Optical Transmitter Bias Control Without Dither Signals
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Solution Overview
Problem
Existing optical transmitters using low frequency dither signals for automatic bias control in optical modulators result in signal quality deterioration due to voltage amplitude changes, and the modulator structures are complex with the need for photodetectors in multiple modulation regions.
Innovation Solution
An optical transmitter design that includes a light source, splitter, multiple optical modulators, and a coupler, with a controller adjusting bias voltages based on a coupled optical signal, allowing for automatic bias control without dither signals and simplifying the configuration by eliminating the need for photodetectors in each modulator.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If low frequency dither signal is used for automatic bias control, then operation point fluctuation is suppressed, but signal quality is deteriorated due to voltage amplitude changes
Solution Approach 1:
The patent extracts and eliminates the dither signal from the system, replacing it with a direct bias voltage control mechanism. By removing the dither signal component, the patent achieves automatic bias control without the harmful voltage amplitude changes that deteriorate signal quality, while still maintaining operation point stability through alternative bias adjustment methods.
Solution Approach 2:
The patent changes the control parameter from dither signal amplitude to direct bias voltage levels. Instead of using varying amplitude dither signals to control operation points, the system uses adjusted bias voltages that directly set the operating points, thereby achieving the same control effect without introducing the harmful voltage fluctuations that degrade signal quality.
2Reliability
If photodetectors are arranged for all modulation regions, then automatic bias control is achieved, but device complexity increases
Solution Approach 1:
The patent makes the bias control mechanism universal by using a single photodetector that can detect optical signals from multiple modulation regions. This single photodetector serves the function of monitoring multiple regions simultaneously, eliminating the need for separate photodetectors in each modulation region while maintaining automatic bias control capability.
Solution Approach 2:
The patent merges the functions of multiple photodetectors into a single photodetector that can monitor multiple modulation regions. By combining the detection functions, the system achieves the same automatic bias control with fewer components, thereby reducing device complexity while maintaining the required reliability.
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
Enables automatic bias control of optical modulators with improved signal quality by adjusting bias voltages based on coupled optical signals, maintaining signal integrity without the complexity of dither signals and photodetector arrangements.
Implementation Method 1
a light source configured to output light
Implementation Method 2
an optical modulator configured to modulate the branched light based on a drive voltage
Implementation Method 3
a coupler configured to couple the modulated optical signal and output a coupled optical signal
Data Source
AI summary
It is difficult to carry out automatic bias control to an optical modulator without a dither signal with a simple configuration, therefore, an optical transmitter comprising the controller configured to adjust an adjusted bias voltage based on the coupled optical signal, the adjusted bias voltage being one of a first bias voltage applied to the first optical modulator, a second bias voltage applied to the second optical modulator and a third bias voltage applied to the third optical modulator and maintain a value of bias voltages other than the adjusted voltage in the first bias voltage, the second bias voltage and the third voltage.