Eccentric Polarization Maintaining Fiber Fixing Structure
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Solution Overview
Problem
The existing optical fiber fixing structures for semiconductor laser modules using polarization maintaining optical fibers face issues with stress application, which deteriorates the polarization extinction ratio due to thermal expansion coefficient mismatches and improper alignment, leading to birefringence sensitivity and polarization plane maintenance failures.
Innovation Solution
An optical fiber fixing structure with a cylindrical member and a polarization maintaining optical fiber, where the fiber's center is eccentric to the hole's center by an angle of −22.5° to 22.5° or 67.5° to 112.5°, utilizing low melting point glass to fix the fiber and reduce stress-induced deterioration, thereby improving polarization maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the optical fiber is fixed at the center of the hole in the metal pipe, then the alignment is simple and manufacturing is easier, but stress is applied on the optical fiber due to thermal expansion coefficient mismatch, deteriorating the polarization extinction ratio
Solution Approach 1:
The patent applies asymmetry by intentionally positioning the optical fiber eccentrically (off-center) within the metal pipe hole rather than at the center. This asymmetric arrangement creates a specific stress distribution pattern that actually improves polarization extinction ratio by reducing harmful stress on the fiber, while the eccentricity amount is controlled within a specific range to maintain manufacturing feasibility.
Solution Approach 2:
The patent changes the positional parameter of the optical fiber from centered to eccentric positioning. By adjusting the eccentricity amount to a specific range (0.01mm to 0.05mm), the stress distribution on the fiber is optimized, thereby improving the polarization extinction ratio while maintaining practical manufacturability.
2Reliability
If the optical fiber is positioned eccentrically to reduce stress, then the polarization extinction ratio is improved, but the alignment precision and manufacturing difficulty increase
Solution Approach 1:
The patent transforms the alignment from a binary centered/not-centered state to a controlled eccentric position within a specific parameter range (0.01mm to 0.05mm eccentricity). This parameter-based approach allows optimization of polarization extinction ratio while keeping the manufacturing precision requirement within achievable limits through precise control of the eccentricity amount.
Solution Approach 2:
The patent introduces an intermediary element (adhesive or fixing material) that facilitates the eccentric positioning of the optical fiber. This intermediary allows the fiber to be held at the desired eccentric position without requiring extremely precise mechanical alignment features, thereby reducing manufacturing difficulty while maintaining the beneficial stress distribution.
3Reliability
If the optical fiber is fixed with adhesive material, then hermetic sealing is achieved, but thermal expansion stress is applied on the fiber due to coefficient mismatch between metal pipe, adhesive, and fiber
Solution Approach 1:
The patent uses asymmetric (eccentric) fiber positioning to create a stress distribution pattern that compensates for the thermal expansion stress from the adhesive. The eccentric position allows the fiber to be located where the net stress (combining adhesive stress and thermal expansion stress) is minimized, thereby protecting the fiber while maintaining hermetic sealing.
Solution Approach 2:
The patent converts the harmful thermal expansion stress from the adhesive and metal pipe into a beneficial effect by strategically positioning the fiber eccentrically. The stress distribution created by eccentric positioning causes the thermal expansion forces to act in a manner that actually reduces the net stress on the fiber, transforming a harmful factor into a beneficial one.
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 configuration effectively suppresses the deterioration of the polarization extinction ratio, ensuring reliable polarization maintenance and hermetic sealing, even when the fiber is offset from the center, without requiring complex alignment techniques.
Implementation Method 1
The metal pipe and the optical fiber are fixed with an adhesive such as low melting point glass and hermetically sealed
Implementation Method 2
the polarization maintaining optical fiber has a core and a cladding that is formed on the outer periphery of the core and includes a pair of stress imparting parts arranged in lateral regions to the core. In this polarization maintaining optical fiber, the stress imparting parts impart stress to the core, and a birefringence phenomenon due to stress is used to maintain a polarization plane
Implementation Method 3
the thermal expansion coefficients of the metal pipe and the low melting point glass are larger than that of the optical fiber. Thus, stress is applied on the optical fiber
Data Source
AI summary
An optical fiber fixing structure includes: a cylindrical member; an optical fiber inserted into a hole of the cylindrical member; and a fixing material configured to fix the cylindrical member and the optical fiber, wherein the optical fiber is a polarization maintaining optical fiber having a polarization axis, and a center of the optical fiber is arranged so as to be eccentric to a center of the hole, and an angle formed by an eccentric direction connecting the center of the hole and the center of the optical fiber and the polarization axis is −22.5° to 22.5°, or 67.5° to 112.5°.