Graded Index Optical Fiber with Trench Cladding for Low Bend Loss
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Solution Overview
Problem
Existing single mode optical fibers face challenges in achieving low bend losses, particularly at small and large bend diameters, which is crucial for applications in access and fiber to the premises optical networks where physical demands like tight bend radii and compression induce signal loss.
Innovation Solution
A single mode optical fiber design featuring a graded index germania doped central core region with a specific refractive index profile, including a second inner cladding region with a non-constant relative refractive index that decreases with increasing radius, and an outer cladding region, which together enhance macrobending performance and comply with ITU-G.652 standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional single mode optical fiber design is used, then the fiber structure is simple and easy to manufacture, but the bend loss increases at small and large bend diameters
Solution Approach 1:
The cladding region is segmented into multiple distinct regions (first inner cladding region with outer radius r2, second inner cladding region with outer radius r3, and outer cladding region) with different refractive index characteristics. This segmentation allows each region to contribute differently to bend loss reduction, enabling low bend loss performance at both small and large bend diameters while managing structural complexity through functional division.
Solution Approach 2:
Different cladding regions are assigned specific refractive index profiles tailored to their locations and functions. The first inner cladding region has relative refractive index Δ2, the second inner cladding region has relative refractive index Δ3 that becomes more negative with increasing radius, and the outer cladding region has relative refractive index Δ4. This local differentiation of optical properties optimizes bend loss characteristics across various bend conditions.
2Loss of energy
If the second inner cladding region has a non-constant relative refractive index that becomes more negative with increasing radius, then low bend loss at small and large diameters is achieved, but the manufacturing precision requirements increase
Solution Approach 1:
The refractive index parameter Δ3 in the second inner cladding region is designed to vary systematically with radius, becoming more negative as radius increases. This controlled parameter change creates an optimized refractive index profile that reduces bend loss across different bend diameters. The systematic variation, rather than random complexity, helps manage manufacturing precision requirements through predictable profile characteristics.
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 design achieves low bend losses at both small and large diameters, ensuring optimal optical performance and compliance with industry standards, including a mode field diameter between 8.2 and 9.6 microns at 1310 nm and zero dispersion wavelength between 1300 and 1324 nm.
Implementation Method 1
a graded index germania doped central core region having outer radius r1, having a relative refractive index Δ1, a maximum relative refractive index Δ1max and having an alpha profile, alpha core, of 0.5 ≤ alpha core ≤ 4
Implementation Method 2
a cladding region comprising (i) a first inner cladding region having an outer radius r2 ≤ 10 microns and relative refractive index Δ2 and 0.65 ≤ r1/r2 < 1.3; (ii) a second inner cladding region surrounding the first inner cladding region and comprising a relative refractive index Δ3 and a minimum relative refractive index Δ3min
Data Source
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AI summary
One embodiment of a single mode optical fiber includes: a graded index central core region having outer radius r1 and relative refractive index Δ1; a cladding region comprising (i) a first inner cladding region having an outer radius r2 < 10 microns and relative refractive index Δ2 and 0.65 ≤r1 /r2 ≤ 1; (ii) and a second inner cladding region (i.e., trench) having an outer radius r3 > 10 microns and comprising a minimum relative refractive index Δ3, wherein said second inner cladding region has at least one region with a relative refractive index delta that becomes more negative with increasing radius; and (iii) an outer cladding region surrounding the second inner cladding region and comprising relative refractive index Δ4, wherein Δ1 > Δ2 > Δ3, Δ3 <Δ4.