Stokes-Vector Detection for Polarization-Division-Multiplexed Optical Signals
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Solution Overview
Problem
Conventional optical communication systems using coherent detection of optical polarization-division-multiplexed (PDM) signals are complex and costly, requiring polarization diversity and a local oscillator, whereas direct optical detection lacks efficient methods for recovering data due to polarization state changes in optical fibers caused by environmental factors.
Innovation Solution
An optical system employing Stokes-vector detection and digital signal processing to independently amplitude-modulate orthogonal polarizations and modulate their relative phase, allowing direct optical detection and data recovery without the need for coherent detection or polarization rotation, using a Stokes-vector detector and digital signal processor to estimate the original polarization state and decode data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coherent detection with polarization diversity and local oscillator is used, then data recovery from PDM signals is reliable, but device complexity and cost increase
Solution Approach 1:
The patent extracts and eliminates the local oscillator and polarization diversity components from the coherent detection system, retaining only the essential polarization beam splitter and detector elements needed for direct detection of PDM signals
Solution Approach 2:
The patent replaces expensive coherent detection components with simpler, lower-cost direct detection components including a polarization beam splitter and standard photodetectors, achieving cost-effective PDM signal reception
2Reliability
If polarization rotation is applied to compensate for birefringence, then data recovery is enabled, but device complexity increases
Solution Approach 1:
The patent employs self-service through polarization-mode dispersion compensation where the system automatically adapts to polarization changes caused by birefringence without requiring external polarization controllers or rotation mechanisms
Solution Approach 2:
The patent replaces mechanical polarization rotation devices with a mathematical transformation approach, using coordinate system rotation in the detection plane to compensate for polarization state changes without physical polarization control elements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach simplifies signal processing at the receiver, reduces costs, and enables direct optical detection of PDM signals, providing a cost-effective alternative to conventional systems by leveraging Stokes-space representation and digital signal processing to recover data from PDM signals.
Implementation Method 1
a polarization splitter configured to split an optical polarization-division-multiplexed (PDM) signal into two light beams
Implementation Method 2
an optical-to-electrical converter configured to generate first, second, and third electrical signals by optically detecting different combinations of light of the two light beams
Data Source
AI summary
We disclose an optical transport system configured to transport data using a PDM-modulation format, in which each of two orthogonal polarizations is independently amplitude-modulated, and the relative phase between the carrier waves of the two polarizations may also be modulated. This modulation format enables the optical receiver to perform direct optical detection using a Stokes-vector detector to fully recover the encoded data. In an example embodiment, the corresponding signal processing at the optical receiver may include: determining a Stokes-space rotation matrix corresponding to the polarization-state rotation encountered by the PDM signal in the optical transport link; applying the determined Stokes-space rotation matrix to the Stokes sub-vector measured by the Stokes-vector detector to estimate the Stokes sub-vector of the PDM signal at the originating optical transmitter; converting the estimated Stokes sub-vector into the corresponding Jones vector; and recovering the data by decoding the polarization components of the Jones vector.