Method and system for determining in-band optical noise

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, said signal contribution being mostly polarized and said noise contribution being mostly unpolarized, the method comprising:

• acquiring a first and a second optical spectrum trace of the input optical signal corresponding to respective first and second polarization analysis conditions, said first and second polarization analysis conditions being mutually different and arbitrary relative to said data-carrying signal contribution such that the data-carrying signal contribution is not substantially suppressed on any of the optical spectrum traces, said optical spectrum traces exhibiting mutually different non-zero signal-to-noise ratios;
• mathematically discriminating said signal contribution from said noise contribution within said optical signal bandwidth based on said optical spectrum traces, said discriminating comprising:
• calculating, from said optical spectrum traces, a difference optical spectrum substantially indicative of said data-carrying signal contribution;
• and
• solving for said noise contribution using said optical spectrum traces and said difference optical spectrum;
• and
• determining said noise parameter from the discriminated noise contribution, the noise parameter being indicative of the noise contribution within the optical signal bandwidth.

A system for determining a noise parameter on an input optical signal within an optical signal bandwidth, the system comprising:

• an input for receiving said input optical signal comprising a data-carrying signal contribution and a noise contribution within said optical signal bandwidth, said signal contribution and said noise contribution having mutually different degrees of polarization;
• a polarization optics arrangement for obtaining a first and a second sample of the input optical signal under mutually different polarization analysis conditions such that at least one of the first and the second sample is polarization analyzed, a state of polarization of the at least one polarization analyzed sample being arbitrary relative to a state of polarization of the data-carrying signal contribution such that the data-carrying signal contribution is not substantially suppressed on any of said first and said second sample:
• an optical spectrum analyzer for acquiring a first and a second optical spectrum trace respectively of the first and second samples, the first and second optical spectrum traces exhibiting mutually different non-zero signal-to-noise ratios;
• a spectrum processor adapted for mathematically discriminating said noise contribution in said input optical signal within said optical signal bandwidth based on said first and second optical spectrum traces, said spectrum processor comprising:
• a differentiator for calculating, from said optical spectrum traces, a difference optical spectrum substantially indicative of said signal contribution;
• and
• a noise solver for evaluating said noise contribution using calculations involving said optical spectrum traces and said difference optical spectrum;
• and
• a noise calculator for evaluating said noise parameter within the optical signal bandwidth from the discriminated noise contribution.