AQ6151 - WLM Accuracy

If first peak is 1dBm and second - 40dBm, what will be wavelength measurement accuracy difference for second peak?

The WLM does not have 40dB of dynamic range, so the second peak cannot be measure properly. If the second peak is 20dB below the first peak, the wavelength of the second peak can be measured as accurately as the first peak. This is in case of two peaks. If there are more peaks, the accuracy gets worse. (AQ6151 - WLM Accuracy)