Patent ID: 7457032

Claim:
Arrangement comprising: a WDT (wavelength-dependent tap) configured to recieve an input optical signal having noise and a plurality of channels at respective channel wavelengths, the WDT having a first output and a second output and being configured to: i) couple to the first output some of the input optical signal at the channel wavelengths and most of the input optical signal at wavelengths between the channel wavelengths; and ii) couple a remaining portion of the input optical signal to the second output; wherein the remaining portion of the input optical signal comprises most of the input optical signal at the channel wavelengths; and an optical performance monitoring function configured to determine an OSNR (Optical Signal-to-Noise Ratio) of the input optical signal as a function of: a first power from the first output of at least one channel wavelength of the channel wavelengths, the first power approximating channel power at the at least one channel wavelength of the channel wavelengths; and a second power from the first output of at least one wavelength that is between the channel wavelengths, the second power approximating noise power at the at least one wavelength that is between the channel wavelengths.