Multimode Optical Fiber Trench Design for Bend Resistance
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Solution Overview
Problem
Existing multimode optical fibers with trench assistance suffer from increased leaky modes, which degrade optical characteristics and bandwidth, despite improved bend resistance, due to the impact of depressed trench design on refractive index profiles.
Innovation Solution
The design of a multimode optical fiber with a graded-index profile and a depressed trench, where the dimensions and location of the trench are optimized to minimize the impact of leaky modes, ensuring high bend resistance while maintaining optical characteristics, by controlling the refractive index differences and trench geometry to limit leaky mode propagation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a depressed trench is added to improve bend resistance, then macrobending losses are reduced, but the number of leaky modes increases
Solution Approach 1:
The patent applies local quality by creating an inner cladding layer with a specific refractive index profile that differs from the outer cladding. The inner cladding has a refractive index that is higher than the outer cladding but lower than the core, forming a localized refractive index structure that confines leaky modes without affecting the overall trench-assisted bend resistance mechanism.
Solution Approach 2:
The patent uses a composite refractive index structure consisting of three distinct layers: core, inner cladding, and outer cladding. Each layer has a specifically engineered refractive index to achieve multiple functions simultaneously - the core for light transmission, the inner cladding for leaky mode confinement, and the outer cladding with depressed trench for bend resistance.
2Loss of energy
If the depressed trench is made deeper to reduce leakage losses, then bend resistance improves, but the number of leaky modes increases
Solution Approach 1:
The patent segments the cladding region into two distinct parts: an inner cladding layer adjacent to the core and an outer cladding layer containing the depressed trench. This segmentation allows independent optimization of each layer's refractive index profile to address different requirements - the inner cladding manages leaky modes while the outer cladding provides bend resistance.
Solution Approach 2:
The patent changes the refractive index parameter distribution by introducing a three-layer structure with specifically controlled refractive indices. The inner cladding has a refractive index intermediate between the core and outer cladding, creating a gradual transition that reduces leaky mode generation while maintaining the deep trench's ability to reduce leakage losses.
3Reliability
If the core radius is increased to maintain mode confinement, then optical characteristics are maintained, but the impact of leaky modes increases
Solution Approach 1:
The inner cladding acts as an intermediary layer between the core and outer cladding. It provides a refractive index transition zone that mediates the interaction between guided modes in the core and leaky modes in the outer regions, reducing the coupling and propagation of leaky modes while maintaining core mode confinement.
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 effectively reduces macrobending losses and maintains core size consistency over long lengths, achieving bend-insensitive performance with reduced leaky mode effects, as demonstrated by specific refractive index profiles and macrobending loss measurements.
Implementation Method 1
the refractive index profile is generally qualified in relation to the tracing of the graph which plots the function associating the refractive index with the optical fiber radius
Implementation Method 2
the refractive index of the inner core n c is greater than the refractive index of the outer cladding n g
Data Source
Figure 1~2
Figure 3
AI summary
This multimode optical fiber comprises, from the center to the periphery, an inner core, an inner cladding, a depressed trench and an outer cladding, wherein the inner core has a radius r1 comprised between 22 µm and 28 µm and a graded-index profile with a relative refractive index percent Δ=n02-ncl22n02>0.8%, where n0 is the maximum index value of the inner core and nc1 is the minimum index value of the inner core; the inner cladding has a radius r2 and a refractive index difference Δn2 with respect to the outer cladding; the depressed trench has a radius r3 and a negative refractive index difference Δn3 with respect to the outer cladding and surrounds the inner cladding, wherein 0.0115807 + 0.0127543 × (r2 - r1) + 0.00241674 × 1000Δn3 - 0.00124086 × (r3 - r2) × 1000Δn3 < 2% and wherein ∫r2r31000Δn3rdr is less than -20 µm.