Mach-Zehnder Modulator Bias Stabilization via PRBS
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Solution Overview
Problem
The operating point of Mach-Zehnder optical modulators in optical transmission systems fluctuates due to temperature changes and aging, leading to inter-symbol interference, and existing compensation methods are costly and inefficient, especially at high speeds like 43 Gbps.
Innovation Solution
The use of a Pseudorandom Binary Sequence (PRBS) or supervision code sequence for duobinary modulation, with low-frequency signals to stabilize the operating point of the Mach-Zehnder modulator, reducing inter-symbol interference and spectral width, and allowing for stable operation without expensive high-frequency components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional feedback compensation methods are used to stabilize the operating point, then the operating point stability is improved, but the device complexity and cost increase due to requiring expensive high-frequency components and complex feedback circuits
Solution Approach 1:
The patent extracts and eliminates the complex feedback compensation circuitry and high-frequency components from the system. Instead of using conventional feedback methods that require expensive components, the invention uses a simple DC bias voltage applied to theMZ modulator to stabilize the operating point, thereby removing the need for complex feedback mechanisms while maintaining stability.
Solution Approach 2:
The patent replaces expensive high-frequency components and complex feedback circuits with a simple, low-cost DC bias voltage approach. This substitution uses inexpensive components (ordinary components as mentioned in the patent) to achieve the same stabilization function, significantly reducing system cost and complexity.
2Stability of the object's composition
If dithering voltage is applied to compensate for operating point drift, then the operating point stability is improved, but the spectral width increases and chromatic dispersion tolerance decreases
Solution Approach 1:
The patent converts the harmful effect of operating point drift into a beneficial situation by using a simple DC bias voltage that stabilizes the operating point without introducing the spectral broadening associated with dithering voltage. This approach eliminates the trade-off between stability and dispersion tolerance by using a method that provides stability without the harmful spectral effects.
3Productivity
If manual adjustment of bias voltage is performed to optimize the operating point, then the spectral efficiency is improved, but the time consumption and operational complexity increase
Solution Approach 1:
The patent implements self-service by applying a fixed DC bias voltage that automatically stabilizes the operating point without requiring manual adjustment or optimization. The system maintains optimal performance autonomously, eliminating the time-consuming manual adjustment process while preserving spectral efficiency through the stabilized operating point.
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
This approach effectively stabilizes the operating point of the optical modulator, reducing inter-symbol interference and doubling tolerance to chromatic dispersion, while maintaining high spectral efficiency and reducing costs by using conventional components.
Implementation Method 1
a MZ-type modulator 2 and optical fibers 3. The MZ-type modulator 2 includes on an LiNb03 substrate, an input optical waveguide 2a formed on the substrate for introducing light from the laser diode 1, branching optical waveguides 2b, 2c and an output optical waveguide 2d formed on the substrate for outputting modulated light; two signal electrodes 2e, 2f formed on the substrate for applying phase modulation to the optical signals in the branching optical waveguides 2b, 2c
Data Source
Figure 1~2
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Figure 4
AI summary
The invention relates to an optical modulation apparatus and to a method of controlling an optical modulator, wherein even if the operating point of an optical modulator the optical output of which varies periodically with respect to a driving voltage fluctuates owing to a change in ambient temperature or aging, the fluctuation in operating point can be compensated for in stable fashion.