Grating
Use the Grating node to treat a boundary as a diffraction grating that can release reflected and transmitted rays of multiple diffraction orders. A Diffraction Order subnode for reflected and transmitted rays of order m = 0 is added by default. Change the settings for this default subnode to release rays of a different diffraction order. You can also release rays of multiple diffraction orders from the same boundary by adding more Diffraction Order subnodes from the from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
The Accumulator (Boundary) subnode is also available from the context menu (right-click the parent node) or from the Physics toolbar, Attributes menu.
Releasing Secondary Rays
When two or more rays are released from a Grating boundary, one of the released rays uses the same degrees of freedom as the incident ray. The remaining degrees of freedom must be preallocated in memory as secondary rays. The total number of secondary rays that can be released in the model is controlled by the Maximum number of secondary rays field in the physics interface Ray Release and Propagation section.
For example, if both reflected and transmitted rays of diffraction orders m = −1, m = 0, and m = 1 are released from a boundary, then for every incident ray, a total of five secondary rays are released. If the diffraction order m = −1 is the first subnode to appear in the Model Builder, then the transmitted ray of order m = −1 uses the same degree of freedom as the incident ray, and the other rays are secondary rays. If the Maximum number of secondary rays is 500 and more than 100 rays interact with the grating, then no more secondary rays are emitted and a warning is generated by the solver, indicating that the Maximum number of secondary rays should be increased.
Device Properties
Select an option from the Rays to release list: Reflected and transmitted (the default), Reflected, or Transmitted. Then enter the a Grating constant d (SI unit: m). The default is 600 nm.
If the ray power is solved for, the Store total transmitted power and Store total reflected power check boxes are shown. Select these check boxes to declare auxiliary dependent variables for the total power of all transmitted and reflected diffraction orders, respectively.
Grating Orientation
This section is only available in 3D. In 2D, the lines of the grating are always assumed to point directly out of the plane, as shown in Figure 3-4.
Select an option from the Grating orientation list: Specify direction of grating lines (the default) or Specify direction of periodicity.
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If Specify direction of grating lines is selected, select an option from the Direction of grating lines list: User defined (the default) or Parallel to reference edge. For User defined enter the components of the direction of grating lines Tl (dimensionless) directly. The default is the positive x-axis. For Parallel to reference edge, the Reference Edge Selection section is shown. Select a single edge, which must be adjacent to at least one boundary in the selection for the Grating feature.
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If Specify direction of periodicity is selected, select an option from the Direction of periodicity list: User defined (the default) or Parallel to reference edge. For User defined enter the components of the direction of periodicity Tp (dimensionless) directly. The default is the positive x-axis. For Parallel to reference edge, the Reference Edge Selection section is shown. Select a single edge, which must be adjacent to at least one boundary in the selection for the Grating feature.
The vectors Tl and Tp are illustrated in Figure 3-5, along with typical paths for incident reflected, and transmitted rays.
Figure 3-4: Diagram of diffraction grating orientation in 2D.
Figure 3-5: Diagram illustrating the options to specify grating orientation in 3D.
Grating Theory