Deposition never produces a perfectly abrupt boundary between two materials — there is always a thin region where the index grades from one to the other. Inhomogeneities lets you insert such a graded transition at any interface in your stack and see what it does to the spectrum. Each transition is sliced into many thin sub-layers whose index is mixed linearly from one material to the next along the chosen profile, and the graded stack is evaluated and overlaid against the original step-interface design. The interlayers are a preview only: your design is not changed.

The window configures the interfaces for the surface mode set in the Design Editor — the front stack, the back stack, or both for total.

Settings

λ range / step — the wavelength grid, in nanometres.

AOI / pol — angle of incidence and polarization (s, p, or averaged).

T+R+A / T / R / A — which channel(s) to plot.

Each interface in the stack is listed by the two media it joins. Tick an interface to add a graded interlayer there, then set:

Thickness — the depth of the transition region, in nanometres. The interlayer is added at the interface; the host layers keep their own thicknesses.

Profile — the shape of the index grade across the transition: linear, parabolic, invParabolic, exponential, or sigmoid.

Slices — how many thin sub-layers the transition is divided into for the calculation. Around 10–20 is usually enough; more slices give a smoother grade.

Clear all removes every interlayer.

How to read it

The chart is in percent. Each channel is drawn twice: the original step-interface design as a faint dotted line, and the graded version as a solid line on top. Comparing the two shows what the real, non-abrupt interfaces cost you — typically softened stopband edges and shifted passband ripple. If your design has a Specification, a live verdict in the toolbar tells you whether the graded design still passes. The toolbar also reports how many interlayers are active and their combined thickness.

References

• H. A. Macleod, Thin-Film Optical Filters, 5th ed., §16 (inhomogeneous layers).