Answer:
For a system with a very high bit rate and narrow channel spacing it will be difficult to achieve an open eye, due to channel crosstalk. It may be possible to achieve better results by using pulse shaping at the transmitter side.
However, attached you will find a simple example of how a 3 channel system could be simulated in OptiSystem. You are also welcome to follow the link below to a lesson on 16 channel WDM system design.
16 Channel WDM System Design
https://optiwave.com/resources/applications-resources/optical-system-16-channel-wdm-system-design/