Optical Modulator Drive Signal Compensation via Spectrum Feedback
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Solution Overview
Problem
Existing optical communication systems face quality deterioration in signal light due to changes in drive signal characteristics applied to optical modulators, which are not effectively addressed by current technologies.
Innovation Solution
An optical transmission apparatus comprising an optical modulator, a detector, and a controller, where the detector monitors changes in the spectrum of output light and the controller adjusts digital signal processing to prevent quality deterioration by notifying external apparatus of band changes exceeding a predetermined threshold.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If digital signal processing is applied to generate signals with various formats (dispersion pre-equalization, Nyquist, QAM), then transmission distance and capacity are expanded, but the optical modulator operates in a linear region making it sensitive to drive signal characteristic changes which deteriorate signal light quality
Solution Approach 1:
The patent implements a feedback mechanism where a detector measures the actual drive signal characteristics (amplitude, waveform) and feeds this information back to a controller. The controller then adjusts the digital signal processing parameters to compensate for deviations, ensuring the optical modulator receives the correct drive signal regardless of the modulation format being used. This closed-loop control maintains signal light quality while preserving flexibility in modulation format selection.
Solution Approach 2:
The patent dynamically adjusts digital signal processing parameters based on detected drive signal characteristics. When the detector identifies deviations in drive signal amplitude or waveform, the controller modifies parameters such as drive signal amplitude, waveform shape, or modulation depth to compensate for the linear region sensitivity. This parameter adjustment maintains optimal modulator operation across different modulation formats.
2Productivity
If the optical modulator is driven by a drive signal with amplitude smaller than 2×Vn to enable various modulation formats, then transmission capacity is improved, but characteristics of modulated signal light change when drive signal characteristics change
Solution Approach 1:
The feedback mechanism continuously monitors drive signal characteristics and adjusts digital signal processing parameters to maintain stable modulated signal light characteristics. The detector measures actual drive signal amplitude and waveform, and the controller compensates for variations by adjusting modulation parameters, ensuring consistent signal output despite operating in the linear region with reduced drive amplitude.
Solution Approach 2:
The system dynamically changes digital signal processing parameters to compensate for drive signal variations. When drive signal amplitude or waveform deviates from optimal values, the controller adjusts parameters such as modulation index, signal level, or waveform characteristics to maintain stable modulated signal output, enabling high-capacity transmission without sacrificing signal stability.
3Reliability
If the optical modulator and driver are operated in a saturated region with drive signal amplitude of 2×Vn, then stable transmission light is obtained, but transmission distance and capacity are limited
Solution Approach 1:
The patent changes the operating parameters of the optical modulator from saturated region operation (2×Vn amplitude) to linear region operation with reduced amplitude. This parameter change enables various high-capacity modulation formats (QAM, Nyquist) while the feedback control mechanism compensates for the loss of inherent stability, achieving both high transmission capacity and acceptable signal stability through active parameter adjustment.
Data Source
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AI summary
An optical transmission apparatus includes an optical modulator that is driven by a drive signal generated from an electrical signal obtained by performing a digital signal processing on a data signal, a detector configured to detect a change in a spectrum of output light of the optical modulator, and a controller configured to control the digital signal processing based on a detection result of the detector.