EDF-SMF Fusion Splice Structure for Low-Loss Optical Amplification
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Solution Overview
Problem
Conventional optical amplification transmission lines face connection loss issues due to differences in core diameter and mode field diameter (MFD) between Er-doped optical fibers and single-mode fibers, which are exacerbated by the expansion of MFD caused by dopant diffusion, leading to increased nonlinearity and polarization mode dispersion.
Innovation Solution
The optical amplification transmission line employs a fusion-spliced structure where the Er-doped fiber and single-mode fiber have a controlled MFD ratio between 1.9 and 2.2, with the Er-doped fiber doped with Ge and Al, and a fluorine-doped cladding to reduce nonlinearity and polarization mode dispersion, while maintaining a core refractive index difference within 1% to 2%, thereby creating a mode field gap that reduces connection loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the core diameter is expanded by diffusion of dopant (Ge) to match MFD between EDF and SMF, then connection loss is reduced, but nonlinearity and polarization mode dispersion increase
Solution Approach 1:
The patent applies local quality by creating a transition section with gradually varying dopant concentration (Ge and Al) and refractive index, rather than uniform doping throughout the fiber. This localized gradient structure allows MFD to change smoothly from EDF to SMF values, reducing connection loss while controlling nonlinearity and polarization mode dispersion through precise local composition control.
Solution Approach 2:
The patent changes physical parameters (dopant concentration, refractive index, core diameter) continuously along the fiber length in the transition section. By controlling the gradient of these parameters, the MFD is transformed from EDF values to SMF values, achieving low connection loss while maintaining control over nonlinear effects through managed parameter transitions.
2Loss of energy
If the MFD of EDF is increased to match SMF, then splicing loss is reduced, but the amplification efficiency decreases due to reduced overlap between pump and signal modes
Solution Approach 1:
The patent segments the fiber structure into distinct functional sections: an amplification section with constant EDF composition for high amplification efficiency, and a transition section for MFD transformation. This segmentation allows the amplification section to maintain optimal small MFD for pump-signal overlap, while the transition section handles the MFD matching function, preventing degradation of amplification efficiency.
Solution Approach 2:
The patent introduces a longitudinal dimension (along the fiber axis) for MFD variation, keeping the transverse MFD small in the amplification section for high efficiency, while achieving MFD transformation through the transition section. This dimensional approach separates the functions of amplification and mode matching in different spatial regions.
3Loss of energy
If a transition section with varying MFD is introduced, then connection loss is reduced, but the device complexity increases
Solution Approach 1:
The patent merges the transition section and stationary section into a single continuous fiber structure with smoothly varying properties, avoiding discrete components or interfaces. The dopant concentration and refractive index change continuously from EDF to SMF values, creating a unified structure that reduces connection loss without requiring complex assembly or multiple separate components.
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 structure effectively reduces splicing loss between the Er-doped fiber and single-mode fiber, enhancing amplification efficiency and suppressing nonlinearity and polarization mode dispersion, achieving a fusion splicing loss of 0.02 dB or less, thereby improving the overall efficiency of optical amplification.
Implementation Method 1
an optical amplification Er-doped optical fiber (EDF) having a core doped with Ge (germanium)
Implementation Method 2
both core diameters are matched because the core diameter is expanded by diffusion of a dopant contained in the core, preferably germanium (Ge)
Implementation Method 3
a first cladding that surrounds the first core and is doped with F (fluorine)
Data Source
AI summary
An optical amplification transmission line of the present disclosure reduces a connection loss between an EDF located upstream of a signal light path and a SMF located downstream of the path, as compared with a conventional optical amplification transmission lines. The optical amplification transmission line includes an EDF and a SMF fusion-spliced to each other. The EDF has an Er-doped core and an F-doped cladding. A core of the SMF is doped with no Er. The ratio (MFD2/MFD1) of the MFD2 of a stationary section of the SMF to the MFD1 of a stationary section of the EDF falls within a range of 1.9 or more and 2.2 or less.