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US 8,532,504 B2Granted
Coherent optical receiver with adaptive equalizer initialization system
AssigneeOpnext Subsystems, Inc.
InventorsAndrew Wagner, Christian Malouin, Theodore J. Schmidt
Life of this patent
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Abstract
An adaptive-equalizer initialization system performs three functions: frequency offset estimation, taps estimation for chromatic dispersion filters, and taps initialization for an adaptive equalizer. The system contains hardware FFT and peak detector units that sense a pure tone that marks the beginning of a known, short data sequence.
Claims18
An optical coherent receiver comprising:
- a chromatic dispersion filter that compensates for chromatic dispersion in two polarizations of a received optical signal, the received optical signal comprising a sequence of known data, the sequence of known data beginning, when transmitted, with a pure tone segment comprising substantially a single first frequency;
- a frequency domain adaptive equalizer that receives output from the chromatic dispersion filter and configured to compensate for impairments in a channel carrying the received optical signal;
- and,
- an adaptive equalizer initialization system, coupled to the chromatic dispersion filter and the adaptive equalizer, the initialization system comprising a sequence start detector configured to receive the received optical signal and perform a frequency domain analysis to determine spectral characteristics of the sequence of known data, the spectral characteristics comprising a peak at a second frequency, the peak corresponding to the pure tone segment of the sequence of known data;
- wherein the initialization system:
- estimates frequency offset from a difference between the first frequency and the second frequency;
- estimates chromatic dispersion from the spectral characteristics of the sequence of known data;
- and
- loads chromatic dispersion taps into the chromatic dispersion filter based on the estimated frequency offset and estimated chromatic dispersion.
6 more elements
A method for initializing an optical coherent receiver, comprising:
- receiving an optical signal comprising a sequence of known data, the sequence of known data beginning, when transmitted, with a pure tone segment comprising substantially a single first frequency;
- performing, by a chromatic dispersion filter, an initial chromatic dispersion compensation on the received optical signal;
- analyzing the received optical signal to determine spectral characteristics of the sequence of known data, the spectral characteristics comprising a peak at a second frequency, the peak corresponding to the pure tone segment of the sequence of known data;
- estimating frequency offset from a difference between the first frequency and the second frequency;
- estimating chromatic dispersion from the spectral characteristics;
- and
- loading chromatic dispersion taps into the chromatic dispersion filter based on the estimated frequency offset and estimated chromatic dispersion.
4 more elements
Dependencies are inferred from the claim text.