Multimode Optical Fiber With Depressed-Index Cladding
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Solution Overview
Problem
High dispersion and attenuation in multimode optical fibers at 850 nm limit the maximum system length and performance, especially at data modulation rates above 25 GHz, making them unsuitable for high-performance computing and data center applications that require longer interconnections with lower electrical power consumption.
Innovation Solution
Development of a multimode optical fiber with a graded index glass core and a cladding structure featuring a depressed-index annular portion, optimized for the 1310 nm and 1550 nm wavelength windows, which reduces dispersion and attenuation, enabling transmission of multiple signals at 25 GHz or higher over distances of up to 500 meters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If multimode optical fiber operates at 850 nm wavelength, then VCSEL laser sources can be used with relaxed alignment tolerances, but fiber dispersion and attenuation are high which limits maximum system length
Solution Approach 1:
The patent changes the operating wavelength parameter from 850 nm to 1310 nm or 1550 nm windows, which fundamentally alters the fiber's dispersion and attenuation characteristics. This parameter change enables long-distance transmission while maintaining compatibility with multimode fiber structures
Solution Approach 2:
The patent introduces a dynamic graded index profile in the core with variable alpha values (1.8 < α ≤ 3.0) that can be optimized for different wavelength operations. This dynamic indexing allows the fiber to adapt its modal dispersion characteristics for optimal performance at different wavelengths and data rates
2Productivity
If data modulation rate is increased to 25 GHz and higher, then bandwidth is improved, but dispersive broadening of optical signals results in large impairments
Solution Approach 1:
The patent optimizes the graded index alpha parameter to specific ranges (1.8 < α ≤ 3.0) that minimize modal dispersion at high data rates. This parameter optimization reduces signal broadening effects even at 25 GHz and higher modulation rates, maintaining signal integrity
Solution Approach 2:
The patent creates a simplified index profile structure that replicates the ideal dispersion characteristics needed for high-speed transmission. The depressed-index annular portion acts as a virtual barrier that copies the beneficial effects of single-mode operation while maintaining multimode fiber's large core advantages
3Ease of operation
If core diameter is increased to provide relaxed alignment tolerances, then ease of connection is improved, but modal dispersion increases which limits bandwidth
Solution Approach 1:
The patent applies local quality variation through the depressed-index annular portion surrounding the core. This localized index modification creates different propagation conditions for different modes, reducing modal dispersion effects while maintaining the large core diameter benefits for alignment tolerance
Solution Approach 2:
The patent creates a composite index structure combining the core region with the depressed-index annular portion. This composite structure effectively separates the functions of large core diameter (alignment tolerance) from modal dispersion control, achieving both goals simultaneously
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 fiber achieves significantly lower dispersion and attenuation in the 1310 nm and 1550 nm windows, allowing for efficient transmission of multiple signals at high data rates with reduced electrical power consumption, thereby addressing the limitations of conventional systems operating at 850 nm.
Implementation Method 1
a graded index having an alpha profile wherein 1.95 ≤ α ≤ 2.04 and a maximum relative refractive index in the range between 0.6 % and 1.8 %
Implementation Method 2
The cladding includes a depressed-index annular portion
Data Source
Figure 1
Figure 2
Figure 3~3A
AI summary
One exemplary multimode optical fiber includes a graded index glass core having a diameter in the range of 41 microns to 80 microns, a graded index having an alpha less than 2.04 and a maximum relative refractive index in the range between 0.6% and 1.8%. The cladding includes a depressed-index annular portion. The fiber has an overfilled bandwidth greater than 2.5 GHz-km at at least one wavelength between 1200 nm and 1700 nm.