Optical Fiber Strain Measurement Using Wavelength Separation
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional optical fiber strain measurement apparatuses using Brillouin OTDR face challenges in achieving sufficient signal-to-noise ratio (S/N) due to the weakness of spontaneous Brillouin scattered light, leading to prolonged measurement times and inadequate polarization control, especially when there is a mismatch between the center wavelength of Brillouin backscattered light and the narrow band pass filter.
Innovation Solution
An optical fiber strain and temperature measurement apparatus that employs a wavelength control unit with a wavelength separation filter and a band rejection type variable wavelength filter to separate and remove remaining Rayleigh scattered light, allowing for precise control of polarization states even when the wavelength of scattered light changes, thereby enhancing the S/N ratio and measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If heterodyne detection is used to improve signal-to-noise ratio, then light receiving sensitivity is improved, but measurement time is prolonged due to averaging process
Solution Approach 1:
The patent applies preliminary action by performing polarization control at the light source side before the light enters the optical fiber. The polarization controller adjusts the polarization state of the probe light in advance, ensuring that the Brillouin scattered light maintains a consistent polarization state throughout the measurement process. This eliminates the need for post-measurement polarization adjustments and averaging processes, thereby reducing measurement time while maintaining high signal-to-noise ratio through heterodyne detection
2Measurement precision
If narrow band pass filter is used to separate Brillouin scattered light, then wavelength selectivity is improved, but polarization control becomes inadequate when wavelength mismatch occurs
Solution Approach 1:
The patent introduces an intermediary element - a polarization controller placed at the light source side - that mediates between the probe light generation and the Brillouin scattering process. This polarization controller acts as an intermediary device that pre-adjusts the polarization state of the probe light, ensuring that even when wavelength filtering occurs through the narrow band pass filter, the polarization control remains accurate and reliable throughout the measurement system
3Measurement precision
If averaging process is performed to improve signal-to-noise ratio, then measurement accuracy is improved, but measurement time is significantly increased
Solution Approach 1:
The patent performs preliminary polarization control at the light source side before light enters the optical fiber. By pre-adjusting the polarization state of the probe light using a polarization controller, the system ensures that Brillouin scattered light maintains consistent polarization characteristics throughout the measurement. This preliminary action eliminates the need for repeated measurements and averaging processes, thereby achieving high signal-to-noise ratio without the time penalty associated with averaging
Solution Approach 2:
The system achieves self-service by maintaining stable polarization conditions through preliminary control, allowing the measurement system to operate without requiring post-processing averaging. The polarization controller at the light source side creates optimal conditions that enable single-shot or reduced-number measurements to achieve the required signal-to-noise ratio, making the system self-sufficient without needing extensive averaging to compensate for polarization variations
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 apparatus effectively suppresses the reduction of S/N by matching the set wavelength of the band rejection type variable wavelength filter with the Rayleigh scattered light, enabling sufficient polarization control and reducing unnecessary power loss, thus improving the measurement efficiency and accuracy of optical fiber strain and temperature measurements.
Implementation Method 1
a wavelength separation filter that separates Rayleigh scattered light from the backscattered light
Implementation Method 2
a band rejection type variable wavelength filter that removes remaining components of Rayleigh scattered light
Implementation Method 3
by using self-delayed heterodyne BOTDR (SDH-BOTDR) technique, changes in frequency of light are measured as phase differences of the beat signal given by coherent detection
Implementation Method 4
optical fiber strain measurement apparatus and an optical fiber strain measurement method which use spontaneous Brillouin scattered light
Implementation Method 5
The frequency shift and the spectral line width of the BGS are referred to as the Brillouin frequency shift (BFS) and the Brillouin line width, respectively. The BFS and the Brillouin line width vary depending on the material of the optical fiber and the wavelength of the incident light
Data Source
AI summary
By removing remaining components of Rayleigh scattered light, control is sufficiently performed of polarization states even when the wavelength of scattered light has changed. A light source unit configured to generate probe light, a wavelength control unit configured to receive backscattered light emitted from an optical fiber to be tested by the probe light and to output Brillouin backscattered light included in the backscattered light, and a self-delayed heterodyne interferometer to which the Brillouin backscattered light is input are included. The wavelength control unit includes a wavelength separation filter, a variable wavelength filter, an optical intensity measurement unit, and a control unit. The wavelength separation filter has two output ports, outputs and transmits, from one of the two output ports, the Brillouin backscattered light to the variable wavelength filter, and outputs and transmits, from the other output port, Rayleigh scattered light to the optical intensity measurement unit. The optical intensity measurement unit measures a center wavelength and a peak intensity of the Rayleigh scattered light. The control unit controls a cutoff wavelength of the variable wavelength filter in accordance with a direction and amount of change of the center wavelength.