Hi Ibn Aziz,
First, just want to make sure if I understood your question correctly. Are you trying to make a Photonic Envelope Detector for signals using OptiSystem or you are just trying to analyze it at some access point. Photonic Envelope Detector can be performed using a single Mach-Zehnder modulator and a fiber Bragg grating (you can find papers about that online if you need). After such detection you should be able to obtain eye diagram using corresponding analyzer of OptiSystem…