Optical Fiber Clock Synchronization Asymmetry Correction
Solution Overview
Problem
Existing time and frequency alignment methods in optical communications networks, such as PTP and NTP, are limited by asymmetry in transit delays due to differences in forward and reverse path lengths through optical fiber strands, which restricts the accuracy of time transfer in fiber-optic networks.
Innovation Solution
The method involves calibrating the asymmetry between optical fiber strands by measuring the phase difference of wave-fronts at close but distinct frequencies, and using these measurements to estimate and correct the time-alignment error, thereby improving the synchronization accuracy between network elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate fiber strands are used for forward and reverse signal transmission, then signal isolation is improved, but transit delay asymmetry increases
Solution Approach 1:
The patent applies asymmetry by intentionally introducing a compensating delay in the shorter path to match the longer path, transforming the inherent asymmetry problem into a controlled symmetric state. This resolves the contradiction by maintaining separate fiber strands for signal isolation while correcting the transit delay asymmetry through deliberate path equalization.
Solution Approach 2:
The patent changes the delay parameter of one path by introducing adjustable delay elements to match the delay of the other path. This parameter adjustment equalizes the round-trip delays while preserving the separate fiber strand configuration, thereby maintaining signal isolation while improving time alignment accuracy.
2Measurement precision
If path length variation is reduced, then time alignment accuracy is improved, but deployment flexibility is reduced
Solution Approach 1:
The patent measures and records the actual path lengths during deployment before final configuration, then uses these measurements to calculate and apply appropriate delay compensations. This preliminary measurement action enables accurate time alignment while allowing flexible deployment configurations to be established first and corrected later.
Solution Approach 2:
The patent introduces delay adjustment mechanisms as intermediary elements that can be configured based on measured path differences. These intermediaries enable the system to accommodate various deployment configurations while maintaining accurate time alignment, thus preserving deployment flexibility without sacrificing precision.
3Measurement precision
If GPS satellite timing signals are used, then time alignment accuracy is improved, but system cost and complexity increase
Solution Approach 1:
The patent creates a virtual timing reference by measuring and compensating for path delays in the existing fiber infrastructure, effectively copying the function of GPS-based absolute timing without requiring satellite reception equipment. This approach achieves accurate relative time alignment between network elements using only the existing communication infrastructure.
Solution Approach 2:
The patent enables the network infrastructure itself to provide timing synchronization by using the communication channels already present in the system. The fiber optic cables that carry data traffic also serve as the timing reference medium, eliminating the need for separate GPS receivers and external timing sources at each network element.
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 precision of time alignment by reducing the time-alignment error introduced by asymmetry, allowing for more accurate synchronization of clocks in optical fiber networks, achieving improved time transfer accuracy and stability.
Implementation Method 1
measuring the phase difference of wave-fronts at close but distinct frequencies
Data Source
AI summary
A clock at a first network element that is connected to a second network element over an optical fiber link is aligned in time/phase using packet protocols such as PTP. The invention discloses how to correct the asymmetry error inherent in traditional packet-based time-transfer methods.