Patent ID: 8358930

Claim:
A method for determining a noise parameter on an input optical signal having a data-carrying signal contribution and a noise contribution within an optical signal bandwidth, the method comprising: obtaining at least two optical spectrum traces from said input optical signal, said optical spectrum traces being taken under different conditions such that they show different non-zero signal-to-noise ratios, mathematically discriminating said signal contribution from said noise contribution within said optical signal bandwidth based on a mathematical combination of said optical spectrum traces, determining an in-band noise level on said input optical signal from the discriminated noise contribution, and determining the noise parameter from the determined in-band noise level, the noise parameter being indicative of the noise contribution within the optical signal bandwidth; wherein the signal contribution and the noise contribution have at least one of different degrees of polarization and different states of polarization from one another and wherein said obtaining at least two optical spectrum traces comprises: producing at least two samples of the input optical signal, under different polarization analysis conditions, states of polarization of the two samples being arbitrary relative to said input optical signal; and acquiring an optical spectrum of each one of the first and the second samples to obtain said optical spectrum traces, wherein said polarizing at least part of the input optical signal comprises polarization beam splitting said input optical signal into said samples, said samples having states of polarization orthogonal from one another; wherein said discriminating comprises: subtracting said optical spectrum traces from one another to obtain a difference optical spectrum substantially proportional to an optical spectrum of said signal contribution, estimating an optical spectrum of said input optical signal using said difference optical spectrum, determining an optical spectrum of said input optical signal from at least one of the first and second optical spectrum traces; and determining a level of said optical noise by subtracting the estimated optical spectrum of said signal contribution for the determined optical spectrum of said input optical signal; wherein said optical spectrum traces each have a signal contribution and a noise contribution and wherein said performing calculations further comprises estimating a factor K related to a proportion between the signal contributions of said optical spectrum traces for use in said estimating an optical spectrum of said input optical signal; wherein said calculating further comprises: re-estimating said factor K considering the evaluated in-band noise; and calculating the optical spectrum of said optical noise using the re-estimated factor K.