Structure Configuration

Structure is the structural modeling page in Dreapex TMM. It defines the incidence medium, the optical stack itself, and the transmission medium. This page determines the object to be solved; if the structure is invalid, Run, Run Sweep, and Run Optimizer may still be visible, but the model will not produce a usable result.

This chapter defines a practical method for building valid thin-film models. It covers top-level stack editing, refractive-index models, Layer Group, surrounding media, and structure validation.

Page Structure and Setup Order

The Structure page contains four functional regions:

The footer status bar updates continuously while you edit. The correct editing rhythm is: make one round of changes, then check the footer once, rather than making many changes and debugging them only at the end.

Structure setup order:

1. Confirm Incidence Medium first.
2. Edit normal layers or create a Layer Group.
3. Adjust the stack order if needed.
4. Configure Transmission Medium last.
5. Move to Optics only after the footer status returns to passed.

This order reduces rework because index models, incoherent settings, surrounding-medium absorption rules, and layer order all interact.

Top-Level Editing: Toolbar and Structure Table

The page toolbar only controls the top-level structure table. It does not control the internal table inside the Layer Group dialog.

If Insert, Duplicate, Move Up, Move Down, or Delete is disabled, the first thing to check is whether the target row is selected.

Click the 3D button in the toolbar to switch to 3D visualization. The 3D view provides camera presets (Front/Isometric/Dimetric/Trimetric), shape (Square/Circle), display options (Lighting/Names/Thickness/Incident Ray/Explode), and image export.

Each row in the structure table is one top-level structure element. A row can be either a normal Layer or a Layer Group. The key columns are:

In practical use, the structure table is governed by four rules that matter most:

1. Not all top-level elements may be disabled.
2. Top-level names must be unique; duplicated rows should be renamed immediately.
3. Normal-layer thickness must be strictly greater than 0; if a layer should be excluded temporarily, disable it instead of setting thickness to 0.
4. Incoherent applies only to normal layers; once enabled, that layer should not be configured as a birefringent material.

Transparency can be used to express the intended modeling role of a layer, but it does not replace physical material parameters. A transparent layer still requires valid refractive-index inputs.

Refractive-Index Model Selection

For normal layers, the parameter editor changes with the selected refractive-index model. Choosing the correct model is one of the central structural decisions on this page.

For most work, the correct choice can be made as follows:

1. For concept checks or rapid reference models, start with Constant.
2. For anisotropic studies without external data, use Const. Birefringence.
3. For realistic dispersion, use File.

When switching to Const. Birefringence, the parameter area expands from two inputs to four. This is the clearest visual indicator that the index model changed.

In File mode, the editor exposes six controls:

The recommended sequence is fixed: check the database first, import a local file only if needed, preview the curve before continuing, and clear the current file before replacing it.

Layer Group: Periodic Structure Modeling

When the stack contains a repeated unit, Layer Group should be used instead of manually duplicating a large number of normal layers. Typical examples are DBRs, repeated bilayers, and periodic functional units.

There are two entry points:

1. Add > Layer Group: append a group to the end of the top-level stack.
2. Insert > Layer Group: insert a group after the currently selected top-level row.

The editor is identical in both cases; only the insertion position changes.

The dialog can be divided into four parts:

The most important rules for a group are:

One implementation detail must be remembered clearly:

1. Inside the Layer Group dialog, the Repeat Count control is limited to 1-100 by the UI.
2. After returning to the top-level structure table, the repeat count can be increased further to 1-1000.
3. The underlying validation logic accepts positive integers in the range 1-1000.

Therefore, if the target repeat count is above 100, the correct procedure is to create the group first and then increase the repeat count from the top-level table.

Internal editing behaves like top-level editing, but only within the current group. Internal sub-layers must still satisfy the same core rules: non-empty names, names unique within the group, thickness greater than 0, and parameters consistent with the selected index model.

Three differences matter in practice:

1. Internal sub-layers expose Transparency, but not Incoherent.
2. Internal reordering changes only the current group, not the top-level stack order.
3. Changes are written back only when Save is clicked; Cancel discards the current dialog edits.

If coherent/incoherent switching is expected to happen often, normal top-level layers are usually a better choice than putting those layers inside a Layer Group.

Surrounding-Medium Configuration

The Structure page provides Incidence Medium above the stack and Transmission Medium below it. These are boundary conditions for the stack, not layers inside the stack.

Both panels share the same baseline rules:

1. The name cannot be empty.
2. Only Constant and File are supported as index models.
3. Birefringent constant mode is not supported for surrounding media.
4. Birefringent refractive-index files are also not supported for surrounding media.

The practical differences are:

The most important engineering restriction is that the incidence medium must remain non-absorbing. Even in file mode, every value in the imported k column must remain 0, otherwise validation fails.

The transmission medium is the natural place to model substrates or output media. In constant mode it accepts an explicit k; in file mode it can load a material directly from the refractive-index database. Absorbing substrates and lossy output media should therefore usually be modeled on the transmission side.

Refractive-Index Database

When a normal layer or a surrounding medium uses File mode, the Database button opens the refractiveindex.info Database dialog, which provides access to the built-in refractive-index material catalog.

Dialog Layout

The dialog is divided into two panels:

Search

The search bar at the top accepts material names, materialId values, or database source paths. Press Enter to jump directly to the matched material and load its preview.

Material Metadata

After selecting a material, the right panel displays:

Selection Workflow

1. Expand Shelf > Book > Material in the left-panel tree, or type a keyword in the search bar and press Enter.
2. Click a material entry; the right panel loads the refractive-index curve preview automatically.
3. Verify the metadata and curve, then click Confirm to apply the material to the current layer or surrounding medium.
4. To cancel, click Cancel or close the dialog.

After confirmation, the layer row shows the material file name. The chart preview dialog will display a Linked to Database tag, indicating that the current data originates from the database.

Interpolation Method

When a layer or surrounding medium uses File mode, an Interpolation dropdown appears at the end of the layer row. It controls how refractive-index data are interpolated between data points.

RI Status Check

The RI Status button in the page toolbar checks whether all database-linked layers have up-to-date refractive-index data.

Check Workflow

Clicking RI Status compares each database-linked layer against the remote database version. A toast message displays one of three states:

When updates are found, each row in the action table corresponds to a layer that requires attention:

• updated: A newer version exists in the database; click Refresh to update.
• missing: The material no longer exists in the latest database; only Detach is available to remove the database link.

Bulk Operations

The dropdown menu next to the RI Status button provides two bulk operations:

Chart Preview Dialog

Click the Preview button (magnifying-glass icon) on a layer row or surrounding medium to open the refractive-index chart preview dialog.

The dialog contains:

The chart area displays n/k refractive-index curves as a function of wavelength, allowing a quick visual check that the dispersion profile matches expectations.

For database-linked materials, the dialog footer shows a Linked to Database tag along with Refresh From Database and Detach Database Link buttons for managing the database synchronization state.

Wavelength Coverage Check

Before running a calculation (Run, Run Sweep, Run Optimizer), the software automatically verifies that the refractive-index data wavelength range of every File-mode layer and surrounding medium covers the configured wavelength sampling range.

If any layer's RI data does not fully cover the requested wavelength sampling range, the run is blocked. The error message identifies the layer name, the data coverage range, and the requested range.

Structural Validation

The most common structural failures can be reduced to the following cases:

Before leaving this page, the correct structural self-check is:

1. At least 1 top-level element is enabled.
2. Top-level names are unique.
3. Every thickness value is greater than 0.
4. Each normal layer uses parameters consistent with its current index model.
5. Both surrounding media satisfy the naming, type, and absorption constraints.
6. The footer validation status has returned to passed.

Baseline Modeling Procedure

To build a standard “air / single film / substrate” model, use the following sequence:

1. Keep Incidence Medium as a non-absorbing constant medium.
2. Edit the default normal layer by setting its name, thickness, and refractive-index model.
3. If realistic dispersion is required, switch that layer to File mode and load a database material.
4. Configure the substrate in Transmission Medium; if the substrate is absorbing, define k there.
5. Check the footer and confirm that the structure passes validation.
6. Then move to Optics for angle, wavelength, and detector configuration.

For periodic structures, replace step 2 with: create a Layer Group, define one repeated unit in the dialog, and set the repeat count.

After the structure passes validation, continue with the next chapter: Optical Parameters.