you may read Taflove's book. you can introduce the plane wave by 1D incident field, then interploate the incident field on the line(surface) of Total field/scattered field.
Please check D. M. Sullivan (Electromagnetic simulation using FDTD method), its a well known book, you will find 2D and 3D using (total/scatter field) with a plane wave
I hope this help you if you need more information please contact me