Optical Fiber Depressed Cladding Refractive Index Control
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Solution Overview
Problem
Existing optical fibers with depressed cladding structures face challenges in achieving single-mode propagation and low transmission loss at signal light wavelengths due to non-uniform fluorine doping in the second cladding, leading to higher order modes and increased transmission loss.
Innovation Solution
The optical fiber features a depressed cladding structure with a core made of silica-based glass containing Cl and a second cladding divided into a uniform outer region and an inner region with a refractive index higher than the outer region, with a refractive index difference of 0.10% or smaller and a radial thickness of 25 µm or smaller, ensuring optimal fluorine doping and reduced refractive index variation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If fluorine doping is applied to the second cladding to reduce refractive index, then the refractive index of the second cladding is reduced, but non-uniform doping occurs leading to higher order modes and increased transmission loss
Solution Approach 1:
The patent divides the second cladding into two distinct regions with different fluorine doping concentrations: an inner region with higher doping (lower refractive index) and an outer region with lower doping (higher refractive index). This local differentiation optimizes both mode control and transmission characteristics by assigning different functional properties to different parts of the second cladding.
Solution Approach 2:
The patent systematically varies the fluorine doping concentration parameter across the second cladding radius, creating a graded refractive index profile. By controlling the doping concentration to achieve specific refractive index differences (0.01-0.10% between inner and outer regions), the patent optimizes transmission loss while maintaining single-mode operation.
2Reliability
If the refractive index difference in the second cladding is increased to control modes, then mode control is improved, but transmission loss increases
Solution Approach 1:
The patent optimizes the refractive index difference parameter within a specific range (0.01-0.10% between inner and outer regions of the second cladding) to achieve the best balance between single-mode propagation reliability and transmission loss minimization.
Solution Approach 2:
By creating a differentiated refractive index profile within the second cladding (higher index in outer region, lower index in inner region), the patent achieves effective mode control while minimizing overall transmission loss through optimized local optical properties.
3Shape
If a pipe structure is used to form the second cladding (rod-in-collapse process), then the depressed cladding structure is achieved, but production cost and process complexity increase
Solution Approach 1:
The patent segments the second cladding formation process into controlled doping zones (inner and outer regions) that can be achieved through modified MCVD or OVD processes, avoiding the need for complex rod-in-collapse pipe structures while maintaining the depressed cladding refractive index profile.
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 configuration enables single-mode propagation and low transmission loss at signal light wavelengths by controlling the refractive index difference and thickness of the second cladding, reducing production costs and maintaining practicality in manufacturing.
Implementation Method 1
an optical fiber that includes a core, which is made of silica based glass containing Cl, and a first cladding, which is made of silica based glass containing fluorine so as to have a refractive index lower than the refractive index of the core
Data Source
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AI summary
Provided is an optical fiber that has a depressed cladding structure including a core, which is made of silica based glass containing Cl, and a first cladding and a second cladding, which are made of silica based glass containing fluorine, and that can perform single-mode propagation at a signal light wavelength. The optical fiber includes the core, the first cladding, and the second cladding. The core is made of silica based glass containing Cl. The first cladding and the second cladding are made of silica based glass containing fluorine. The refractive index of the first cladding is lower than the refractive index of the core. The refractive index of the second cladding is lower than the refractive index of the core and higher than the refractive index of the first cladding. The second cladding is divided into an outer region that has a uniform refractive index and an inner region that has a refractive index higher than the refractive index of the outer region. The difference ΔP between the maximum refractive index of the inner region and the refractive index of the outer region is 0.02% or greater and 0.10% or smaller in terms of relative refractive index with respect to pure silica glass. The radial thickness R of the inner region is 10 µm or greater and 25 µm or smaller.