Patent ID: 8364034

Claim:
A method for determining an in-band noise parameter on an input optical signal (P(λ)) having a data-carrying signal contribution (S(λ)) and a noise contribution (N(λ)) within an optical signal bandwidth, said signal contribution being at least partly polarized and said noise contribution being mostly unpolarized, the method comprising: acquiring, for a number n SOP of varied State-Of-Polarization (SOP) analysis conditions of the input optical signal (P(λ)), n SOP polarization-analyzed optical spectrum traces (Pa(λ)); mathematically discriminating said signal contribution from said noise contribution within said optical signal bandwidth using said polarization-analyzed optical spectrum traces (Pa(λ)), said mathematically discriminating comprising: obtaining a differential polarization response (S′(λ)) that is related to the optical spectrum of said signal contribution (S(λ)) by a constant of proportionality; estimating the constant of proportionality of a differential polarization response (S′(λ)) to the optical spectrum of said signal contribution (S(λ)) by a constant-of-proportionality evaluation step comprising one of i) an ab initio calculation as a function of said number n SOP and ii) using values of said polarization-analyzed optical spectrum traces (Pa(λ)) at least close to a peak wavelength where the noise contribution is minimal relative to the signal contribution; estimating, to within a given uncertainty, the optical spectrum of said noise contribution N(λ) from said input optical signal (P(λ)), within said optical signal bandwidth using said constant of proportionality and said differential polarization response (S′(λ)), said given uncertainty depending upon the number n SOP ; and determining said in-band noise parameter on said input optical signal from the mathematically discriminated noise contribution.