Coherent Optical Receiver Digital Imbalance Correction
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Solution Overview
Problem
High-speed optical transmission systems over fiber face impairments such as polarization-mode dispersion, chromatic dispersion, polarization gain imbalance, and delay imbalance, which degrade performance and cannot be completely eliminated by conventional methods, especially in coherent optical receivers using Quadrature Amplitude Modulation (QAM) and Quadrature Phase Shift Keying (QPSK).
Innovation Solution
A coherent optical receiver system with digital circuitry that iteratively determines and corrects for optical angle and magnitude imbalance and delay imbalance between quadrature paths using correction coefficients, updated through gradient descent algorithms, without the need for training symbols, allowing real-time correction during operation and applied entirely in the digital domain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional analog design methods are used to minimize impairments, then device complexity is reduced, but measurement precision and reliability deteriorate due to incomplete elimination of angle, magnitude, and delay imbalances
Solution Approach 1:
The patent replaces the mechanical/analog quadrature demodulator system with a digital signal processing system. Instead of using analog components to achieve orthogonality, the invention uses digital circuitry to receive the modulated signal and iteratively determine and correct angle and magnitude imbalances through computational algorithms, thereby achieving higher precision without being constrained by analog component limitations.
Solution Approach 2:
The patent changes the operating parameters from fixed analog settings to dynamically adjustable digital parameters. Correction coefficients are iteratively updated based on received signals to optimize the compensation of angle and magnitude imbalances. This allows the system to adapt to varying conditions and achieve precise correction that cannot be obtained through fixed analog design.
2Measurement precision
If training symbols are used for compensation as in conventional methods, then measurement precision improves, but productivity decreases due to loss of transmission efficiency
Solution Approach 1:
The patent implements a self-service mechanism where the system compensates for its own impairments using the received data itself. The iterative updating circuitry processes the received signals to automatically determine correction coefficients without requiring external training symbols. This allows the system to maintain high transmission efficiency while achieving accurate compensation of angle, magnitude, and delay imbalances.
Solution Approach 2:
The patent employs feedback mechanisms where the received signals are fed back through iterative updating circuitry to continuously refine the correction coefficients. This feedback loop allows the system to adapt to changing conditions in real-time and maintain accurate compensation without sacrificing transmission efficiency, as no separate training period is needed.
3Measurement precision
If iterative updating with gradient descent algorithms is implemented, then measurement precision and adaptability improve, but device complexity increases
Solution Approach 1:
The patent designs a universal digital processing platform that handles multiple functions: receiving quadrature modulated signals, performing analog-to-digital conversion, iteratively determining correction coefficients, and compensating for various impairments. This multi-functional approach consolidates what would otherwise require separate specialized components, managing complexity while achieving high precision real-time tracking of angle, magnitude, and delay imbalances.
4Device complexity
If delay imbalance is not corrected, then device complexity remains low, but reliability deteriorates due to performance degradation
Solution Approach 1:
The patent merges the correction of angle imbalance, magnitude imbalance, and delay imbalance into a single integrated digital signal processing framework. Instead of implementing separate correction mechanisms for each type of impairment, the invention combines them into a unified iterative updating process that simultaneously addresses all three issues, achieving high reliability without proportionally increasing device complexity.
Data Source
AI summary
The present disclosure relates to coherent optical receiver systems and methods for determining and correcting for optical angle and magnitude imbalance and for delay imbalance between quadrature paths. The present invention iteratively determines and corrects imbalance error and differential delay entirely in the digital domain (after an analog to digital conversion) in the presence of all the other impairments (polarization mode dispersion, chromatic dispersion, polarization gain imbalance, and polarization delay imbalance) using only the corrupted received signal during normal operation, i.e. without the use of training data. The present invention provides an effective adaptive scheme to drive impairments to zero, without using of any calibration of training, and may be applied during normal operation of the receiver via electrical circuitry or the like.