DGTD solver - Simulation object

General tab

The DGTD solver contains several settings:

• SIMULATION REGION:  Select the simulation region the solver will use.
• SIMULATION TIME (FS):  The maximum duration of the simulation to be performed. The actual simulation may be shorter if the autoshutoff criteria are satisfied before this maximum simulation time is exceeded.

Mesh tab

Global Mesh Constraints

The global mesh settings section contains several settings:

• EDGES PER WAVELENGTH:  The number of edges per wavelength of a triangle (in 2D) or tetrahedron (3D) used in the mesh.
• REFINE BASED ON MATERIAL PROPERTIES:  If checked (default setting), the effective wavelength in the material (λ0/n) is used. Otherwise, the solver will use the wavelength of light in vacuum for all material regions.
• POLYNOMIAL ORDER:  Set the order of the basis function in the finite-element solver. A higher order basis function allows to resolve nonlinear variations in the electric field better even with a coarser mesh.

Time Step

The time step settings section contains several settings:

• AUTO ADJUST DT: Uses an internal algorithm to automatically determine the largest stable DT factor for the simulation. This option is enabled by default.
• DT STABILITY FACTOR: A setting which determines the size of the time step used during the simulation.  A larger number will result in faster simulation times, and a smaller number will result in slower simulation times. This setting must be less than 1 for the DGTD algorithm to remain numerically stable and can only be determined when the AUTO ADJUST DT feature is disabled.
• DT: The time step of the DGTD/Propagator simulation. This is determined by the values of the spatial grid to ensure numerical stability and cannot be directly set by the user.

Advanced Options (2D simulations only)

• Geometry Options
  • DEFLECTION TOLERANCE (UM):  Controls how curved surfaces are broken up into multiple linear segments.  A smaller deflection tolerance will force the geometry builder to break up a curved surface into smaller segments. Only available for 2D simulations.
• Mesh Options
  • TRIANGLE QUALITY: The quality of mesh triangle, defined the minimum angle used in the triangular mesh cells. The higher the angle, the higher the quality of the triangle. Only available for 2D simulations.

Advanced tab

Global Solver Controls

• MULTITHREADING:  If enabled, the user can choose to divide up and run the simulation over multiple threads.
• FLOATING POINT PRECISION:  Select the floating point precision used by the solver (default is single).

Auto shutoff

• USE EARLY SHUTOFF: This will automatically end the simulation when most of the energy has left the simulation volume.
• AUTO SHUTOFF MIN: The simulation will end when the total energy in the simulation volume drops to this fraction of the maximum energy injected. The simulation data will automatically save.
• USE DIVERGENCE CHECKING: This will automatically end the simulation when the total energy in the simulation volume is this many times larger than maximum energy injected.
• AUTO SHUTOFF MAX: The simulation will end when the total energy in the simulation volume rises to this many times the maximum energy injected. The simulation data will automatically save.

Use global excitation

If "Use global excitation" is enabled, a source with a random field profile will be added to the entire simulation region with the following settings:

• 2D POLARIZATION: If the simulation region is 2D, select the type of polarization to be excited:
• "TM": the only non-zero field components are \(H_{x}\), \(H_{y}\) and \(E_{z}\).
• "TE": the only non-zero field components are \(E_{x}\), \(E_{y}\) and \(H_{z}\).
• "TE and TM": a superposition of TE and TM polarizations.
• SEED VALUE: The value provided here is used to initialize the random number generator for the random field profile.
• SET FREQUENCY/WAVELENGTH: Select the range of frequency or wavelength that will be excited. The user can choose to either set the center and span or the minimum and maximum frequencies/wavelengths.

Results returned

Once the simulation region has been meshed, the DGTD simulation object returns the mesh as a grid dataset that shows the area of the mesh cells, ID of the partitioned regions and the material index.

After the simulation has been run successfully, the energy in the simulation region as a function of time is returned: