LED Curing Optical Fiber Coatings at High Draw Speeds
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Solution Overview
Problem
Current methods for curing coatings on optical fibers using ultraviolet (UV) curable acrylate polymers with mercury discharge lamps are inefficient, particularly at high draw speeds, as they emit a broad spectrum of light and have low efficiency.
Innovation Solution
An optical fiber draw system employing light-emitting diodes (LEDs) to cure coatings at specific wavelengths, with a first and second photoinitiator-absorbing wavelengths for sequential curing of coating compositions, allowing for high-speed fiber drawing and improved curing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If mercury discharge lamps are used to cure coatings, then the coatings can be cured with a broad spectrum of ultraviolet light, but the curing efficiency is low and the process is not suitable for high speed draw
Solution Approach 1:
The patent changes the wavelength parameter of the curing light from broad spectrum UV to specific narrow bandwidth wavelengths (e.g., 365nm, 385nm, 405nm) using LEDs. This parameter change enables high-speed draw by providing concentrated energy at specific wavelengths that match photoinitiator absorption peaks, dramatically improving curing efficiency while maintaining broad spectrum coverage through multiple LED types.
Solution Approach 2:
The patent uses composite coating formulations containing multiple photoinitiators that absorb at different wavelengths (e.g., Type I photoinitiators absorbing at 365nm and Type II photoinitiators absorbing at 395nm). This composite approach allows the coating to be cured by multiple LED wavelengths simultaneously, achieving complete cure at high draw speeds while maintaining the benefits of both narrow and broad spectrum curing.
2Loss of energy
If a single wavelength LED is used for curing, then the curing efficiency at that specific wavelength is high, but the degree of cure is insufficient compared to broad spectrum UV
Solution Approach 1:
The patent merges multiple LED light sources emitting at different wavelengths (e.g., 365nm, 385nm, 405nm) into a single curing assembly. This combination provides both the high curing efficiency of narrow bandwidth LEDs at each wavelength and the comprehensive degree of cure equivalent to broad spectrum UV, as multiple photoinitiators in the coating absorb at different wavelengths and initiate polymerization throughout the coating thickness.
Solution Approach 2:
The patent segments the curing process into multiple wavelength zones, with different LED types targeting different photoinitiators in the coating. This segmentation allows each LED wavelength to optimize its curing efficiency at its peak absorption wavelength while the collective effect of all wavelengths achieves complete cure, resolving the contradiction between efficiency and degree of cure.
3Productivity
If high draw speed is used, then the productivity increases, but the curing degree of the coating decreases due to reduced exposure time
Solution Approach 1:
The patent implements continuous curing action by using multiple LED arrays arranged along the draw path, ensuring that the coating receives curing radiation continuously as it passes through the assembly. This continuous exposure compensates for the reduced residence time at high draw speeds, maintaining high degree of cure while enabling productivity increases through sustained polymerization throughout the coating thickness.
Solution Approach 2:
The patent changes the intensity parameter of the curing light by using high-power LEDs with optimized emission profiles. The increased photon flux density compensates for the reduced exposure time at high draw speeds, maintaining sufficient energy delivery to achieve complete cure even when the coating passes through the curing zone more quickly.
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
The system achieves a significant increase in the degree of cure of the primary coating composition by 15-50% in subsequent curing assemblies, resulting in a higher overall degree of cure of the optical fiber coatings, enhancing their mechanical and thermal properties.
Implementation Method 1
the first coating composition comprises a first photoinitiator, the first photoinitiator absorbing at a first wavelength
Implementation Method 2
the first photoinitiator absorbing at a first wavelength
Implementation Method 3
a first plurality of light sources comprising light-emitting diodes, the first plurality of light sources emitting at the first wavelength
Data Source
AI summary
An optical fiber draw system and method of coating an optical fiber. The system includes a furnace for heating an optical fiber preform, a draw assembly for drawing the optical fiber at a draw speed greater than 50 meters per second, a first coating applicator for applying a first coating onto the fiber, and a first curing assembly comprising a first plurality of light sources comprising light-emitting diodes for partially curing the first coating. The optical fiber draw system also includes a second coating applicator for applying a second coating onto the fiber on top of the first coating, and a second curing system comprising a second plurality of light sources for curing the second coating, wherein the first coating is further cured in the range of 15-50 percent after leaving the first curing assembly.