Fig. 1. GCD device structure and graphene characterization. (a) Schematic diagram of GCD device; (b) side view of GCD device; (c) graphene Raman spectrum; (d) scanning electron microscope (SEM) image of graphene

Fig. 2. Actively mode-locked laser system based on GCD devices

Fig. 3. Modulation principle and transmission efficiency of graphene modulator. (a) Relationship between absorption of graphene and Fermi level; (b) principle diagram of evanescent wave coupling effect; (c) optical transmission characteristics inside corroded fiber covered with graphene under bias voltages of 5 V (as shown in the figure above) and 0 V (as shown in the figure below); (d) relationship between optical transmission efficiency and voltage amplitude at 80 mW

Fig. 4. Output power of fiber laser. (a) Relationship between average output power and pump power; (b) variations of average output power and insertion loss with voltage

Fig. 5. Schematic diagrams of pulse sequence under different demodulation signals at 80 mW pump power. (a) Pulse sequence diagrams under 1 V and 3 V AC voltage signals; (b) mode locked pulse sequences under continuous wave and 5 V AC signal; (c) synchronous diagram of driving voltage signal and pulse sequence; (d) autocorrelation curves

Fig. 6. Output characteristics of fiber laser. (a) Spectrogram; (b) frequency spectrum

Fig. 7. Schematic diagram of harmonic mode-locked signal under 80 mW pump power. (a) Second harmonic mode-locked pulse sequence diagram; (b) autocorrelation curve chart; (c) spectral chart; (d) frequency spectrum

Table 1. Comparison of parameters of mode-locked lasers based on various modulation techniques