Learning Forum

[asun]

Hi, I’m having trouble simulating a pulse propagating a photonic crystal using FDTD Solutions. At first, i used a broad-band source for transmission calculation. Then i changed it to an ultra short pulse (~200 fs) to detect transmission, and the result turned out to be four orders of magnitude smaller than 0.02 calculated using the broad-band source.

Why the difference in transmission between two kinds sources is so huge? There’s even no nonlinear effect and absorption set in material. Is it possible other parameters i set were not proper?

[Guilin Sun]

When you change to ultra short pulse, do you know if the spectrum changes or not? FDTD mesh depends on the smallest wavelength inside the material. For simple dispersive material, it depends on min(wavelength/real(n)). So if the starting wavelength changes, the mesh is different, and thus the result may be different. In addition, if source changes, the material fitting will be changed. You can fix the meshing and material fitting. Please refer this post: Ansys Insight: 光谱宽度会影响同波长的透过率吗？分段仿真如何得到光滑的结果 One important question: is there any specific reason you want to use ultra-short pulse? are you simulating nonlinear material? if not, except some special cases, I would recommend to use standard source pulse.