Optical Signal Polarization Control for PDL Suppression
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Solution Overview
Problem
Optical communication systems face signal degradation due to polarization-dependent loss (PDL) and loss of orthogonality, which affect transmission quality and are not efficiently addressed by existing methods, particularly in WDM/DWDM transmissions.
Innovation Solution
A method involving the transmission of a training signal with specific polarization states to estimate a Mueller matrix, allowing for rotation control and power level adjustment of polarization components based on Stokes parameters, to maintain orthogonality and balance power levels, thereby suppressing PDL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If polarization multiplexing or polarization time multiplexing is used to improve spectrum utilization efficiency, then transmission capacity is improved, but signal degradation occurs due to PDL causing power level imbalance and loss of orthogonality
Solution Approach 1:
The patent applies preliminary action by transmitting a training signal with known polarization states before actual data transmission. The receiver estimates the Mueller matrix from this training signal to predict PDL characteristics, then uses this information to adjust the transmission signal in advance, preventing power level imbalance and loss of orthogonality before they degrade signal quality
Solution Approach 2:
The patent implements feedback by having the receiver estimate the Mueller matrix from the transmitted training signal and feed back the estimated parameters (or the trained model itself) to the transmitter. The transmitter then uses this feedback to adjust its polarization control, creating a closed-loop system that continuously compensates for PDL effects and maintains signal quality
2Reliability
If existing PDL suppression methods are used, then some signal degradation is reduced, but nonlinear degradation increases when transmission line status changes dynamically
Solution Approach 1:
The patent applies dynamics by making the PDL compensation adaptive rather than static. The receiver continuously estimates the Mueller matrix from training signals and updates the transmission parameters dynamically. This allows the system to adapt to changing transmission line conditions (such as temperature variations, stress changes, or component aging) in real-time, maintaining signal quality under dynamic conditions
Solution Approach 2:
The patent changes the approach from fixed polarization control to parameter-adaptive control. By estimating the Mueller matrix parameters (which describe the transmission line's polarization characteristics) and using them to adjust transmission parameters, the system can respond to dynamic changes in the transmission environment, improving both reliability and adaptability
3Measurement precision
If conventional PDL measurement methods are used, then basic PDL is measured, but the influence of nonlinear degradation is not accounted for
Solution Approach 1:
The patent applies universality by making the Mueller matrix estimation serve multiple functions simultaneously. The same estimation process not only measures PDL characteristics but also captures nonlinear degradation effects, polarization mode dispersion, and other transmission impairments. This multi-functional measurement approach eliminates the need for separate measurements and provides comprehensive channel characterization
Data Source
AI summary
A method of controlling a transmission signal, includes transmitting a training signal including four polarization states having a given relation; and performing rotation control and transmission power level control of a polarization component of a data signal, based on a rotation control matrix for a polarization state and an inverse-operation control matrix for a power level imbalance, which are estimated from Stokes parameters related to input power level present on a Poincare sphere acquired from the training signal and Stokes parameters related to output power level present on the Poincare sphere.