PON Transmitter Evaluation Using Time-Shifted Eye Sampling
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Solution Overview
Problem
The existing TDEC measurement method for validating optical transmitters in passive optical networks (PON) is inaccurate for high modulation rates like 50G NRZ due to eye closure and noise enhancement, especially when non-linear equalizers are used, leading to unreliable performance predictions.
Innovation Solution
A time-shifted sampling point is introduced in the eye diagram to collect data samples, allowing for accurate performance evaluation without the need for equalization, using a method that incorporates a time-shifted sampling point in the eye diagram to collect data samples, providing a more accurate measure of transmitter performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If standard TDEC measurement is used for 50G NRZ transmitter validation, then measurement process is simple, but measurement accuracy deteriorates due to eye closure and noise enhancement
Solution Approach 1:
The patent changes the sampling time parameter from the conventional mid-eye position to a time-shifted position (e.g., 0.4 UI or 0.6 UI). This parameter change allows the eye diagram to be sampled at points where signal levels are more clearly pronounced and less affected by eye closure, thereby improving measurement accuracy without complicating the measurement process
Solution Approach 2:
Instead of trying to open the closed eye through equalization (which amplifies noise), the patent inverts the approach by sampling at time points where the signal naturally provides better differentiation between logic levels. This avoids the noise enhancement problem while still achieving accurate transmitter performance measurement
2Reliability
If equalization is applied to open the NRZ eye at 50G rate, then eye closure is reduced, but noise enhancement increases
Solution Approach 1:
The patent extracts only the necessary information for transmitter performance validation by sampling at specific time points, rather than attempting to fully open the eye through equalization. This extraction approach obtains sufficient measurement data without introducing the noise enhancement that comes with equalization processing
Solution Approach 2:
The patent converts the potentially harmful effect of eye closure into a beneficial measurement opportunity by identifying that certain time-shifted sampling points provide naturally better signal differentiation. The eye closure that would normally be problematic becomes irrelevant when sampling at these optimized time points
3Adaptability or versatility
If mid-eye sampling is used for TDEC measurement, then conventional measurement standards are followed, but measurement accuracy deteriorates for high modulation rates
Solution Approach 1:
The patent modifies the sampling time parameter from the standard mid-eye position to time-shifted positions (0.4 UI or 0.6 UI). This parameter change maintains compatibility with the overall TDEC measurement framework while improving accuracy for high modulation rates like 50G NRZ
Data Source
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AI summary
A method and apparatus is proposed for accurately evaluating the performance of optical transmitters under test conditions (such as high bit-rate modulation formats) that compromise the operability of standard test equipment used for this purpose. The proposed apparatus and method are similar to the elements associated with existing testing standards based on an optical eye diagram, with an important distinction that allows for accurate measurements of the transmitter's performance to be made. In particular, the sampling point for collecting eye diagram data samples in the inventive arrangement is shifted by half a period with respect to the conventional mid-eye sampling point, eliminating the need to include representative reference equalizer in the test equipment and providing an evaluation not influenced by the test equipment, resulting in a more accurate measurement of transmitter-related distortions.