Multi-core fiber with depressed layer for low crosstalk
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Solution Overview
Problem
Current multi-core fibers with higher core densities and reduced inter-core crosstalk have not been adequately studied and require improvements to achieve higher core densities while minimizing inter-core crosstalk.
Innovation Solution
A multi-core fiber design with a core pitch of 20 μm or smaller, a mode field diameter of 5 μm or smaller at 1550 nm, and inter-core crosstalk of −20 dB/km or less, along with a pitch converter that adjusts core pitch from 30 μm to 20 μm, utilizing refractive index profiles such as step-shaped, W-shaped, and trench-shaped to reduce crosstalk and enhance bending resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the number of core portions is increased to achieve higher core density, then the transmission capacity is improved, but the distance between cores decreases causing increased inter-core crosstalk
Solution Approach 1:
The patent applies local quality by creating a depressed layer with lower refractive index specifically in the region between adjacent core portions. This localized refractive index modification forms optical barriers that confine light within each core, preventing crosstalk while allowing high core density. The depressed layer is positioned only where needed between cores, leaving the core regions themselves unchanged for optimal light transmission.
Solution Approach 2:
The patent changes the refractive index parameter by introducing a depressed layer with refractive index lower than both the core portions and the cladding portion. This parameter change creates an optical barrier effect that reduces inter-core crosstalk. The refractive index profile is specifically designed with three regions: high-index cores, low-index depressed layer, and medium-index cladding, which effectively confines light while enabling high core density.
2Quantity of substance
If the core pitch is reduced to increase core density, then the transmission capacity is improved, but the bending loss increases due to tighter curvature requirements
Solution Approach 1:
The depressed layer with lower refractive index is positioned locally between core portions to create optical barriers. This local modification strengthens light confinement without requiring larger core pitch, thereby reducing macrobending loss while maintaining high core density. The depressed layer acts as a protective barrier that prevents light leakage during bending.
Solution Approach 2:
The patent creates a composite refractive index structure consisting of core portions, depressed layer, and cladding portion with different refractive indices. This composite structure provides both strong light confinement and bending resistance. The multi-layer composite design allows the fiber to maintain performance at small core pitches while being tolerant to bending.
3Object-generated harmful factors
If the mode field diameter is reduced to decrease inter-core crosstalk, then the crosstalk is improved, but the coupling efficiency with conventional fibers deteriorates
Solution Approach 1:
The patent changes the refractive index parameter by introducing the depressed layer, which allows the mode field diameter to be reduced for crosstalk suppression while maintaining coupling efficiency. The depressed layer creates an optical barrier that confines light more tightly within each core, effectively reducing the mode field diameter without sacrificing coupling performance to conventional single-mode fibers.
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 achieves reduced inter-core crosstalk and increased core density, improving bending resistance and enabling efficient connection of multi-core fibers with different core pitches, thus enhancing the handleability and operability of multi-core fiber connections.
Implementation Method 1
a cladding portion surrounding outer circumferences of the plurality of core portions and having a refractive index lower than a maximum refractive index of the plurality of core portions
Implementation Method 2
the plurality of core portions and the cladding portion have a diameter decreasing portion that decreases in diameter in a tapered form to 2/3 of a diameter or less from the first end face to the second end face
Data Source
AI summary
A multi-core fiber includes: a plurality of core portions; and a cladding portion surrounding outer circumferences of the plurality of core portions and having a refractive index lower than a maximum refractive index of the plurality of core portions. The multi-core fiber has a mode field diameter of 5 μm or smaller at a wavelength of 1550 nm, the multi-core fiber has a core pitch of 20 μm or smaller, the core pitch being an interval between centers of nearest neighboring ones of the plurality of core portions in a cross section orthogonal to a longitudinal direction. The multi-core fiber has inter-core crosstalk of −20 dB/km or less. The multi-core fiber has a macrobending loss of 0.1 dB/m or less at the wavelength of 1550 nm when the multi-core fiber is bent at a radius of 5 mm.