Patent ID: 8731400

Claim:
A method for characterizing a selected one of a plurality of frequency channels of an optical signal in an optical network, the method comprising: (a) coupling the optical signal to an input port of a tunable optical filter, and coupling a controller to a first output port of the tunable optical filter, for detecting an optical signal filtered by the tunable optical filter, wherein a spectral bandwidth of the tunable optical filter σ TF is smaller than one half of a channel spacing Δƒ of the optical network; (b) upon completion of step (a), using the controller to tune a center frequency of the tunable optical filter to first, second, and third measurement frequencies proximate a center frequency Fs of the selected frequency channel, and to measure first, second, and third optical signals P 1 , P 2 , and P 3 at the first output port at the first, second, and third measurement frequencies, respectively, wherein the first, second, and third optical signals P 1 , P 2 , and P 3 originate from the selected frequency channel; (c) using the controller to determine the center frequency Fs of the selected frequency channel from the first, second, and third optical signals P 1 , P 2 , and P 3 measured in step (b), and to determine first and second frequency offsets ƒ 1 and ƒ 2 between the first and second measurement frequencies, respectively, and the center frequency Fs; and (d) upon completion of step (c), using the controller to determine a total optical power Ps and a spectral width σ s of the selected frequency channel from the first and second measured optical signals P 1 , and P 2 , and the first and second frequency offsets ƒ 1 and ƒ 2 .