Sampling Clock Synchronization Under Optical Spectral Narrowing
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Solution Overview
Problem
Spectral narrowing in optical signals due to multiple-stage optical filtering reduces detection sensitivity of sampling clock phase shifts, leading to decreased jitter and wander tolerance, and degraded reception quality in digital coherent reception systems.
Innovation Solution
A sampling clock synchronizing apparatus comprising an A/D converter and a digital filter that compensates for spectral narrowing by using filter characteristics opposite to those of the narrowing, allowing for accurate detection and synchronization of sampling clock phase shifts, thereby enhancing jitter and wander tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If multiple-stage optical filtering is applied to the optical signal, then wavelength selectivity and signal filtering are improved, but spectral narrowing occurs which reduces detection sensitivity of sampling clock phase shifts
Solution Approach 1:
The patent applies inverse filter characteristics in the digital filter to compensate for the spectral narrowing caused by optical filtering. Instead of accepting the narrowed spectrum, the system inverts the filtering effect by applying opposite filter characteristics, thereby restoring the spectral shape and improving detection sensitivity without removing the optical filters.
Solution Approach 2:
The patent changes the filter characteristics parameter from the original optical filter response to an inverse response. By adjusting the digital filter parameters to have opposite characteristics to the optical filtering, the system compensates for spectral narrowing and restores the frequency components necessary for accurate sampling clock phase shift detection.
2Measurement precision
If spectral narrowing is compensated using a digital filter with opposite characteristics, then detection sensitivity of sampling clock phase shifts is improved, but device complexity increases
Solution Approach 1:
The digital filter is designed to perform multiple functions simultaneously: it compensates for spectral narrowing, restores frequency components, and enables accurate sampling clock phase shift detection. This multi-functionality reduces the need for separate compensation circuits and simplifies the overall system architecture despite the sophisticated filtering required.
3Adaptability or versatility
If optical filters are used for wavelength multiplexing and demultiplexing, then channel separation is improved, but jitter and wander tolerance decreases due to spectral narrowing
Solution Approach 1:
The patent replaces optical domain filtering with digital domain filtering to achieve spectral compensation. Instead of using additional optical components to broaden the spectrum, the system uses digital signal processing to restore the spectral shape, thereby improving jitter and wander tolerance while maintaining the benefits of optical filtering for channel separation.
Data Source
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AI summary
In a sampling clock synchronizing apparatus, an A/D converter converts an analog signal to a digital signal based on a sampling clock, and a processor compensates a band limitation due to spectral narrowing by filter characteristics of characteristics opposite to those of the spectral narrowing with respect to a signal produced from the A/D converter subjected to the spectral narrowing, and detects a phase shift in the sampling clock based on a signal after the compensation of the spectral narrowing and synchronizes sampling timing.