  Laser has unique advantages such as abundant spectrum resources and low
propagation divergence in wireless charging and wireless communications,
compared with radio frequency. Resonant beams, as a kind of intra-cavity laser
beams, have been proposed as the carrier of wireless charging and
communication, as it has unique features including high power, intrinsic
safety, and self-aligned mobility. However, this system has problems such as
intra-cavity echo interference and power fluctuation. To study the time-domain
behavior of the resonant beam system, we create a simulation algorithm by
discretizing the laser rate equations which model the dynamics of the excited
atom density in the gain medium and the photon density in the cavity. The
simulation results are in good agreement with theoretical calculation. We also
propose a delay-divide demodulation method to address the echo interference
issue, and use the simulation algorithm to verify its feasibility. The results
show that the resonant beam charging and communication system with the proposed
demodulator is feasible and performs well. The analysis in this work also helps
researchers to deeply understand the behavior of the resonant beam system.
