Optical Reflectometer Coherence Correction for Distance Resolution
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Solution Overview
Problem
Existing optical reflectometry techniques, such as OFDR, face limitations in measurement distance due to the coherence length of the frequency sweep light source, leading to deteriorated resolution and inability to perform accurate measurements beyond half the coherence length.
Innovation Solution
The optical reflectometer corrects the spectrum spread by utilizing a monitoring beat signal and phase information to compensate for phase noise, allowing measurements beyond the coherence length through advanced signal processing and interferometric techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If OFDR measurement is performed beyond half the coherence length of the frequency sweep light source, then the measurement distance is extended, but the resolution deteriorates due to spectral width spreading of the beat signal
Solution Approach 1:
The patent uses a feedback mechanism where the phase information from the monitoring beat signal is fed back to correct the measurement beat signal. The processing unit extracts phase information from the monitoring beat signal and uses it to correct the measurement beat signal, thereby compensating for the spectral width spreading and maintaining resolution even when measurement distance exceeds half the coherence length.
Solution Approach 2:
The patent introduces an intermediary monitoring beat signal that carries phase information about the light source. This monitoring beat signal acts as a mediator between the light source characteristics and the measurement beat signal, allowing the system to compensate for coherence length limitations without directly altering the measurement process.
2Length of stationary object
If the measurement distance exceeds half the coherence length, then the optical path difference increases, but coherency between local light emission and backscattered light is eliminated causing spectral width spreading
Solution Approach 1:
The system continuously monitors the phase information from the monitoring beat signal and feeds it back to correct the measurement beat signal. This feedback mechanism compensates for the loss of coherency by dynamically adjusting the phase reference, allowing measurements beyond half the coherence length while maintaining signal integrity.
Solution Approach 2:
The patent creates a copy of the light source characteristics through the monitoring beat signal. By generating and analyzing a monitoring beat signal that replicates the phase variations of the light source, the system can compensate for coherency loss in the main measurement path without requiring the actual light paths to remain coherent over extended distances.
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 optical reflectometry measurements irrespective of the measurement distance, enhancing distance resolution and overcoming the limitations imposed by the coherence length of the frequency sweep light source.
Implementation Method 1
output light emitted from a frequency sweep light source is branched into two
Implementation Method 2
backscattered light (reflected light that the measurement light is reflected and generated at each position corresponding to a propagation distance of the measured optical circuit)
Implementation Method 3
an interference beat signal that is generated by interference between light reflected from a measurement target and one of pieces of branched light
Implementation Method 4
The interference beat signal generated by the multiplexing of the branched light and the backscattered light is detected to analyze a spectrum of the interference beat signal
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3
AI summary
An object of the invention is to provide an optical reflectometry and an optical reflectometer, in which accurate measurement can be performed irrespective of a measurement distance. In the optical reflectometry and optical reflectometer according to the invention, in which a distribution of backscattered light intensity from a measurement target in an optical propagation direction is measured using Optical Frequency Domain Reflectometry (OFDR), a coherence monitor unit 12 that monitors a coherence property of a frequency sweep light source 1 is provided, and measurement result of a measuring unit 11 is corrected based on the monitor result of the coherence monitor unit 12.