Tapered Active Optical Fiber for Pump Absorption
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Solution Overview
Problem
Existing double clad active optical fibers face limitations in pump power absorption, leading to restricted power scaling capability and inefficient light amplification due to non-uniform population inversion and modal spectrum changes during propagation.
Innovation Solution
A tapered active optical fiber structure with a core and inner cladding layers, where the outer cladding has a smaller refractive index, and a method for fabricating this structure by altering parameters during fiber drawing, such as preform speed and temperature, to create a continuous mode conversion process along the fiber length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a double clad active optical fiber with uniform cross-section is used, then the fiber structure is simple and easy to manufacture, but the pump absorption is limited and power scaling capability is restricted
Solution Approach 1:
The patent applies the dynamics principle by transforming the static uniform fiber structure into a dynamic tapered structure where the core and cladding dimensions vary continuously along the fiber length. This gradual change in geometry enables continuous mode conversion, allowing pump radiation to transition from higher-order modes to fundamental modes that are more effectively absorbed by the doped core, thereby significantly improving pump power absorption while maintaining manufacturing feasibility through controlled drawing processes
Solution Approach 2:
The patent employs parameter changes by systematically varying the physical dimensions of the fiber structure - specifically the core diameter and cladding diameter - as a function of position along the fiber. This continuous parameter change creates the tapered profile that enables mode coupling and enhances pump absorption, while the parameters are controlled within manufacturable ranges to maintain ease of production
2Power
If the core diameter is increased to accommodate higher power, then the power handling capability improves, but the fundamental mode propagation requirement is violated and modal spectrum becomes unstable
Solution Approach 1:
The tapered structure creates a dynamic transition zone where the fiber dimensions change gradually along the length. This dynamic geometry enables continuous mode conversion, allowing the fiber to support higher power through larger effective area while maintaining fundamental mode propagation at the output end. The gradual dimensional change stabilizes the modal spectrum by providing a controlled transformation path rather than abrupt mode changes
Solution Approach 2:
The fiber is effectively segmented into different functional zones along its length - the input end with larger dimensions for high power acceptance and mode mixing, the transition zone for continuous mode conversion, and the output end with smaller dimensions for fundamental mode propagation. This spatial segmentation allows each section to optimize for its specific function while maintaining overall system stability
3Power
If pump radiation is launched into the fiber, then light amplification occurs, but non-uniform population inversion develops along the fiber length causing deterioration in pump conversion efficiency
Solution Approach 1:
The tapered structure creates a dynamic interaction between pump radiation and the doped core along the fiber length. As the fiber dimensions change gradually, pump modes continuously convert between different mode orders, increasing the interaction length and uniformity of pump absorption. This dynamic mode mixing ensures more uniform population inversion along the fiber, improving pump conversion efficiency while maintaining high light amplification
Solution Approach 2:
The continuous tapered profile ensures that the mode conversion process occurs continuously along the entire length of the fiber rather than at discrete points. This continuous action allows pump radiation to be gradually converted and absorbed along the fiber length, creating a more uniform population inversion distribution and maintaining high pump conversion efficiency throughout the amplification process
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 tapered fiber design significantly enhances pump-light absorption and efficiency by increasing the effective optical length and utilizing mode coupling, allowing for higher power scaling and improved light amplification capabilities.
Implementation Method 1
The tapered profile of the fiber enables a continuous mode conversion process for the pump power... utilizing mode coupling, which improves pump-light absorption dramatically
Implementation Method 2
The inner cladding layer for propagating pump power... having an index of refraction smaller than the index of refraction of the core
Data Source
Figure 1
Figure 2A~2F
Figure 3A~3B
AI summary
A section ofactive optical fiber (11) which comprises an active core (1),an inner cladding layer (2) andan outer cladding layer (3).The diameter of said core (1) and the thickness of said inner cladding (2) change gradually along the length of said section of active optical fiber (11). This formsa tapered longitudinal profile enabling a continuous mode conversion process alongthe length of the section of fiber (11). The method for fabricating a section of tapered active optical fibercomprises the steps of fabricating a preform for drawing active optical fiber from said preform,installing said preform into a drawing tower, drawing optical fiber in said drawing tower and altering at least one of the two parameters including the take-off preform speed and the take-up fiber speed during drawing of the optical fiber.