2D Metalens: Huygens-Fresnel Diffraction

This simulator computes the real diffracted light field of a geometric-phase (Pancharatnam-Berry) metalens instead of animating an assumed wavefront shape. Roughly a hundred aperture point-sources, each carrying the exact rotation-encoded phase a real nano-antenna array would imprint, are summed with the true 2D scalar Green's function of the Helmholtz equation to build the propagated field U(x,z) at every point behind the surface — the same Huygens-Fresnel principle underlying real diffraction theory. Flip the circular-polarization handedness to watch the identical fixed aperture phase profile either focus light to a genuine, numerically-located diffraction-limited spot or spread it as a diverging wave with no interior focus, and redesign the lens with the aperture, focal length and wavelength sliders to see the simulated focus position and spot width respond exactly as the geometric-phase equations predict.