Optical Transmission Apparatus Group Delay Compensation
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Solution Overview
Problem
Direct modulation of semiconductor lasers in optical communication systems experiences degradation in reception quality due to group delay time differences caused by wavelength variation with light intensity, leading to errors in demodulation of multi-value signals.
Innovation Solution
An optical transmission apparatus is configured with a modulation mapping unit, skew units, an addition unit, an electric-optic conversion unit, and a skew control unit to adjust signal delays and convert electrical signals into optical signals with varying light intensity, compensating for group delay time differences by aligning symbol arrival times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If direct modulation of semiconductor laser is used for multi-value amplitude modulation, then optical transmission speed is improved, but reception quality degrades due to group delay time differences
Solution Approach 1:
The patent applies preliminary action by introducing pre-equalization processing before the optical signal is transmitted. The pre-equalization unit processes the electrical signal in advance to compensate for the group delay time differences that will occur during transmission, thereby maintaining reception quality while using direct modulation for high-speed transmission
Solution Approach 2:
The patent changes the parameter of the electrical signal by applying pre-equalization that adjusts the signal characteristics before modulation. This involves modifying the signal parameters (amplitude, timing) to counteract the wavelength-dependent group delay effects, enabling accurate demodulation after transmission
2Reliability
If pre-equalization is applied to MZ modulator, then waveform deformation is suppressed, but device complexity increases
Solution Approach 1:
The patent extracts the pre-equalization function from the modulation device itself and implements it as a separate processing unit before the modulator. This separates the equalization function from the modulation function, reducing the complexity of the modulation device while maintaining waveform quality through external signal processing
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 apparatus effectively suppresses the degradation of reception quality by compensating for group delay time differences, ensuring accurate demodulation of multi-value signals and improving transmission reliability.
Implementation Method 1
an electric-optic conversion unit that converts the sum signal into the optical signal and transmits the optical signal wherein a light intensity of the optical signal is modulated in accordance with strength of the sum signal and a wavelength of the optical signal varies in accordance with the light intensity
Data Source
AI summary
An optical transmission apparatus and an optical transmission method are provided. In particular, an optical transmission apparatus is disclosed as being configured to add strength to a signal. The signal corresponds to a value that an input signal has, and the strength added to the signal is strength according to the value. The optical transmission apparatus is further configured to give delays to a plurality of signals that includes the signal and to convert the sum of the plurality of signals into an optical signal.