  We discuss the analytical temporal response of a microring resonator excited
through a bus waveguide by an optical rectangular pulse. Finite difference time
domain (FDTD) simulations illustrate the analytical solution and help in
understanding the meaning of the different coupling regimes. In addition, we
show that the temporal dynamics allows determing the coupling regime while the
commonly used spectral characterization in the stationary regime does not. We
also take advantage of the simulation to highlight the phase shift between the
input and the output signals in the different coupling regimes. Finally,
measurements on a Si3N4 microring resonator are performed and analyzed in the
case of under-coupling regime to illustrate how the time response study leads
to the Q-factor determination.
