Patent ID: 7184672

Claim:
An apparatus for processing an optical signal, the optical signal comprising at least a first channel signal at a first wavelength modulated by a first frequency, a second channel signal at a second wavelength modulated by a second frequency, and a third channel signal at a third wavelength modulated by a third frequency, the apparatus comprising: an input for receiving the optical signal; a splitter arranged to split the received optical signal into at least two optical bands, a first optical band comprising at least the first channel signal, without the third wavelength and a second optical band comprising at least the third channel signal, without the first wavelength; a first photo detector arranged to receive the first optical band, and to output a first electrical signal proportional to the total optical power of the first optical band; a second photo detector arranged to receive the second optical band, and to output a second electrical signal proportional to the total optical power of the second optical band; circuitry to compensate the first and second electrical signals for at least some of SRS induced amplitude modulations on at least the first and third wavelengths, induced by power transfer of amplitude modulations from other wavelengths, and circuitry to determine the modulation amplitudes at the first and third frequencies, from the compensated first and second electrical signals, and to determine the optical power levels at different wavelengths from the modulation amplitudes.