Optical Fiber Clock Synchronization Using Wavelength Asymmetry
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Solution Overview
Problem
Existing time and frequency alignment methods in optical communications networks face limitations due to asymmetry in transit delays caused by differences in fiber path lengths and propagation velocities, which affect the accuracy of time transfer protocols like PTP and NTP.
Innovation Solution
The method involves using two distinct wavelength channels for forward and reverse timing signals over optical fiber links to compensate for transit delay asymmetry, allowing for precise synchronization of clocks by determining the ratio of velocities and path lengths using timing information exchanged between master and slave nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If separate fiber strands are used for forward and reverse signal transmission, then signal isolation is improved, but path length asymmetry increases causing timing accuracy to deteriorate
Solution Approach 1:
The patent applies asymmetry by intentionally introducing a known fixed path length difference through delay elements in one direction, rather than attempting to achieve symmetric paths. This known asymmetry can be compensated for in the timing calculation, resolving the contradiction between signal isolation and timing accuracy.
Solution Approach 2:
The patent introduces delay elements as intermediary components that actively manage the path length difference. These intermediaries compensate for the asymmetry introduced by using separate fiber strands, allowing both signal isolation and timing accuracy to be maintained.
2Measurement precision
If different wavelengths are used for forward and reverse timing signals, then transit delay asymmetry is compensated, but system complexity increases
Solution Approach 1:
The patent changes the wavelength parameter of the optical signals to compensate for transit delay asymmetry. By using different wavelengths for forward and reverse directions, the system exploits wavelength-dependent propagation characteristics to equalize effective delays, improving time transfer accuracy despite increased wavelength management complexity.
3Measurement precision
If GPS satellite timing signals are used for time alignment, then time synchronization is achieved, but cost increases and reliability decreases due to signal visibility requirements
Solution Approach 1:
The patent uses an intermediary master clock system that receives GPS timing signals and distributes synchronized time information through the optical fiber network. This intermediary approach shields individual network elements from direct GPS dependency, improving reliability while maintaining time alignment accuracy through the centralized master clock.
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 enhances the accuracy of time transfer in fiber-optic networks by mitigating asymmetry-related errors, ensuring precise clock synchronization even in environments with varying environmental conditions.
Implementation Method 1
transmit timing information from a master network element to a slave network element over an optical fiber link
Implementation Method 2
asymmetry in the physical medium, asymmetry in the construction of the forward and reverse paths in the network elements, and other sources. PTP and NTP assume that transit delays between master and slave clocks are symmetric
Data Source
AI summary
A clock at a first network element that is connected to a second network element over first and second optical links that are physically distinct from each other is aligned using optical timing signals having different wavelengths. Transit delays between the first and second network elements may be determined using the same optical timing signals.