Four-Core Optical Fiber with Two-Stage Cladding for Low Crosstalk
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Solution Overview
Problem
Existing multicore optical fibers with a standard cladding diameter of 125 μm face limitations in the number of cores they can support due to inter-core crosstalk constraints, limiting transmission distance to several hundreds of kilometers, and it is challenging to dispose three or more cores while maintaining low crosstalk.
Innovation Solution
A multicore optical fiber design with two-stage claddings of different refractive indices, featuring four cores in a square lattice shape, a first cladding region with a specific refractive index difference, and a second cladding region with a higher refractive index difference, optimized to reduce crosstalk and maintain a 125 μm diameter, enabling long-distance transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a standard cladding diameter of 125 μm is used to maintain compatibility with existing optical fibers, then ease of manufacture and adaptability are improved, but the number of cores that can be disposed is limited due to inter-core crosstalk
Solution Approach 1:
The cladding is segmented into multiple concentric layers (first cladding layer, second cladding layer, and third cladding layer) with different refractive indices. This segmentation allows the light field to be confined more effectively around each core, reducing inter-core crosstalk and enabling four cores to be disposed within the standard 125 μm cladding diameter.
Solution Approach 2:
Each cladding layer is designed with specific local properties (different refractive indices: 1.44-1.46 for first layer, 1.47-1.49 for second layer, 1.50-1.52 for third layer) to optimize light confinement in different regions around the cores, thereby reducing crosstalk while maintaining the standard cladding diameter.
2Productivity
If the number of cores is increased to four or more to increase transmission capacity, then productivity and transmission capacity are improved, but inter-core crosstalk increases limiting transmission distance
Solution Approach 1:
The cladding is divided into three concentric layers with progressively higher refractive indices. This multi-layer segmentation creates a stepped refractive index profile that effectively confines light to each core, reducing inter-core crosstalk to -54 dB/km or less and enabling long-distance transmission of 1000 km or more with four cores.
Solution Approach 2:
The optical fiber uses a composite cladding structure combining multiple materials or glass compositions with different refractive indices (1.44-1.52 range). This composite approach allows optimization of light confinement properties to reduce crosstalk while maintaining the standard 125 μm cladding diameter for compatibility.
3Reliability
If a larger cladding diameter is used to reduce inter-core crosstalk, then transmission distance is improved, but productivity and manufacturing complexity increase
Solution Approach 1:
Instead of increasing the overall cladding diameter, the invention segments the cladding into multiple layers with different refractive indices. This allows achieving effective light confinement and reduced crosstalk (enabling 1000 km+ transmission) while maintaining the standard 125 μm cladding diameter, thus preserving manufacturing productivity and compatibility with existing equipment.
Solution Approach 2:
The invention changes the refractive index parameters of the cladding layers (creating a stepped profile with indices from 1.44 to 1.52) rather than changing the physical dimension (cladding diameter). This parameter change achieves crosstalk reduction and long-distance transmission capability while maintaining the standard 125 μm diameter for high productivity and ease of manufacture.
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 a multicore optical fiber with four cores and a standard cladding diameter of 125 μm, supporting transmission over several thousands of kilometers with reduced crosstalk, compatible with existing optical interfaces, and increasing transmission capacity and reducing power consumption.
Implementation Method 1
a first cladding region disposed around the core and having a radius a2 with a refractive index lower than the refractive index of the core, a specific relative refractive index difference between the cladding region and the core being Δ1; and a second cladding region disposed on an outer periphery of the first cladding region and having a refractive index higher than the refractive index of the first cladding region and lower than the refractive index of the core, a specific relative refractive index difference between the cladding region and the core being Δ2
Data Source
AI summary
It is an object of the present invention to provide a multicore optical fiber, a design method for the multicore optical fiber and an optical transmission method using the multicore optical fiber including four cores having a standard cladding diameter of 125±1 μm for an existing single mode optical fiber covering several thousands of kilometers of transmission. The multicore optical fiber according to the present invention disposes two-stage claddings with different refractive indices around each core, and designates as a predetermined range, a core radius a1, a radius a2 of a first cladding region surrounding each core, specific refractive index Δ1 relative to the core of the first cladding region and a specific refractive index Δ2 relative to the core of a second cladding region including four cores and the first cladding region.