Quantum Frequency-Division Multiplexer (2D)

Quantum networks increasingly carry many frequency-bin-encoded photon channels down a single optical fiber, exactly the way classical DWDM telecom links do — this 2D schematic shows the whole round trip from directly overhead. Photons from each channel converge into one shared fiber (the multiplexer), then hit a diffraction grating at the far end that disperses them back into separate angles and separate detectors (the demultiplexer), following the real grating equation sinθ = λ/d. Tune the channel count, the frequency spacing between channels, and the grating's groove density to watch the angular separation between channels shrink or grow — push the spacing too low relative to the grating's resolving power and photons start crossing into the wrong detector, tracked live as crosstalk and routing fidelity, and visible directly in the overlaid Gaussian beam-profile chart.