Case Study 11: Cube Beam Splitter CAD And Virtual Plane

Goal

This case study documents the current cube beam-splitter workflow without overstating what imported CAD can do:

use a vendor cube CAD/STL body as mechanical geometry;
label the external cube faces;
save a virtual internal 45 degree splitter plane as authoring metadata;
understand why the CAD body alone does not create reflected/transmitted ray branches;
compare that CAD workflow with the validated cube beam-splitter primitive.

The screenshots in this tutorial are generated from the live Tk UI with:

python -m KrakenOS.UI.capture_cube_virtual_plane_case_study_screenshots

The capture script generates a 25 mm cube STL proxy so the tutorial is reproducible without running STEP meshing during documentation builds. The row still records the vendor reference path:

attachment/68551/step_68551.step

Load Or Import The Cube Body

In a live design, choose File -> Import Optical CAD/STL Solid... and select the vendor cube STEP/STL/IGES file. For this tutorial, the screenshot uses a generated 25 mm cube proxy with the same row metadata.

The important row is the file-backed Solid_3d_stl optical solid:

Cube CAD proxy loaded as an optical STL solid — The cube row stores material, pose, the generated STL path, and the original Edmund 68551 STEP source path. It is a real optical solid row, but not yet a traced beam-splitter coating.

Observe The Passive CAD Trace

Click Update with Trace mode = Non-Sequential Preview.

Passive CAD cube trace without reflected splitter branch — The ray bundle interacts with the closed cube body. It does not split into reflected and transmitted branches because a mechanical CAD file does not encode split ratio, phase, loss, or polarization behavior.

Assign External Faces And Build A Virtual Plane

Select the cube row and choose Actions -> Assign CAD/STL Optical Faces. Label the external faces:

Left, Right, Up, Down = Transmit/Port
Front, Back           = Absorber/Mechanical or unused mechanical faces

Then use the Virtual Internal Plane workbench:

Diagonal = Left + Up (reflect +Y)
Split    = 0.5
Loss     = 0.02
Phase    = 180 deg

Click Auto Cube Splitter Plane.

Cube CAD face assignment dialog with a virtual internal splitter plane — The dialog stores the external face labels and one virtual internal beam-splitter plane in `OpticalSolidFaces` metadata. The virtual plane is visible in 3D preview and placement tools.

Read The Virtual Plane Report

The generated report shows the exact metadata saved for the internal plane.

Cube CAD virtual internal plane report — The synthetic hit sequence inserts `face_hit -> virtual_plane -> face_hit` between the external Left and Right faces. This is authoring and diagnostic metadata; it is not yet the active branch-tracing engine for a CAD cube.

Use The Primitive For Splitter Physics Today

For real reflected/transmitted branch physics today, use a Beam Splitter row or the cube beam-splitter primitive. The Michelson preset uses an Edmund 68551-sized cube reference body plus an internal 45 degree Beam Splitter row for deterministic 50/50 splitting and recombination.

Michelson cube beam-splitter primitive with reflected and transmitted branches — This is the current validated workflow when reflected/transmitted branches, phase, coherent detector paths, and interferograms matter.

Check Mesh Readiness

The cube proxy used for this tutorial is deliberately simple, but the same mesh diagnostics apply to vendor CAD converted to STL.

Cube proxy STL mesh diagnostics report — A useful optical CAD/STL body should have finite scale, no open boundary edges, no non-manifold edges, no degenerate triangles, and usable winding.

Run The Validators

Use these checks after changing the virtual-plane, face-role, or hit-sequence code:

python -m KrakenOS.UI.validate_optical_solid_virtual_plane
python -m KrakenOS.UI.validate_optical_solid_hit_sequence
python -m KrakenOS.UI.validate_optical_solid_face_roles

What This Proves

This case study exercises the cube-CAD side of the non-sequential-first architecture:

external cube CAD/STL import as mechanical geometry;
face-role labeling for a closed optical solid;
saved virtual internal splitter-plane metadata;
transformed 3D preview records for the virtual plane;
hit-sequence insertion of a virtual internal plane for diagnostics;
clear separation between CAD authoring intent and active beam-splitter branch physics.

Common Mistakes

I imported a cube STEP and expected it to split rays.: A STEP file usually contains only mechanical boundary geometry. It does not contain split ratio, coating phase, loss, or Jones/polarization data. Use a Beam Splitter row or cube primitive for active branch physics.
I built a virtual internal plane but still see no reflected branch.: That is expected today. The virtual plane is saved authoring metadata for preview, placement, and diagnostics. It is a bridge toward CAD-first splitter authoring, not the current traced branch engine.
Can I still use vendor CAD in a real design?: Yes. Use it for mechanical envelope, placement, exported STEP overlays, and face/port documentation. Keep the internal Beam Splitter row for traced optical behavior until active virtual-plane branch tracing is implemented.
Which workflow should I present?: Present both: the CAD row proves the UI can import and label real geometry; the Michelson/cube primitive proves the current physics path for splitting, phase, recombination, and interferogram analysis.