Optical Reception Apparatus Dispersion Compensation
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Solution Overview
Problem
The DMT modulation scheme in optical transmission systems experiences frequency dips due to frequency chirping and dispersion, limiting the number of bits that can be allocated to subcarriers and thereby reducing transmission capacity.
Innovation Solution
An optical reception apparatus and method that includes a receiver, monitor, and controller to detect frequency dips in transmission characteristics and control dispersion compensation, allowing for tunable dispersion compensation to mitigate these dips and optimize subcarrier allocation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If DMT modulation scheme is applied to optical transmission system, then frequency usage efficiency and transmission capacity are improved, but frequency dips occur due to frequency chirping and dispersion
Solution Approach 1:
The patent applies preliminary action by performing dispersion compensation before the frequency dip occurs. The system pre-calculates the optimal dispersion compensation value based on transmission distance and applies it proactively to prevent frequency dips, rather than reacting after they occur. This is implemented through the controller that determines compensation values based on predetermined relationships between transmission distance and dispersion characteristics.
Solution Approach 2:
The patent applies parameter changes by dynamically adjusting the dispersion compensation value based on transmission conditions. The system changes the compensation parameter according to transmission distance, allowing the transmission system to adapt to varying conditions and maintain optimal performance across different link lengths while preventing frequency dips.
2Productivity
If bit loading is applied to allocate bits to subcarriers, then frequency usage efficiency is improved, but the number of bits is limited at frequency dips
Solution Approach 1:
The patent applies preliminary action by determining the optimal number of bits for each subcarrier before transmission, taking into account the dispersion compensation that will be applied. The system pre-calculates bit allocation based on the compensated transmission characteristics, ensuring that subcarriers that would otherwise experience frequency dips can still accommodate more bits since the dips are prevented through prior dispersion compensation.
3Device complexity
If direct modulation scheme is used with semiconductor laser, then system size and cost are reduced, but modulation speed enhancement is difficult
Solution Approach 1:
The patent applies mechanics substitution by replacing the need for complex external modulation schemes with a direct modulation approach enhanced by digital signal processing. Instead of using complex optical modulators to achieve high speeds, the system uses electronic bit loading and dispersion compensation algorithms to overcome the limitations of direct modulation, substituting mechanical/optical complexity with electronic processing capabilities.
Data Source
AI summary
An optical reception apparatus may include a receiver, a monitor, and a controller. The optical reception apparatus receives multi-carrier modulated signal light modulated by a multi-carrier modulation scheme. The multi-carrier modulation scheme is available to allocate different transmission conditions for each of a plurality of subcarriers in accordance with transmission characteristics of the subcarriers. The receiver may receive from an optical transmission line a training signal light allocated with the same transmission conditions for each of the subcarriers. The monitor may monitor the transmission characteristics of the training signal light to detect a frequency at which a dip of the transmission characteristics occurs. The controller may control, based on the frequency detected by the monitor, a dispersion compensation for the multi-carrier modulated signal light having received a dispersion from the optical transmission line.