Optical Receiver Polarization Tracking Using Tone Information
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Solution Overview
Problem
Existing polarization tracking techniques in coherent optical communications, such as those using least mean squares (LMS) equalizers, are insufficient to handle ultra-fast polarization changes in optical fibers, leading to uncorrected code words and loss of frames.
Innovation Solution
An optical receiver system that utilizes tone information to determine Stokes parameters and apply corrective operations, such as rotations and phase retardations, to the polarization multiplexed signal, complementing the LMS equalizer for ultra-fast polarization tracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If least mean squares (LMS) equalizers are used for polarization tracking, then the system can maintain simplicity in implementation, but the system fails to track ultra-fast polarization changes resulting in uncorrected code words and loss of frames
Solution Approach 1:
The patent segments the polarization tracking function into two distinct components: a traditional LMS equalizer handling slow polarization changes, and a new tone-based tracker handling ultra-fast polarization changes. This segmentation allows each component to be optimized for its specific speed range, with the tone-based tracker processing pilot tones at a higher rate than the LMS equalizer can handle, thereby resolving the contradiction between tracking accuracy and tracking speed.
2Speed
If the LMS equalizer operates at high speed to track ultra-fast polarization changes, then tracking speed improves, but the equalizer complexity and computational requirements increase significantly
Solution Approach 1:
The patent introduces pilot tones as an intermediary element that carries polarization information through the transmission channel. Instead of directly processing the entire data signal at high speed, the system extracts polarization information from these dedicated pilot tones. This intermediary approach enables fast polarization tracking without requiring the entire LMS equalizer to operate at ultra-high speeds, thus reducing overall system complexity while maintaining tracking performance.
3Reliability
If tone information is extracted and processed separately for polarization tracking, then ultra-fast polarization changes can be tracked accurately, but the system complexity and processing overhead increase
Solution Approach 1:
The patent applies preliminary action by embedding pilot tones with known polarization states into the transmitted signal before it enters the optical fiber. These pre-configured tones serve as reference markers that enable the receiver to proactively track polarization changes without having to reactively analyze the entire data stream. By performing this preliminary setup, the system reduces the complexity of real-time polarization tracking, as the receiver only needs to monitor changes in the known pilot tone patterns rather than analyzing complex modulated data signals.
Data Source
AI summary
A digital signal processor (DSP) of an optical receiver may receive information representing a polarization multiplexed signal including tone information. The polarization multiplexed signal may have an uncorrected state of polarization (SOP). The DSP may determine sets of Stokes parameters based on the tone information. The DSP may determine a set of polarization parameters based on the sets of Stokes parameters. The DSP may apply, based on the set of polarization parameters, a set of operations to the information representing the polarization multiplexed signal. An operation, of the set of operations, may represent a rotation or a phase retardation of the polarization multiplexed signal and may correspond to a polarization parameter of the set of polarization parameters. The set of operations may be applied to the information representing the polarization multiplexed signal in order to generate information representing the polarization multiplexed signal with a corrected SOP.