Bend Resistant Multimode Optical Fiber Cladding Design
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Solution Overview
Problem
Existing multimode optical fibers are sensitive to bending and profile errors, leading to increased attenuation and reduced bandwidth due to the use of down-doped cladding regions, which affects the stability of optical core diameter and numerical aperture.
Innovation Solution
The design incorporates a graded-index core with a cladding region featuring a depressed-index annular portion surrounded by a raised-index annular region, which mitigates profile errors and enhances bandwidth by effectively stripping leaky modes, resulting in low bend-induced attenuation and stable optical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a down-doped cladding region is used to improve bending characteristics, then bend sensitivity is reduced, but profile errors at the core/clad interface increase causing bandwidth degradation
Solution Approach 1:
The patent applies local quality by creating distinct regions with different refractive index characteristics: a down-doped moat region immediately adjacent to the core for bend sensitivity, and an up-doped outer cladding region for profile error mitigation. Each region serves a specific local function that collectively resolves the contradiction between bend sensitivity and profile error sensitivity.
Solution Approach 2:
The cladding is segmented into multiple functional regions: the down-doped moat region for bend control and the up-doped outer cladding region for profile error compensation. This segmentation allows independent optimization of each region's properties to simultaneously achieve bend sensitivity and reduced profile error impact.
2Reliability
If a down-doped cladding region is used to improve bending characteristics, then bend sensitivity is reduced, but bandwidth is reduced due to trapped leaky modes
Solution Approach 1:
The up-doped outer cladding region acts as an intermediary that strips leaky modes trapped by the down-doped moat region. This intermediary region facilitates the removal of harmful modes while preserving the bend-sensitive characteristics of the moat, thereby maintaining both bend sensitivity and high bandwidth.
3Device complexity
If a simple down-doped cladding is used to reduce device complexity, then manufacturing is easier, but optical properties become unstable along fiber length
Solution Approach 1:
The patent introduces local quality variations in the cladding structure with distinct doped regions serving specific functions. The up-doped outer cladding region provides stable reference properties that compensate for variations along the fiber length, ensuring optical property stability while maintaining relatively simple manufacturing processes.
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 design achieves high bandwidth and low bend losses, with overfilled bandwidths exceeding 3.5 GHz/km at 850 nm and numerical aperture greater than 0.185, while maintaining low macrobend attenuation and stable optical core diameter and numerical aperture along the fiber length.
Implementation Method 1
the elevated cladding region helps to strip out leaky and radiation modes that may be trapped as a result of the down doped cladding region
Implementation Method 2
a central multimode core region comprising maximum refractive index delta percent Δ1
Data Source
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AI summary
Bend resistant multimode optical fibers are disclosed herein. Multimode optical fibers disclosed herein comprise a core region(20) and a cladding region(200) surrounding and directly adjacent to the core region, the cladding region comprising a first region(30) having index delta percent ?2, a depressed-index annular portion(50) having ?3, and a third annular region(60) surrounding the depressed annular region comprising refractive index delta percent ?4; wherein ?I??? > ?4> ?2 > ?3, wherein the difference between ?4 and ?2 is greater than or equal to 0.03%.