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Abstract

In methods and apparatus for monitoring the performance of optical transmission systems, an optical signal is modulated with a low frequency dither signal to provide a modulated optical signal having a known modulation depth. A portion of the optical signal is tapped, and both a total power and a dither amplitude of the tapped portion of the optical signal are measured. Both signal and noise components of the tapped portion of the optical signal are estimated by comparing the measured dither amplitude to the measured total signal power. In wavelength division multiplexed optical transmission systems, optical signals at each distinct wavelength are modulated with distinct dither signals and dither amplitudes of each distinct dither signal detectable in the tapped portion of the optical signal are measured. Both signal and noise components are estimated for the optical signals at each distinct wavelength. The relative signal powers of optical signals at distinct wavelengths are controlled in response to the measured dither amplitudes. The methods and apparatus are particularly applicable to high capacity long haul terrestrial optical fiber transmission systems using optical amplifiers.

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First Claim