Multimode Optical Fiber with Segmented Cladding for Low Bending Losses
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Solution Overview
Problem
Multimode optical fibers face challenges in achieving reduced bending losses and high bandwidth while minimizing the cladding effect for high-data-rate applications, as existing designs often result in higher bending losses and lower bandwidth due to manufacturing constraints and the cladding effect.
Innovation Solution
A multimode optical fiber design featuring a central core with an alpha-index profile interrupted at the outer radius, surrounded by an inner cladding and a depressed trench, optimizing the refractive index differences and dimensions to minimize bending losses and maximize bandwidth, with specific refractive index profiles and dimensions that satisfy certain inequalities to achieve low bending losses and high bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the core diameter is reduced to increase bandwidth, then bandwidth is improved, but bending losses increase
Solution Approach 1:
The cladding is segmented into two distinct regions: an inner cladding adjacent to the core and an outer cladding surrounding the inner cladding. The inner cladding has a first refractive index and the outer cladding has a second refractive index that is lower than the first. This segmentation allows independent optimization of each cladding region to simultaneously achieve high bandwidth and low bending losses.
Solution Approach 2:
Different regions of the optical fiber are assigned different refractive index characteristics tailored to their specific functions. The inner cladding is designed with higher refractive index to maximize bandwidth by reducing modal dispersion, while the outer cladding is designed with lower refractive index to minimize bending losses by providing better optical confinement. This local quality differentiation resolves the contradiction between bandwidth and bending losses.
2Loss of energy
If the refractive index difference between core and cladding is increased to reduce bending losses, then bending losses are reduced, but bandwidth decreases
Solution Approach 1:
The cladding is divided into inner and outer regions with different refractive indices. The inner cladding maintains a larger refractive index difference with the core to support high bandwidth, while the outer cladding has a smaller refractive index difference to reduce bending losses. This segmentation allows the system to achieve both low bending losses and high bandwidth simultaneously.
Solution Approach 2:
The refractive index profile is optimized locally in different regions. The inner cladding region has properties optimized for bandwidth (higher refractive index), while the outer cladding region has properties optimized for bending loss reduction (lower refractive index). This local optimization resolves the contradiction between bending losses and bandwidth.
3Loss of energy
If a depressed trench is added to reduce bending losses, then bending losses are reduced, but device complexity increases
Solution Approach 1:
The cladding is segmented into inner and outer regions with different refractive indices, creating a dual-cladding structure. This segmentation provides bending loss reduction functionality while maintaining a relatively simple overall fiber geometry, avoiding the need for complex depressed trench profiles.
Solution Approach 2:
Instead of modifying the geometric shape of the cladding (as in depressed trench designs), the invention changes the refractive index parameter of the cladding material. By adjusting the refractive index of the inner and outer cladding regions, bending losses are reduced without introducing geometric complexity or additional structural elements.
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 proposed optical fiber design achieves bending losses of less than 0.1 dB for two turns around a 15 mm bend radius and maintains high bandwidth, with an effective modal bandwidth of at least 10,000 MHz·km, while reducing the cladding effect, thus supporting high-data-rate applications over extended distances.
Implementation Method 1
An optical fiber (i.e., a glass fiber typically surrounded by one or more coating layers) conventionally includes an optical fiber core, which transmits and/or amplifies an optical signal, and an optical cladding, which confines the optical signal within the core. Accordingly, the refractive index of the core nc is typically greater than the refractive index of the optical cladding ng (i.e., nc>ng).
Data Source
AI summary
The present invention embraces an optical fiber that includes a central core having an alpha-index profile with respect to an outer cladding. The optical fiber also includes an inner cladding, a depressed trench, and an outer cladding. Typically, the alpha-index profile of the central core is interrupted at a point having a positive refractive index difference with respect to the outer cladding. The optical fiber achieves reduced bending losses and a high bandwidth with a reduced cladding effect for high-data-rate applications.