Coherent Optical Receiver Inter-Channel Skew Detection
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Solution Overview
Problem
In coherent optical receivers, inter-channel skew caused by unequal lengths of signal lines leads to signal delay, impairing polarization demultiplexing and phase estimation, resulting in inadequate demodulation and reduced receiving performance.
Innovation Solution
A coherent optical receiver with a 90° hybrid circuit, optoelectronic converters, and a digital signal processing unit that includes a skew compensation unit and an FFT operation unit to calculate and compensate for the difference in propagation delay based on peak values from the FFT process, ensuring accurate demodulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the lengths of signal lines are made equal to avoid inter-channel skew, then receiving performance is improved, but device complexity and manufacturing difficulty increase due to the need for precise matching of multiple signal paths
Solution Approach 1:
The patent introduces a skew detection device as an intermediary component that measures the propagation delay difference between signal lines. This mediator enables the system to detect skew without requiring complex physical matching of all signal paths, thus improving receiving performance while avoiding excessive device complexity
Solution Approach 2:
The patent changes the approach from physically matching signal line lengths to electronically measuring and compensating for delay differences. By measuring propagation delay as a parameter and using this information for compensation, the system achieves good receiving performance without the manufacturing complexity of precise physical matching
2Measurement precision
If skew compensation is implemented through complex equalization processes, then demodulation accuracy is improved, but processing time and computational complexity increase
Solution Approach 1:
The patent performs skew detection and measurement before the main demodulation process. By preliminarily measuring the propagation delay difference and preparing compensation information in advance, the actual demodulation process can proceed more efficiently without excessive processing time loss
Solution Approach 2:
The patent replaces complex mechanical/electrical signal path matching with a measurement and compensation approach using digital signal processing. This substitution reduces the need for time-consuming physical adjustments while maintaining demodulation accuracy through computational compensation
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 enables sufficient demodulation even with inter-channel skew, thereby maintaining or improving the receiving performance by compensating for signal delays.
Implementation Method 1
the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components
Implementation Method 2
the optoelectronic converter detects the optical signals and outputs detected electrical signals
Data Source
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AI summary
In a coherent optical receiver, sufficient demodulation becomes impossible and consequently receiving performance deteriorates if an inter-channel skew arises, therefore, a coherent optical receiver according to an exemplary aspect of the invention includes a local light source, a 90° hybrid circuit, an optoelectronic converter, an analog to digital converter, and a digital signal processing unit; wherein the 90° hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs a plurality of optical signals separated into a plurality of signal components; the optoelectronic converter detects the optical signals and outputs detected electrical signals; the analog to digital converter quantizes the detected electrical signals and outputs quantized signals; the digital signal processing unit includes a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and an FFT operation unit for performing a fast Fourier transform process on the quantized signals; and wherein the difference in propagation delay is calculated on the basis of a plurality of peak values with a central focus on one peak value in the results of performing the fast Fourier transform process.