Single-Branch Coherent Optical Receiver for Low-Signal Access Links
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Solution Overview
Problem
Coherent optical transmission technologies used in metro and core network segments are not suitable for 5G mobile technology and FTTH evolution due to high complexity, cost, and noise issues, while existing solutions for network access segments face low signal strength and sensitivity challenges.
Innovation Solution
A cost-effective coherent optical receiver design using a single-branch configuration with a polarization-diversity actuator and electronic circuitry for domain-switching and phase-refining procedures, eliminating the need for complex DSP and OPLL, to enhance optical receiver sensitivity and maintain boosting effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coherent optical transmission is used in metro and core network segments, then high spectral efficiency and good optical receiver sensitivity are achieved, but device complexity and manufacturing cost increase significantly
Solution Approach 1:
The patent extracts and eliminates the complex Digital Signal Processing (DSP) arrangement and Optical Phase Lock Loop (OPLL) from the coherent optical receiver, retaining only the essential local oscillator and photodetection components. This extraction maintains optical receiver sensitivity while dramatically reducing device complexity and manufacturing cost for access network deployment
Solution Approach 2:
The patent employs a simplified receiver design that uses inexpensive, easily manufacturable components suitable for high-volume deployment in access networks, sacrificing the long-range performance of complex metro-grade equipment in favor of cost-effectiveness and ease of deployment
2Reliability
If full polarization diversity with complex DSP is used to track state of polarization, then transmission continuity is ensured, but device complexity and deployment cost increase
Solution Approach 1:
The patent removes the complex polarization tracking mechanisms including endless polarization transformers and adaptive control loops, relying instead on the inherent robustness of coherent detection with a local oscillator to maintain transmission continuity without active polarization management
Solution Approach 2:
The local oscillator automatically compensates for polarization changes through the coherent mixing process, eliminating the need for external polarization tracking devices. The system self-adjusts to maintain transmission continuity without complex control mechanisms
3Productivity
If coherent optical transmission is deployed in network access segments, then high data rates are achieved, but optical receiver sensitivity decreases due to low signal strength
Solution Approach 1:
The local oscillator performs preliminary amplification and phase reference establishment before the weak optical signal from high split-ratio networks is detected by the photodiode. This preliminary action boosts the effective signal strength and improves optical receiver sensitivity, enabling high data rate transmission in access networks with low input signal levels
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
The solution provides a low-complexity, cost-effective optical receiver suitable for network access segments, improving signal strength and data rates, and reducing deployment complexity and cost.
Implementation Method 1
a 2x2 coupler, having one input aiming at receiving the amplitude-shift keying modulated optical signal received from the coherent optical transmitter and the other input receiving another optical signal which is output by a set formed by a local oscillator and the polarization diversity actuator, so as to enable the local oscillator to provide a boosting effect to the amplitude-shift keying modulated optical signal
Implementation Method 2
one output connected to a set formed by a photodiode followed by a Direct Current filter
Data Source
AI summary
A coherent optical receiver comprises a local oscillator, a polarization-diversity actuator configured for modifying an optical signal output by the local oscillator and a 2×2 coupler for coupling the optical signal output by the polarization-diversity actuator and a modulated optical signal received from a coherent optical transmitter. The local oscillator thus provides a boosting effect to the amplitude-shift keying modulated optical signal. The coherent optical receiver comprises a controlling unit performing a domain-switching procedure acting on ellipticity main axis orientation and/or ellipticity phase shift for coarse control of the polarization-diversity actuator, and a phase-refining procedure acting on a controlled error signal injected in the phase of the optical signal output by the polarization-diversity actuator for fine control of the polarization-diversity actuator.