Multimode Fiber Trench Design for 400GbE Bandwidth
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Solution Overview
Problem
Current multimode optical fibers fail to achieve sufficient bandwidth for next-generation 400GbE systems, particularly at wavelengths greater than 950nm, due to limitations in core-cladding geometry optimization and increased sensitivity with fewer modal groups, leading to reduced overfilled launch bandwidth.
Innovation Solution
A multimode optical fiber design with a graded-index profile and a trench in the cladding, where the core-cladding geometry is optimized based on the number of mode groups supported, using a specific refractive index profile and trench volume criteria to minimize modal dispersion and maximize bandwidth across the 950nm to 1310nm wavelength range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the core-cladding interface is optimized for traditional wavelengths, then bandwidth is improved at those wavelengths, but bandwidth at wavelengths greater than 950nm deteriorates due to increased sensitivity and fewer modal groups
Solution Approach 1:
The patent modifies the core-cladding interface geometry parameters (specifically the outer radius R1 and the trench volume V2) to optimize bandwidth performance at wavelengths greater than 950nm. By changing these geometric parameters, the fiber achieves improved overfilled launch bandwidth across the extended wavelength range while maintaining compatibility with VCSEL sources.
2Reliability
If the trench volume is increased to reduce cladding effect, then modal dispersion is reduced, but manufacturing complexity increases due to precise volume control requirements
Solution Approach 1:
The patent defines a specific trench volume V2 that satisfies the inequality -2.20×Ln(N)-1100 < V2 < -2.20×Ln(N)-865, where N is a parameter related to the number of mode groups. This parameter optimization reduces modal dispersion and improves bandwidth while providing a quantifiable design criterion that can be implemented in manufacturing.
3Measurement precision
If the refractive index difference Dn2 is increased to improve mode control, then bandwidth is improved, but loss of energy increases due to higher reflection and scattering
Solution Approach 1:
The patent optimizes the refractive index difference Dn2 between the trench and the outer cladding as part of the overall core-cladding interface design. By carefully selecting Dn2 along with the trench volume V2 and outer radius R1, the patent achieves improved bandwidth performance while managing optical loss through balanced parameter selection.
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 an overfilled launch bandwidth greater than 10000MHz.km at wavelengths between 950nm and 1310nm, enhancing the fiber's performance for high-speed applications by carefully controlling the trench volume and refractive index difference to reduce time delay differences between mode groups.
Implementation Method 1
the different modes experience a different propagation medium, which affects their speed of propagation differently. By adjusting the value of the parameter α, it is thus possible to theoretically obtain a group velocity, which is virtually equal for all the modes
Data Source
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Figure 3
AI summary
The invention concerns a multimode optical fiber, with an ct-profile graded-index core with an a-value between 1.96 and 2.05 and a N value defined as N= (R1/λ)2(n1 2-n0 2) between 7 and 52, where R1 is the multimode core radius, n1 is the maximum index of the multimode core and n0 is the minimum index at the outer edge of the graded index core. According to the invention, a depressed region directly surrounds the graded/ index core and satisfies the criteria: -2.20 < Dn2 < 0, where Dn2 is the index difference of depressed region with external cladding, and 220 Ln(N)-1100 < V2 < 220Ln(N)-865, where V2 is the volume of the depressed region. Such a multimode fiber shows an increased OFL-bandwidth above 10000Hz.km at an operating wavelength between 950nm and 1310nm.