Patent ID: 7715092

Claim:
A method for compensating for Raman tilt in an optical signal, defined by a center wavelength, transmitted in an optical fiber link, which includes an optical amplifier, comprising the steps of: a) tapping off a portion of the optical signal including a plurality of wavelength channels λ′, including a first wavelength λ 1 ; b) determining a measure of optical power of the optical signal, from the tapped off portion; c) determining the Raman tilt from the measure of optical power; and d) adjusting gain provided by the optical amplifier to compensate for the Raman tilt; wherein step b) includes: i) separating the tapped off portion into first and one or more second sub-portions; ii) passing the first sub-portion to a first photo-detector to determine the measure of optical power P tot ; and iii) passing each of the second sub-portions to an optical filter with a predetermined transmission function based on the optical signal's second moment of power terms P 2 forming a filtered second sub-portion; and iv) passing each of the filtered second sub-portions to a second photo-detector to determine a measure proportional to the optical signal's second moment of power terms P 2 ; wherein P 2 = ∑ λ ′ ⁢ ⁢ P ⁡ ( λ ′ ) · ( λ ′ - λ 1 ) 2 ; wherein step c) includes determining the Raman tilt based on the equation T=a×P tot +3b×P 2 , in which a and b are predetermined based on the optical fiber link.