Digital Optical Transmitter Pre-Equalization for Waveform Distortion
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Solution Overview
Problem
In digital optical transmitters employing a Mach-Zehnder type optical modulator, waveform distortion due to imperfections in the interferometer leads to deteriorated reception characteristics, especially when multi-level modulation signals or pre-equalization signals with complex waveforms are used.
Innovation Solution
A digital optical transmitter is designed with a pre-equalization signal generation unit and a pre-equalization factor computation unit that compensates for waveform distortion by transforming input data using computed factors, which are then applied to the optical modulators to maintain signal quality and system performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an MZ type optical modulator is used for multi-level modulation or pre-equalization, then transmission capacity and flexibility are improved, but waveform distortion occurs due to interferometer imperfections leading to deteriorated reception characteristics
Solution Approach 1:
The patent applies preliminary action by computing pre-equalization factors that anticipate and compensate for waveform distortion before the optical modulation occurs. The distortion compensation unit calculates correction values based on expected interferometer imperfections and applies them to the modulation signals in advance, thereby preventing reception characteristic deterioration while maintaining high transmission capacity through multi-level modulation
2Ease of manufacture
If interferometer imperfections are present in the MZ type optical modulator, then manufacturing cost is reduced, but waveform distortion occurs leading to system performance degradation
Solution Approach 1:
The system applies self-service by using the distortion compensation unit to automatically detect and correct waveform distortion caused by interferometer imperfections. The compensation factors are computed based on the actual characteristics of each modulator unit, allowing the system to self-correct without requiring manual calibration or higher precision manufacturing, thereby maintaining ease of manufacture while achieving acceptable waveform quality
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively maintains the quality of output transmit signals and system performance even when waveform distortion occurs, improving the yield of components and reducing costs by relaxing the performance requirements of optical modulators and analog front-end devices.
Implementation Method 1
An MZ type optical modulator is formed by installing optical-waveguide type optical phase modulators into an optical-waveguide type MZ type interferometer. In such an MZ type optical modulator, various kinds of optical modulation including intensity modulation and phase modulation are performed by adjusting the applied voltage and the interferometer configuration.
Data Source
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AI summary
A digital optical transmitter of the present invention comprises an optical modulator, pre-equalization factor computation means for generating transform functions for compensating waveform distortion to occur in the optical modulator, and pre-equalization signal generation means for outputting third data and fourth data after creating them by performing a pre-equalization process on first data and second data. Here, through the transform functions, the first data is added to the fourth data, in a manner depending on a characteristic of the optical modulator, and the second data is added to the third data, in a manner depending on a characteristic of the optical modulator.