Coherent Receiver CMRR Control via Variable Gain Amplifier Feedback
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Solution Overview
Problem
Coherent optical receivers face challenges in achieving optimal common mode rejection ratio (CMRR) due to gain differences between photodetectors and optical paths, leading to imperfect cancellation of directly detected components and reduced signal quality.
Innovation Solution
The implementation of variable gain amplifiers to balance the gains of photodetector paths, using methods such as DC current measurement, dither signal injection into optical attenuators or local oscillators, and feedback control mechanisms to adjust gains and ensure equal signal processing across both paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If balanced photodetectors are used in a coherent optical receiver, then direct detection components can be canceled, but gain differences between optical paths and photodetectors cause imperfect cancellation and reduce common mode rejection ratio
Solution Approach 1:
The patent implements feedback control mechanisms that continuously monitor the gain balance between optical paths and dynamically adjust the gains to maintain optimal common mode rejection ratio. This feedback loop compensates for drift and variations in real-time, ensuring sustained precision without requiring perfect initial matching.
Solution Approach 2:
The system dynamically changes the gain parameters of the photodetector paths to optimize common mode rejection. By adjusting the gain of individual photodetectors or optical paths, the system adapts to variations in component characteristics and environmental conditions, maintaining high CMRR despite manufacturing tolerances.
2Reliability
If variable gain amplifiers are added to balance photodetector paths, then common mode rejection ratio improves, but device complexity increases
Solution Approach 1:
The patent combines the gain balancing function with the existing signal processing chain by integrating variable gain amplifiers into the existing photodetector output paths. This merging approach allows CMRR optimization without adding completely separate control systems, reducing overall complexity while maintaining effectiveness.
Solution Approach 2:
The system implements self-adjusting mechanisms where the gain balancing is performed automatically based on monitored signal characteristics, eliminating the need for manual calibration and complex external control systems. The receiver autonomously optimizes its own performance by detecting and compensating for gain imbalances.
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 approach enhances the CMRR, effectively canceling out unwanted signal components and improving the optical signal-to-noise ratio, enabling better performance in multi-channel systems without the need for optical filters.
Implementation Method 1
The received optical signal is converted to a first electrical signal and a second electrical signal through a first photodetector and a second photodetector, respectively
Data Source
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AI summary
An optical signal is received at a coherent optical receiver. The received optical signal is converted to a first electrical signal and a second electrical signal through a first photodetector and a second photodetector, respectively. The first electrical signal is input into a first single input variable gain amplifier, and the second electrical signal is input into a second single input variable gain amplifier. A gain of at least one of the first single input variable gain amplifier or the second single input variable gain amplifier is controlled to balance the output of the first single input variable gain amplifier and the output of the second single input variable gain amplifier. The output of the first single input variable gain amplifier and the output of the second single input variable gain amplifier are input into a differential amplifier. A receiver output is obtained at an output of the differential amplifier.