Polarization-Diversity Coherent Receiver for Rapid SOP Tracking
Solution Overview
Problem
Current optical communication systems face signal impairments due to polarization-mode-dispersion (PMD) and rapid SOP rotation in single-mode fibers, which limit transmission capacity and can cause optical-link outages, especially under ambient events like lightning or mechanical vibrations.
Innovation Solution
A polarization-diversity coherent optical receiver is employed to sample four quadrature components of an intensity-modulated OSC signal at a high sampling rate, enabling rapid polarization tracking by calculating Stokes parameters and combining them to determine the intensity of the signal, allowing for high-time-resolution SOP measurements and data recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional direct detection is used for intensity-modulated optical signals, then the system is simple to implement, but it cannot track rapid SOP rotations and suffers from polarization-related signal impairments
Solution Approach 1:
The optical signal is segmented into four quadrature components through coherent detection, allowing independent measurement of each polarization component. This segmentation enables accurate tracking of rapid SOP rotations by capturing the full polarization state information that would be lost in conventional direct detection schemes.
Solution Approach 2:
An optical local oscillator is introduced as an intermediary to enable coherent mixing with the incoming signal. This local oscillator serves as a reference that allows the receiver to track phase and polarization information, resolving the contradiction between simplicity and the ability to handle rapid SOP rotations.
2Measurement precision
If high sampling rate is used to track rapid SOP rotations, then polarization tracking time resolution is improved, but data processing complexity and computational load increase
Solution Approach 1:
The four quadrature components are sampled and processed in parallel at high rate before final combination. This preliminary action of capturing all polarization components simultaneously allows for efficient subsequent calculation of Stokes parameters and intensity, reducing the computational burden compared to sequential processing approaches.
Solution Approach 2:
The patent replaces complex mechanical or optical switching mechanisms with direct digital signal processing of four parallel quadrature components. This substitution allows high-time-resolution SOP measurements through computational methods rather than physical switching, reducing mechanical complexity while maintaining measurement precision.
3Speed
If polarization diversity coherent reception is implemented, then rapid polarization tracking capability is improved, but the receiver structure and cost increase
Solution Approach 1:
The polarization-diversity coherent receiver structure is designed to handle both conventional intensity-modulated signals and signals requiring polarization tracking using the same hardware platform. By making the receiver universal, the patent avoids needing separate specialized systems for different signal types, thereby reducing overall system complexity and cost.
Solution Approach 2:
The receiver employs dynamic digital signal processing algorithms that can adapt to varying SOP rotation speeds. The system transitions from static detection to dynamic tracking by continuously updating Stokes parameters and intensity calculations based on real-time quadrature component measurements, enabling rapid SOP tracking without requiring overly complex fixed hardware structures.
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 solution effectively tracks SOP rotations at high speeds, improving the reliability of optical communication systems by maintaining signal integrity even during rapid SOP changes, thus preventing outages and enhancing transmission capacity.
Implementation Method 1
an optical hybrid configured to mix the intensity-modulated optical data signal and an optical local-oscillator signal to generate first and second pluralities of mixed optical signals
Implementation Method 2
a first plurality of light detectors connected to generate first and second streams of digitalizations in response to the first plurality of mixed optical signals, the first and second streams of digitalizations providing measurements of different phase components
Data Source
AI summary
An optical receiver, e.g., for an Optical Supervisory Channel (OSC), whose optical front end comprises a polarization-diversity coherent optical receiver configured to receive a conventional intensity-modulated (e.g., OSC) signal. Four quadrature components of the received OSC signal detected by the polarization-diversity coherent optical receiver are sampled at a relatively high sampling rate and are used to calculate the Stokes parameters of the OSC signal. As a result, the Stokes parameters can be updated at the high sampling rate, which can be suitably selected to enable polarization tracking with a relatively high time resolution and/or at relatively high SOP-rotation speeds. The four detected quadrature components are appropriately combined in the receiver DSP to determine the intensity of the received OSC signal, which is then used in a conventional manner to recover the OSC data encoded therein.