Photonic Crystal Bragg Stack

This simulator builds a real one-dimensional photonic crystal — a quarter-wave stack of alternating high- and low-index dielectric layers, the structure behind dielectric mirrors and distributed-Bragg-reflector lasers — and solves it exactly with the optical transfer-matrix method. Tune the design wavelength, the number of layer pairs and the index contrast to watch the reflectance spectrum open a photonic band gap, then sweep the probe wavelength through it: outside the gap the electromagnetic field propagates straight through the stack, while inside the gap it decays exponentially, exactly as a real Bragg mirror rejects that band of light.