Programmable Clock Recovery Bandwidth for Dense Optical Channels
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Solution Overview
Problem
In optical communications, increasing channel density in gridless systems leads to interchannel interference and clock jitter due to spectral energy leakage from adjacent channels, affecting clock synchronization and data recovery.
Innovation Solution
A flexible grid optical receiver circuit with a programmable clock recovery bandwidth that decouples VCO phase noise suppression from the clock recovery loop, using a phase rotator or adjustable reference clock to minimize interference and improve synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If channel density is increased in gridless optical systems, then bandwidth utilization is improved, but interchannel interference and clock jitter increase due to spectral energy leakage from adjacent channels
Solution Approach 1:
The patent segments the clock recovery process into two independent parts: a narrowband clock recovery loop for accurate clock extraction and a separate wideband phase noise suppression loop. This segmentation allows the system to maintain high channel density while preserving clock synchronization accuracy by filtering out spectral leakage from adjacent channels in the narrowband loop.
Solution Approach 2:
The patent introduces an intermediary narrowband clock recovery loop that acts as a mediator between the high-density channel environment and the clock synchronization requirement. This intermediary structure filters out harmful spectral energy from adjacent channels while preserving the useful clock signal, thereby resolving the contradiction between high channel density and clock synchronization accuracy.
2Productivity
If guard bands are reduced to increase channel density, then spectral efficiency is improved, but spectral energy from adjacent channels leaks into the excess bandwidth area affecting clock recovery integrity
Solution Approach 1:
The patent extracts the harmful spectral energy leakage from adjacent channels by using a narrowband clock recovery loop that selectively recovers only the clock signal while rejecting out-of-band interference. This extraction process removes the harmful effect of spectral leakage while maintaining the benefits of reduced guard bands and increased channel density.
Solution Approach 2:
The patent converts the harmful spectral energy leakage into a benefit by using it as a reference for phase noise suppression. The wideband phase noise suppression loop uses the leaked energy information to suppress phase noise in the clock signal, thereby transforming the harmful interference into a useful mechanism for improving clock recovery performance in high-density channel environments.
3Measurement precision
If excess bandwidth is used for clock recovery, then clock jitter estimation is improved, but adjacent channel interference affects the extracted data clock integrity
Solution Approach 1:
The patent segments the bandwidth usage into two distinct functions: a narrowband clock recovery loop for accurate clock and jitter estimation, and a wideband phase noise suppression loop for interference rejection. This segmentation allows the system to maintain high clock jitter estimation accuracy while eliminating adjacent channel interference that would otherwise corrupt the clock recovery process.
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 2~3
AI summary
Techniques and circuits are proposed to increase averaging in the clock recovery band based on an amount of channel overlap in receivers using excess bandwidth for clock recovery, to mitigate the impact of spectral energy leaking into an active channel of interest from an adjacent active channel and to improve the accuracy of the phase estimate of the received transmitted clock.