Coherent Optical Receiver Skew Compensation via Digital Signal Processing
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Solution Overview
Problem
In coherent optical receivers, inter-lane skew between the optical fiber and coaxial wire channels leads to signal delay, making polarization demultiplexing and phase estimation difficult, resulting in poor demodulation performance.
Innovation Solution
A coherent optical receiver with a 90-degree hybrid circuit, optoelectronic converter, analog-to-digital converter, skew addition unit, and FFT operation unit, which compensates for propagation delay skew by adding an opposite skew amount to the digital signal and performing a fast Fourier transform to calculate and correct the skew.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the lengths of four lanes from the outputs of the 90-degree hybrid circuit to the inputs of the analog-to-digital converters are made equal, then demodulation performance is improved, but manufacturing precision requirements become excessively high and device complexity increases
Solution Approach 1:
The patent introduces a skew detection unit and skew compensation unit as intermediary components between the analog-to-digital converters and the digital signal processing unit. These intermediaries measure the actual skew in each lane and apply compensation to equalize the signal arrival times, thereby achieving good demodulation performance without requiring extremely precise physical lane length matching during manufacturing
Solution Approach 2:
The patent dynamically adjusts the skew compensation parameters based on detected skew measurements. By changing the compensation parameters adaptively, the system can maintain optimal demodulation performance even when physical lane lengths vary due to manufacturing tolerances or environmental changes, avoiding the need for fixed high-precision physical configurations
2Reliability
If skew compensation is implemented through physical lane length equalization, then signal synchronization is improved, but manufacturing cost and device complexity increase
Solution Approach 1:
The patent replaces the mechanical approach of physically equalizing lane lengths with a digital signal processing approach. Instead of mechanically adjusting fiber optic cable lengths or connector positions during manufacturing, the system uses digital skew compensation algorithms that can be implemented through software or programmable logic, significantly simplifying the manufacturing process while maintaining signal synchronization
3Device complexity
If inter-lane skew is not compensated, then device complexity is reduced, but demodulation performance deteriorates
Solution Approach 1:
The patent implements a self-service mechanism where the coherent optical receiver automatically detects and compensates for its own inter-lane skew. The skew detection unit measures the skew within the receiver itself, and the skew compensation unit automatically applies the necessary correction, eliminating the need for external calibration equipment or complex manual adjustment procedures
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 solution enables sufficient demodulation and improves reception performance even with inter-lane skew, preventing performance deterioration.
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 signal and outputs a detected electrical signal
Data Source
AI summary
The disclosed coherent optical receiver includes a local light source; a 90-degree hybrid circuit; an optoelectronic converter; an analog-to-digital converter; a skew addition unit; and a FFT operation unit. The 90-degree hybrid circuit makes multiplexed signal light interfere with local light from the local light source, and outputs multiple optical signals separated into a plurality of signal components. The optoelectronic converter detects the optical signal and outputs a detected electrical signal. The analog-to-digital converter digitizes the detected electrical signal and outputs a detected digital signal. The skew addition unit adds to the detected digital signal an additional skew amount whose absolute value is equal to, whose sign is opposite to a skew amount of a difference in propagation delay in each lane connected to each output channel of the 90-degree hybrid circuit. The FFT operation unit performs a fast Fourier transform on the output from the skew addition unit.