The output from a Fabry-Pérot cavity with initial state zero. The mirror has reflectivity \(r = 0.9\) and the duration of the delay is 1. The two output ports represent the signal reflected and the signal transmitted through the cavity. The signal enters the system from port 0 and exists from both ports 0 and 1 (see Figure 13). In steady-state, the norm of output 0 converges to zero, an the norm of output 1 converges to 1. The stated number of modes in each diagram is the number of modes used in the delay. We see that adding more modes eventually converges to a piecewise step function. The steps result from the round-trip of the signal inside the cavity.