One key technique for fast physical-optics modeling with VirtualLab Fusion is the channel concept which enables connecting solvers (see Connecting Solvers by Master Channels). Fields enter channels through the channel master region which may be subdivided into subregions (see High Flexibility by Subchannels). Often the fields which enter a region is larger than the region and must be truncated or decomposed into the field inside the region and its complement.
The most straightforward way would be cutting the complex field amplitude along the region boundaries, that means its multiplication with a step-function, one inside the region and 0 outside, along the boundary. But the result possesses an abrupt change of values at the boundary and such functions can not be sampled in an accurate way. Thus, in VirtualLab Fusion we do not use a step-function for truncation but a smooth part of a cosine function [Asoubar2012]. It is illustrated Fig. 1 and enables a well-defined sampling, e.g., a minimum of four sampling points per width a. A small choice of the width a leads to a small sampling period and vice versa.
Fig. 1: Smooth truncation function of width a which is used in VirtualLab Fusion to cut complex amplitudes along region boundaries.
The management of the soft boundaries is available in different dialogues in VirtualLab Fusion. In version 2021.1 we have started to communicate it via the Region Boundary Management tab in the Channel Configuration dialogue of components. This feature is available in the Microlens Components and shown in Fig. 2. It provides the settings on how VirtualLab Fusion cuts and decomposes fields at boundaries of the master region and its subregions.
VirtualLab Fusion provides three modii how the soft truncation function of Fig. 1 is adjusted with respect to the boundary. They are illustrated in Fig. 3. The cases (1) – (3) refer to the three cases in the dialogue shown in Fig. 2. The width a of the soft transition can be determined relative to the size of the region or in absolute values.
Fig. 2: The tab Region Boundary Management enables the configuration of the truncation and decomposition of fields along region boundaries.
The three cases are illustrated in Fig. 3 and Fig. 4. In Fig. 3 the truncation along one boundary is shown for the three modii. Figure 4 illustrates how a field can be decomposed along a boundary, e.g., in case of adjacent subchannels. It should be emphasized, that in the third mode, shared soft boundary, the fields of both regions add up to the undisturbed incident field along the boundary. That makes this mode of truncation particularly useful for field decompositions [Asoubar2012].
Fig. 3: Three modii of adjustment of truncation function with respect to the boundary: (1) soft function inside the region, (2) soft function outside the region, (3) middle of soft function at boundary position.
Fig. 4: Illustration of the use of the soft boundary concept for two adjacent regions: inner soft boundary (left), outer soft boundary (middle; part of field shown only), and shared soft boundary (right; part of fields shown only).
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