Optical Signal Propagation Delay Measurement via Loopback
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Solution Overview
Problem
Existing methods for measuring the propagation time of an optical signal between two devices in an optical transmission network are inaccurate due to asymmetry between the two optical fibers, particularly when the fibers have different lengths, leading to errors that cannot be quantified, especially in cases where the difference is small but significant, affecting applications requiring precise synchronization and resource allocation.
Innovation Solution
A method that involves using loopback means to inject a return signal into the first optical fiber, allowing for accurate measurement of the propagation time by determining the time difference between the transmission and reception of the measurement signal, while also accounting for internal processing time to correct for asymmetry, using optical components and electronic processing to achieve precise timing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a round-trip propagation time measurement is performed using separate optical links for each direction, then the internal processing time can be obtained, but the measurement precision deteriorates due to link asymmetry
Solution Approach 1:
The patent merges the forward and return signal paths by using the same optical fiber for both directions. The loopback mechanism at the remote device sends the measurement signal back through the same fiber it arrived on, eliminating the asymmetry between separate links and enabling accurate one-way propagation time measurement.
Solution Approach 2:
Instead of measuring round-trip time through separate links and dividing by two (which introduces error due to asymmetry), the patent inverts the approach by having the remote device loop back the signal on the same link, directly measuring the one-way propagation time without the asymmetry error.
2Productivity
If separate optical fibers are used for bidirectional transmission, then simultaneous communication in both directions is enabled, but propagation time measurement accuracy deteriorates due to fiber length differences
Solution Approach 1:
The patent combines the measurement path for both directions into a single optical fiber by implementing a loopback at the remote device. This allows the same fiber to carry the measurement signal in both directions, eliminating the precision errors caused by using separate fibers with different lengths.
Solution Approach 2:
The loopback mechanism acts as an intermediary at the remote device that receives the measurement signal on one optical fiber and returns it on the same fiber, enabling accurate one-way propagation time measurement while maintaining bidirectional communication capabilities.
Data Source
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AI summary
The invention relates to a technique for measuring a propagation delay of an optical signal between two devices (N1, N2) in an optical transmission network, the optical signal being transmitted from the first device to the second device via a first optical fibre (FO1) and from the second device to the first device via a second optical fibre (FO2), separate from the first optical fibre, the second device including a so-called loopback means, capable, in a first mode, of enabling the optical signal to be routed between the two devices. A measurement method includes the following steps implemented by the second device: a detection step (F11) during which the triggering of a measurement of the propagation delay of a measurement signal is detected, the measurement signal being transmitted by the first device via the first optical fibre; a step (F12) of configuring the loopback means in a second mode, said second mode enabling a return signal of the measurement signal transmitted by the first device to be fed into the first optical fibre. The first device, in turn, implements a method for determining the propagation delay. Said determination method includes the following steps implemented by the first device: a step of triggering (E11, E14) a measurement of the propagation delay of a measurement signal via the first fibre, the measurement signal being transmitted towards the second device via the first optical fibre; a step of receiving (E15) a return signal transmitted by the second device over the first optical fibre; a step of determining (E16) said propagation delay according to one instant of transmitting the measurement signal and one instant of receiving the return signal.