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US 2011/0236025 A1Published application
Sub-rate sampling in coherent optical receivers
AssigneeOpnext Subsystems, Inc.
InventorsAndrew Wagner, Christian Malouin, Theodore J. Schmidt
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Abstract
Apparatus and methods for optimizing the interplay between the sampling rate of an ADC of a receiver system and a bandwidth of analog anti-aliasing filters are described. The described technology can be used to mitigate aliasing for receiver systems that operate at fractional sampling rates by optimizing a bandwidth of optical and electrical filters included in the receiver systems.
Claims19
An optical receiver comprising:
- low-pass filters configured to filter a signal carrying symbols;
- an analog-to-digital converter (ADC) operating at a fractional sampling clock rate to convert the filtered signal carrying the symbols to digital ADC output samples;
- an interpolator to interpolate at an interpolation clock rate different than the fractional sampling clock rate between digital values derived from said the digital ADC output samples to provide moving interpolations;
- and
- an interpolation feedback loop to synchronize the moving interpolations with the symbols.
2 more elements
A method comprising:
- filtering a signal carrying the symbols using low-pass filters;
- converting the filtered signal carrying the symbols to digital ADC output samples at a fractional sampling clock rate;
- interpolating at an interpolation clock rate different than the fractional sampling clock rate between digital values derived from the digital ADC output samples to provide moving interpolations;
- and
- synchronizing the moving interpolations with the symbols using feedback from the moving interpolations.
2 more elements
An optical receiver comprising:
- a low-pass optical filter having an optical bandwidth and configured to filter an incoming optical signal carrying symbols into a filtered optical signal carrying symbols;
- a photo-detector arranged down-stream from the low-pass optical filter and configured to convert the filtered optical signal carrying symbols into an electrical signal carrying symbols;
- a low-pass electrical filter having an electrical bandwidth, the low-pass electrical filter arranged down-stream from the photo-detector and configured to filter the electrical signal carrying symbols into a filtered signal carrying symbols;
- an analog-to-digital converter (ADC) arranged down-stream from the electrical low-pass filter, the ADC configured to operate at a fractional sampling clock rate to convert the filtered signal carrying the symbols to digital ADC output samples, wherein the fractional sampling clock rate is configured to provide fewer than two of the digital ADC output samples for one of the symbols;
- an interpolator to interpolate at an interpolation clock rate different than the fractional sampling clock rate between digital values derived from said the digital ADC output samples to provide moving interpolations;
- and
- an interpolation feedback loop to synchronize the moving interpolations with the symbols,
- wherein the optical bandwidth and the electrical bandwidth are selected to mitigate aliasing caused during operation of the ADC at the fractional sampling clock rate that provides fewer than two of the digital ADC output samples for one of the symbols.
5 more elements
Dependencies are inferred from the claim text.