Polarization-Folding Coherent Receiver for Short-Reach Optical Links
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Solution Overview
Problem
Coherent optical communication systems often require complex 4D vector receivers to handle polarization changes during transmission, which increases costs and complexity, especially in short-reach applications where high spectral efficiency is not critical.
Innovation Solution
Implementing a 2D or 1D coherent receiver system that uses polarization-folding techniques, including a polarization beam splitter, delay element, and optical coupler to rotate and combine polarization components, reducing the need for extensive electronic components and external polarization controllers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a 4D vector receiver is used to handle polarization changes during transmission, then the system can maintain signal integrity and tolerance towards polarization mode dispersion, but the device complexity and cost increase significantly
Solution Approach 1:
The patent extracts and removes the polarization diversity function from the receiver by implementing polarization folding at the transmitter. The transmitter folds both polarization states into a single polarization state using polarization beam combiners, so the receiver only needs to handle one polarization state, eliminating the need for complex 4D vector receiver architecture while maintaining signal integrity
Solution Approach 2:
Instead of having the receiver adapt to handle changing polarization states (conventional approach), the patent inverts the approach by having the transmitter actively control and fold the polarization states into a fixed configuration before transmission. This reversal of adaptation responsibility simplifies the receiver while maintaining reliability
2Reliability
If a 4D vector receiver is deployed to ensure tolerance towards linear optical impairments, then the system achieves higher robustness, but the manufacturing cost and component quantity increase
Solution Approach 1:
The patent removes the need for expensive polarization diversity receiver components by implementing polarization folding at the transmitter. This extraction of the polarization handling function from the receiver side eliminates the need for multiple photodetectors, amplifiers, and associated electronics, significantly reducing manufacturing cost while maintaining robustness
Solution Approach 2:
The patent creates redundant signal paths through polarization folding where the same information is encoded in both polarization states and then combined. This copying approach provides diversity gain and robustness against linear optical impairments without requiring a full 4D receiver, reducing manufacturing cost
3Stability of the object's composition
If external polarization controllers are added to maintain state of polarization, then the system achieves better polarization stability, but the device complexity and component count increase
Solution Approach 1:
The patent implements preliminary polarization folding at the transmitter before the signal enters the fiber channel. By pre-establishing the polarization relationship and folding both states into a single state at the transmitter, the system eliminates the need for external polarization controllers at the receiver end, reducing component count while maintaining polarization stability
Solution Approach 2:
The polarization folding mechanism at the transmitter makes the system self-sufficient regarding polarization management. The transmitter actively controls and folds the polarization states, making the receiver independent of external polarization controllers, thus reducing component count and simplifying the overall system
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 receiver design, reduces component count by half, and enhances robustness against polarization changes, making it suitable for short-reach applications like data center interconnects and mobile networks while maintaining performance comparable to 4D receivers.
Implementation Method 1
a polarization beam splitter having an input port, a first optical output port and a second optical output port, the input port coupled to an optical communication channel, the first optical output port providing a first optical signal derived from an encoded optical signal received over the optical communication channel and the second optical output port providing a second optical signal derived from the encoded optical signal
Implementation Method 2
a polarization rotator configured to rotate a polarization component of either the second optical signal or the delayed second optical signal into a polarization state corresponding to the first polarization component
Data Source
AI summary
Coherent optical communications technology for recovery of 1D and 2D formatted optical signals. For example, 1D or 2D formatted signals that travel through fiber optic media may be recovered by separating the light into X- and Y-polarization components, rotating one polarization component (e.g., Y-component) into the polarization space of the other component (e.g., Y-component into the X-polarization space), delaying the rotated component enough to avoid destructive interference and combining the delayed component with the undelayed component to form a folded optical signal, which may then be processed as a X-polarized signal.