Fig. 1. Simulated PRBS phase modulation spectra. (a) Unfiltered PRBS modulation spectrum; filtered PRBS modulation spectra at modulation depths of (b1) 0.1π, (b2) 0.3π, (b3) 0.5π,and (b4) 0.7π ; filtered PRBS modulation spectra when ratio of filter cutoff frequency to modulation frequency is (c1) 0.23, (c2) 0.73, and (c3) 0.93

Fig. 2. Schematic of PM all-fiber amplifier based on phase modulation seed

Fig. 3. Characteristics of output spectra. (a) Phase modulation spectra under different RF powers; (b) frequency domain interference trace corresponding to flat-top spectrum

Fig. 4. Output spectrum and temporal traces of PRBS signal. (a) Output spectrum after phase modulation; time domain traces of PRBS signals (b1) before and (b2) after filtering; (c) linear spectrum; (d) logarithmic spectrum

Fig. 5. Output characteristics. (a) Measured forward laser power and backward laser power versus pump power; (b) forward temporal trace and corresponding Fourier spectrum distribution at maximum laser power; (c) evolution diagram of output laser spectrum with power variation; (d) measured spectrum in wide wavelength range at maximum output power

Fig. 6. Output characteristics. (a) Measured beam quality at maximum output power; (b) measured PERs at different laser powers