Water-Cooled Optical Fiber Head Packaging With Dry Ferrule Seal
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Solution Overview
Problem
High-power fiber lasers face reliability issues due to degradation of low refractive index coatings in dual acrylate coated optical fibers when exposed to temperature and humidity, leading to increased attenuation and potential damage from residual pump power and amplified spontaneous emission, especially when delivering laser light to free space.
Innovation Solution
A water-cooled packaging scheme for the optical fiber head that includes a front and rear optical end cap, a glass ferrule, and a housing, where the delivery optical fiber's cladding is exposed but not immersed in cooling water, using a glass ferrule to prevent water ingress and a conical surface to avoid optical loss, with bonding agents and heat-treated components to ensure long-term reliability and beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the delivery optical fiber is immersed in cooling water to manage heat, then heat dispersion is improved, but the reliability and optical performance deteriorate due to water ingress causing OH ingression and coating degradation
Solution Approach 1:
The optical fiber is divided into two distinct sections: a water-cooled section for heat management and a dry section for reliability. The water-cooled section allows effective thermal management, while the dry section prevents water ingress and its associated degradation mechanisms, thus resolving the contradiction between heat dispersion and reliability.
Solution Approach 2:
A sealed ferrule or hermetic seal acts as an intermediary component between the water-cooled section and the dry section. This intermediary prevents water from reaching the optical fiber core and coating while allowing heat to be dissipated from the water-cooled section, thereby maintaining both thermal management and reliability.
2Temperature
If the low refractive index coating is exposed to temperature and humidity for cooling, then heat dispersion is improved, but the optical performance deteriorates due to coating degradation and increased attenuation
Solution Approach 1:
The optical fiber is segmented into a water-cooled section where thermal management occurs and a protected section where the low refractive index coating is shielded from environmental degradation. This segmentation allows heat dispersion without exposing the coating to harmful temperature and humidity conditions that cause attenuation.
Solution Approach 2:
A hermetic seal or sealed ferrule serves as an intermediary barrier that prevents moisture and temperature extremes from reaching the low refractive index coating, while still allowing the water-cooled section to effectively manage thermal load. This protects the coating from degradation and maintains optical performance.
3Illumination intensity
If the optical fiber cladding is exposed to remove residual pump power, then laser beam quality is improved, but the reliability deteriorates when water contacts the exposed cladding
Solution Approach 1:
The optical fiber structure is segmented into a water-cooled section with exposed cladding for effective removal of residual pump power and improved beam quality, and a separate protected section where the cladding is shielded from water contact. This segmentation maintains laser beam quality while preventing water-related reliability issues.
Solution Approach 2:
A hermetic seal or sealed ferrule acts as an intermediary that isolates the exposed cladding section from water contact. This allows the exposed cladding to effectively remove residual pump power and maintain beam quality without exposing the fiber to water ingress that would compromise reliability.
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 solution maintains long-term reliability and beam quality by preventing water ingress and thermal damage, reducing power density, and effectively managing heat dispersion, thus ensuring stable high-power laser delivery to free space without accumulating heat or causing damage.
Implementation Method 1
The rear optical end cap is a coreless piece of optical fiber configured to expand a beam size of the laser light delivered by the section of the delivery optical fiber with the cladding exposed, thereby reducing power density not exceeding a damage threshold
Implementation Method 2
The glass ferrule is connected and sealed between the front optical end cap and the rear optical end cap. The glass ferrule is configured to keep cooling water from immersing the section of the delivery optical fiber with the cladding exposed, thereby maintaining long-term reliability thereof
Implementation Method 3
a water-cooled cavity enclosed by the front optical end cap, the rear optical end cap, the glass ferrule, and the inner wall is formed with cooling water accommodated inside the water-cooled cavity, facilitating thermal dispersion
Implementation Method 4
The second end face is fusion-spiced with a section of the delivery optical fiber with a cladding exposed
Data Source
AI summary
A water-cooled package of an optical fiber head comprising a delivery optical fiber (DOF), a front optical end cap (OEC), a rear OEC, a glass ferrule, and a housing operates for delivering the laser light from DOF to free space. The rear OEC is fusion-spiced with a section of DOF with a cladding exposed whereas the section of DOF is enclosed in a bore of the glass ferrule. When the glass ferrule is connected and sealed between the front OEC and the rear OEC, cooling water in the water-cooled package is prevented from immersing the section of DOF to maintain reliability of DOF. It is, therefore, not needed to bond the section of DOF in a bore of the front OEC to be waterproof, minimizing varying stress-induced speckle patterns and ultimately maintaining beam quality of the laser light exiting from DOF to free space.