Optical Fiber Testing with BOTDA for Higher-Order Mode Loss
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Solution Overview
Problem
Existing methods fail to accurately measure the maximum loss of higher-order modes at optical fiber connection points due to varying electric field distributions, which differ between round trips, necessitating a method to measure one-way loss with changing electric field distributions.
Innovation Solution
An optical fiber test method and device using Brillouin Optical Time Domain Analysis (BOTDA) to measure maximum loss by varying probe and pump light wavelengths, allowing for precise detection of connection losses through changing electric field distributions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If back-scattered light measurement is used to evaluate connection loss, then measurement can be performed, but only average loss values are obtained and maximum loss cannot be acquired due to varying electric field distributions
Solution Approach 1:
Instead of measuring back-scattered light from the input end, the invention launches test light from the output end of the optical fiber and measures the light after it has propagated through the fiber. This inversion of the measurement direction allows capturing the actual one-way loss characteristics including maximum loss values that occur with varying electric field distributions of higher-order modes.
Solution Approach 2:
The invention changes the propagation mode parameter by exciting higher-order modes (such as LP11 mode) instead of using only fundamental modes. By specifically selecting higher-order modes with non-uniform electric field distributions, the measurement can capture the maximum loss characteristics that vary with electric field distribution, thereby obtaining maximum loss information that was previously unavailable.
2Measurement precision
If higher-order modes are used for measurement, then maximum loss can be captured, but loss values vary with electric field distribution changes
Solution Approach 1:
The invention performs multiple measurements at different positions along the optical fiber and combines these measurements to determine the maximum loss. By systematically varying the measurement position and collecting multiple data points, the method captures the variations in loss values caused by electric field distribution changes and identifies the maximum loss through periodic sampling and comparison.
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 accurate acquisition of maximum loss values at optical fiber connection points by capturing variations in higher-order mode losses using wavelength-dependent Brillouin interaction, thereby improving evaluation of transmission line quality.
Implementation Method 1
allowing pulsed pump light, which is shifted to a high frequency side by a frequency at which a Brillouin interaction occurs with respect to the probe light
Data Source
AI summary
An object is to provide an optical fiber test method and an optical fiber test device capable of acquiring a maximum loss of a higher-order mode at a connection point of an optical fiber transmission line through which a plurality of modes propagate.The optical fiber test device according to the present invention includes: a light source unit 10 that allows probe light L1, which has a tunable wavelength and is continuous light, to enter one end T1 of an optical fiber in a fundamental mode and allows pulsed pump light L2, which is shifted to a high frequency side by a frequency at which a Brillouin interaction occurs with respect to the probe light L1, to enter the other end T2 of the optical fiber in a higher-order mode as a measurement target; and an analysis unit 20 that acquires, from a light intensity of the probe light L3 amplified by the pump light L2, a time waveform of an amplification component, calculates a connection loss of the pump light L2 at a connection point from a ratio of the amplification components before and after the connection point, acquires a wavelength dependency of the connection loss, detects a maximum value of the connection loss from the wavelength dependency of the connection loss, and sets the maximum value as a maximum loss of the higher-order mode at the connection point.