Nonlinear Spatially Resolved Interferometer for Optical Cable Characterization
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Solution Overview
Problem
Current methods for characterizing optical properties of submarine cables, such as dispersion maps and power profiles, are limited by the inability to measure these properties at arbitrary wavelengths and the difficulty in detecting polarization-dependent loss and polarization-mode dispersion across multi-span systems due to blocked counter-propagating waves and weak back-scattered signals.
Innovation Solution
The use of pump-probe measurements on multi-span optical links allows for the determination of wavelength-dependent power profiles, gain evolution, and location of high polarization-dependent loss and polarization-mode dispersion regions by spatially overlapping pump and probe pulses at specific positions along the link, utilizing high-loss loopbacks and coherent references to isolate nonlinear interactions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pump-probe measurements are used to measure power profile at arbitrary wavelengths, then measurement capability is improved, but device complexity increases due to need for multiple wavelengths and HLLB channels
Solution Approach 1:
The patent employs high-loss loopback (HLLB) channels that can reflect optical signals at multiple wavelengths, allowing the same infrastructure to serve multiple measurement purposes across different wavelength bands, thereby improving measurement capability without proportionally increasing complexity
Solution Approach 2:
The patent introduces HLLB channels as intermediary elements that enable the extraction of probe signals from the return path, facilitating wavelength-dependent power profile measurements without requiring direct access to amplifier outputs at all wavelengths
2Measurement precision
If coherent OTDR is used to measure loss along the link, then loss measurement capability is improved, but inability to measure dispersion map and power profile at arbitrary wavelengths remains
Solution Approach 1:
The patent combines coherent OTDR technology with pump-probe measurements and HLLB channels, merging the advantages of loss measurement capability with the ability to measure dispersion maps and power profiles at arbitrary wavelengths, thereby achieving comprehensive optical link characterization
Solution Approach 2:
The patent enables continuous measurement of multiple optical parameters (loss, dispersion, power profile) across different wavelengths by integrating multiple measurement techniques into a unified approach, eliminating gaps in measurement coverage
3Measurement precision
If P-OTDR is used to measure polarization state, then polarization measurement capability is improved, but reach is limited to several kilometers due to weak back-scattered signal
Solution Approach 1:
The patent uses HLLB channels as intermediaries to extract and redirect probe signals that have interacted with the optical link, enabling polarization measurements at distances beyond the conventional P-OTDR reach by avoiding the limitation of weak back-scattered signals from the far end
4Measurement precision
If pump-probe measurements are used to determine wavelength-dependent power profile and dispersion map, then diagnostic accuracy is improved, but measurement time increases
Solution Approach 1:
The patent employs periodic modulation of pump and probe signals, allowing measurements to be performed in repeated cycles that can be averaged to improve signal-to-noise ratio, thereby achieving high measurement accuracy while managing measurement time through efficient periodic sampling
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 enables accurate diagnostic and maintenance activities for deployed cables by providing detailed optical property characterization, including wavelength-dependent power profiles and dispersion maps, and identifying regions of high PDL and PMD, enhancing commissioning and maintenance processes.
Implementation Method 1
The pump pulse and the probe pulse spatially overlap in the optical fiber to generate a nonlinear interaction between the pump pulse and the probe pulse
Implementation Method 2
the calculated physical properties of the pump pulse provide insight into physical characteristics of the optical link
Implementation Method 3
High-loss loopbacks (HLLBs) installed at amplifier sites along the optical link are used to extract the probe pulse from the return path. The HLLB reflects the probe wavelength into the return path while blocking the pump wavelength
Implementation Method 4
The optical amplifier amplifies the probe wavelength signal in the return path
Implementation Method 5
A coherent receiver at the second transceiver measures the phase and polarization state of the probe pulse
Data Source
AI summary
Using pump-probe measurements on multi-span optical links may result in the determination of one or more of the following: 1) wavelength-dependent power profile and gain evolution along the optical link; 2) wavelength-dependent dispersion map; and 3) location of regions of high polarization-dependent loss (PDL) and polarization-mode dispersion (PMD). Such measurements may be a useful diagnostic for maintenance and upgrade activities on deployed cables as well as for commissioning new cables.