Multimode Fiber Effective Bandwidth Computation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for computing the effective bandwidth of multimode fibers are not representative of the power penalty at a given bit error rate, especially for longer optical links and higher data bit rates, due to inaccuracies in assessing chromatic and modal dispersion interactions.
Innovation Solution
The use of multiple weight functions, each dedicated to different transverse modes of the light launched into the multimode fiber, applied to the differential mode delay (DMD) plot to compute a more accurate effective bandwidth, which is better correlated with system performances and power penalty.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single weight function is used to compute effective modal bandwidth from DMD measurements, then the computation is simple and fast, but the computed bandwidth becomes less representative of power penalty at a given bit error rate when optical link length and/or data bit rate increase
Solution Approach 1:
The patent segments the single weight function into multiple weight functions, each dedicated to a specific transverse mode of the VCSEL source. This segmentation allows each weight function to accurately capture the modal dispersion characteristics for its specific mode, thereby improving the representativeness of the computed effective bandwidth for longer links and higher bit rates while maintaining computational tractability through the structured approach.
2Object-affected harmful factors
If spectrally narrow sources are used to mitigate chromatic dispersion, then chromatic dispersion impairments are reduced, but the cost of the source increases significantly
Solution Approach 1:
The patent uses feedback by incorporating actual DMD measurements from the specific multimode fiber into the computation of effective bandwidth. This feedback mechanism allows the system to account for the actual interaction between chromatic and modal dispersions in the specific fiber, enabling accurate performance prediction without requiring expensive spectrally narrow sources, thus resolving the contradiction between reducing chromatic dispersion impairments and maintaining cost-effectiveness.
3Measurement precision
If DMD measurement is performed on all multimode fibers to assess modal dispersion, then fiber selection can be performed, but it is not feasible to accurately assess the alpha profile from the DMD plot for fibers with complex DMD patterns
Solution Approach 1:
The patent changes the approach from trying to assess the alpha profile parameter directly (which fails for complex DMD patterns) to computing effective bandwidth using multiple mode-specific weight functions applied to the measured DMD data. This parameter change bypasses the difficulty of alpha assessment while still achieving the goal of predicting fiber performance for chromatic dispersion mitigation.
Data Source
Figure 1~3
Figure 4a~5
Figure 6
AI summary
The invention concerns a method of assessing power penalty at a given bit error rate of a multimode fiber (4), comprising at least a step (S1) of differential mode delay measurement, measuring a set of elementary fiber responses corresponding respectively to different offset launches (r) of light over the core radius into multimode fiber (4), a step (S2) of generating a global fiber response by applying, to the set of elementary fiber responses, a set of weighting coefficients and delays respectively depending on the different offset launches (r) of the elementary fiber responses, a step (S5) of computing a parameter representative of a fiber power penalty from the global fiber response, wherein, in the step of generating a global fiber response, the set of weighting coefficients includes several subsets (W(r, 1) to W(r, 6)) of weighting coefficients being time delayed relatively to one another, with at least one relative time delay that is not set to zero, weighting coefficients of each subset respectively depending on the different offset launches (r) of the elementary fiber responses.