Optical Fiber Brillouin Measurement Using Second Harmonic Detection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The measurement accuracy of optical fiber characteristics using the homodyne BOCDR method is compromised by amplitude modulation (AM) noise, which degrades the spectrum of Brillouin scattered light, necessitating complex configurations to suppress this noise.
Innovation Solution
An optical fiber characteristics measurement apparatus and method that utilizes a second harmonic component of the frequency components of interference light between Brillouin scattered light and reference light, eliminating the need for noise suppression by detecting the second harmonic component instead of the direct current (DC) component, thereby simplifying the circuit and enhancing measurement stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If homodyne BOCDR method is used to measure optical fiber characteristics, then measurement capability is achieved, but measurement accuracy is degraded by AM noise
Solution Approach 1:
The patent extracts and isolates the second harmonic component (2f) from the homodyne detection signal, which contains the Brillouin scattered light spectrum information free from AM noise contamination. By selectively detecting only this frequency component through frequency filtering or spectral analysis, the harmful AM noise at other frequencies is effectively removed, achieving high-precision measurement of optical fiber characteristics.
2Measurement precision
If normalization processing is applied to remove AM noise, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
Instead of applying complex normalization processing to remove AM noise, the patent directly extracts the useful signal component (second harmonic at 2f) from the homodyne detection output. This frequency-selective extraction approach eliminates the need for complex normalization algorithms, achieving both high measurement accuracy and simplified system complexity through pure frequency-domain filtering.
3Measurement precision
If complex normalization processing is used to remove noise and bias, then measurement accuracy improves, but measurement process complexity increases
Solution Approach 1:
The patent simplifies the measurement process by directly extracting the second harmonic component (2f) from the homodyne detection signal, which inherently contains the Brillouin spectrum information without AM noise or bias. This frequency-domain extraction approach replaces complex normalization processing, achieving accurate measurements through a simpler, more direct process that requires no additional normalization algorithms or steps.
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
The method improves measurement accuracy and stability of optical fiber characteristics by reducing the influence of AM noise, eliminating the need for normalization processing, and ensuring long-term stability of Brillouin gain spectrum (BGS) measurements.
Implementation Method 1
a first optical splitter configured to split a modulated light subjected to frequency modulation into a pump light and a reference light
Implementation Method 2
extracting Brillouin scattered light generated within the fiber under test
Implementation Method 3
a signal yielded by homodyne detection of interference light between the Brillouin scattered light and the reference light
Data Source
AI summary
An optical fiber characteristics measurement apparatus includes a first optical splitter that splits modulated light into pump light and reference light, a second optical splitter that causes the pump light to be incident on a fiber under test from one end and extracts Brillouin scattered light generated within the fiber under test, an adjuster that changes frequency of at least one of the reference light and pump light to a plurality of frequencies, and a calculator that measures characteristics of the fiber under test based on a second harmonic component among frequency components of a signal yielded by homodyne detection of interference light between the Brillouin scattered light and the reference light at each frequency, the second harmonic component having a frequency that is two times the modulation frequency of the modulated light.