Wavelength Dispersion Estimation Circuit for Optical Receivers
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Solution Overview
Problem
Residual chromatic dispersion that cannot be compensated by a chromatic dispersion compensator at the front stage leads to incomplete removal of waveform distortion, which hampers the adaptive equalizer's capability to compensate for polarization mode dispersion.
Innovation Solution
A chromatic dispersion estimating circuit that calculates residual dispersion using the filter coefficients of an adaptive equalizer, performing Fourier transforms, differentiating eigenvalues, and determining the proportionality factor to accurately estimate and compensate for residual dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a chromatic dispersion compensator is used to compensate for chromatic dispersion, then waveform distortion caused by chromatic dispersion is suppressed, but residual dispersion remains that cannot be perfectly compensated
Solution Approach 1:
The patent uses the output of the adaptive equalizer (which processes the signal after chromatic dispersion compensation) as feedback to estimate residual dispersion. By analyzing the filter coefficients and signal characteristics from the adaptive equalizer output, the system can determine how much dispersion remains uncompensated and adjust accordingly.
Solution Approach 2:
The adaptive equalizer serves as an intermediary device that not only compensates for polarization mode dispersion but also provides the means to estimate residual chromatic dispersion. The filter coefficients and signal processing operations in the adaptive equalizer contain information about the remaining dispersion that can be extracted through analysis of the equalized signal.
2Reliability
If residual dispersion is not accurately determined, then the adaptive equalizer cannot properly compensate for polarization mode dispersion
Solution Approach 1:
The system continuously monitors the output of the adaptive equalizer and uses the filter coefficients to estimate residual dispersion. This feedback mechanism allows the system to adjust the adaptive equalizer's operation to properly compensate for polarization mode dispersion while accounting for any remaining chromatic dispersion.
Solution Approach 2:
The patent analyzes changes in signal parameters (filter coefficients, signal power spectral density) through the adaptive equalizer processing to extract information about residual dispersion. By monitoring how these parameters change during equalization, the system can determine the remaining dispersion characteristics.
3Adaptability or versatility
If the adaptive equalizer processes signals with remaining waveform distortion, then polarization mode dispersion can be compensated, but the capability is hampered by incomplete distortion removal
Solution Approach 1:
The adaptive equalizer uses feedback from signal analysis to adjust its filter coefficients in real-time. By continuously monitoring the signal characteristics and using this feedback to update the equalizer parameters, the system can maintain optimal performance even when residual dispersion is present, separating the compensation of polarization mode dispersion from the effects of remaining chromatic dispersion.
Data Source
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AI summary
A Fourier-transformer (11) performs Fourier transform on a filter coefficient output from an adaptive equalizer (6) which comprises a finite impulse response filter of N taps (N represents an integer of 2 or more) in a time direction. An eigenvalue sum calculator (15) integrates a frequency-differentiation result of the Fourier-transformed filter coefficient and a complex conjugate of the Fourier-transformed filter coefficient to calculate a matrix, and calculates a sum of two eigenvalues of the matrix. A proportionality factor calculator (14) calculates a proportionality factor for frequency from the sum of the two eigenvalues.