Learning Forum

[sagar]

I am trying to do an off-normal incident with a plane wave source, so I did it initially with a plane wave source and Bloch BC; it is giving reflectivity 2D map (w.r.t wavelength) correct up to a particular value of theta, and after that, it is giving value more than 1 for higher wavelength. And for BFAST, things are getting worse, and I am always getting reflections of more than 1 (like 10-12). I followed this link: https://optics.ansys.com/hc/en-us/articles/360034902273 and did the same as suggested, but it is still not working. Please suggest some suggestions. 

[sagar]

With the plane wave source and Bloch boundary conditions, I am able to get the reflection and transmission data up to a certain angle, like 30 degrees, where I did the sweep from 0 to 75 degrees. For higher angle values, I am getting the power normalization is not working properly as I am getting reflectivity of more than 1. And with BFAST source and Bloch boundary conditions (BBC), although it is overwritten by itself if FDTD setting, I am getting normalized values after some angle like 30 degrees; the normalization is not happening properly at a lower value of the angle. I am getting more than 1 reflectivity for lower values of angle. So, the problems are the opposite for plane wave source with BBC and BFAST with BBC.

Please suggest something to resolve this problem with an off-normal incident plane wave source in a periodic structure. Thank you. 

[Guilin Sun]

When the incident angle is large, say 75 deg, BFAST may not provide enough benefits due to simulation time and accuracy.

 

Larger than 1 reflection usually means the simulation time is not long enough and (or) the autoshutoff min is not smaller enough. Please increase the simulation time 100 times longer and let the autoshutoff min to terminate the simulaiton. The default autofshutoff min is 1e-5 for most cases, but it can be reduced futher to 1e-6 or even smaller.

In addition, when the incident angle is large and there are higher diffraction orders, the diffraction angle can be very large or reach to 90deg, which makes PML performance degraded. Please also try to use Steep Angle PML with more PML layers.