Dual-wavelength cross absorption modulation theory based on graphene

The cross absorption modulation effect on monolayer undoped graphene is analyzed theoretically under ultrafast dual-wavelength pulses. A four-level system based on the two-level system with redistribution of electrons in the intraband relaxation and Pauli exclusion principle of interband transition is established to analyze this effect. By adjusting the modulation intensity, modulation wavelength and intraband relaxation time, the variations in output characteristics are taken into consideration: signal saturable absorption is decreased with the enhancement of modulation intensity; shorter modulation wavelength leads to larger modulation depth in high modulation intensity region; with the increasement of modulation wavelength, the modulation saturation intensity is decreased by nearly one order of magnitude. Additionally, the growth of intraband relaxation time also leads to a sharp decline in modulation saturation intensity; the modulation depth of signal light can be considerably adjusted by doping graphene. The simulation results may provide theoretical support in experimental design such as controllable saturable absorber, variable synchronous pulse laser and flexible all-optical modulator.