Multimode Fiber Combiner Cladding Mode Absorber
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Solution Overview
Problem
Ultra-high power multimode fiber laser systems face challenges in efficiently filtering out unwanted forward-propagating and backreflected cladding light, which leads to power losses and structural damage due to thermal loads and mechanical coupling issues during the fabrication and deployment of high-power combiners.
Innovation Solution
A multi-layer configuration for the fibers with an inner layer of silicone dioxide and an outer layer doped with fluorine ions, along with a cladding mode absorber with upstream, intermediary, and downstream zones, is used to minimize damage and remove unwanted light, employing polymers with specific refractive indices to manage light propagation and absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If multiple low-mode fiber laser systems are optically and mechanically coupled together in a LM-MM combiner to achieve high power levels, then the output power is improved, but structural defects and mechanical coupling issues occur during fabrication and deployment
Solution Approach 1:
The fiber structure is segmented into multiple functional layers: inner cladding, outer cladding, and protective coating layers. This segmentation allows each layer to address specific issues - the inner cladding guides light, the outer cladding protects against structural defects, and the coating layers provide mechanical protection during fabrication and deployment.
Solution Approach 2:
The patent employs composite fiber structures combining different materials with complementary properties. The multi-layer fiber design integrates materials with different thermal, mechanical, and optical properties to simultaneously achieve high power transmission and structural reliability during the combiner fabrication process.
2Power
If forward and backreflected light propagate through the fiber system at high power levels, then power transmission is achieved, but thermal loads damage the polymeric coating and fiber components
Solution Approach 1:
The patent introduces intermediary elements including heat sink structures and thermally conductive materials positioned between the fiber components and the environment. These intermediaries act as thermal buffers that conduct heat away from the polymeric coating and fiber components, preventing thermal damage while allowing high power transmission.
Solution Approach 2:
The patent converts the harmful thermal energy into a manageable form by implementing heat dissipation structures that transform the thermal load into controlled heat flow toward heat sinks. The backreflected light, which would normally cause damage, is redirected through optical elements that channel its energy into controlled thermal pathways that can be managed by the heat dissipation system.
3Ease of manufacture
If the combiner is fabricated by fusing and tapering aligned output fibers, then optical coupling is achieved, but structural defects and burrs affect beam quality and power output
Solution Approach 1:
The patent applies preliminary protective actions during the fabrication process by pre-coating the fiber surfaces with protective layers before fusion and tapering operations. These pre-applied coatings prevent the formation of structural defects and burrs during mechanical manipulation, ensuring that the subsequent optical coupling process does not compromise beam quality.
Solution Approach 2:
The patent modifies fabrication parameters including temperature profiles, fusion power levels, and tapering rates to minimize the formation of structural defects. By optimizing these parameters, the fabrication process achieves both good optical coupling and high manufacturing precision, producing burr-free interfaces that maintain beam quality.
4Loss of energy
If cladding light is not removed from the waveguide, then power losses occur and system components are damaged, but adding removal mechanisms increases device complexity
Solution Approach 1:
The patent merges the light removal function with the existing fiber structure by integrating absorptive materials into the cladding or coating layers. This consolidation eliminates the need for separate, complex light removal devices while simultaneously addressing power loss and component protection requirements through the unified multi-layer fiber design.
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 solution effectively reduces power losses and protects fiber components from thermal deformation, ensuring high-quality beam emission and reliable coupling of fibers, while efficiently managing unwanted light and heat-induced damage.
Implementation Method 1
The outer layer is made from SiO2 doped with ions of fluorine ("F") and having a relatively low melting temperature
Implementation Method 2
The absorber is configured with upstream, intermediary and downstream consecutive zones responsible for removing unwanted light
Implementation Method 3
employing polymers with specific refractive indices to manage light propagation and absorption
Data Source
Figure 1~3
AI summary
An ultra-high power fiber laser system includes a multimode combiner which is configured with a plurality of low mode fibers bundled together and tapering toward its downstream end. The system further includes a clad mode absorber extending along the tapered downstream end of the combiner and extending over a portion of the combiner's output fiber. The absorber is configured with sequentially located zones which are provided with respective refractive indices. In a forward propagating direction of light signal, the upstream zone includes polymeric material with the refractive index higher than that of the cladding of the combiner end fiber. This zone is configured to remove the back reflected core guided light bled into the cladding of the combiner through a splice between combiner end and output fibers. The intermediate zone includes polymeric material configured with a refractive index lower than that of the cladding of the combiner output fiber so it can prevent clad guided signal light from decoupling the cladding under the material. The downstream zone is configured with, polymeric material having a refractive index lower than that of the cladding of the combiner output fiber. The polymeric material of the downstream zone is impregnated with a plurality of light diffusers scattering high numerical aperture rays of the clad-guided signal light.