Optical Transmission Device Phase Bias Control
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Solution Overview
Problem
In optical transmitters with quadrature optical modulators, temporal discontinuity in synchronous detection results can lead to incorrect phase bias control, deteriorating the output signal.
Innovation Solution
An optical transmission device is configured with a quadrature optical modulator, a light intensity detector, a synchronous detection circuit, and a bias signal generator that monitors amplitude changes in the modulation signal, generating a bias signal based on synchronous detection signals to maintain phase bias when changes exceed a threshold, preventing signal deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the control unit controls phase bias based on synchronous detection results, then phase bias control is achieved, but signal deterioration occurs when synchronous detection becomes temporally discontinuous
Solution Approach 1:
The bias signal generator stores past bias signals in a buffer before modulation format changes occur. When discontinuity is detected, the system retrieves and restores the appropriate stored bias signal in advance, preventing signal deterioration before it can occur. This preliminary preparation of backup bias signals resolves the contradiction between maintaining phase bias control and ensuring signal quality during transient disruptions.
Solution Approach 2:
The system prepares multiple stored bias signals in advance to cushion against future discontinuities. By having pre-stored bias signals ready in the buffer, the system creates a protective cushion that prevents signal deterioration when synchronous detection becomes temporally discontinuous, thus maintaining both phase bias control capability and signal quality.
2Stability of the object's composition
If the bias signal is updated continuously based on synchronous detection, then phase bias is maintained, but incorrect phase bias control occurs when modulation format changes
Solution Approach 1:
The bias signal generator continuously monitors the modulation signal and compares current characteristics with stored reference information. When changes exceeding a threshold are detected (indicating modulation format changes), the feedback mechanism triggers switching to stored bias signals. This feedback loop resolves the contradiction by maintaining phase bias stability through continuous monitoring while preventing incorrect phase bias control through intelligent selection based on modulation format detection.
Solution Approach 2:
The system changes the parameter of bias signal selection based on detected modulation format characteristics. When modulation format changes are detected through parameter comparison, the system switches from using current synchronous detection results to using pre-stored bias signals with different characteristics. This parameter change strategy resolves the contradiction between maintaining phase bias stability and ensuring phase bias accuracy under varying modulation conditions.
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 device effectively suppresses signal deterioration by maintaining appropriate phase bias even when synchronous detection becomes temporally discontinuous, ensuring stable output.
Implementation Method 1
a light intensity detector to detect light intensity of modulated light output from the quadrature optical modulator
Implementation Method 2
a synchronous detection circuit to perform synchronous detection of a light intensity signal indicating light intensity detected by the light intensity detector and a dither signal, and output a synchronous detection signal indicating a result of the synchronous detection
Data Source
AI summary
An optical transmission device includes: an IQ optical modulator to modulate incident light with a modulation signal, and adjust a phase of the modulated light with a phase bias, or adjust a phase of the incident light with the phase bias, and modulate the phase adjusted light with the modulation signal, a light intensity detector to detect light intensity of modulated light, a synchronous detection circuit to synchronously detect a light intensity signal and a dither signal, and a bias signal generating unit to monitor a change in amplitude of the modulation signal, generate the bias signal according to the synchronous detection signal when a range of the change is equal to or less than a first threshold, and generate a bias signal maintaining a phase bias before the range of the change becomes larger than the first threshold as the bias signal.