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OSNR (Optical Signal-to-Noise Ratio)


OSNR (Optical Signal-to-Noise Ratio)

OSNR stands for Optical Signal-to-Noise Ratio. In simple terms, it tells you how clean an optical signal is compared to the noise around it — like comparing music volume to background static.

What it means

  • Signal: the actual light carrying your data
  • Noise: unwanted light (amplifier noise, spontaneous emission, etc.)
  • OSNR measures the ratio between them

OSNR is usually expressed in decibels (dB).

Why it matters

OSNR is critical in fiber-optic communications:

  • Higher OSNR → cleaner signal → lower bit-error rate
  • Lower OSNR → more errors, distortion, or link failure

It is especially important in:

  • DWDM systems
  • Optical amplifiers (e.g., EDFAs)
  • Long-haul fiber links

Typical OSNR values

  • 30–40 dB: Clean signal, healthy network
  • 20–25 dB: Marginal, may still work
  • < 20 dB: High error risk

How it’s measured

OSNR is commonly measured using an Optical Spectrum Analyzer (OSA) by comparing the signal power within its bandwidth to the noise power in nearby unused bandwidth.

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