Patent ID: 8078054

Claim:
A method of monitoring a plurality of wavelength channels of an optical wavelength division multiplex (WDM) signal, each wavelength channel being modulated with at least one tone, the method comprising: filtering the optical WDM signal into at least two bands, the at least two bands including a long-wavelength band and a short-wavelength band; converting individually each of the at least two bands of the filtered optical WDM signal into an electrical signal; detecting a tone in at least one of the electrical signals; and determining a power of a wavelength channel from the detected tone, wherein the at least one tone with which the wavelength channel is modulated is detected in each of the electrical signals of two adjacent bands of the at least two bands and determining the power of the wavelength channel includes summing the powers of the at least one tone as detected in the electrical signals of the two adjacent bands.