Optical Signal Pre-Equalization for Accurate Compensation Coefficients
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Solution Overview
Problem
Existing methods for optical signal compensation in optical transmitters face challenges in accurately obtaining a level diagram due to attenuation in electric wires, making it difficult to calculate compensation coefficients effectively.
Innovation Solution
An optical transmission system with pre-equalization, digital-to-analog conversion, and scale estimation units to accurately determine compensation coefficients by correlating amplitude distributions of transmission and received signals, using a compensation filter to improve signal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the optical receiver analyzes the reception waveform to calculate the compensation coefficient, then the nonlinear response compensation can be implemented, but the level diagram cannot be accurately obtained due to attenuation in electric wires
Solution Approach 1:
The patent introduces an intermediary process of transmitting test signals and measuring amplitude distributions at both transmitter and receiver ends. By using these measured amplitude distributions as intermediaries, the system can calculate the slope and determine output levels without directly measuring the attenuated reception waveform, thus resolving the contradiction between implementing compensation and accurately obtaining the level diagram.
Solution Approach 2:
The patent creates a copy of the transmission signal path by transmitting test signals through the same electric wires and measuring the amplitude distributions. This copying approach allows the system to characterize the attenuation effects and compensate for them in the compensation coefficient calculation, enabling accurate level diagram determination despite the attenuation in the actual signal path.
2Ease of manufacture
If the DAC output level is set without considering electric wire attenuation, then the system design is simplified, but the compensation coefficient calculation becomes inaccurate
Solution Approach 1:
The system performs self-characterization by transmitting test signals and automatically measuring its own amplitude distributions at both ends. This self-service approach allows the system to autonomously determine the output levels and compensation coefficients without requiring external calibration equipment or complex manual design processes, thus maintaining ease of manufacture while achieving high accuracy.
Solution Approach 2:
The patent implements a feedback mechanism where the measured amplitude distributions from the receiver are used to calculate the slope, which then feeds back to determine the optimal DAC output levels and compensation coefficients. This feedback loop ensures that the system automatically adapts to the actual attenuation characteristics of the electric wires, resolving the contradiction between design simplicity and compensation accuracy.
3Device complexity
If the reception waveform is used directly for compensation coefficient calculation, then the process is simplified, but the output level determination becomes inaccurate due to attenuation
Solution Approach 1:
The patent performs preliminary measurement of amplitude distributions at both the transmitter and receiver ends before calculating the compensation coefficient. This preliminary action of characterizing the signal path attenuation allows the system to pre-determine the correct output levels and compensation coefficients, avoiding the need for complex real-time adjustments while maintaining high accuracy in the output level determination.
Data Source
AI summary
A transmission apparatus causes a digital-to-analog conversion unit to perform digital-to-analog conversion on transmission signals pre-equalized by using a compensation filter, then converts electrical signals into optical signals, and outputs the optical signals. A receiving apparatus converts the received optical signals into received electrical signals, then performs analog-to-digital conversion, and demodulates the received signals. A scale estimation unit calculates a slope near an amplitude 0 in a correlation between an amplitude distribution of the pre-equalized transmission signals and an amplitude distribution of the received signals. A scale unit scales amplitude of the received signals on the basis of the calculated slope. A coefficient estimation unit calculates a filter coefficient of the compensation filter on the basis of the pre-equalized transmission signals and the scaled received signals. An output amplitude level determination unit determines output levels of the transmission signals from the digital-to-analog conversion unit on the basis of a correlation between distributions of amplitudes of non-pre-equalized and pre-equalized transmission signals.