np Density and Temperature Index Perturbation - Simulation object

This page describes how to use the np Density and Temperature grid attribute objects to export electron-hole (np) density and temperature grid attribute recorded on a finite-element mesh directly from a CHARGE and HEAT simulation, and import it to FDTD or MODE.

Exporting index perturbation grid attributes from CHARGE and HEAT

np density grid attribute To export np density data, the simulation file should contain an unstructured data set called ‘charge’ with scalar attributes ‘n’ and ‘p’. This would typically be exported from CHARGE as shown in the Mach Zehnder example. This can be done by right-clicking the charge monitor and selecting the save data with a user-specified filename.

Temperature grid attribute The temperature grid attribute data can be exported from HEAT using scripts. Once a simulation has run, click on the 'HEAT' solver object in the object tree. This will bring up the results related to the thermal analysis. The dataset called 'thermal' is the one to be export. The script as shown below can be used to do that: out = getresult("HEAT","thermal"); matlabsave("filename.mat",out);

Importing index perturbation grid attributes to FDTD or MODE

The procedure for importing the np density and temperature grid attributes are the same.

For parameterized datasets, all parameter index will be set to 1 when the dataset is imported, even if there was a previously imported dataset with the same parameter names. This is an expected behavior, and the dataset is imported properly.

Import using GUI

Importing in FDTD

Importing in MODE

1. Add grid attribute object
   • For FDTD, you can find it in the “FDTD” tab under the “Attributes” group
   • For MODE, you can find it as a part of the “Attributes” button in the main toolbar
2. Right-click the grid attribute object in the object tree
3. Click the import data button and specify the filename

Import using script

It is also possible to import the np density and temperature grid attributes using scripts. Please refer to importdataset for further information.

Creating an index perturbation material model

The np density and temperature attributes contain information about the charge density and temperature for the specified region in the simulation. The information needs to be translated into index changes by creating an index perturbation material model. Below are steps to be taken to create such material model. 

Defining Index Perturbation material in FDTD

Defining Index Perturbation material in MODE

1. Open the Material Database
   • For FDTD, you can find it in the “Design” tab under the “Materials” group
   • For MODE, you can find it as the “Materials” button in the main toolbar
2. Click 'Add' and select 'index perturbation' material model
3. Specify the material name
4. In the material properties, select the type(s) of index perturbation to be included in the material model, ie. np density and temperature. You can include only one of them or both. The index of the base material is then perturbed in accordance with options you choose for the conversion of np density / temperature to index changes.

There are three conversion options available for np Density grid attribute:

• Drude
• Soref and Bennett
• Custom

and two options for Temperature grid attribute:

• linear sensitivity
• table of values

For more information about models for np Density material, please visit Charge to index conversion.

Note: Parameters for the models

These parameters are material and frequency dependent, the default parameters are set for silicon at 1.55 um.

See also

Charge to index conversion, Transferring data between electrical and optical solvers, importdataset