Learning Forum

[XiaJi]

I used the example from https://support.lumerical.com/hc/en-us/articles/360042088353. in my model, the size and material of disk are changed, and the operating wavelength of dimple is moved to 1500nm-1600n. All other settings are the same as the example, we have tried many times but I cannot get the solution. when the solution is running, the autoshutoff level did not degrade linearly to zero and it fluctuated from 0.7-0.4. Please use the file below to help check, thanks. looking forwards your reply.

[Guilin Sun]

This could be due to several different causes. One is the device performance its self. For example, the device has high Q resonance, which will need much longer simulation time. You can use a point time monitor and then check its spectrum to know this. If long simulation time does not resolve this, you may also reduce the autoshutoff min. In general, you may need to increase the simulation time, and reduce the autshotoff min (you can check the log file and the transmission curve (if it is smooth) to determine if it is necessary).
The second cause might be due to the PML settings. If you kept the original override mesh with 10nm mesh size, it can be too fine for longer wavelength. I would suggest to disable the override mesh first, and see if the mesh accuracy 2 can resolve the disk well, eg, more than 10 meshes on each axis. You may need to change mesh size. When operating at longer wavelength and finer mesh size, the PML performance may be degraded as it depends on the thickness for the given parameters to absorb light striking on it. So you may 1) increase the number of layers; 2) increase the FDTD spans to make the PML away from the disk, such as half wavelength.
You may also need to change the PML type from the current "uniaxial anisotropic" to "stretched coordinate" PML, then choose "Standard", or "Steep Angle" depending on the disk interaction with light. If light radiates from the disk at near glazing angle, the "Steep Angle" PML may be used.

Please try those methods and see if it works for you.

[XiaJi]

many thanks for your help, please see the log contents below, we have change several settings, but cannot resolve them.

number of processors is 4
processors are distributed as: 2x2x1
Running 2D Simulation
Starting meshing
Simulation size in gridpoints: 171 x 171 x 1
Refined 230 mesh cells (0.786567%)
Completed meshing!
Meshing complete in 0 seconds of CPU time
Starting meshing
Simulation size in gridpoints: 171 x 171 x 1
Refined 230 mesh cells (0.786567%)
Completed meshing!
Meshing complete in 0 seconds of CPU time
finished material properties
Selected kernel with optimization level: 2 and split-field propagation direction: 0
-----------------------------------------
Beginning initialization of 2D FDTD Simulation
Including TE Simulation
Starting to add sources to simulation

Adding dipole source
Adding dipole source
Adding dipole source
Adding dipole source
Starting to add boundary conditions to simulation
Adding PML BC
Adding parallel BC
Adding PML BC
Adding parallel BC
Starting to add monitors to Simulation
Adding analysis monitor
Adding frequency monitor
Adding frequency monitor
Adding time monitor
Finished initialization of 2D Simulation
-----------------------------------------
All processes are communicating and ready to proceed to simulation...
Starting 490350 total iterations
0% complete. Max time remaining: 1 min, 60 secs. Auto Shutoff: 1
1% complete. Max time remaining: 4 mins, 17 secs. Auto Shutoff: 0.680187
2% complete. Max time remaining: 3 mins, 47 secs. Auto Shutoff: 0.717108
5% complete. Max time remaining: 2 mins, 43 secs. Auto Shutoff: 0.594182
5% complete. Max time remaining: 2 mins, 35 secs. Auto Shutoff: 0.667119
6% complete. Max time remaining: 2 mins, 29 secs. Auto Shutoff: 0.55346
7% complete. Max time remaining: 2 mins, 22 secs. Auto Shutoff: 0.702363
9% complete. Max time remaining: 2 mins, 10 secs. Auto Shutoff: 0.580757
10% complete. Max time remaining: 2 mins, 1 secs. Auto Shutoff: 0.698509
12% complete. Max time remaining: 1 min, 54 secs. Auto Shutoff: 0.613076
14% complete. Max time remaining: 1 min, 57 secs. Auto Shutoff: 0.632172
15% complete. Max time remaining: 1 min, 54 secs. Auto Shutoff: 0.581801
16% complete. Max time remaining: 1 min, 48 secs. Auto Shutoff: 0.633133
18% complete. Max time remaining: 1 min, 44 secs. Auto Shutoff: 0.618996
20% complete. Max time remaining: 1 min, 39 secs. Auto Shutoff: 0.652962
21% complete. Max time remaining: 1 min, 35 secs. Auto Shutoff: 0.570505
23% complete. Max time remaining: 1 min, 32 secs. Auto Shutoff: 0.598836
25% complete. Max time remaining: 1 min, 28 secs. Auto Shutoff: 0.665252
26% complete. Max time remaining: 1 min, 26 secs. Auto Shutoff: 0.558706
28% complete. Max time remaining: 1 min, 23 secs. Auto Shutoff: 0.622354
30% complete. Max time remaining: 1 min, 22 secs. Auto Shutoff: 0.586379
30% complete. Max time remaining: 1 min, 20 secs. Auto Shutoff: 0.595074
32% complete. Max time remaining: 1 min, 19 secs. Auto Shutoff: 0.581171
33% complete. Max time remaining: 1 min, 19 secs. Auto Shutoff: 0.698187
34% complete. Max time remaining: 1 min, 18 secs. Auto Shutoff: 0.700284
35% complete. Max time remaining: 1 min, 17 secs. Auto Shutoff: 0.671393
35% complete. Max time remaining: 1 min, 16 secs. Auto Shutoff: 0.665563
36% complete. Max time remaining: 1 min, 15 secs. Auto Shutoff: 0.523175
38% complete. Max time remaining: 1 min, 13 secs. Auto Shutoff: 0.589918
40% complete. Max time remaining: 1 min, 11 secs. Auto Shutoff: 0.644462
41% complete. Max time remaining: 1 min, 11 secs. Auto Shutoff: 0.591402
41% complete. Max time remaining: 1 min, 11 secs. Auto Shutoff: 0.613122
42% complete. Max time remaining: 1 min, 10 secs. Auto Shutoff: 0.592692
43% complete. Max time remaining: 1 min, 9 secs. Auto Shutoff: 0.63814
45% complete. Max time remaining: 1 min, 7 secs. Auto Shutoff: 0.622791
46% complete. Max time remaining: 1 min, 5 secs. Auto Shutoff: 0.594216
47% complete. Max time remaining: 1 min, 4 secs. Auto Shutoff: 0.630353
49% complete. Max time remaining: 1 min, 2 secs. Auto Shutoff: 0.651082
51% complete. Max time remaining: 60 secs. Auto Shutoff: 0.537526
51% complete. Max time remaining: 58 secs. Auto Shutoff: 0.580277
53% complete. Max time remaining: 56 secs. Auto Shutoff: 0.583417
55% complete. Max time remaining: 55 secs. Auto Shutoff: 0.610679
56% complete. Max time remaining: 54 secs. Auto Shutoff: 0.652343
57% complete. Max time remaining: 52 secs. Auto Shutoff: 0.654488
59% complete. Max time remaining: 50 secs. Auto Shutoff: 0.593748
60% complete. Max time remaining: 49 secs. Auto Shutoff: 0.596322
61% complete. Max time remaining: 46 secs. Auto Shutoff: 0.585222
63% complete. Max time remaining: 44 secs. Auto Shutoff: 0.631147
65% complete. Max time remaining: 42 secs. Auto Shutoff: 0.56314
66% complete. Max time remaining: 42 secs. Auto Shutoff: 0.559213
66% complete. Max time remaining: 41 secs. Auto Shutoff: 0.537773
67% complete. Max time remaining: 40 secs. Auto Shutoff: 0.626042
69% complete. Max time remaining: 37 secs. Auto Shutoff: 0.523291
71% complete. Max time remaining: 35 secs. Auto Shutoff: 0.565509
72% complete. Max time remaining: 33 secs. Auto Shutoff: 0.575397
74% complete. Max time remaining: 31 secs. Auto Shutoff: 0.562628
76% complete. Max time remaining: 29 secs. Auto Shutoff: 0.618122
77% complete. Max time remaining: 27 secs. Auto Shutoff: 0.602597
79% complete. Max time remaining: 25 secs. Auto Shutoff: 0.524987
81% complete. Max time remaining: 23 secs. Auto Shutoff: 0.576407
82% complete. Max time remaining: 21 secs. Auto Shutoff: 0.531143
83% complete. Max time remaining: 20 secs. Auto Shutoff: 0.639518
85% complete. Max time remaining: 18 secs. Auto Shutoff: 0.606287
86% complete. Max time remaining: 16 secs. Auto Shutoff: 0.534688
88% complete. Max time remaining: 14 secs. Auto Shutoff: 0.57409
90% complete. Max time remaining: 12 secs. Auto Shutoff: 0.583377
91% complete. Max time remaining: 10 secs. Auto Shutoff: 0.619757
93% complete. Max time remaining: 8 secs. Auto Shutoff: 0.485043
94% complete. Max time remaining: 7 secs. Auto Shutoff: 0.569016
95% complete. Max time remaining: 6 secs. Auto Shutoff: 0.529833
96% complete. Max time remaining: 5 secs. Auto Shutoff: 0.578902
97% complete. Max time remaining: 3 secs. Auto Shutoff: 0.537238
99% complete. Max time remaining: 1 secs. Auto Shutoff: 0.592508
100% complete. Max time remaining: 0 secs. Auto Shutoff: 0.617288
Completed 490350 iterations, or 5.000002e-011s of Simulation Time
Process 0 starting to collect data
collecting TE monitor data
collecting TE source data
Finished collecting data
Simulation completed successfully at: Thu Jul 22 14:02:55 2021
Overall wall time measurements in seconds:
time to mesh and initialize: 0
time to run FDTD simulation: 118
time to finalize data and save to files: 1
FDTD solver speed: 121.511 Mnodes/s
total FDTD solver speed on 4 processes: 486.045 Mnodes/s

[XiaJi]

(1) I mesh with a large size(disable the mesh and choose the accuracy 2); (2) in the boundary conditions the type has been changed as stretched coordinate PML, and tried both steep angle and standard types, also increase the layers to 64; (3) the auto shutoff min has been reduced to 1e-9. but it cannot be resolved after all these done.

[Guilin Sun]

It seems you have used Metal BCs or Periodic BCs. Please make sure you are using PML, and PML is far away from the disk, at least half wavelength. If problem still exists, please post some structure settings and Boundary conditions here.