Few-mode fiber optical receiver for atmospheric turbulence adaptation
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Solution Overview
Problem
Existing optical space communication systems face challenges in rapidly controlling filter coefficients to adapt to variations in atmospheric turbulence when performing diversity combining of dual-polarization signals, leading to inefficiencies in signal reception between a satellite and the ground.
Innovation Solution
The system employs a plurality of dual-polarization coherent receivers and matrix filters for polarization separation and equalization, with combining filters that weight and combine signals in quadrature, and control filter coefficients based on deviations from a desired state to minimize signal deviations, allowing for rapid adaptation to atmospheric turbulence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a single-mode fiber is used for high-speed optical space communication, then the communication speed is improved, but the coupling efficiency degrades significantly due to atmospheric turbulence causing fading
Solution Approach 1:
The patent segments the single communication channel into multiple propagation modes (LP01, LP11a, LP11b modes) within the few-mode fiber. By dividing the signal transmission into multiple independent modes that experience different atmospheric turbulence effects, the system achieves diversity reception, reducing fading and improving reliability while maintaining high communication speed.
2Reliability
If diversity reception using multiple receivers is implemented to combat fading, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The patent merges multiple propagation modes (LP01, LP11a, LP11b) into a single few-mode fiber receiver structure. Instead of using multiple separate receivers, the system combines multiple modes within one fiber, achieving diversity reception effects while simplifying the overall device structure and reducing complexity.
Solution Approach 2:
The few-mode fiber serves multiple functions simultaneously: it acts as both the transmission medium and the diversity reception structure. The fiber supports multiple propagation modes that provide diversity against atmospheric turbulence, eliminating the need for separate diversity reception hardware and reducing device complexity.
3Adaptability or versatility
If filter coefficients are controlled adaptively to follow atmospheric turbulence variations, then the adaptability is improved, but the control speed becomes insufficient to track rapid turbulence changes
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing optimal filter coefficients for different turbulence conditions in a lookup table. When atmospheric turbulence changes, the system quickly retrieves pre-computed coefficients based on current channel conditions, avoiding the need for slow real-time adaptive calculation and enabling rapid tracking of turbulence variations.
Data Source
AI summary
An optical reception terminal includes a plurality of matrix filters (40, 41) respectively provided for a plurality of modes and configured to perform polarization separation and equalization on a coherently received signal in a corresponding mode, and two combining filters (50, 51) respectively provided for two polarizations and configured to combine signals in corresponding polarization among signals output from the plurality of matrix filters (40, 41) after weighting the signals. Filter coefficients of the plurality of matrix filters (40, 41) and weighting coefficients of the two combining filters (50, 51) are controlled based on a deviation from a desired state of both signals in two polarizations after combining by the two combining filters (50, 51), so as to minimize a sum of deviations.