Optical Fiber Coupling via Modal Decomposition Alignment
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Solution Overview
Problem
The existing methods for optically coupling single-mode and multimode fibers, particularly in center launch configurations, are complex due to the need to precisely align and match mode field diameters, and measuring the quality of coupling is challenging as it involves controlling multiple parameters simultaneously.
Innovation Solution
A method and equipment that modally decompose light radiation to isolate and optimize the contribution of secondary modes, allowing for simplified and faster alignment and fixing of fibers by adjusting the relative position and size of the fundamental mode to maximize optical power transfer, while using modal decomposition devices to measure and adjust the optical power in specific groups of secondary modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If precise transverse and angular alignment of optical axes is performed, then optical coupling quality is improved, but alignment time and complexity increase
Solution Approach 1:
The patent segments the alignment optimization process into two distinct phases: first optimizing transverse position to maximize fundamental mode coupling, then optimizing angular orientation to minimize secondary mode excitation. This segmentation allows each parameter to be optimized independently and sequentially, reducing the overall complexity and time required compared to simultaneous multi-parameter optimization.
Solution Approach 2:
The patent applies preliminary action by first establishing optimal transverse alignment before addressing angular alignment. By pre-positioning the fibers at their optimal transverse separation distance, the subsequent angular optimization becomes simpler and faster, as the system already operates near the optimal coupling condition.
2Reliability
If mode field diameter matching is performed, then optical coupling efficiency is improved, but process complexity increases
Solution Approach 1:
The patent replaces mechanical adjustment of mode field diameters (such as physical tapering or lens systems) with an optical measurement-based approach. By using secondary mode excitation as an indicator of mode field mismatch and optimizing angular alignment to minimize this excitation, the method achieves mode field matching without complex mechanical intervention.
3Measurement precision
If multiple parameters are controlled simultaneously to maximize transmitted power, then coupling quality is improved, but adjustment complexity and time increase
Solution Approach 1:
The patent divides the multi-parameter optimization into sequential steps: first optimizing transverse position using fundamental mode coupling measurement, then optimizing angular orientation using secondary mode excitation measurement. This segmentation transforms a complex simultaneous multi-parameter problem into two simpler sequential optimizations.
Solution Approach 2:
The patent uses secondary mode excitation as an intermediary indicator to assess angular alignment quality. Instead of directly measuring and optimizing multiple parameters simultaneously, the method uses the secondary mode power level as a proxy metric that simplifies the optimization process while still achieving high coupling quality.
4Reliability
If conventional alignment methods are used, then optical coupling is achieved, but measurement of coupling quality becomes difficult
Solution Approach 1:
The patent introduces secondary mode excitation as an intermediary measurement that provides direct feedback on angular alignment quality. By measuring the power in secondary modes, the system obtains a clear quantitative indicator of alignment precision without requiring complex measurement systems.
Solution Approach 2:
The patent uses the distribution of optical power across different modes (analogous to color distribution in spectroscopy) as a diagnostic tool. By analyzing how optical power is distributed between fundamental and secondary modes, the system can precisely measure and optimize coupling quality through modal decomposition measurements.
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 simplifies the optical coupling process by isolating misalignment and mode size correspondence issues, enabling faster and more precise alignment and fixing of fibers, ensuring high-quality optical coupling by optimizing the optical power transfer in both the fundamental and secondary modes.
Implementation Method 1
a single-mode optical fiber propagating light radiation that consists of a fundamental mode to a multimode fiber propagating light radiation that comprises a fundamental mode and a plurality of secondary modes
Implementation Method 2
modally decomposing the light radiation collected at the injection end of the multimode fiber and measuring a quantity representative of the optical power present in a first group of secondary modes
Data Source
AI summary
A method for fixing a single-mode fiber to a multimode fiber comprises the following steps: injecting light radiation into the injection end of the single-mode fiber and positioning the junction ends of the single-mode fiber and of the multimode fiber relative to one another so as to propagate at least part of the light radiation in the multimode fiber; modally decomposing the light radiation collected at the injection end of the multimode fiber and measuring a quantity representative of the optical power present in a first group of secondary modes; and adjusting the relative position of the junction ends and freezing them with respect to one another in a determined relative coupling position. Coupling equipment for carrying out the fixing method is also disclosed.