OptiFDTD provides two dimension nonlinearity and multiple input wave simulations, thereby enabling you to simulate the Four Wave Mixing (FWM) effect. The following lesson outlines how OptiFDTD performs a FWM simulation.

To create the Four Wave Mixing layout, perform the following procedures.

Designing a four-wave mixing layout

To design the four-wave mixing materials, perform the following procedures.

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

The Initial Properties dialog box appears.

3Click Profiles and Materials.

The Profile Designer window appears.

4Under the Materials folder, right-click the Dielectric folder and select New.

A new FDTDDielectric1 material dialog box appears.

5Select/type the following information:

Name: FDTD_1.65

Const Ref. Idx

N Re: 1.65

6To save the material, click Store.

FDTD_1.65 appears in the Dielectric folder in the directory and in the dialog box title bar.

7Under the Materials folder, right-click the FDTD-Nonlinear folder and select New.

A new FDTDNonlinear1 material dialog box appears.

8Select Kerr.

The Kerr tab appears in the dialog box.

9Select/type the following:

Name: FDTD_NL_Kerr

Relative Linear Permittivity: 2.7225

Response Time: 2.0e-15

Permittivity: 2.0e-18

10To save the material, click Store.

FDTD - Figure 19 FDTD_NL_Kerr material

Figure 19: FDTD_NL_Kerr material

To define the channel profile, perform the following procedure.

StepAction
1Under the Profiles folder, right-click the Channel folder and select New.

The ChannelPro1 dialog box appears.

2Create the following channel profile:

Profile name: NL_Kerr

2D profile definition

Material: FDTD_NL_Kerr

3Click Store.
4Create a second profile:

Profile name: Linear_WG

2D profile definition

Material: FDTD_1.65

5Click Store.
6Close the Profile Designer.

To define the wafer and waveguide properties, perform the following procedure.

StepAction
1In the Initial Properties dialog box, , type/select the following:

Waveguide Properties

Width [μm]: 1.0

Profile: NL_Kerr

Wafer Dimensions

Length [μm]: 15.0

Width [μm]: 10.0

2D Wafer Properties

Material: Air

2Click OK.

The Initial Properties dialog box closes and the layout window appears.

To create the waveguide, perform the following procedure.

StepAction
1From the Draw menu, select Linear Waveguide.
2In the layout window, drag the linear waveguide from the start point to the end point.

A linear waveguide appears in the layout window.

Note: Release the Linear Waveguide selection tool by clicking the Select tool after the Linear Waveguide is drawn in the layout.

3To adjust the position and the shape of the waveguide, in the layout window, double-click the Linear Waveguide.

The Linear Waveguide Properties dialog box appears.

4Click the Start tab.
5Under Offset, type the following values:

Horizontal: 4.0

Vertical: 0

6Click the End tab
7Under Offset, type the following values:

Horizontal (µm): 13.00

Vertical (µm): 0.0

8In Channel Thickness Tapering, select Use Default (Channel:None).
9Type/select the following:

Width (µm): 8.0

Depth (µm): 0.0

Label: linear4

Profile: NL_Kerr

10Click OK.
11Repeat steps [1] through [3] to create three input linear waveguides in the layout.

Note: The input waveguide is used to input three different wavelength waves into the nonlinear material.

Input Waveguide 1 properties:

StepAction
1In Start > Offset, type the following values.

Horizontal: 0

Vertical: 0

2In End > Offset, type the following values:

Horizontal: 4

Vertical: 0

3In Channel Thickness Tapering, select Use Default (Channel:None).
4Type/select the following:

Width (µm): 1.0

Label: linear1

Depth (µm): 0.0

Profile: Linear_WG

5Click OK.

Input Waveguide 2 properties:

StepAction
1In Start > Offset, type the following values.

Horizontal: 0

Vertical: 1.2

2In End > Offset, type the following values:

Horizontal: 4

Vertical: 1.2

3In Channel Thickness Tapering, select Use Default (Channel:None).
4Type/select the following:

Width (µm): 1.0

Depth (µm): 0.0

Label: linear2

Profile: Linear_WG

5Click OK.

Input Waveguide 3 properties:

StepAction
1In Start > Offset, type the following values.

Horizontal: 0

Vertical: -1.2

2In End > Offset, type the following values:

Horizontal: 4

Vertical: -1.2

3In Channel Thickness Tapering, select Use Default (Channel:None).
4Type/select the following:

Width (µm): 1.0

Depth (µm): 0.0

Label: linear3

Profile: Linear_WG

5Click OK.

FDTD - Figure 20 Input waveguides

Figure 20: Input waveguides

Setting the input wave

StepAction
1From the Draw menu, select Vertical Input Plane.
2To insert the input plane, click in the layout window where you want it placed.

The input plane appears in the layout.

3To edit the input plane, double-click on the input plane in the layout.

The Input Plane Properties dialog box appears.

4On the General tab, type/select the following:

Continuous Wave

Wavelength [μm]: 1.4

Input Field Transverse: Modal

Plane Geometry:

Z Position [μm]: 1.0

5On the 2D Transverse tab, click Find Modes.

The Mode Solver 2D dialog box appears.

6On the Waveguides tab, select Linear1.
7Click Calculate Mode.

The Modes tab is activated.

8On the Modes tab, select the mode.
9Click Apply Data.

The Mode Solver 2D closes.

10On the 2D Transverse tab, select the Amplitude radio button and type the following:

Amplitude [V/m]: 2.0e09

11Click OK.

The Input Field Properties dialog box closes.

12Repeat steps [1] through [10] to create a second vertical input plane with the following data:

Vertical Input Plane 2 properties:

StepAction
1In the Input Field Properties dialog box, select/type the following:

Continuous Wave

Wavelength [μm]: 1.55

2On the General tab, type/select the following:

Input Field Transverse: Modal

Plane Geometry:

Z Position [μm]: 1.0

3Click Find Modes.

The Mode Solver 2D dialog box appears.

4On the Waveguides tab, select Linear2.
5Click Calculate Mode.

The Modes tab is activated.

6On the Modes tab, select the mode.
7Click Apply Data.

The Mode Solver 2D closes.

8On the 2D Transverse tab, select the Amplitude radio button and type the following:

Amplitude [V/m]: 2.0e09

9Click OK.

The Input Field Properties dialog box closes.

Vertical Input Plane 3 properties:

StepAction
1In the Input Field Properties dialog box, select/type the following:

Continuous Wave

Wavelength [μm]: 1.60

2On the General tab, type/select the following:

Input Field Transverse: Modal

Plane Geometry:

Z Position [μm]: 1.0

3Click Find Modes.

The Mode Solver 2D dialog box appears.

4On the Waveguides tab, select Linear3.
5Click Calculate Mode.

The Modes tab is activated.

6On the Modes tab, select the mode.
7Click Apply Data.

The Mode Solver 2D closes.

8On the 2D Transverse tab, select the Amplitude radio button and type the following:

Amplitude [V/m]: 2.0e09

9Click OK.

The Input Field Properties dialog box closes.

Setting up the Observation Point

StepAction
1From the Draw menu, select Observation Point.
2Place the Observation Point in the desired position in the layout.
3Double-click the observation point.

The Observation Properties — Point dialog box appears.

4On the General tab:

In Center, Offset, type/select the following: Horizontal: 6.0μm

Vertical: 0.0μm

Center depth: 0.0 μm

Label: Observation Point1

5On the Data Components tab, ensure that 2D TE: Ey is selected (default).
6Click OK.

The Observation Properties — Point dialog box closes.

7Repeat steps 1 to 5 and create another Observation Point with the following information.
8On the General tab:

In Center, Offset, type/select the following: Horizontal: 6.0μm

Vertical: 1.2μm

Center depth: 0.0 μm

Label: Observation Point2

Click OK.

9Repeat steps 1 to 5 and create another Observation Point with the following information.
10On the General tab:

In Center, Offset, type/select the following: Horizontal: 6.0μm

Vertical: -1.2μm

Center depth: 0.0 μm

Label: Observation Point3

11On the Data Components tab, ensure that 2D TE: Ey is selected (default).
12Click OK.

Setting the 2D simulation parameters

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

The Simulation Parameters dialog box appears.

2Type/select the following information:

Polarization: TE

Mesh Delta X [μm]: 0.1

Mesh Delta Y [μm]: 0.1

3Click Advanced….

The Boundary Conditions dialog box appears.

4Type/select the following information:

-X: Anisotropic PML

+X: Anisotropic PML

-Z: Anisotropic PML

+Z: Anisotropic PML

Anisotropic PML Calculation Parameters

Number of Anisotropic PML Layers: 10

Theoretical Reflection Coefficient: 1.0e-12

Real Anisotropic PML Tensor Parameters: 5.0

Power of Grading Polynomial: 3.5

5In Time Parameters, click Calculate.

The default time step size is calculated.

6Select Run for 3000 Time Steps (Results Finalized).
7Select Key Input Information: Input Plane1 and wavelength:1.4.

Note: The input plane’s center wavelength is used for DFT calculations.

8Click OK to close the Simulation Parameters dialog box without running the simulation, or click Run to start the OptiFDTD Simulator.

Note: Save your layout before starting the simulation.

Observing the simulation results

Key things to observe:

  • wave propagation pattern in time domain (see Figure 21)
  • field response in time domain and frequency domain for observation point (select View > Observation Point to see the dynamic time domain and frequency domain response (see Figure 22).

FDTD - Figure 21 OptiFDTD Simulator—wave propagation pattern in time domain

Figure 21: OptiFDTD Simulator—wave propagation pattern in time domain

FDTD - Figure 22 OptiFDTD Simulator—time domain and frequency domain for observation point

Figure 22: OptiFDTD Simulator—time domain and frequency domain for observation point