Mode Field Diameter Measurement for Higher-Order Modes
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Solution Overview
Problem
Current methods are unable to measure the mode field diameter for higher-order modes beyond the first higher-order mode in few-mode optical fibers, which is crucial for estimating splice loss and inter-mode crosstalk.
Innovation Solution
A method and device that use far-field scanning to measure the far-field pattern of test light incident on an optical fiber, allowing calculation of the mode field diameter for arbitrary higher-order modes using specific equations based on the electric field distribution in both the far and near fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a far-field scanning technique is used to measure the mode field diameter of higher-order modes, then the measurement capability is extended to arbitrary higher-order modes, but the measurement complexity and device requirements increase
Solution Approach 1:
The measurement process is segmented into distinct steps: mode selective excitation, far-field pattern measurement, and mode field diameter calculation. This segmentation allows each component to be optimized independently and simplifies the overall system architecture.
Solution Approach 2:
A mode field diameter calculation unit is introduced as an intermediary that processes the measured far-field pattern data and computes the mode field diameter using mathematical relationships between near-field and far-field distributions. This intermediary component bridges the measurement and final parameter extraction.
2Measurement precision
If the spot size at the beam waist is used to represent the mode field diameter, then the estimation of splice loss and inter-mode crosstalk becomes possible, but existing methods cannot measure higher-order modes beyond the first higher-order mode
Solution Approach 1:
The measurement system is designed with universal applicability to measure the mode field diameter of any higher-order mode in few-mode fibers, not limited to specific modes. The far-field scanning technique combined with mathematical calculation provides a universal measurement approach for all propagable modes.
Solution Approach 2:
The method utilizes the mathematical relationship between near-field and far-field parameter changes to determine the mode field diameter. By measuring the far-field pattern and applying the appropriate mathematical transformation, the near-field spot size parameter can be derived without directly measuring the near-field distribution.
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
Enables the acquisition of mode field diameters with high dynamic range and resolution for arbitrary higher-order modes, addressing the limitations of existing methods by providing a precise measurement of spot size at the beam waist.
Implementation Method 1
an optical fiber under test... capable of propagating a plurality of modes
Implementation Method 2
measures a far-field pattern of the mode subject to measurement, with respect to a divergence angle θ at the other end of the optical fiber under test
Data Source
AI summary
The purpose of the present disclosure is to provide a mode field diameter test method and test device that enable acquisition of a mode field diameter for an arbitrary higher-order mode. The present disclosure is a mode field diameter test method including: a test light incidence procedure for selectively causing test light to be incident in a mode subject to measurement, on one end of an optical fiber 10 under test; a far-field pattern measurement procedure for measuring a far-field pattern of the mode subject to measurement, with respect to a divergence angle θ at the other end of the optical fiber under test, by a far-field scanning technique; and a mode field diameter calculation procedure for calculating, using an equation, a mode field diameter from information about incident mode orders in the test light incidence procedure and the far-field pattern measured in the far-field pattern measurement procedure.