OptiFDTD provides two types of Dispersive material simulations:

  • Multiple Resonant Lorentz
  • Drude

The Drude model is supposed to be used for the Noble Metal and Surface Plasma in optical band.

Note: It is recommended that you read the section in the Technical Background describing the Drude model equation. OptiFDTD also provides a sample for a Drude model simulation. The following explanation uses this sample file as an example.

The corresponding layout file is available in the sample folder of OptiFDTD:

Sample15_2D_TE_Drude_Model_Emitting_Diode.FDT.

The corresponding results file is available on the OptiFDTD setup CD:

Sample15_2D_TE_Drude_Model_Emitting_Diode.FDA.

Creating a project with Drude material

StepAction
1Start Waveguide Layout Designer.
2To create a new project, from the File menu, select New.

The Initial Properties dialog box appears.

3Click the Profiles And Materials.

The Profile Designer appears.

4In the directory under OptiFDTD_Designer1 of the Profile Designer, under the Materials folder, right-click the FDTD-Dispersive folder, and select New. The FDTDDielectric1 material definition dialog box appears.
5In the FDTD Dielectric1 material definition dialog box, select Drude Dispersive.

The Dispersive Material Definition dialog box appears (see Figure 1).

FDTD - Figure 1 Dispersive Material Definition dialog box

Figure 1: Dispersive Material Definition dialog box

6In the Drude Material Definition dialog box, define the following parameters:

Name: Drude_Silver_Ag

ε∞  (F/m): 1.999

Plasma Frequency: 1.346390e+016

Collision Frequency: 9.617120e+013

7Click Store to save the material.
8In the directory under OptiFDTD_Designer1 of the Profile Designer, under the Materials folder, right-click the Dielectric folder, and select New.

The Dielectric1 material definition dialog box appears.

9Design a linear material with refractive index equal to 1.414 and Material name Dielectricn=1.414.
10Click Store.
11In the directory under OptiFDTD_Designer1, Profile folder, right-click the Channel folder, and select New.

The ChannelPro1 dialog box appears.

12In the ChannelPro1 dialog box, set Profile Name to Ag and 2D Profile Material to Drude_Silver_Ag.
13Save the profile.
14Design another 2D channel profile with the name Core and material Dielectricn=1.414.
15Click Store.
16Close the Profile Designer.

Designing the waveguides

StepAction
1In the Initial Properties dialog box, set the following parameters:

Waveguide Properties Width: 0.12μm

Profile: Core

Wafer dimension

Length: 1.8μm

Width: 1.4μm

2D Wafer Material: Air

2Click OK to start the Layout Designer.

The OptiFDTD designer window appears.

3From the Draw menu, select Linear Waveguide.
4Draw the waveguide in the layout at desired the position.

The waveguide appears in the layout.

Note: Click the Select tool after drawing the waveguide.

5Double click the waveguide to edit the waveguide position and properties.

The Linear Waveguide properties dialog box appears.

6Set the following parameters:

Waveguide start position

Horizontal: 0

Vertical: 0

Waveguide end position

Horizontal: 1.8

Vertical: 0

Select Use Default checkbox.

Width: 0.12

Depth: 0.0

Profile: Core

7Design another linear waveguide with following properties:

Waveguide start position

Horizontal: 0

Vertical: –0.24

Waveguide end position

Horizontal: 1.8

Vertical: –0.24

Select Use Default checkbox.

Start thickness: 1.0

End thickness: 1.0

Width: 0.36

Depth: 0.0

Profile: Ag

The two waveguides appear in the layout, the upper one is the linear waveguide, which will guide the wave, and the lower one is the Substrate Silver layer in the emitting diode (see Figure 2).

FDTD - Figure 2 Waveguides in the layout

Figure 2: Waveguides in the layout

To enhance the Light Fitting, a corrugated surface plasma is deposited in the core. To do this, periodic rectangular linear waveguides are designed following the waveguide design outline in the previous procedure.

Each of the rectangular linear waveguides that make up the corrugated surface plasma has the following common parameters (see Figure 3):

Width: 0.02μm

Depth: 0.0μm

Select Use Default checkbox.

Note: Thickness is only used for 3D layout definitions.

Profile: Ag

Start vertical: 0.05μm

End vertical: 0.05μm

The six Start/End horizontal positions are:

i. 0.4μm/0.5μm

ii. 0.6μm/0.7μm

iii. 0.8μm/0.9μm

iv. 1.0μm/1.1μm

v. 1.2μm/1.3μm

vi. 1.4μm/1.5μm

FDTD - Figure 3 Waveguide materials

Figure 3: Waveguide materials

Setting the Input Plane

StepAction
1From the Draw menu, select Vertical Input Plane.
2Insert the Input Plane into the layout at the desired position.

A red line representing the input plane appears in the layout window.

3Double-click the Input Plane.

The Input Field Properties dialog box appears.

4Select Continuous Wave.
5Set the center wavelength to 0.4um.
6Click the General tab, and then click Modal.
7Click the 2D Transverse tab to start solving the 2D TE fundamental mode for the Core (Waveguide Linear1) waveguide.
8Click Calculate Mode button.
9On the Modes tab, select Solved Mode.
10Click Apply Data.
11Return to the Input Field Properties dialog box and click General tab.
12Set Plane Geometry Position to 0.125.
13Select Positive direction.
14Click OK.

Setting up 2D Simulation parameters

StepAction
1From the Simulation menu, select 2D Simulation Parameters.

The Simulation Parameters dialog box appears (see Figure 4).

FDTD - Figure 4 Simulation Parameters dialog box

Figure 4: Simulation Parameters dialog box

2Click TE.
3Set x-direction mesh and z-direction mesh to 0.005.
4Click Advanced.
5Set the Anisotropic PML boundary condition parameters:

Number of Anisotropic PML layer: 14

Theoretical Reflection Coefficient: 1.0e-12

Real Anisotropic PML Tensor Parameter: 1.0

Power of Grading Polynomial: 3.5

6Click Calculate to get the Time Step Size.
7Set Run for 2000 time steps for finalization.
8From the Key Input Plane drop-down list, select Input Plane1 and Wavelength to 0.4.

Note: The Key Input Plane’s Center Wavelength will be used for the DFT calculation.

9Click OK to close the Simulation Parameters dialog box without running the simulation, or click Run to start the OptiFDTD Simulator.

Performing the simulation

When the Simulator starts, the emitting field can be observed (see Figure 5).

Note: Please use the Rainbow_Banded Palette to view the graph. Right-click on the graph to set the graph control.

FDTD - Figure 5 OptiFDTD_Simulator

Figure 5: OptiFDTD_Simulator

Performing data analysis

With the example used in this lesson, in the Analyzer you can perform the following analysis:

  • Observe the Layout, Refractive Index Poynting Vector, field propagation pattern (DFT results) for the Input Wavelength (see Figure 6).

FDTD -Figure 6 X-direction Poynting Vector

Figure 6: X-direction Poynting Vector

  • Select the Cross Cut in the Tools menu to get the Mode Analysis, slice power, and far field transformation. The X-Z Slice viewer appears (see Figure 7).

FDTD - Figure 7 X-Z Slice viewer

Figure 7: X-Z Slice viewer