Boundary Conditions
中文/English
1. Define the boundary conditions
2. Press the【創建 (Create)】button => Create the total grid size (Include the boundary condition & add space)
Add space grids
The distance between structure interface and PML(boundary) at least half maximum wavelength will be more safe.
This is due to the evanescent field might affect the PML and the observation.
If the observation (Transmission/Reflection) position inside the evanescent field range, then might stored the return energy flux and lead to some oscillation spectrum
Detailed Instructions :
Boundary condition
PML (Perfectly matched layer)：or open space boundary condition
As the propagating wave touched the boundary, the wave will be absorbed.
The figure at lower side shows the how the PML absorb the EM wave, the green area means PML in left figure. and right figure shows a point Hy source excite at the center.
none structure : (PML 16 layers)
|E|=sqrt(Ex^2+Ez^2); point Hz source at center
The PML default are 16 layers, the total length is 16*dx. The PML layer doesn't set too small, or the propagating wave will not fully absorb by the PML. There are two examples show PML = 5 layers and PML = 3 layers at lower side. We can see if the PML layer not enough, the propagating wave will reflect at the boundaries.
(PML 5 layers)
(PML 3 layers)
PEC (Perfect electric conductor) :
This is set the electric filed equal to zero at the boundary
set PEC boundaries at four sides.
As the propagating wave touched the boundaries, the wave will be reflected by the PEC wall.
PMC (Perfect magnetic conductor) :
This is set the electric filed equal to zero at the boundary
set PMC boundaries at four sides.
As the propagating wave touched the boundaries, the wave will be reflected by the PMC wall.
Bloch periodic boundary condition :
Based on Bloch's theorem, use while the simulation structures are periodicity.
the Bloch's boundary condition
E(x+a)=E(x)*exp(j*k*a)
a is periodic length
k Bloch Vector
The figure shows infinity 2D slit array, the slit array are combined by a unit cell that shows at lower side. The lower side figure shows three different unit cell separate methods. These three unit cell set will obtain the same result in simulation.
Period :
One of the Bloch boundary condition, the period boundary use for "normal incident".
From Bloch's condition E(x+a)=E(x)*exp(j*k*a)
If there isn't exist the optical path length is left and right side, the k=0,
also can refer to these two software description.
對照引用 Comparison & Reference： Lumerical FDTD SolutionsLumerical FDTD Solutionshttp://docs.lumerical.com/en/ref_sim_obj_boundary_conditions_tab.htmlOptiFDTDhttp://optiwave.com/optifdtd-manuals/fdtd-pbc-boundary-conditions/