Coherent Receiver Skew Compensation via Digital Signal Processing
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Solution Overview
Problem
In coherent optical receivers, interchannel skew between signal lines causes demodulation failures and deteriorated reception performance due to unequal lengths of signal lines from the 90-degree hybrid circuit to the analog-to-digital converters, leading to imperfect polarization demultiplexing and phase estimation.
Innovation Solution
A coherent optical receiver with a 90-degree hybrid circuit, optoelectronic converters, and a digital signal processing unit that includes a skew compensation unit and a demodulation unit, utilizing a test light source and FFT operation to detect and compensate for propagation delays between signal components, ensuring accurate demodulation even with interchannel skew.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If signal line lengths are made equal to avoid interchannel skew, then demodulation accuracy is improved, but device complexity and manufacturing difficulty increase due to precise length matching requirements
Solution Approach 1:
The patent introduces a skew detector as an intermediary device that measures the propagation delay difference between signal lines. This mediator allows the system to detect skew without requiring precise physical length matching, thereby resolving the contradiction between demodulation accuracy and device complexity.
Solution Approach 2:
The patent changes the approach from controlling physical length parameters to measuring and compensating for delay time parameters. By using the skew detector to measure propagation delay differences and adjusting timing accordingly, the system achieves accurate demodulation without requiring equal signal line lengths.
2Reliability
If signal line lengths are made equal to prevent interchannel skew, then reception performance is improved, but manufacturing precision requirements become more stringent
Solution Approach 1:
The skew detector serves as an intermediary measurement device that enables the system to identify and compensate for timing differences caused by unequal signal line lengths. This eliminates the need for high manufacturing precision in signal line length matching while maintaining reliable reception performance.
Solution Approach 2:
The system performs self-diagnosis and self-correction by using the skew detector to automatically identify timing skew and enabling compensation mechanisms to correct it. This self-service approach allows the system to maintain high reception performance without requiring external precision control during manufacturing.
3Device complexity
If interchannel skew is left uncorrected to simplify the device structure, then device complexity is reduced, but demodulation accuracy deteriorates
Solution Approach 1:
The skew detector is introduced as a relatively simple intermediary component that enables accurate skew measurement without significantly increasing overall device complexity. This allows the system to maintain demodulation accuracy while keeping the device structure relatively simple compared to alternative approaches that would require complex equalization circuits.
4Manufacturing precision
If interchannel skew is left uncorrected to ease manufacturing, then manufacturing precision requirements are reduced, but reception performance deteriorates
Solution Approach 1:
The skew detector acts as an intermediary that bridges the gap between relaxed manufacturing tolerances and high reception performance. By measuring and enabling compensation for timing skew, it allows manufacturers to use less precise signal lines while still achieving reliable reception.
Solution Approach 2:
The system employs self-correction mechanisms where the skew detector identifies timing differences and the system automatically compensates for them. This self-service capability allows the system to maintain high reception performance even when manufacturing precision is reduced, as the system corrects its own deficiencies.
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 and maintains high reception performance by accurately compensating for interchannel skew, preventing signal degradation and ensuring reliable data transmission.
Implementation Method 1
the 90-degree 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 interchannel skew arises, therefore, a coherent optical receiver according to an exemplary aspect of the invention includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; and a digital signal processing unit, wherein the 90-degree 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; and the digital signal processing unit includes a skew compensation unit for compensating a difference in propagation delay between the plurality of signal components, and a demodulation unit for demodulating the quantized signals.