tidy3d.EMESimulation#

class EMESimulation[source]#

Bases: AbstractYeeGridSimulation

EigenMode Expansion (EME) simulation.

Parameters:

attrs (dict = {}) – Dictionary storing arbitrary metadata for a Tidy3D object. This dictionary can be freely used by the user for storing data without affecting the operation of Tidy3D as it is not used internally. Note that, unlike regular Tidy3D fields, attrs are mutable. For example, the following is allowed for setting an attr obj.attrs['foo'] = bar. Also note that Tidy3D` will raise a TypeError if attrs contain objects that can not be serialized. One can check if attrs are serializable by calling obj.json().
center (Union[tuple[Union[float, autograd.tracer.Box], Union[float, autograd.tracer.Box], Union[float, autograd.tracer.Box]], Box] = (0.0, 0.0, 0.0)) – [units = um]. Center of object in x, y, and z.
size (Union[tuple[Union[pydantic.v1.types.NonNegativeFloat, autograd.tracer.Box], Union[pydantic.v1.types.NonNegativeFloat, autograd.tracer.Box], Union[pydantic.v1.types.NonNegativeFloat, autograd.tracer.Box]], Box]) – [units = um]. Size in x, y, and z directions.
medium (Union[Medium, AnisotropicMedium, PECMedium, PoleResidue, Sellmeier, Lorentz, Debye, Drude, FullyAnisotropicMedium, CustomMedium, CustomPoleResidue, CustomSellmeier, CustomLorentz, CustomDebye, CustomDrude, CustomAnisotropicMedium, PerturbationMedium, PerturbationPoleResidue] = Medium(attrs={}, name=None, frequency_range=None, allow_gain=False, nonlinear_spec=None, modulation_spec=None, heat_spec=None, type='Medium', permittivity=1.0, conductivity=0.0)) – Background medium of simulation, defaults to vacuum if not specified.
structures (Tuple[Structure, ...] = ()) – Tuple of structures present in simulation. Note: Structures defined later in this list override the simulation material properties in regions of spatial overlap.
symmetry (Tuple[Literal[0, -1, 1], Literal[0, -1, 1], Literal[0, -1, 1]] = (0, 0, 0)) – Tuple of integers defining reflection symmetry across a plane bisecting the simulation domain normal to the x-, y-, and z-axis at the simulation center of each axis, respectively.
sources (Tuple[NoneType, ...] = ()) – Sources in the simulation. NOTE: sources are not currently supported for EME simulations. Instead, the simulation performs full bidirectional propagation in the ‘port_mode’ basis. After running the simulation, use ‘smatrix_in_basis’ to use another set of modes or input field.
boundary_spec (BoundarySpec = BoundarySpec(attrs={}, x=Boundary(attrs={},, plus=PECBoundary(attrs={},, name=None,, type='PECBoundary'),, minus=PECBoundary(attrs={},, name=None,, type='PECBoundary'),, type='Boundary'), y=Boundary(attrs={},, plus=PECBoundary(attrs={},, name=None,, type='PECBoundary'),, minus=PECBoundary(attrs={},, name=None,, type='PECBoundary'),, type='Boundary'), z=Boundary(attrs={},, plus=PECBoundary(attrs={},, name=None,, type='PECBoundary'),, minus=PECBoundary(attrs={},, name=None,, type='PECBoundary'),, type='Boundary'), type='BoundarySpec')) – Specification of boundary conditions along each dimension. If None, PML boundary conditions are applied on all sides. NOTE: for EME simulations, this is required to be PECBoundary on all sides. To capture radiative effects, move the boundary farther away from the waveguide in the tangential directions, and increase the number of modes. The ‘ModeSpec’ can also be used to try different boundary conditions.
monitors (Tuple[Annotated[Union[tidy3d.components.eme.monitor.EMEModeSolverMonitor, tidy3d.components.eme.monitor.EMEFieldMonitor, tidy3d.components.eme.monitor.EMECoefficientMonitor, tidy3d.components.monitor.ModeSolverMonitor], FieldInfo(default=PydanticUndefined, discriminator='type', extra={})], ...] = ()) – Tuple of monitors in the simulation. Note: monitor names are used to access data after simulation is run.
grid_spec (GridSpec = GridSpec(attrs={}, grid_x=AutoGrid(attrs={},, type='AutoGrid',, min_steps_per_wvl=10.0,, max_scale=1.4,, dl_min=0.0,, mesher=GradedMesher(attrs={},, type='GradedMesher')), grid_y=AutoGrid(attrs={},, type='AutoGrid',, min_steps_per_wvl=10.0,, max_scale=1.4,, dl_min=0.0,, mesher=GradedMesher(attrs={},, type='GradedMesher')), grid_z=AutoGrid(attrs={},, type='AutoGrid',, min_steps_per_wvl=10.0,, max_scale=1.4,, dl_min=0.0,, mesher=GradedMesher(attrs={},, type='GradedMesher')), wavelength=None, override_structures=(), snapping_points=(), type='GridSpec')) – Specifications for the simulation grid along each of the three directions. This is distinct from ‘eme_grid_spec’, which defines the 1D EME grid in the propagation direction.
version (str = 2.7.2) – String specifying the front end version number.
lumped_elements (Tuple[Union[LumpedResistor, CoaxialLumpedResistor], ...] = ()) – Tuple of lumped elements in the simulation. Note: only tidy3d.LumpedResistor is supported currently.
subpixel (Union[bool, SubpixelSpec] = SubpixelSpec(attrs={}, dielectric=PolarizedAveraging(attrs={},, type='PolarizedAveraging'), metal=Staircasing(attrs={},, type='Staircasing'), pec=PECConformal(attrs={},, type='PECConformal',, timestep_reduction=0.3), type='SubpixelSpec')) – Apply subpixel averaging methods of the permittivity on structure interfaces to result in much higher accuracy for a given grid size. Supply a SubpixelSpec to this field to select subpixel averaging methods separately on dielectric, metal, and PEC material interfaces. Alternatively, user may supply a boolean value: True to apply the default subpixel averaging methods corresponding to SubpixelSpec() , or False to apply staircasing.
simulation_type (Optional[Literal['autograd_fwd', 'autograd_bwd', None]] = None) – Tag used internally to distinguish types of simulations for autograd gradient processing.
freqs (Union[Tuple[float, ...], ArrayLike[dtype=float, ndim=1]]) – Frequencies for the EME simulation. The field is propagated independently at each provided frequency. This can be slow when the number of frequencies is large. In this case, consider using the approximate ‘EMEFreqSweep’ as the ‘sweep_spec’ instead of providing all desired frequencies here.
axis (Literal[0, 1, 2]) – Propagation axis (0, 1, or 2) for the EME simulation.
eme_grid_spec (Union[EMEUniformGrid, EMECompositeGrid, EMEExplicitGrid]) – Specification for the EME propagation grid. The simulation is divided into cells in the propagation direction; this parameter specifies the layout of those cells. Mode solving is performed in each cell, and then propagation between cells is performed to determine the complete solution. This is distinct from ‘grid_spec’, which defines the grid in the two tangential directions, as well as the grid used for field monitors.
store_port_modes (bool = True) – Whether to store the modes associated with the two ports. Required to find scattering matrix in basis besides the computational basis.
normalize (bool = True) – Whether to normalize the port modes to unity flux, thereby normalizing the scattering matrix and expansion coefficients.
port_offsets (Tuple[NonNegativeFloat, NonNegativeFloat] = (0, 0)) – Offsets for the two ports, relative to the simulation bounds along the propagation axis.
sweep_spec (Union[EMELengthSweep, EMEModeSweep, EMEFreqSweep, NoneType] = None) – Specification for a parameter sweep to be performed during the EME propagation step. The results are stored in ‘sim_data.smatrix’. Other simulation monitor data is not included in the sweep.
constraint (Optional[Literal['passive', 'unitary']] = passive) – Constraint for EME propagation, imposed at cell interfaces. A constraint of ‘passive’ means that energy can be dissipated but not created at interfaces. A constraint of ‘unitary’ means that energy is conserved at interfaces (but not necessarily within cells). The option ‘none’ may be faster for a large number of modes. The option ‘passive’ can serve as regularization for the field continuity requirement and give more physical results.

Notes

EME is a frequency-domain method for propagating the electromagnetic field along a specified axis. The method is well-suited for propagation of guided waves. The electromagnetic fields are expanded locally in the basis of eigenmodes of the waveguide; they are then propagated by imposing continuity conditions in this basis.

The EME simulation is performed along the propagation axis axis at frequencies freqs. The simulation is divided into cells along the propagation axis, as defined by eme_grid_spec. Mode solving is performed at cell centers, and boundary conditions are imposed between cells. The EME ports are defined to be the boundaries of the first and last cell in the EME grid. These can be moved using port_offsets.

An EME simulation always computes the full scattering matrix of the structure. Additional data can be recorded by adding ‘monitors’ to the simulation.

Other Bases

By default, the scattering matrix is expressed in the basis of EME modes at the two ports. It is sometimes useful to use alternative bases. For example, in a waveguide splitter, we might want the scattering matrix in the basis of modes of the individual waveguides. The functions smatrix_in_basis and field_in_basis in EMESimulationData can be used for this purpose after the simulation has been run.

Frequency Sweeps

Frequency sweeps are supported by including multiple frequencies in the freqs field. However, our EME solver repeats the mode solving for each new frequency, so frequency sweeps involving a large number of frequencies can be slow and expensive. If a large number of frequencies are required, consider using our FDTD solver instead.

Passivity and Unitarity Constraints

Passivity and unitarity constraints can be imposed via the constraint field. These constraints are imposed at interfaces between cells, possibly at the expense of field continuity. Passivity means that the interface can only dissipate energy, and unitarity means the interface will conserve energy (energy may still be dissipated inside cells when the propagation constant is complex). Adding constraints can slow down the simulation significantly, especially for a large number of modes (more than 30 or 40).

Too Many Modes

It is important to use enough modes to capture the physics of the device and to ensure that the results have converged (see below). However, using too many modes can slow down the simulation and result in numerical issues. If too many modes are used, it is common to see a warning about invalid modes in the simulation log. While these modes are not included in the EME propagation, this can indicate some other issue with the setup, especially if the results have not converged. In this case, extending the simulation size in the transverse directions and increasing the grid resolution may help by creating more valid modes that can be used in convergence testing.

Mode Convergence Sweeps

It is a good idea to check that the number of modes is large enough by running a mode convergence sweep. This can be done using EMEModeSweep.

Example

>>> from tidy3d import Box, Medium, Structure, C_0, inf
>>> from tidy3d import EMEModeSpec, EMEUniformGrid, GridSpec
>>> from tidy3d import EMEFieldMonitor
>>> lambda0 = 1
>>> freq0 = C_0 / lambda0
>>> sim_size = 3*lambda0, 3*lambda0, 3*lambda0
>>> waveguide_size = (lambda0/2, lambda0, inf)
>>> waveguide = Structure(
...     geometry=Box(center=(0,0,0), size=waveguide_size),
...     medium=Medium(permittivity=2)
... )
>>> eme_grid_spec = EMEUniformGrid(num_cells=5, mode_spec=EMEModeSpec(num_modes=10))
>>> grid_spec = GridSpec(wavelength=lambda0)
>>> field_monitor = EMEFieldMonitor(
...     size=(0, sim_size[1], sim_size[2]),
...     name="field_monitor"
... )
>>> sim = EMESimulation(
...     size=sim_size,
...     monitors=[field_monitor],
...     structures=[waveguide],
...     axis=2,
...     freqs=[freq0],
...     eme_grid_spec=eme_grid_spec,
...     grid_spec=grid_spec
... )

`eme_grid`	The EME grid as defined by 'eme_grid_spec'.
`grid`	Grid spatial locations and information as defined by grid_spec.
`max_num_modes`	Max number of modes in the simulation.
`max_port_modes`	Max number of modes at the two ports.
`mode_solver_monitors`	A list of mode solver monitors at the cell centers.
`monitors_data_size`	Dictionary mapping monitor names to their estimated storage size in bytes.
`port_modes_monitor`	EME Mode solver monitor for only the port modes.
`version`	DO NOT EDIT: Modified automatically with .bump2version.cfg
`attrs`

`from_scene`(scene, **kwargs)	Create an EME simulation from a :class:.`Scene` instance.
`plot`([x, y, z, ax, source_alpha, ...])	Plot each of simulation's components on a plane defined by one nonzero x,y,z coordinate.
`plot_eme_grid`([x, y, z, ax, hlim, vlim])	Plot the EME grid.
`plot_eme_ports`([x, y, z, ax, hlim, vlim])	Plot the EME ports.
`plot_eme_subgrid_boundaries`(eme_grid_spec[, ...])	Plot the EME subgrid boundaries.
`subsection`(region[, grid_spec, ...])	Generate a simulation instance containing only the `region`.
`validate_pre_upload`()	Validate the fully initialized EME simulation is ok for upload to our servers.

tidy3d.EMESimulation

Contents

tidy3d.EMESimulation#