identity pair,assembly and port

My name is Guanjun Wang, a Chinese undergraduate student, recently, I had encountered a problem about the identity pair. Using the assembly between two unions and creating a identity pair which consists of source boundary and destination boundary ,then i enable the port on the identity pair( you can see it in the attached image ), and set the port as a light source(a plane wave whose E field is polarized in the x
direction),yet no matter what kind of methods i used to divided the meshes(including copy one face of the identity pair to the other one), the energy(or light) can't go into the structure above. A more detailed description will be presented in the attached image.
Any suggestion will be highly appreciated.
Guanjun Wang
1/11/2014