Hello Ranjeet,
As far as C++ co-simulation with Optisystem is concerned , I think it is same as co-simulation with Matlab. All you need to do is just write a C++ code for any component you wish to use just like we use to do in Matlab and then proceed similarly as we do in interfacing the Matlab with Optisystem. I feel there shouldn’t be any problem in doing that and i think the link provided by Fayiqa just serves your purpose. you can refer to it to learn about it. I hope you find it useful.
Regards