Double Cladding Crystal Fiber for High Power Laser Efficiency
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Solution Overview
Problem
Existing double-clad optical fibers suffer from reduced optical efficiency due to thermal loading, quenching, and light scattering when used in high power laser applications, particularly because of the use of bulk glass and nano-particles in the inner cladding, which absorb and scatter pumping light.
Innovation Solution
A double-cladding crystal fiber structure is developed using a YAG or sapphire crystal core with an inner and outer glass cladding, where the inner cladding is made of low refractive index glass to minimize light absorption and scattering, and the core is doped with transition metals and rare earth elements, fabricated using the Laser-Heated Pedestal Growth (LHPG) method with multiple-step diameter reduction to achieve a minimum core diameter of 20 μm, enhancing optical efficiency and beam quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a higher doping concentration is used in bulk crystal to improve pump absorption, then pump absorption efficiency is improved, but thermal loading, quenching, and energy transfer up-conversion increase causing optical efficiency degradation
Solution Approach 1:
The invention divides the gain medium into a distributed fiber structure rather than a single bulk crystal. The pump energy is distributed along the fiber length, allowing lower doping concentration while maintaining total pump absorption. This segmentation avoids the concentration of thermal and energy transfer effects in a single location, thereby reducing thermal loading and up-conversion losses.
Solution Approach 2:
The invention replaces the bulk crystal mechanical structure with an optical fiber waveguide structure. This substitution enables the pump light to be guided and distributed along the fiber length, improving pump absorption efficiency while maintaining low doping concentration to avoid thermal loading and up-conversion effects that plague bulk crystals.
2Loss of energy
If single-crystal fiber with small diameter is used to reduce volume and enhance optical efficiency, then optical efficiency is improved, but the fiber lacks cladding making it unsuitable for high power cladding-pumped configurations
Solution Approach 1:
The invention implements a nested structure where the single-crystal core fiber is placed inside a glass capillary tube that serves as the inner cladding. This nested configuration provides the required cladding structure for high power applications while preserving the small core diameter for high optical efficiency. The inner cladding is itself nested within an outer cladding structure.
Solution Approach 2:
The invention creates a composite structure combining a single-crystal core with glass cladding materials. The single-crystal core provides low loss and high optical efficiency, while the glass cladding (inner and outer) provides structural support and enables high power pump delivery. This composite approach integrates the advantages of both material systems.
3Device complexity
If inner cladding is made of crystal-glass mixture with nanoscale crystalline particles to achieve double cladding structure, then cladding structure is formed, but light scattering and absorption loss occur reducing optical efficiency
Solution Approach 1:
The invention extracts the harmful nanoscale crystalline particles from the inner cladding material and replaces them with homogeneous glass material. This extraction eliminates the light scattering and absorption losses caused by the particles while maintaining the cladding structure's ability to guide pump light. The inner cladding is made purely of glass, not a crystal-glass mixture.
4Volume of moving object
If core diameter is reduced to minimum to reduce volume, then volume is reduced and optical efficiency is enhanced, but manufacturing precision becomes more difficult to achieve
Solution Approach 1:
The invention uses preliminary action by first forming a larger diameter single-crystal rod using the LHPG method, then progressively reducing the diameter through controlled pulling and drawing processes. This stepwise diameter reduction allows precise control of the final core diameter while maintaining manufacturing feasibility. The preliminary formation of the crystal structure at larger size provides a foundation for subsequent precision reduction.
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 mitigates thermal issues and improves optical efficiency by reducing the core diameter and using glass claddings that do not absorb or scatter pumping light, making the fiber suitable for high power cladding-pumped configurations with reduced propagation loss and enhanced output beam quality.
Implementation Method 1
heating the glass capillary for inner cladding and the glass capillary for outer cladding by means of the LHPG method, in such a way that the glass capillary for inner cladding together with the glass capillary for outer cladding are softened and melted simultaneously
Implementation Method 2
the glass capillary for inner cladding together with the glass capillary for outer cladding are softened and melted simultaneously to collapse onto the circumference of the single crystal fiber
Implementation Method 3
growing the single crystal rod into a single crystal fiber having a predetermined diameter by means of the Laser-Heated Pedestal Growth (LHPG) method
Data Source
AI summary
The present invention relates to a manufacturing method of a double cladding crystal fiber, in which growing an YAG or a sapphire into a single crystal fiber by LHPG method, placing the single crystal fiber into a glass capillary for inner cladding, placing the single crystal fiber together with the glass capillary for inner cladding into a glass capillary for outer cladding in unison, heating the glass capillary for inner cladding and outer cladding by the LHPG method to attach to the outside of the single crystal fiber, and thus growing into a double cladding crystal fiber. When the present invention is applied to high power laser, by using the cladding pumping scheme, the high power pumping laser is coupled to the inner cladding layer, so the problems of heat dissipation and the efficiency impairment due to energy transfer up-conversion of high power laser are mitigated.