Quantum Frequency-Division Multiplexer

Multiplexer Setup

Channels 4

Channel spacing Δν 400 GHz

Grating groove density 900 /mm

Photon emission rate 2.0 Hz/ch

Channel Map

Live Readouts

Angular separation

0.0°

Crosstalk (est.)

0.0%

Routing fidelity

100.0%

Photons routed

How it works

Each channel carries frequency-bin-encoded photons at ν_i = ν₀ + iΔν. All channels are combined into one fiber (wavelength-division multiplexing), then a diffraction grating at the receiver separates them again by angle — the demultiplexer:

grating equation:  sinθ = λ/d      (normal incidence, order m = 1)
wavelength:        λ = c/ν
resolving power:   R = λ/Δλ = mN   (N = illuminated grooves)
crosstalk:         X ≈ exp(−Δθ² / 2σ²)

Channels — how many frequency bins share the fiber; more channels need either wider spacing or a finer grating to stay separable.
Channel spacing Δν — the frequency gap between neighboring channels; larger spacing gives larger angular separation Δθ at the grating.
Groove density — sets both the dispersion (how much angle per unit wavelength) and, through the illuminated groove count, the angular beam width σ that each channel arrives with at the detector array.
Crosstalk — modeled as the Gaussian overlap between a channel's diffracted beam and its neighbor's detector; when Δθ is small relative to σ, a photon can land in the wrong detector — visible below as a particle veering into an off-color detector.

Real quantum networks use exactly this frequency-multiplexing idea — dense wavelength-division multiplexing (DWDM) grids in the telecom C-band (~193 THz) let many entangled-photon or single-photon channels share one fiber between quantum repeater nodes, with arrayed-waveguide gratings playing the role of the grating here.

Correctly routed photon Misrouted (crosstalk)

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