What does SMSR 40 dB actually mean? Turn datasheet dB readings back into intuitive ratios.
Ratios of optical or electrical power use 10·log₁₀ — SMSR, extinction ratio (PER), insertion loss and coupling ratio all belong here: SMSR 40 dB means the main mode carries 10⁴ = 10,000× the power of the strongest side mode; PER 20 dB means a 100:1 split between polarization axes. Ratios of amplitude (voltage/current) use 20·log₁₀, since power ∝ amplitude² — a 20 dB difference in PD output voltage on a scope corresponds to only 10 dB of optical power. Always check which one an instrument or paper means; this calculator uses the power convention (10·log).
The "half" in FWHM comes from here too: −3 dB ≈ 0.501 — the point where power drops to one half.
Related tools: dBm↔mW · Spectral ripple & FSR
※ Formulas on this page assume ideal models; all device parameters shown are typical values — refer to the datasheet and the serialized factory test report shipped with each unit. For selection support, contact sales@lncetek.com.