Adaptive Subcarrier Equalization in Optical MIMO Links
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Solution Overview
Problem
High data or baud rate optical communication systems face noise issues due to impedance mismatches and path variations in analog circuits, leading to unpredictable optical subcarrier noise that conventional methods struggle to correct effectively.
Innovation Solution
The implementation of digital circuitry, specifically multiple-input multiple-output (MIMO) circuits with finite-impulse response (FIR) filters at both the transmit and receive ends of the optical link, which include adaptive coefficients to minimize subcarrier noise by pre-compensating and compensating signals for path impairments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high data rates greater than 16 Gbaud are used, then productivity is improved, but noise is generated due to impedance mismatches and path variations in analog circuits
Solution Approach 1:
The patent applies preliminary action by implementing pre-compensation in the transmit path using digital circuitry that anticipates and corrects for impairments before they occur. The transmit-side DSP applies equalization and calibration to counteract the effects of impedance mismatches and path variations before the signal is transmitted through the analog circuits, thereby preventing noise generation at high data rates.
Solution Approach 2:
The patent implements feedback mechanisms through calibration procedures that measure the actual impairments in the transmit and receive paths and use this information to adjust the digital circuitry parameters. The system continuously monitors and corrects for path variations by comparing expected versus actual signal characteristics and adapting the equalization parameters accordingly.
2Device complexity
If conventional correction approaches are used, then device complexity is reduced, but the ability to correct optical subcarrier noise is insufficient
Solution Approach 1:
The patent applies dynamics by implementing adaptive equalization with time-varying parameters. The digital circuitry includes adjustable equalizers with parameters that can be dynamically modified based on operating conditions. The calibration procedures enable the system to adapt to different data rates, modulation formats, and environmental conditions, providing reliable noise correction without requiring overly complex fixed-structure circuits.
Solution Approach 2:
The patent utilizes parameter changes by modifying digital signal processing parameters such as equalizer coefficients, calibration factors, and compensation values based on measured impairments. The system changes these parameters dynamically to optimize performance across different operating conditions, achieving effective noise correction with relatively simple circuit implementations by leveraging software-defined adaptability.
3Reliability
If path variations are corrected, then reliability is improved, but device complexity increases due to additional digital circuitry
Solution Approach 1:
The patent implements universality by designing the digital circuitry to perform multiple functions simultaneously. The same digital signal processing blocks are used for both calibration and operational equalization, and the transmit and receive paths share common processing architectures. This multi-functionality approach enables reliable path variation correction without proportionally increasing device complexity, as the digital circuits serve dual purposes during calibration and normal operation.
Data Source
AI summary
Consistent with the present disclosure, the above-described subcarrier noise, which may be characterized as a linear filtering effect, may be reduced or eliminated by providing a first multiple-input multiple output (MIMO) circuits at the transmit end of an optical link and providing a second MIMO circuit at the receive end of the optical link. The first MIMO may include a first plurality of filters, each of which may include a finite-impulse response (FIR) filter having variable coefficients or tap weights that may be changed or adapted to minimize subcarrier noise associated with the modulator, as well as D/A and analog circuitry, at the transmit end of the optical link. In addition, the second MIMO may include a second plurality of filters, each of which may also include an FIR filter having variable coefficients or tap weights that may be changed or adapted to minimized subcarrier noise associated with the optical hybrids, as well as A/D and analog circuitry, at the receive end of the optical link. In one example, a least means square (LMS) technique may be employed to calculate desired coefficients or tap weights whereby an error determined based on the signal detected at the receiver is minimized to update the coefficients of the FIR filters.