Dipole Source Illuminating a Photonic Crystal Cavity (photonicCrystalDipoleSrcT.pre)

Keywords:

dipole source, photonic crystal, transmission efficiency

Problem description

This example illustrates how to model a dipole source that is illuminating a cavity inside a hexagonal photonic crystal lattice. The physical arrangement is shown in Fig. 263 and Fig. 264.

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Fig. 263 Top view of photonic lattice.

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Fig. 264 Side view of photonic lattice.

A point-like dipole lies above the simulation domain, which is comprised of three layers: a vacuum region above and a solid dielectric below, which together sandwich a central dielectric layer that contains a lattice of holes. This example includes two possible time signals with which to ring the dipole source, as shown in Fig. 265.

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Fig. 265 Two possible time signals for ringing the dipole source.

This simulation can be performed with a VSimEM license.

Opening the Simulation

This Photonic Crystal example is accessed from within VSimComposer through the following steps:

  • Select the NewFrom Example… menu item in the File menu.
  • In the resulting Examples window, expand the VSim for Electromagnetics option.
  • Expand the Photonics (Text-based setup) option.
  • Select “Dipole Source Illuminating a Photonic Crystal Cavity (Text-based setup)” and press the Choose button.
  • In the resulting dialog, create a new folder if desired, and press the Save button to create a copy of this example.

The basic variables of this problem should now be alterable via the text boxes in the left pane of the Setup Window, as shown in Fig. 266. A WideBand simulation type (see the SimType input value) will be used to demonstrate the functionality of this example.

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Fig. 266 The Setup Window for the Dipole Source Illuminating a Photonic Crystal Cavity (Text-based setup)example

Input File Features

The Input File is shown in Fig. 266. This specifies the parameters of the simulation in SI units, see Fig. 264 for clarification.

General simulation parameters:
  • NDIM = Number of dimensions (3).
  • SimType = {WideBand, SingleFrequency}
    • WideBand = Runs the simulation with a wideBand electromagnetic wave as the source in the simulation. The CyclesDrive parameter dictates how large this pulse is.
    • SingleFrequency = Runs the simulation with a single frequency source. This frequency is determined by the waveLengthCtr parameter.
  • SimCycles = Number of cycles run in simulation.
  • CyclesDrive = Number of cycles that the signal is driven.
  • CyclesPerDump = Number of cyles per dump.
  • NominalCellSize = The size of your cells; should be small enough to resolve your dielectric cavities in the crystal.
Photonic crystal specifications:
  • HoleDiam = Hole diameter, in meters.
  • HolePitch = Hole spacing in the hexagonal lattice, in meters.
  • NumHolesY = Number of rows of holes in the photonic crystal lattice.
  • NumHolesZ = Number of columns of holes in the photonic crystal lattice.
  • HtVacuum = Height of vacuum, along x-axis.
  • HtSi = Height of silicon layer, along x-axis.
  • HtSiO2 = Height of silica layer, along x-axis.
  • IndexRefrSiO2 = Index of refraction for silica.
  • IndexRefrSi = Index of refraction for silicon.
  • MarginY = Size of buffer zone on each side of the photonic crystal in the y-direction.
  • MarginZ = Size of buffer zone on each side of the photonic crystal in the z-direction.
Source specifications:
  • HtDipole = Height of dipole, along x-axis.
  • PVec{x,y,z} = The {x,y,z}-component of your dipole vector.
  • WaveLengthCtr = The central wavelength of your wideband signal, and is the frequency used as the single frequency simulation type.
  • WaveLengthBand = The wavelength width of your wideband signal, only used in wideBand simType.

Running the Simulation

After performing the above actions, continue as follows:

  • Proceed to the Run Window by pressing the Run button in the left column of buttons.
  • One can enable MPI options to utilize multi-core systems.
  • The default values of Number of Time Steps and Dump Periodicity are calculated from the CycleDrive and CyclesPerDump in the Setup Window shown in Fig. 266.
  • To run the file, click on the Run button in the upper left corner of the Logs and Output Files pane. You will see the output of the run in the right pane. The run has completed when you see the output, “Engine completed successfully.” This is shown in Fig. 267.
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Fig. 267 The Run Window for the Dipole Source Illuminating a Photonic Crystal Cavity (Text-based setup) example

Visualizing the results

After performing the above actions, continue as follows:

  • Proceed to the Visualize Window by pressing the Visualize button in the left column of buttons.
  • In the top field of Visualization Controls, click the drop down menu entitled Data View and select History.

In the simulation, there are specific grid points which store field histories. These histories are placed in various positions of the simulation.

In Fig. 268, one can see there are 4 possible graphs to view at one time in the Visualize Window. For each graph, one can select the following fields to anaylize: (0 = x, 1 = y, 2 = z).

  • {E,B}_AtCtr_{0,1,2} = {0,0} in {y,z} plane in the middle of SiLayer.
  • {E,B}_AtDet_{0,1,2} = Just above the upper x boundary.
  • {E,B}_AtSrc_{0,1,2} = Just below the source.
  • {E,B}_InCav_{0,1,2} = In the cavity off center.
  • E_AtHole_{0,1,2} = In the middle of the second hole.
  • E_AtMargin{Z,Y}_{0,1,2} = Just inside the Z or Y margin.
  • poyntingFluxDet = Just above the upper x boundary.
  • poyntingFluxSrc = Just below the source.

In each individual graph, one can choose the FFT option to view the frequency domain of your field. This can enable the analysis of the frequency response of the photonic crystal cavity. Fig. 268 depicts four graphs of histories. The first two graphs are amplitude vs time, and the second two are a FFT of the first two on a log scale. The first and third graphs depict the history AtSrc_1, while the second and fourth graphs show the AtHole2_1 history.

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Fig. 268 The Visualize Window for the Dipole Source Illuminating a Photonic Crystal Cavity (Text-based setup) example

Further Experiments

By using the wide-band source and examining the field strength detected below the crystal lattice, one may study the frequency response of this photonic crystal as one changes the device geometry, the dielectric constants, and the location and polarizations of the radiation source and detector.