FDTD Solutions中的最新BFAST光源技术及其应用


#1

在2016a最新版中,Lumerical的FDTD Solutions新添了宽谱固定角度光源技术Broadband Fixed Angle Source Technique (BFAST),其最大优点是,可以在斜入射情况下,一次仿真可以得到周期结构的正确宽谱结果,所有波长的实际入射角是相同的:

而Bloch+平面波技术一般来说需要扫描波长,每次只有一个频率的角度是正确,其它波长的入射角理论上讲不同于中心频率的角度(即所设置的角度),参见这个帖子

这是一种基于分离场的技术,将入射角完全固化在场的迭代方程中,且在有角度的平面内使用自己特有的边界条件,不同于以前的FDTD。

如何选择BFAST光源?
在添加的平面波General中,plan wave type 选BFAST就可以:

选择BFAST光源后如何设置边界条件?

因为次技术只能用于周期结构,所以
沿光源入射轴方向仍然是PML;
在有角度的平面(传播的切向)使用BFAST光源技术本身的边界条件,原来设置的不管是什么边界条件,都将被BFAST光源技术本身的边界条件锁替代,同时显示红三角警示,见下图。
而在有没有角度的平面(传播的切向)使用正常的周期边界;如果有对称性,则可以使用合适的对称性边界条件

使用小贴士
1.BFAST: Always check “BFAST” in the “plane wave type” at the source if you want to simulate angled-broadband source using BFAST; this ensures that all the wavelengths will have exactly the same incident angle.

2.dt multiplier: The default dt multiplier of 0.5 is chosen for most cases. However, to speed up the simulation, users can increase it up to 1 (eg., for pure dielectric without dispersion) if simulation does not diverge.

3.dt multiplier: For strongly dispersive materials, smaller dt multiplier may be required to have stable simulation.

4.mesh: Users may use a little higher mesh accuracy than usual (2 by default);

5.mesh: Uniform mesh is recommended in the transverse directions.

6.mesh: if strong dispersive material is involved, override region should be larger than the structure as shown above.

7.accuracy: Better accuracy can be achieved even at larger incident angles if the materials involved in the simulation are dielectric without dispersion.

8.accuracy: The accuracy may degrade when the indent angle is large. You may need to test the results by use of the Bloch BCs to see if you are satisfied with the accuracy.

9.speed up: Usual symmetry BCs can be used if the source has zero incident angle in that plane;

10.speed up: if the smallest refractive index (constant dielectric material, including the background) in the simulation is not 1, set “bfast alpha” to the smallest dielectric refractive index;

11.PML: If relatively large incident angle is simulated, you may choose “steep angle” PML;

12.PML: along the axis of source injection, PML BCs are used. When higher mesh accuracy is used, users may need more number of PML layers from default setting.

13.BCs: in the transverse plane, the BCs in the plane of angled incidence are automatically overridden for whatever the previous BCs are set. However, in the plane of no angle, the symmetry BCs are conserved.

14.critical angle: Currently it will not support the case where the incident angle is very close to and larger than the critical angle. This can happen when the source is located at higher index material than that in the rest of the simulation region.

注意:BFAST不能仿真非线性!

例子:
简单的平面结构:bfast_stack.fsp (242.0 KB) bfast_stack.lsf (1.2 KB)
闪耀光栅
光栅衍射级分析
表面等离激元太阳能光伏器件


周期结构、宽光谱平面波斜入射时仿真应该使用什么边界条件(综合贴)
关于光栅衍射级及其计算
想要做光源旋转的模型,不想展开,应该怎么做
FDTD收敛性问题,对结果影响有多大?
想计算斜入射的反射谱,但发现入射角度大了就会发散,为什么?
如何激励出表面等离激元(SPPs)
提取FDTD中采用Bloch周期性边界条件的远场情况!
非周期结构如何实现圆偏振光入射
FDTD solution能不能进行非线性材料的模拟,如:kerr nonlinear 等;以及关于斜入射是边界条件的处理
用Bloch边界扫描波长的问题(也适合斜入射TFSF光源)
FDTD的TFSF斜入射时采用bloch边界一定是对应周期性结构吗?
关于斜入射计算的问题
有关钙钛矿太阳能电池在FDTD中的问题
#2