grating based coupler

Hi,
I am trying to simulate a four port grating-based coupler (or filter) by comsol 3.5 but I have some problems :

first : I used port condition for 4 ports that one of them is in-port but I don't know where I should enter the input (in which part )?

second : I don't know which kind of input I should apply?

third : I need to get outputs in three other ports ,so which kind of solver I should use and how can I see the output figures?
I really need help, can anyone guide me?

I attached the figure

Thanks.

sara