 1; (b) laser 2

Fig. 12. Spectra of lasers after increasing frequency. (a) Laser 1; (b) laser 2

Fig. 13. Effect of cross feedback level of single laser on frequency increase

Fig. 14. Effect of cross feedback levels of two lasers on frequency increase

Fig. 15. Chaotic frequency increasing effect of two lasers with cross-phase conjugation double-feedback. (a) Laser 1; (b) laser 2

Fig. 16. Laser frequency spectra via cross-phase conjugation double-feedback. (a) Laser 1; (b) laser 2

Fig. 17. Effects of cross reverse feedback levels of two lasers on frequency increase

Fig. 18. Spectra after frequency increasing via cross-phase conjugation reverse dual-feedback. (a) Laser 1; (b) laser 2