Coherent Detection Local Oscillator Modulation
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Solution Overview
Problem
Existing optical coherent detection systems in optical fiber telecommunications face challenges in maintaining signal coherence due to random variations in optical polarization, requiring complex polarization control and electronic post-processing to compensate for signal distortions.
Innovation Solution
A coherent detection device that modulates the oscillation signal with a repetitive pattern aligned to the symbol time of the incoming useful signal, using a clock and phase recovery circuit to optimize the alignment and reduce distortions, thereby improving signal detection accuracy and reducing the need for electronic post-processing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If polarization control mechanisms are implemented to maintain coherence between signal and local oscillator, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The system uses the received signal itself to generate the reference signal for coherent detection, eliminating the need for a separate local oscillator and its associated polarization control mechanisms. The received signal serves dual purposes: as the signal to be detected and as the reference for mixing, thereby self-resolving the polarization alignment issue.
Solution Approach 2:
The invention extracts and removes the local oscillator component from the coherent detection system. By eliminating the local oscillator, the system removes the source of polarization mismatch and the complex control mechanisms required to maintain polarization alignment between the local oscillator and the received signal.
2Reliability
If electronic post-processing is used to compensate for signal distortions, then signal quality is improved, but processing time and complexity increase
Solution Approach 1:
The system performs preliminary action by directly detecting the received signal without requiring subsequent electronic post-processing for polarization compensation. By using the received signal as the reference and performing coherent mixing in the optical domain, the system resolves polarization issues before detection, eliminating the need for time-consuming electronic post-processing.
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 enhances the detection accuracy by optimizing the alignment of the modulation pattern, leading to lower bit error rates and improved signal quality, effectively addressing the coherence and distortion issues in optical coherent detection systems.
Implementation Method 1
an amplitude modulator configured to modulate the oscillation signal before its entry into the mixer, the modulation pattern comprising repetitive pulses of the same interval and the same time alignment as a symbol time of the incoming useful signal
Implementation Method 2
a signal mixer where one of the signals from the first or second fiber is separated into two signals of orthogonal polarizations, and where the other of the signals from the first or second fiber is mixed with the two separated signals, producing a mixed signal
Implementation Method 3
a detector of said transported data, present in the mixed signal
Data Source
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AI summary
The invention relates to a device for coherent detection of data transported in an optical signal referred to as incoming useful signal, the device comprising: - a first incoming single-mode optical fibre (PLSOF), injecting the incoming useful signal, - a second incoming single-mode optical fibre (LOSOF), injecting an optical signal of optical frequency substantially equal to that of the incoming useful signal, referred to as oscillation signal, - a signal mixer (MEL) in which one of the signals from the first or second fibre is separated into two signals having orthogonal polarisations, and where the other one of the signals from the first or second fibre is mixed with the two separate signals, producing a mixed signal, - a detector (DET) of said transported data present in the mixed signal, - an amplitude modulator (MOD) configured to modulate the oscillation signal before it enters the mixer, the modulation pattern comprising repetitive pulses of the same interval as a symbol time of the incoming useful signal.