Long-Range Optical Frequency-Domain Reflectometry Using Delayed Local Light
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Solution Overview
Problem
Existing optical frequency domain reflectometry systems are limited to measuring distances of 10 m with a spatial resolution of 100 µm or lower due to limitations in clock quality and sampling intervals, preventing accurate analysis of backscattered light waveforms beyond the coherence length of the light source.
Innovation Solution
An optical frequency domain reflectivity measuring apparatus and method that utilizes a local light delay fiber and a 90-degree hybrid to assign positive and negative beat frequencies, enabling long-distance measurements exceeding 1 km with a spatial resolution of 100 µm or lower by compensating for wavelength dispersion and using a reference interferometer shorter than the laser coherence length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the fiber length of the reference interferometer is made longer to increase measurement distance, then the measurable distance increases, but the clock quality deteriorates and the beat signal cannot be sampled at equal intervals
Solution Approach 1:
The measurement process is divided into two independent parts: a short reference interferometer for generating high-quality clock signals and a long delay optical fiber for extending measurement distance. This segmentation allows each component to be optimized independently - the short interferometer maintains good clock quality while the long fiber enables long-distance measurement.
Solution Approach 2:
A delay optical fiber is introduced as an intermediary element between the light source and the reference interferometer. This delay fiber compensates for the phase difference caused by the long measurement distance, allowing the short reference interferometer to still generate accurate clock signals for sampling the backscattered light waveform.
2Length of moving object
If the fiber length of the reference interferometer is made longer to increase measurement distance, then the measurable distance increases, but the spatial resolution degrades
Solution Approach 1:
The system separates the functions of distance extension and resolution maintenance into different components. The delay optical fiber handles distance extension, while the short reference interferometer maintains the spatial resolution through high-quality clock signals that enable precise sampling of the backscattered light waveform.
3Length of moving object
If the fiber length of the reference interferometer is made longer to increase measurement distance, then the measurable distance increases, but the backscattered light waveform cannot be analyzed correctly
Solution Approach 1:
The delay optical fiber acts as an intermediary that compensates for the phase delay in long-distance measurements. This allows the short reference interferometer to generate accurate clock signals that can properly sample and analyze the backscattered light waveform, preventing information loss in the waveform analysis.
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 measurement of long distances up to 1 km with ultra-high spatial resolution of 100 µm, allowing for the diagnosis of the health of optical devices installed at great distances.
Implementation Method 1
a delay optical fiber for delaying local light by a prescribed time
Implementation Method 2
combining the backscatter light from the optical fiber under measurement and the local light delayed by the delay optical fiber
Implementation Method 3
measuring an in-phase component and an orthogonal component of a beat signal obtained by combining
Data Source
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AI summary
The present disclosure aims to enable measurement of a long distance exceeding 1 km with a spatial resolution of 100 um or lower, and diagnosis of health of an optical device installed at a long distance. An apparatus according to the present disclosure is an optical frequency domain reflectivity measuring apparatus that includes: a local light delay fiber that delays local light; an optical 90-degree hybrid that receives an input of the local light delayed by the local light delay fiber and backscattered light from the measurement target, causes the local light and the backscattered light to interfere with each other, and generates an in-phase component and an orthogonal component of a beat signal generated by the interference; and a balance photodetector that detects the in-phase component and the orthogonal component of the beat signal. In the apparatus, an optical frequency response of the measurement target is measured with respect to a relative distance based on the local light delay fiber.