Multi-core optical fiber with trench refractive index design
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Solution Overview
Problem
Standard cladding diameter multi-core fibers face challenges in extending transmission distance due to crosstalk limitations and inability to maintain single-mode operations at wavelengths of 1.53 μm or shorter, restricting the expansion of transmission wavelength bands.
Innovation Solution
A multi-core optical fiber with a square lattice pattern and specific refractive index distributions, including a cladding region with a relative refractive index difference, core radius, and mode field diameter, optimized to reduce crosstalk and extend transmission distance by ensuring single-mode operations across a broader wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a standard cladding diameter multi-core fiber is designed to maintain single-mode operations in all communication wavelength bands, then compatibility with existing standard technologies is improved, but transmission distance is limited due to crosstalk
Solution Approach 1:
The patent applies local quality by creating a trench-type refractive index distribution where the cladding region has a different refractive index characteristic than the core regions. Specifically, the cladding region has a lower refractive index than the core regions, forming a trench structure that locally modifies the optical properties to reduce crosstalk between cores while maintaining standard compatibility
Solution Approach 2:
The patent employs parameter changes by optimizing the refractive index difference between core and cladding regions, and by carefully controlling the cladding diameter and core spacing parameters. These parameter adjustments enable the fiber to achieve both standard compatibility and reduced crosstalk for extended transmission distance
2Duration of action of moving object
If the single-mode operation region is limited to 1.530 to 1.625 μm to reduce crosstalk, then transmission distance is improved, but the transmission wavelength band cannot be expanded to include 1.53 μm or shorter wavelengths
Solution Approach 1:
The patent uses parameter changes by adjusting the refractive index distribution parameters and cladding dimensions to shift the single-mode operation band. The trench-type structure with optimized parameters enables single-mode operation at extended wavelength bands including 1.53 μm and shorter wavelengths while maintaining low crosstalk performance
3Quantity of substance
If intense optical confinement is used to dispose four identical cores in a fiber, then space division multiplexing capacity is improved, but crosstalk increases limiting transmission distance
Solution Approach 1:
The patent applies local quality by introducing a trench-type refractive index distribution that creates a local optical barrier between adjacent cores. The cladding region with lower refractive index forms a trench structure that locally confines optical modes within each core, reducing evanescent field overlap and crosstalk between the four cores
Solution Approach 2:
The patent uses an intermediary approach by introducing a cladding region with specific refractive index properties that acts as a mediator between the core regions. This intermediate layer with lower refractive index provides optical isolation between cores while allowing each core to maintain its light transmission capability
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 enables the expansion of transmission wavelength bands and increases transmission distance by effectively reducing crosstalk, allowing for single-mode operations across the S-band and beyond.
Implementation Method 1
a cladding region that is formed around the outer peripheral portions of the cores and has a lower refractive index than the cores
Implementation Method 2
trench-type refractive index distribution with intense optical confinement
Implementation Method 3
the absolute value of the relative refractive index difference between the cores and the cladding region
Data Source
AI summary
The present invention is to provide a multi-core optical fiber that can expand its transmission wavelength band, and extend its transmission distance by reducing crosstalk, and also provide a method for designing the multi-core optical fiber. A multi-core optical fiber according to the present invention includes: four cores that are arranged in a square lattice pattern in a longitudinal direction; and a cladding region that is formed around the outer peripheral portions of the cores and has a lower refractive index than the cores, the absolute value of the relative refractive index difference between the cores and the cladding region being represented by A. In the multi-core optical fiber, the diameter of the cladding region is 125+1 μm, the cutoff wavelength is 1.45 μm or shorter, the mode field diameter MFD at a wavelength of 1.55 μm is 9.5 to 10.0 μm, the bending loss at a wavelength of 1.625 μm and with a bending radius of 30 mm is 0.1 dB/100 turns or smaller, and the inter-core crosstalk at the wavelength of 1.625 μm is −47 dB/km or smaller.