Wavelength-Dependent Reflective Element for OTDR Link Characterization
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Solution Overview
Problem
In point-to-multipoint optical networks, classical OTDR measurements are hindered by the summation of backreflected light from multiple links, making it difficult to unambiguously characterize individual links and measure optical path loss due to overlapping reflective events, especially when high splitter return loss and other wavelength-independent reflective events are present, which can obscure the peak detection accuracy and reduce fiber fault localization capabilities.
Innovation Solution
The method involves using an OTDR to launch light at two different wavelengths into the optical path, with a wavelength-dependent reflective element that is highly reflective at one wavelength but not at the other, allowing for the distinction of peaks corresponding to the reflective element from other localized reflectances by comparing the OTDR traces at each wavelength, thereby enhancing peak detection accuracy and reducing interference from other reflective events.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a highly reflective element is placed at a demarcation point to enable individual link characterization, then link identification capability is improved, but peak detection accuracy deteriorates due to interference from other wavelength-independent reflective events
Solution Approach 1:
The reflective element is designed to have wavelength-dependent reflectivity, being highly reflective at a first wavelength (e.g., 1310nm) and highly transmissive at a second wavelength (e.g., 1550nm). This local quality differentiation allows the system to selectively detect peaks from the reflective element by comparing OTDR traces at different wavelengths, thereby improving peak detection accuracy while maintaining link identification capability.
Solution Approach 2:
The invention changes the wavelength parameter of the OTDR measurements to differentiate between the reflective element peaks and other reflective events. By performing measurements at two different wavelengths and comparing the results, the system can identify which peaks correspond to the wavelength-dependent reflective element, thus resolving the peak detection accuracy issue.
2Measurement precision
If a highly reflective element is used to mark demarcation points, then fiber fault localization is enabled, but Rayleigh Backscattering signal measurement is obscured due to strong reflections
Solution Approach 1:
The system performs periodic OTDR measurements at different wavelengths. By alternating between measurements at the first wavelength (where the reflective element is highly reflective) and the second wavelength (where it is highly transmissive), the system can obtain both fault localization information and undisturbed Rayleigh Backscattering signals for loss measurement.
Solution Approach 2:
The wavelength-dependent reflective element acts as an intermediary that can be selectively activated or deactivated by changing the measurement wavelength. At the second wavelength, the element becomes effectively transparent, allowing the Rayleigh Backscattering signal to pass through without obstruction while still enabling fault localization at the first wavelength.
3Productivity
If classical OTDR measurements are made from the common point in point-to-multipoint networks, then all links can be monitored, but individual link characterization becomes ambiguous due to summation of backreflected light
Solution Approach 1:
The wavelength-dependent reflective element introduces a unique local quality characteristic to each link or demarcation point. This allows the OTDR system to distinguish and characterize individual links by identifying the specific wavelength-dependent peaks in the composite OTDR trace, even when monitoring all links simultaneously from the common point.
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
This approach improves the accuracy of peak detection and reduces interference from other reflective events, enabling better localization of fiber breaks and measurement of Rayleigh Backscattering signals, thus enhancing the reliability of optical path loss measurement in point-to-multipoint networks.
Implementation Method 1
The reflective element is generally highly reflective at an out-of-band wavelength reserved for testing (e.g. in the U band) and highly transmissive in the wavelength bands normally used for data-carrying optical signals
Implementation Method 2
supervisory systems of point-to-point optical networks to use Optical Time Domain Reflectometer (OTDR) measurements to monitor optical links
Implementation Method 3
measurement of Rayleigh Backscattering (RBS) of the optical path
Data Source
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Figure 3a~3c
AI summary
A method of distinguishing a wavelength-dependent reflective element (HRD) from wavelength-independent events in an optical network, the reflective element (HRD) being highly-reflective at a first predetermined wavelength (?1) and significantly less reflective at at least one other predetermined wavelength (?2), comprising the steps of: connecting the wavelength-dependent reflective element (HRD) to said optical path at a first position, and, using an optical time domain reflectometer (22) connected to said optical path at a position remote from said reflective element, launching into said optical path light at said first wavelength (?1) and at said second wavelength (?2), detecting corresponding backreflected light from said optical paths and obtaining therefrom first and second OTDR traces (OTDR-?1,OTDR-?2) corresponding to said first (?1) and second (?2) wavelengths, respectively, of detected backreflected light as a function of optical distance from said point; comparing the first and second OTDR traces to distinguish a peak corresponding to said wavelength-dependent reflective element from peaks corresponding to said wavelength-independent reflective events; and outputting at least one parameter value of the distinguished peak as a measure of a parameter of said wavelength-dependent reflective element.