4x2 Widely Linear Filter for Optical Signal Distortion Compensation
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Solution Overview
Problem
High-order multilevel modulated signals in optical fiber communication systems are susceptible to distortion due to incomplete components in transmitter-receivers, which hinders the advancement of higher multileveling and requires high-accuracy equalization processing.
Innovation Solution
A digital signal processing circuit that includes a first carrier phase compensation filter, a 4×2 widely linear (WL) filter, and a filter coefficient updating unit, which compensates for carrier phase and distortion in polarization-multiplexed optical signals and updates filter coefficients based on the output of the 4×2 WL filter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple separate filters are used for polarization mode dispersion compensation, polarization separation, and in-transmitter distortion compensation, then the equalization accuracy is improved, but the circuit size and device complexity increase
Solution Approach 1:
The patent combines polarization mode dispersion compensation, polarization separation, and in-transmitter distortion compensation into a single 4×2 widely linear filter. This merging of multiple filter functions into one unified structure reduces the overall circuit size and device complexity while maintaining the equalization accuracy that would otherwise require multiple separate filters
Solution Approach 2:
The 4×2 widely linear filter is designed to perform multiple functions simultaneously: it compensates for polarization mode dispersion, separates polarizations, and compensates for in-transmitter distortion. This multi-functional design allows a single filter structure to replace what would traditionally require multiple specialized filters, thereby reducing circuit complexity
2Measurement precision
If a high tap count is used in the filter to improve equalization accuracy, then the distortion compensation performance is improved, but the circuit size increases
Solution Approach 1:
The patent employs widely linear filtering with a specific 4×2 configuration that changes the mathematical parameters of the filtering operation. This parameter change enables the filter to achieve high distortion compensation accuracy with a reduced tap count compared to traditional approaches, thereby reducing circuit size while maintaining equalization performance
Data Source
AI summary
A detector is configured to coherently receive a polarization-multiplexed optical signal transmitted from a transmitter via a transmission line. A digital signal processing circuit is configured to perform equalization signal processing on the reception signal coherently received. A carrier phase compensation filter is configured to compensate for a carrier phase in the reception signal. A 4×2 WL filter is disposed after the carrier phase compensation filter and configured to compensate for distortion included in the polarization-multiplexed optical signal. A filter coefficient updating unit is configured to update a filter coefficient of the carrier phase compensation filter and a filter coefficient of the 4×2 WL filter by use of an output of the 4×2 WL filter.