Interpretation of transient dynamics of the system in the Fabry-Pérot cavity considered. Before the system achieves steady-state, we can learn about the output by tracing the possible paths the signal may follow. The arrows in the diagram between the two mirrors represent the possible paths the signal may follow before leaving through an output port. We use the vertical direction to represent time. For each arrow in each output direction, some of the signal leaves through one of the mirrors. We will therefore see a step in the output as a function of time. This gives a physical interpretation of the steps seen in Figure 12.