Fig. 1. Schematic diagram using nonlinear phase demodulation

Fig. 2. Spectra when using nonlinear phase demodulation to compress spectrum

Fig. 3. Experimental setup

Fig. 4. Output power and forward spectrum. (a) Output power versus pump power; (b) forward spectrum under maximum seed output power

Fig. 5. Modulated seed spectra and output laser spectra under different modulation methods. (a)(b) WNS; (c)(d) WNS+FM;

Fig. 6. Optimal demodulating phase measurement. (a) Output laser spectra under different phase differences of FM and AM modulation signals; (b) signal-to-noise ratio of carrier to +1-order sideband versus demodulation phase; (c) signal-to-noise ratio of carrier to -1-order sideband versus demodulation phase; (d) RMS linewidth of output spectrum versus demodulation phase

Fig. 7. Modulation depth versus laser power. (a) FM modulation depth versus laser power when AM modulation depth is fixed; (b) AM modulation depth versus laser power when FM modulation depth is fixed

Fig. 8. Backward power versus forward power under different modulation methods

Fig. 9. Laser spectra under combination of PRBS modulation and nonlinear demodulation techniques