Optical Fiber Mode Delay Measurement Using Autocorrelation Signals
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional low-coherence optical interferometry requires precise optical path length adjustment and stable installation environments, limiting the measurable optical fiber length to short lengths, making it difficult to measure km-order long optical fibers used in actual transmission paths.
Innovation Solution
A device using two light sources, a first light source for incident light and a second light source for local light, multiplexes transmitted light with local light and performs digital signal processing on the combined signal to calculate an autocorrelation function, allowing mode dispersion measurement without an interferometer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional low-coherence optical interferometry is used to measure mode dispersion, then measurement precision can be achieved, but the device complexity and requirement for precise optical path length adjustment increase
Solution Approach 1:
The patent extracts the interferometer from the measurement system and replaces it with a simplified apparatus that uses a single light source and digital signal processing. The core function of measuring mode dispersion is maintained while removing the complex optical path adjustment mechanism, thereby reducing device complexity while preserving measurement precision.
Solution Approach 2:
The patent replaces the mechanical optical path length adjustment system with a digital signal processing system. Instead of physically adjusting optical paths to achieve measurement, the system uses computational methods (autocorrelation function calculation) to extract mode dispersion information from the received light signal, eliminating mechanical complexity.
2Measurement precision
If conventional low-coherence optical interferometry is used, then mode dispersion can be measured, but the measurable optical fiber length is limited to short lengths
Solution Approach 1:
The patent replaces the mechanical interferometer with a digital measurement system that does not rely on physical optical path length adjustment. This substitution enables the measurement of long optical fibers (km-order) by using digital signal processing to detect mode dispersion characteristics without being constrained by the physical length adjustment capabilities of traditional interferometers.
Solution Approach 2:
The patent transitions from a spatial dimension-based measurement (optical path length adjustment) to a temporal dimension-based measurement (autocorrelation function analysis). By measuring the time-domain characteristics of the light signal through autocorrelation processing, the system can determine mode dispersion for long fibers without being limited by spatial adjustment ranges.
3Measurement precision
If conventional low-coherence optical interferometry is used, then mode dispersion measurement is possible, but the ease of operation decreases due to stable installation environment requirements
Solution Approach 1:
The patent extracts the sensitive optical interference measurement function from the conventional interferometer and implements it through digital signal processing of intensity fluctuations. This extraction eliminates the need for stable installation environments while maintaining measurement precision, as the digital processing can compensate for various environmental variations.
Solution Approach 2:
The measurement system performs self-calibration and compensation through digital signal processing. The autocorrelation function calculation automatically accounts for various environmental factors and optical characteristics, making the system robust against installation environment variations and eliminating the need for careful environmental control.
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 mode dispersion measurement over a wide range without the need for precise optical path length adjustment, simplifying the measurement process and extending the measurable optical fiber length beyond conventional limits.
Implementation Method 1
a first light source for outputting incident light to a measured optical fiber or optical device
Implementation Method 2
a second light source for outputting local light for being multiplexed with transmitted light through the measured optical fiber or optical device
Implementation Method 3
The signal processing unit is configured to calculate an autocorrelation function between the light-receiving signal I(t) and a signal I(t+τ) obtained by shifting the light-receiving signal by a time τ
Implementation Method 4
The signal processing unit is configured to measure a delay time difference between propagation modes in the measured optical fiber or optical device, using a peak position of the autocorrelation function R(τ) with respect to τ
Implementation Method 5
The signal processing unit is configured to measure mode dispersion in the measured optical fiber or optical device, using a distribution of peaks of the autocorrelation function R(τ) with respect to τ
Data Source
AI summary
The present disclosure relates to a device, including: a first light source for outputting incident light to a measured optical fiber or optical device; a second light source for outputting local light for being multiplexed with transmitted light through the measured optical fiber or optical device; and a signal processing unit for performing digital signal processing on a light-receiving signal I(t) obtained by multiplexing the transmitted light and the local light, wherein the signal processing unit is configured to calculate an autocorrelation function between the light-receiving signal I(t) and a signal I(t+τ) obtained by shifting the light-receiving signal by a time τ, and to measure a delay time difference between propagation modes in the measured optical fiber or optical device, from a peak position of the autocorrelation function.