plane wave fdtd

In order to generate normal incident planewave, we can easily implant it using TF/SF boundary condition or periodic boundary condition.

However, if I want to excite oblique incident planewave, it is not easy for me.
Is there any good reference or example for this?

u can implement an oblique incident wave by multiplying the field you would use for a normal incident wave with a phase term.
the phase term is a function of position.
for example, lets assume you excite an incident wave in a 2D simulation by forcing the E field at y=y0: Ez(x,y0)=Ez(t).
this is a plane wave traveling in the y directions.
if you add a phase term such as Ez(x,y0)=Ez(t)*exp(j*β*x) you can now simulate an oblique incident wave which incident angle is a function of β.

For the basics Taflove or even Kunz&Lubbers should be ok.

For more accurate methods check the relevant papers by J. Schneider (google for john Schneider FDTD) and the papers referenced there

This is the simplest method. If the results are accurate enough for you then I would use it.
The problem is that the analytical formula does not match the wave speed at different angles.
As a result you get lots of spurious reflections. How to reduce these is the topic of some of
the papers I mentioned above.

Another problem, also addressed in these papers is the case when you have material
interfaces crossing the TF/SF boundaries.