Photonic Waveguide Coupler — Phasor & Parameter Map

Integrated photonic chips route light through etched waveguides only a few hundred nanometres across, and when two of them run close and parallel their evanescent fields overlap — light launched into one waveguide leaks continuously into its neighbour and back again as it propagates. Rather than a 3D render of the chip, this view puts the exact coupled-mode-theory solution front and center: a phasor diagram traces the two complex mode amplitudes rotating on the complex plane as they propagate, a scrubbable power-vs-distance chart shows the full bar/cross split along the whole chip length, and a live parameter-map heatmap lets you drag through every waveguide-gap and chip-length combination at once. Adjusting the gap changes the coupling strength exponentially, adding a phase mismatch caps how much power can ever cross over, and the same physics makes directional couplers the standard on-chip beamsplitter for photonic quantum circuits.