Coherent Optical Transponder Bandwidth and Nonlinearity Compensation
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Solution Overview
Problem
Existing optical transponders face challenges in accurately compensating bandwidth limitations and modulation nonlinearity, especially at high baud rates, due to coupled effects and inadequate compensation methods that often fail to address the transfer function and nonlinear amplitude response of optical modulators.
Innovation Solution
An apparatus and method using a controller with a memory and processor to send stimulus signals to tributary channels, adjusting amplitude and frequency to determine bandwidth limitations and modulation nonlinearities, and then applying filters to reduce these issues independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If known solutions are used to compensate bandwidth limitation, then compensation is provided, but the compensation lacks accuracy for high baud rate transponders due to coupled effects with modulation nonlinearity
Solution Approach 1:
The patent segments the coupled effects of bandwidth limitation and modulation nonlinearity into separate measurable components. By using a stimulus signal with controlled amplitude and frequency variations, the system independently measures bandwidth limitation characteristics and modulation nonlinearity characteristics, then applies separate compensation for each effect, thereby achieving accurate compensation without excessive complexity
Solution Approach 2:
The patent introduces a stimulus signal as an intermediary tool to separately characterize bandwidth limitation and modulation nonlinearity. This stimulus signal serves as a mediator that allows independent measurement of each effect's contribution to signal degradation, enabling precise compensation through separate compensation filters
2Reliability
If known solutions are used to compensate modulation nonlinearity, then partial compensation is provided, but results are unsatisfying because they address only one aspect (transfer function or nonlinear amplitude response) rather than both
Solution Approach 1:
The patent segments modulation nonlinearity into two distinct components: transfer function nonlinearity and nonlinear amplitude response. By using stimulus signals with specific amplitude and frequency characteristics, the system independently measures and compensates for each component separately, achieving complete nonlinearity compensation rather than partial compensation
Solution Approach 2:
The stimulus signal acts as an intermediary that enables separate measurement of transfer function characteristics and nonlinear amplitude response characteristics. This intermediary approach simplifies the measurement process by decoupling the two nonlinearity aspects, making them independently detectable and compensatable
3Productivity
If high baud rate operation is implemented to meet growing demand, then data transmission capacity increases, but bandwidth limitation and modulation nonlinearity effects become more pronounced and harder to compensate
Solution Approach 1:
The patent applies preliminary characterization of bandwidth limitation and modulation nonlinearity using stimulus signals before actual high baud rate data transmission. By pre-measuring and pre-compensating for impairments at the specific operating baud rate, the system optimizes performance for high capacity operation without suffering from inaccurate real-time compensation
Solution Approach 2:
The patent adjusts compensation parameters based on the operating baud rate. By characterizing impairments at different baud rates and adapting compensation filters accordingly, the system maintains high measurement precision and compensation accuracy even as operational parameters change to increase data transmission capacity
Data Source
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Figure 1B
Figure 2A~2D
AI summary
In some embodiments, an apparatus includes a memory and a processor operatively coupled to the memory. The processor is configured to send a stimulus signal at a frequency that corresponds to a first frequency value to a tributary channel of a coherent optical transponder. The processor is configured to adjust an amplitude of the stimulus signal and receive a first plurality of output optical power values. The processor is configured to adjust the frequency of the stimulus signal and receive a second plurality of output optical power values. The processor is configured to determine a bandwidth limitation and a modulation nonlinearity, and then send a first signal to a first filter to reduce the bandwidth limitation and a second signal to a second filter to reduce the modulation nonlinearity.