Electro-Optic Modulator Bias Control via Signal Correlation
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Solution Overview
Problem
Existing methods for controlling the bias of electro-optic modulators are costly and inefficient, especially for low modulation frequencies, and introduce signal distortions due to the use of dither signals.
Innovation Solution
A method that records and correlates modulation voltage and output power over time to determine the required bias adaptation without dithering, using low-pass filtering and reordering techniques to identify medium-term offsets, allowing for accurate bias control across various frequency ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If dither signals are applied to control the bias of the electro-optic modulator, then the bias control is achieved, but the signal quality decreases due to additional signal distortions and multiple electronic components are required increasing cost
Solution Approach 1:
The patent extracts and eliminates the dither signal from the system by using the existing modulation signal itself for bias control. The method correlates the modulation voltage with the output power to determine bias drift, removing the need for separate dither signals and their associated electronic components, thereby reducing signal distortions while maintaining bias control functionality
Solution Approach 2:
The patent makes the modulation signal serve multiple functions: it both modulates the optical carrier and provides the reference signal for bias control through correlation with output power. This multi-functionality eliminates the need for dedicated dither signals and simplifies the electronic component structure while maintaining effective bias control
2Reliability
If dither signals are applied to control the bias, then bias control is achieved, but the device complexity increases due to multiple electronic components
Solution Approach 1:
The patent removes the dither signal generation and processing electronics from the system by utilizing the existing modulation signal for bias control purposes, thereby reducing device complexity while maintaining bias control capability
Solution Approach 2:
The modulation signal is made to serve dual purposes: optical modulation and bias control reference. This eliminates the need for separate dither signal electronics, reducing device complexity without sacrificing bias control functionality
3Speed
If conventional bias control methods are used, then high-speed modulation bias control is achieved, but the method is not effective for low modulation frequencies where data average is not zero
Solution Approach 1:
The patent changes the approach from frequency-dependent dither signal methods to a correlation-based method that works across all frequency ranges. By correlating modulation voltage with output power and detecting the DC component, the system achieves bias control adaptability for both high-speed and low-frequency modulation signals regardless of their average values
4Reliability
If dither signals are applied for bias control, then bias drift compensation is achieved, but the quality of the outputted modulated signal decreases
Solution Approach 1:
The patent extracts the bias control function from the dither signal mechanism and implements it using the existing modulation signal through correlation analysis. This eliminates the harmful dither signal while preserving the essential bias stability function, thereby maintaining signal quality
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 eliminates the need for dithering, reduces costs, and minimizes signal distortions, enabling effective bias control for both high-frequency and low-frequency modulation signals, including those with non-zero average values.
Implementation Method 1
An electro-optic modulator is an optical device in which a signal-controlled element exhibiting an electro-optic effect is used to modulate a beam of light
Data Source
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AI summary
The present invention relates to a method for determining a required adaption of a bias of an electro-optic modulator, wherein the electro-optic modulator comprises an input waveguide that is split into two paths, wherein the two paths are then recombined into an output waveguide, and wherein the method comprises the steps of: - Recording a modulation voltage applied to the electro-optic modulator over a particular amount of time (2,11); - Recording a power at an output of the electro-optic modulator in response to the modulation voltage over the particular amount of time (3,12); - Correlating the recorded modulation voltage and the recorded power (4,13); and - Determining the required adaption of the bias based on the correlation between the recorded modulation voltage and the recorded power (5,14).