Bare Single Mode Fiber Amplifier Pump Absorption
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current optical fiber amplification systems face challenges in achieving high pump-to-signal conversion efficiency and minimizing fiber length due to limitations in core-to-cladding diameter ratio and numerical aperture, leading to parasitic nonlinear effects and amplified spontaneous emission (ASE).
Innovation Solution
A gain fiber assembly with a bare active single-mode fiber having a reduced 1st cladding diameter, utilizing a glass-fluid or glass-vacuum interface to increase numerical aperture and enhance pump absorption, allowing for higher population inversion and shorter fiber lengths while avoiding nonlinear effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the active fiber length is increased to achieve higher output power, then the pump absorption is improved, but parasitic nonlinear effects and ASE begin to dominate
Solution Approach 1:
The patent changes the physical parameters of the fiber by reducing the 1st cladding diameter from conventional sizes (105-200 μm) to a smaller size (40-80 μm). This parameter change increases the core-to-cladding area ratio, which enhances pump absorption per unit length, allowing shorter fiber lengths to achieve the same pump absorption, thereby avoiding parasitic nonlinear effects and ASE that occur in longer fibers.
2Power
If the core-to-cladding diameter ratio is increased to maximize pump absorption, then the population inversion is improved, but the fiber design becomes more constrained
Solution Approach 1:
The patent applies parameter changes by reducing the 1st cladding diameter to 40-80 μm while maintaining the core diameter, thereby increasing the core-to-cladding area ratio. This achieves higher pump absorption efficiency and population inversion. The patent also uses a glass-fluid or glass-vacuum interface to achieve a high numerical aperture (NA ≥ 0.8), which further enhances pump coupling efficiency into the small-cladding fiber, reducing design constraints.
3Power
If the 1st cladding diameter is reduced to increase the core-to-cladding ratio, then the pump absorption per unit length is improved, but the coupling of pump light becomes more difficult
Solution Approach 1:
The patent changes the numerical aperture parameter by using a glass-fluid or glass-vacuum interface at the 1st cladding boundary. This interface achieves a high NA (≥ 0.8), which increases the acceptance angle for pump light coupling. This compensates for the reduced cladding diameter, making pump light coupling easier despite the smaller target area, while simultaneously increasing pump absorption per unit length.
4Object-affected harmful factors
If the active fiber length is shortened to avoid nonlinear effects, then the parasitic effects are suppressed, but the pump absorption efficiency decreases
Solution Approach 1:
The patent changes the 1st cladding diameter parameter to 40-80 μm, which increases the core-to-cladding area ratio. This allows the fiber to achieve high pump absorption in a shorter length, thereby suppressing parasitic nonlinear effects and ASE while maintaining high pump absorption efficiency. The high NA interface further enhances this effect by improving pump coupling into the shorter fiber.
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 achieves higher pump conversion efficiencies and shorter fiber lengths, maximizing output power while suppressing parasitic nonlinear effects and ASE, resulting in improved performance for high-peak power and single-frequency applications.
Implementation Method 1
The high refractive index difference between the bare fiber and the surrounding gas or liquid provides a numerical aperture (NA) of at least 0.8
Implementation Method 2
The pump light travelling in the core is absorbed and re-emitted at a longer wavelength by the gain media in the core increasing the signal power along the length of the fiber
Data Source
AI summary
A gain fiber assembly for use in optical fiber amplification systems such as fiber amplifiers and fiber lasers utilizes an active or “bare” fiber that has a single glass cladding with an outer diameter of less is less than 80 μm and preferably less than 60 μm or even 40 μm. A passive double-clad input fiber is stripped of the outer cladding and tapered to match the outer diameter of the bare fiber. A glass-fluid or glass-vacuum interface along the taper provides guidance of the pump into and along the cladding of the bare fiber and a NA>1 for a vacuum or gasses and an NA>0.8 for liquids. This allows for much shorter fiber lengths to reach max signal power and higher pump conversion efficiencies.