Answer:
The most likely error in your design is the incorrect use of delays and initial delay. Every component in OptiSystem requires all of its inputs to have a signal. If the simulation is run and a component is missing an input signal, it will output an empty signal with no values. To perform the simulation correctly either the Optical Delay component or Initial delay option must be used.
Take a look at the example attached, “Nonlinear Optical Loop Mirror.osd”, in this example Optical Delays are used. The delays function by first outputting an Optical Null signal and then on subsequent iterations acting as a transparent interconnect. The number of iterations can be changed in the Signals tab of the global parameters box. A higher number of iterations will allow the simulation to converge to the correct results.
If you would like a further explanation of both the Optical Delay component and Initial delay option, please follow the link below to a tutorial.