Q Factor to Propagation Loss Converter
Convert intrinsic quality factor Qi to waveguide propagation loss α using the standard ring-resonator relation. Also computes photon lifetime and FWHM linewidth.
E.g., 1e5 or 100000. Loaded Q from a transmission spectrum will give a lower bound on propagation loss; use intrinsic Q for the loss value.
Selecting a platform sets ng automatically. Editing this field reverts to custom.
- α
- 15.1404 dB/cm
- α
- 1.7431 cm⁻¹
- α
- 1514.04 dB/m
- Photon lifetime τ
- 82.28 ps
- Linewidth (FWHM)
- 1.934 GHz
Relation: α [nepers/m] = ω · ng / (c · Q). Conversion: 1 neper = 8.686 dB. Photon lifetime τ = Q / ω. FWHM linewidth = f₀ / Q. All computation in browser.
| Platform | ng | α (dB/cm) | Qi |
|---|---|---|---|
| SOI 220 nm strip | 4.3 | 2 | 1.7 × 10⁵ |
| SOI 220 nm rib | 3.8 | 0.5 | 6.0 × 10⁵ |
| SiN 200 nm | 1.7 | 0.1 | 1.3 × 10⁶ |
| SiN 800 nm | 2.0 | 0.01 | 1.6 × 10⁷ |
| InP shallow ridge | 3.6 | 2 | 1.4 × 10⁵ |
| LNOI ridge | 2.3 | 0.05 | 3.6 × 10⁶ |
Typical foundry values. Best-in-class devices reach 1–2 orders of magnitude higher Q in the SiN and LNOI platforms.
The transmission-spectrum linewidth gives the loaded Q (QL), which combines intrinsic resonator losses and coupling losses: 1/QL = 1/Qi + 1/Qc.
Using QL in this calculator gives a lower bound on the propagation loss. For accurate loss extraction, decompose QL into Qi and Qc from extinction depth or gap-sweep data — see the methodology article below.
For the derivation of the Q–loss relation, the decomposition of loaded Q into intrinsic and coupling Q, and a worked example, see the article Loaded and Intrinsic Q Factor Extraction from Ring Resonator Transmission Spectra. For direct measurement of waveguide propagation loss without a resonator, see Waveguide Propagation Loss by the Cutback Method.