3D IQ Modulator Bias Sweep for Fast Global Calibration
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Solution Overview
Problem
Existing coherent optical modems face challenges in accurately and efficiently reconfiguring IQ modulators for optimal performance due to miniaturized modulators with nonlinear phase tuning characteristics and limited phase adjustment range, necessitating a speedy and thorough method to find global optimum bias sets in a three-dimensional control space.
Innovation Solution
Implementing a three-dimensional sweep using a digital bias digital-to-analog converter (DAC) with a sine-wave dither function to map out the IQ modulator's optimum bias points and power capability, applying time-varying bias signals to a quad-parallel Mach-Zehnder (QPMZ) modulator, and utilizing a modulator bias controller for fast and thorough calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional biasing methods are used for IQ modulator calibration, then the modulator can be configured, but the process is time-consuming and fails to achieve global optimum in three-dimensional control space
Solution Approach 1:
The patent applies three-dimensional sweeps across I, Q, and outer modulator bias inputs simultaneously, moving from traditional one-dimensional or two-dimensional calibration methods. This dimensional expansion enables comprehensive mapping of the entire bias space to identify global optimum points while maintaining calibration speed through efficient signal processing.
Solution Approach 2:
The patent uses periodic sine-wave dither signals applied to bias inputs to systematically explore the bias space. By modulating bias inputs with known periodic signals and analyzing the modulator output, the system efficiently maps the three-dimensional control space and identifies optimal bias points without exhaustive scanning.
2Speed
If miniaturized high speed modulators are used, then data transmission speed increases, but phase adjustment range is limited and nonlinear phase tuning characteristics occur
Solution Approach 1:
The patent changes the approach from directly adjusting phase bias to systematically sweeping through multiple bias parameters (I, Q, and outer modulator inputs) and identifying optimal operating points. This parameter space exploration allows miniaturized modulators to achieve their full performance potential despite limited inherent phase adjustment range and nonlinear characteristics.
3Reliability
If comprehensive calibration is performed to find global optimum bias sets, then transmission performance improves, but calibration time increases
Solution Approach 1:
The patent implements feedback by analyzing the modulator output signals during the three-dimensional sweep and using this information to identify optimal bias points. The system continuously monitors output power and constellation quality, feeding this information back to determine the global optimum bias configuration, thereby achieving comprehensive calibration efficiently.
Solution Approach 2:
The patent performs preliminary three-dimensional mapping of the bias space to identify regions containing optimal bias points before final configuration. By pre-characterizing the modulator's response across the entire bias range and storing this information, the system enables rapid reconfiguration without repeating exhaustive sweeps, reducing calibration time for subsequent adjustments.
Data Source
AI summary
Aspects of the subject disclosure may include, for example, applying a plurality of time-varying bias signals to bias inputs of a quad-parallel Mach-Zehnder (QPMZ) modulator, receiving output signals of the QPMZ modulator, wherein the output signals are produced by the QPMZ modulator responsive to the plurality of time-varying bias signals, and determining a biasing map, optical loss, and optical characteristics including extinction ratio and crosstalk for the QPMZ modulator based on the output signals of the QPMZ modulator. Other embodiments are disclosed.