Single-mode optical fibers with depressed index cladding for low bend loss
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Solution Overview
Problem
Current optical fibers, particularly multimode fibers, have limited transmission distances due to finite modal bandwidth, making them unsuitable for high data rate and long reach links in data centers, while single-mode fibers are needed for extended distances in hyperscale data centers and campus backbones, requiring optical fibers with large effective area and low cutoff wavelengths.
Innovation Solution
Development of single-mode optical fibers with a silica-based core, depressed index cladding, and outer cladding regions, optimized for a mode field diameter of 8.6 to 9.5 microns, low cable cutoff wavelength, and low bend loss, enabling single-mode operation at wavelengths below 1080 nm with G.652D-compliant mode field diameters and zero dispersion wavelengths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multimode optical fibers are used for data center applications, then short distance transmission is supported, but transmission distance is limited to a few hundred meters due to finite modal bandwidth
Solution Approach 1:
The patent changes the fundamental parameter of fiber mode operation from multimode to single-mode, and optimizes the core radius and refractive index parameters to achieve both single-mode operation at 1310nm and extended transmission distance. This parameter transformation resolves the bandwidth-distance limitation of multimode fibers.
Solution Approach 2:
The fiber structure is segmented into distinct regions with specific functions: core region for light confinement, depressed index cladding region for mode control and bend loss reduction, and outer cladding region for mechanical protection. This segmentation allows optimization of each region for its specific function while achieving overall system goals.
2Area of stationary object
If single-mode optical fibers are designed with large effective area for high power transmission, then non-linear effects are reduced, but cutoff wavelength increases making single-mode operation difficult at wavelengths below 1080 nm
Solution Approach 1:
The patent applies local quality by creating a depressed index cladding region with specific refractive index characteristics (Δ3MIN < -0.2%) positioned at a specific radius ratio (r1/r2 > 0.4). This localized structural modification with specific local properties enables the fiber to maintain single-mode operation at short wavelengths while preserving large effective area for high power transmission.
Solution Approach 2:
The fiber employs a composite refractive index structure combining core region (Δ1MAX = 0.25-0.4%), depressed index cladding region (Δ3MIN < -0.2%), and outer cladding region. This composite structure with varying refractive index zones enables simultaneous achievement of large effective area and low cutoff wavelength for reliable single-mode operation.
3Area of stationary object
If optical fiber core radius is increased to achieve large effective area, then power handling capability improves, but bend loss increases
Solution Approach 1:
The patent introduces a depressed index cladding region with specific local properties (refractive index Δ3MIN < -0.2% at radius r2 where r1/r2 > 0.4) that creates a potential well for the optical mode. This localized structural feature with tailored properties confines the mode more effectively during bending, reducing bend loss while maintaining large core radius for high effective area.
Solution Approach 2:
The depressed index cladding region acts as an intermediary structure between the core and outer cladding. It provides a refractive index barrier that mediates the optical field distribution, preventing mode leakage during bending while allowing the core to maintain large dimensions for high power handling 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 optical fibers provide low bend loss and high effective area, enabling extended transmission distances with reduced signal degradation, suitable for data center applications and supporting high data rates over 500-2000 meters.
Implementation Method 1
a silica based core region comprising an outer radius r1 in the range from 3.6 to 5.4 microns, a maximum relative refractive index Δ1MAX between 0.25 to 0.4%
Implementation Method 2
a depressed index cladding region surrounding the core region, the depressed index cladding region comprising an inner radius r2 such that r1/r2 is greater than 0.4, an outer radius r3 and a minimum relative refractive index Δ3MIN less than −0.2%
Data Source
AI summary
Optical fibers having a large effective area and a low cutoff wavelength are disclosed. Three main embodiments of the optical fiber allow for single-mode operation at wavelengths greater than 980 nm, and have a large effective area with low bend losses and low dispersion at 1310 nm. The large effective area optical fiber is expected to be particularly useful for data center applications due to its ability to efficiently optically couple with VCSELs and photonic integrated devices. Integrated systems and optical communication systems that employ the optical fibers are also disclosed.