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Sandbox Physics

Optics 088 · Waveguides, structured light, and modern optics

Boundary Wave Tunnel

An independently initialized three-dimensional apparatus connects Evanescent penetration, Near-field probe, Frustrated total reflection. Two dimensional physical controls, direct probe dragging, a detector trace, and three quantitative checks are recalculated from the stated equation.

Interactive modelBoundary Wave Tunnel
Primary prediction P1\mathcal P_10.500.50
Physical scale P2\mathcal P_250%50\%
Limit check V\mathcal V0.00π0.00\pi
Model regimevalid model regime\text{valid model regime}

Physics tutorial

How to investigate Boundary Wave Tunnel

BackgroundBoundary Wave Tunnel is one independently initialized apparatus with three linked investigations: Evanescent penetration, Near-field probe, Frustrated total reflection. Its two controls—Air gap and Internal angle—feed the governing relation I(z)=I0e−2κzI(z)=I_0e^{-2\kappa z}. The page uses the stated modal, coupled-mode, effective-medium, or envelope approximation and marks its breakdown instead of presenting it as a full-wave result.

Why it mattersHow can an evanescent field cross a narrow gap and restore transmission beyond total reflection?

Start with the essentials

Focus question
How can an evanescent field cross a narrow gap and restore transmission beyond total reflection?
One-sentence intuition
The detector curve and all three numerical readouts are recomputed from I(z)=I0e−2κzI(z)=I_0e^{-2\kappa z}. Geometry and glow are presentation encodings; the equation, units, conservation or limit check, and validity indicator are the quantitative evidence.

Core mathematical model

Governing relation

I(z)=I0e−2κzI(z)=I_0e^{-2\kappa z}

The implementation evaluates this relation with dimensional inputs and an executable analytic or numerical benchmark. The page uses the stated modal, coupled-mode, effective-medium, or envelope approximation and marks its breakdown instead of presenting it as a full-wave result.

Common difficulties

Mistaking glow for measured power

Typical misconceptionA brighter cinematic trail must represent proportionally more optical power.

Better mental modelUse the detector and normalized readouts for comparison. Glow is deliberately nonlinear so weak structure stays visible.

Run the experiment

  1. 01

    Scene 1: Evanescent penetration

    Select Evanescent penetration. Sweep Air gap, hold Internal angle fixed, and then reverse the roles. Drag the stage probe to repeat the first sweep directly.

    What to observe: Read the primary prediction, physical scale, limit check, and validity indicator together. Record where the approximation boundary changes.
  2. 02

    Scene 2: Near-field probe

    Select Near-field probe. Sweep Air gap, hold Internal angle fixed, and then reverse the roles. Drag the stage probe to repeat the first sweep directly.

    What to observe: Read the primary prediction, physical scale, limit check, and validity indicator together. Record where the approximation boundary changes.
  3. 03

    Scene 3: Frustrated total reflection

    Select Frustrated total reflection. Sweep Air gap, hold Internal angle fixed, and then reverse the roles. Drag the stage probe to repeat the first sweep directly.

    What to observe: Read the primary prediction, physical scale, limit check, and validity indicator together. Record where the approximation boundary changes.