Multimode Fiber EMB Prediction via Single-Wavelength DMD
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Solution Overview
Problem
Current methods for assessing the effective modal bandwidth of multimode optical fibers are costly and time-consuming, requiring multiple measurements across a wide wavelength range, which is challenging for next-generation high-speed data networks that demand high EMB values over a broader wavelength range.
Innovation Solution
A method that uses a single wavelength DMD measurement, modifying the DMD plot with a temporal delay to predict the effective modal bandwidth across a wide wavelength range, allowing for pre-selection of fibers likely to meet specifications, thereby reducing the need for extensive in situ measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple DMD measurements are performed across a wide wavelength range, then the accuracy of EMB assessment over the wavelength range is improved, but the measurement time and cost increase significantly
Solution Approach 1:
The patent performs a single DMD measurement at a reference wavelength (850nm) as a preliminary action, then uses mathematical modeling to predict EMB values across the entire wavelength range. This preliminary measurement captures the essential modal dispersion characteristics, eliminating the need for time-consuming repeated measurements at multiple wavelengths while still providing accurate EMB assessment over the wide wavelength range.
Solution Approach 2:
The patent creates a mathematical model that copies the physical DMD measurement results to predict EMB behavior across different wavelengths. By using the measured DMD data at 850nm to generate predicted EMB values for the entire wavelength range through mathematical relationships, the patent avoids performing actual physical measurements at multiple wavelengths, thus reducing measurement time while maintaining assessment accuracy.
2Manufacturing precision
If traditional manufacturing processes are used for multimode fibers, then the manufacturing complexity is kept manageable, but the EMB values cannot guarantee high performance (>2000 MHz-km)
Solution Approach 1:
The patent focuses on precise control of the refractive index profile parameters (α parameter and core-cladding index difference) during manufacturing. By implementing specific parameter ranges for the graded-index profile and using doping techniques to achieve precise index control, the patent enables traditional manufacturing processes to produce fibers with EMB values exceeding 2000 MHz-km, transforming conventional manufacturing capabilities to meet high-performance requirements.
3Manufacturing precision
If the refractive index profile is optimized for a particular wavelength, then the EMB at that wavelength is maximized, but the performance degrades at other wavelengths
Solution Approach 1:
The patent implements a graded-index profile where the refractive index varies continuously from the fiber center to the cladding interface, creating different local propagation conditions for different modes. This local variation in refractive index (n(r) = n0 * sqrt(1 - 2Δ*(r/a)^α)) compensates for modal dispersion across different wavelengths, allowing the fiber to maintain high EMB performance over a wide wavelength range rather than being optimized for a single wavelength.
Data Source
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AI summary
The invention relates to a method for qualifying the actual effective modal bandwidth of a multimode optical fiber over a predetermined wavelength range, comprising the steps of: carrying out (30) a Dispersion Modal Delay (DMD) measurement of the multimode optical fiber at a single wavelength to obtain an actual DMD plot; generating (32) at least two distinct modified DMD plots from the actual DMD plot, each modified DMD plot being generated by applying a temporal delay At to the recorded traces that increases in absolute values with the radial offset value roffset, each modified DMD plot being associated with a predetermined bandwidth threshold (S1; S2); for each modified DMD plot, computing (33) an effective modal bandwidth as a function of said modified DMD plot and comparing (34) the computed effective modal bandwidth (EMBc1; EMBc2) with the bandwidth threshold value to which the modified DMD plot is associated; (35) qualifying the actual effective modal bandwidth as a function of results from the comparing step.