Mitsumasa,
The BPM algorithm has two limitations that must be taken into consideration when using it.1) It operates under the slowly varying approximation and as such the field and therefore the dielectric must be slowly varying, this does not appear to be the case in your design. 2) Special care must be taken when using high dielectric contrast. What are the refractive indices you are use?
Are you able to provide me with information regarding the parameters of the domain, source, and size of the features?
Over 10 thousand polygons is an extremely large number and there may not be a way around that., Also are you able to provide me with the dxf file?