How can I reduce the uncertainty of the OSNR measurement with the WaveAnalyzer?

The OSNR measurement is of the form

and hence the OSNR will inherently fluctuate more intensely as the source of noise approaches zero.

Here are a few suggestions for reducing the uncertainty:

  • Try using the 6-point OSNR method. This allows a larger bandwidth over which the signal and noise floor are sampled.
  • Take some averages using the averages parameter. Something like 8 averages should improve the repeatability.
  • Experiment with measuring signals with lower OSNR (I.e. signals with more noise). Typically when the OSNR is in the regime where it fluctuates significantly, the OSNR values already exceed around 40-50 dB and so are of no serious concern to real networks.
  • If the power of the signal is weak, then the measurement noise may be hidden below the noise floor of the WaveAnalyzer. Try the WaveAnalyzer’s high sensitivity port.
  • If the signal is an un-modulated narrow line-width source like a DBF laser, it’s possible that the signal power as measured by the WaveAnalyzer fluctuates. In this case switching to a modulated source should improve stability.
  • When the 3-point OSNR mode is activated or the OSNR boundary is repositioned (denoted by the grey overlay) the WaveAnalyzer software automatically chooses the smallest noise values on either side of the signal peak. For the most the most accurate OSNR results move the noise markers around so that interpolated line best represents the expected noise within the signal.