I/Q Correlation Dither for Modulator Bias and Orthogonality Control
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Solution Overview
Problem
Existing modulator bias control methods, particularly for electro-optical modulators, suffer from performance penalties due to large dithers required for accurate bias adjustment, leading to signal-to-noise ratio degradation and I/Q mis-orthogonality issues.
Innovation Solution
Introduce a correlation dither between digital I and Q signals to control the bias of a nested Mach-Zehnder modulator, reducing the amplitude of bias dithers and minimizing interference, thereby maintaining orthogonality and improving system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If large dithers are used for accurate bias adjustment, then bias control accuracy is improved, but signal-to-noise ratio deteriorates and I/Q mis-orthogonality occurs
Solution Approach 1:
The patent segments the dither signal into two independent components: a small-amplitude dither applied to the bias control loop for accurate bias adjustment, and a correlation dither applied to the I/Q modulation paths. This segmentation allows each dither to operate at optimal amplitude levels, preventing the SNR degradation caused by large combined dithers while maintaining bias control accuracy.
Solution Approach 2:
The patent introduces a correlation dither mechanism that acts as an intermediary between the I and Q signal paths. By modulating the correlation between I and Q signals rather than applying large direct dithers to the bias, the system achieves accurate bias control through correlation measurement while avoiding the harmful SNR degradation associated with large amplitude dithers.
2Measurement precision
If large dithers are used for accurate bias adjustment, then bias control accuracy is improved, but I/Q orthogonality deteriorates
Solution Approach 1:
The patent segments the dither application into separate paths: small-amplitude dither for bias control and correlation dither for I/Q relationship management. This prevents the large dithers from disrupting I/Q orthogonality while still enabling accurate bias control through the correlated measurement approach.
Solution Approach 2:
The correlation dither serves as an intermediary that measures I/Q orthogonality without directly disturbing it. By using correlation as the measurement mechanism rather than direct large-amplitude modulation, the system maintains I/Q orthogonality stability while achieving accurate bias control.
3Measurement precision
If correlation dither is introduced between I and Q signals, then bias control accuracy is improved with minimal performance penalties, but device complexity increases
Solution Approach 1:
The patent replaces complex hardware-based bias control mechanisms with a digital signal processing approach. By using correlation dither and measuring the correlation between I and Q signals through digital processing, the system achieves accurate bias control without requiring additional complex hardware components, thus minimizing the increase in device complexity.
Data Source
AI summary
Aspects of the subject disclosure may include, for example, obtaining two inputs xI and xQ based on a digital input signal, and causing a modulator to create two substantially orthogonal output dimensions I and Q based on the two inputs xI and xQ, by performing controlled introduction of a correlation between the two inputs xI and xQ for the modulator, and detecting a resulting output power of the modulator to facilitate operation of the modulator. Other embodiments are disclosed.