Monofibre Line Supervision via Probe Signal Polarization
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Solution Overview
Problem
Existing single-fiber optical link supervision methods are unreliable due to Rayleigh and Brillouin scattering effects, which make it difficult to distinguish the probe signal from backscattered light, leading to inaccurate detection of fiber deterioration or cuts.
Innovation Solution
The method involves modifying the polarization of the probe signal at the remote terminal before retransmission, using a Faraday rotator mirror, to differentiate between backscattered and retransmitted signals, allowing the central terminal to isolate and measure only the retransmitted signal for accurate supervision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the probe signal power is increased to improve detection sensitivity, then the ability to detect fiber deterioration improves, but the backscattering effects (Rayleigh and Brillouin) increase making signal differentiation more difficult
Solution Approach 1:
The patent changes the polarization parameter of the probe signal by 90 degrees at the remote terminal. This parameter change allows the retransmitted signal to be differentiated from the backscattered signal based on polarization state, enabling reliable detection even when signal power is increased and backscattering effects become more significant.
2Quantity of substance
If optical filters are used to separate probe wavelength from data wavelengths, then wavelength separation is achieved, but the probe signal cannot be distinguished from backscattered light of the same wavelength
Solution Approach 1:
Instead of relying solely on wavelength filtering, the patent introduces a polarization parameter change. The remote terminal rotates the polarization of the probe signal by 90 degrees before retransmission, creating a distinguishable characteristic that allows the central terminal to differentiate the retransmitted signal from backscattered signal using polarization-sensitive detection.
3Reliability
If the probe signal is continuously transmitted to maintain supervision, then real-time monitoring is achieved, but energy consumption increases and Brillouin scattering occurs at high power levels
Solution Approach 1:
The patent implements periodic probe signal transmission with a period of at least 1 ms. This periodic action maintains real-time monitoring capability while allowing the system to operate at lower average power levels, avoiding continuous high-power transmission that would cause Brillouin scattering and excessive energy consumption.
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 significantly reduces the impact of Rayleigh scattering, enabling reliable detection of fiber malfunctions or breaks by distinguishing between different polarizations of the probe signal, resulting in improved supervision accuracy and reduced energy consumption.
Implementation Method 1
modification of the first polarization of the probe signal to a second polarization
Implementation Method 2
The propagation of light in the fiber gives rise to certain phenomena such as Rayleigh scattering
Implementation Method 3
The second phenomenon (Brillouin) is a non-linear effect appearing in the fiber when the power level of the injected signal is too high
Data Source
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Figure 3~6
AI summary
The invention relates to a method for retransmitting a probe signal, implemented by a device in a remote terminal (RT) connected to a central terminal (CT) by a monofibre optical line (MFOL), the probe signal being received by the remote terminal (RT) and having a predetermined wavelength (λprobe), the central and remote terminals exchanging over said optical lines useful data signals (λd, λu) having wavelengths other than those of the probe signal, including the following steps: receiving the polarised probe signal at a first polarity (P1); retransmitting the probe signal over the monofibre line toward the central terminal; and, prior to the retransmission step, a step of switching the first polarity (P1) of the probe signal to a second polarity (P2).