WDM Add-Drop Multiplexer (2D)

Tunable Drop Ring

Channel to tune CH3 (1552.00 nm)

Heater power (thermo-optic tuning) 0.0

Channel spacing 0.80 nm

Resonator Q factor 8000

Live Readouts

Ring resonance λ_res1552.00 nm

Insertion loss (own channel)0.0 dB

Adjacent-channel isolation28.0 dB

Resonance FWHM0.194 nm

Channels

CH1 — through if not dropped

CH2

CH3

CH4

View

How it works

A wavelength-division-multiplexing (WDM) add-drop router carries several optical channels on one bus waveguide. Each micro-ring resonator sits beside the bus and, at its resonant wavelength, evanescently couples power out to a "drop" waveguide while every other wavelength keeps going straight through:

Resonance:      m·λ_res = n_eff · 2πR      (m integer)
Drop transfer:  T(λ) = 1 / (1 + ((λ-λ_res)/(FWHM/2))^2)
Linewidth:      FWHM = λ_res / Q
Thermo-optic:   Δλ_res ≈ λ_res·(1/n_g)·(dn/dT)·ΔT

Channel to tune / Heater power — a resistive micro-heater raises the ring's local temperature, shifting n_eff and therefore λ_res (thermo-optic tuning, the standard way foundries trim and reconfigure PIC filters after fabrication). Only the selected ring is heated; the other three stay locked exactly on their own channel.
Channel spacing — sets how far apart the four input wavelengths sit; narrower spacing packs more channels but leaves less room before neighbours overlap.
Q factor — set by the ring-to-bus coupling gap. A higher Q gives a narrower, more selective resonance (lower insertion loss on-channel) but also a tighter tuning tolerance, which is exactly the loss-vs-yield trade-off real PIC foundries balance with process control and design margin.
Insertion loss / isolation — as the heater detunes the ring away from its own channel's wavelength, that channel's drop efficiency falls (rising insertion loss) while the resonance can drift toward a neighbouring channel (falling isolation, i.e. cross-talk) — the two failure modes every WDM filter has to be designed and packaged against.
Spectrum panel — plots the exact Lorentzian drop-transfer curve T(λ) for all four rings simultaneously (dashed = unselected, glowing solid = the ring you're tuning), with the four channel wavelengths marked, so the loss/cross-talk trade-off above is visible as an actual curve, not just a number.

Real-world relevance: this is the core building block behind add-drop multiplexers in datacom transceivers, reconfigurable optical routers, and multiplexed ring-resonator sensor arrays on silicon-photonic chips.

Bus waveguide Tuned ring (selected)

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Transmission spectrum T(λ) — all 4 rings