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：
在添加的平面波General中，plan wave type 选BFAST就可以：
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.
•BAFST ALPHA: It is the smallest dielectric refractive index in the simulation region, and should generally be 1. For example, if the background index is set to 1.33 of water in FDTD “General” tab, then 1.33 should be used here instead of the default of 1.
•DT MULTIPLIER: It is used to further reduce the time step “dt” in “Mesh settings” in addition to the “dt factor”. Its largest value is 1, meaning no change for the dt factor. When it is smaller than 1, the actual time step dt becomes smaller, in some cases it can overcome some diverging problems impossible by modifying other settings.