Auto shutdown error in the simulation of bloch periodic conditions for angled injection

To help us solve your issue as quickly as possible, please provide the following information:

1. What device are you trying to simulate? Include diagrams if available.

  • TiO2 nanodisk array embedded in the high index media.
  • Square periodic array with a pitch of 320 nm.
  • Plane wave infection with an angle of 30 degrees.

2. What results are you trying to obtain? Be as specific as possible.
Reflectance and transmittance of TiO2 nanodisk array

3. Description of the problem or issue.
I am studying the reflectance and transmittance of TiO2 nanodot array embedded into high index media like glass. I am trying to get the result under the illumination of a plane wave with different angles because the optical lens was used to focus the beam and measure the reflectance and transmittance of the sample. Based on the previous Q&A (Bloch periodic and symmetric boundary conditions for angled injection), I set the x and y boundary conditions as Bloch. And, I modified PML setting from standard to stabilized and steep angle. However, any simulation couldn’t reach to auto shutoff min (1e-5). I have attached my FDTD file and log file (for steep angle) in this post.

4. Lumerical product and software version.
2019b r6, 8.22.2088

5. Please attach your simulation files, including any logs.
polar_320p_angle.fsp (986.8 KB) polar_320p_angle_p0.log (10.5 KB)

Please take a look and let me know what I should modify.

Thanks in advance,
Handon Um

Hello @handon,

Thank you for the question. I looked at your file, and it is not obvious to me what might be causing this issue. This simulation takes a long time to run, so I haven’t been able to run many tests. Does this issue occur for only this angle? In particular, does it still happen with normal incidence, when you are not using Bloch BCs?

I noticed that you are using a large bandwidth. Usually you should use a BFAST source for angled broadband plane waves. If you don’t require broadband results, I would recommend that you reduce the bandwidth of the source to only be around the wavelengths you are measuring.

Hi @kjohnson,

Thank you for your reply.
It was okay with normal incidence (zero angles) even I used Bloch and symmetric/anti-symmetric BCs.
I tested several simulations you suggested.

  1. Bloch BCs, Bloch/periodic source, large bandwidth (0.3 ~1.2 um)
    This is the original fsp file I uploaded in the previous post. Angle was 30 degrees.
    I tested other angles of 5 and 15 degrees. Log files are here.
    angle_1_p0.log (10.7 KB) angle_2_p0.log (10.7 KB) .
    Results: same problem. It saturated to 0.001 even the simulation conducted 100%.
  2. Bloch BCs, Bloch/periodic source, small bandwidth (0.35 ~0.65 um, a little larger than interesting region)
    polar_320p_angle_smallrange.fsp (452.1 KB)
    polar_320p_angle_smallrange_p0.log (11.3 KB)
    Result: it seems okay. But, auto shutdown didn’t work because it was 1.58835e-005 at the end of the simulation. Could you please take a look at my fsp file and let me know why the simulation coudln’t finish?
  3. asymmetric & Bloch BCs, BFAST source, large bandwidth (0.3 ~1.2 um)
    polar_320p_angle _BFAST.fsp (452.6 KB)
    polar_320p_angle _BFAST_p0.log (8.6 KB)
    Result: ERROR: Early termination of simulation, the electromagnetic fields are diverging.
    How could I modify this BFAST simulation setup to work it?

Thank you