Optical Receiver DSP Compensation for Low-Extinction Symbol Warping
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Solution Overview
Problem
Silicon photonics-based coherent optical transmitters suffer from low extinction ratios, leading to 2-dimensional warping of transmission symbols due to manufacturing errors and wavelength-dependent refractive index variations, which are not adequately addressed by existing pre-distortion methods.
Innovation Solution
An optical receiver equipped with a digital signal processor (DSP) applies a 2-dimensional transfer function to compensate for the warping by adjusting the in-phase and quadrature components of transmission symbols based on amplitude comparisons, mitigating the distortion introduced at the transmitter.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon photonics technology is used for compact form factors and ease of fabrication, then device size and manufacturing complexity are improved, but extinction ratio deteriorates due to high refractive index sensitivity to manufacturing errors and wavelength variations
Solution Approach 1:
The patent applies preliminary anti-action by implementing pre-distortion compensation in the digital signal processor that anticipates and counteracts the low extinction ratio effect before it degrades the signal. The system calculates compensation values based on the known transmitter characteristics and applies them to received symbols to offset the warping distortion, thereby resolving the contradiction between ease of manufacture and manufacturing precision.
2Productivity
If higher order modulation techniques are used to achieve high data throughput in DCI systems, then productivity is improved, but sensitivity to low extinction ratio deteriorates causing increased symbol demapping errors
Solution Approach 1:
The patent implements feedback by using the received signal information to calculate compensation values for the low extinction ratio effect. The digital signal processor analyzes the received symbols, determines the extent of warping distortion, and applies appropriate compensation to improve symbol demapping accuracy, thereby maintaining reliability while enabling high-order modulation for high productivity.
3Manufacturing precision
If conventional pre-distortion methods are applied at the transmitter, then some compensation for low extinction ratio is achieved, but device complexity increases and compensation effectiveness is insufficient for 2-dimensional warping
Solution Approach 1:
The patent applies the inversion principle by moving the pre-distortion compensation function from the transmitter to the receiver. Instead of modifying the transmitter to compensate for low extinction ratio, the system receives the distorted signal and applies the reverse transformation at the digital signal processor, thereby achieving effective 2-dimensional warping compensation while keeping the transmitter simple.
Data Source
AI summary
A digital signal processor (DSP) of an optical receiver processes one or more digital domain signals, which correspond to a received optical signal, to recover receive data from the one or more digital domain signals. The DSP compensates for a two-dimensional (2-D) warping of transmission symbols at a transmitter of the optical signal at least by: calculating a first adjustment of an in phase (I) component of the transmission symbol; modifying the I component of the transmission symbol using the first adjustment; calculating a second adjustment of a quadrature (Q) component of the transmission symbol; and modifying the Q component of the transmission symbol using the second adjustment