Fiber-Optic Time Transfer System with OEO Relaying
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Solution Overview
Problem
Current fiber-optic time transfer technologies face challenges with noise accumulation due to multiple optical amplifications, such as Rayleigh backscattering, which deteriorate the signal-to-noise ratio and limit the length of the fiber link, and existing solutions either compromise on signal quality or require complex calibration.
Innovation Solution
A high-precision long-distance distributed fiber-optic time transfer system using bidirectional time division multiplexing over a single fiber with the same wavelength, where timing signals are passed through a series path with relay and user units performing optical-electric-optical relaying, and bidirectional optical amplifying units to maintain symmetry and avoid noise amplification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If bidirectional optical amplification is performed to compensate for attenuation in long-distance fiber-optic time transfer, then the transmission distance is extended, but noise accumulation from multiple amplifications deteriorates the signal-to-noise ratio
Solution Approach 1:
The fiber link is divided into multiple segments with amplifiers placed at specific intervals. Each amplifier handles a limited section, preventing cumulative noise from propagating through the entire link. The segmentation allows the system to achieve long-distance transmission while controlling noise accumulation within manageable segments.
Solution Approach 2:
Optical amplifiers serve as intermediary devices that boost the optical signal without converting it to electrical form. By using optical amplifiers as mediators, the system extends transmission distance while avoiding the noise accumulation associated with multiple electro-optical conversions. The amplifiers are strategically positioned to provide just enough gain to maintain signal quality over long distances.
2Length of stationary object
If bidirectional amplification is performed to extend transmission distance, then the fiber link length is increased, but the system complexity increases due to multiple amplifiers requiring calibration
Solution Approach 1:
The patent employs asymmetric amplifier configuration where amplifiers are positioned at different locations in the bidirectional path, allowing one direction to have fewer amplification stages than the other. This asymmetry reduces the total number of amplifiers needed while maintaining adequate signal levels, thereby reducing calibration complexity. The asymmetric design accepts some delay asymmetry that can be managed through software correction rather than requiring symmetric hardware configuration.
Solution Approach 2:
The system dynamically adjusts amplifier gain parameters and operational settings based on measured signal characteristics and noise levels. By changing operational parameters rather than hardware configuration, the system adapts to varying conditions without requiring physical recalibration of each amplifier, thereby reducing system complexity while maintaining long-distance transmission capability.
3Measurement precision
If distributed Raman amplification is used to ensure bidirectional delay symmetry, then the time delay symmetry is improved, but noise such as Rayleigh scattering is still multiple optically amplified
Solution Approach 1:
The patent replaces distributed Raman amplification (which uses optical pumping) with discrete optical amplifiers that use electrical pumping. This substitution changes the amplification mechanism from optical to electrical, thereby avoiding the multiple optical amplifications of Rayleigh scattering noise while maintaining time delay symmetry through careful amplifier placement and gain control. The electrical pumping mechanism does not exhibit the same noise amplification characteristics as optical pumping.
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 ensures maximum symmetry of the bidirectional delay and effectively avoids the negative effects of noise amplification, enabling stable and precise long-distance time transfer by utilizing the bidirectional timing signal time interval received by relay and user units.
Implementation Method 1
bidirectional optical amplifying units to maintain symmetry and avoid noise amplification
Implementation Method 2
relay and user units performing optical-electric-optical relaying
Implementation Method 3
utilizing the bidirectional timing signal time interval received by relay and user units
Data Source
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AI summary
A method and a system for fiber-optic time transfer in the field of fiber-optic time and frequency transfer. The system for high-precision long-distance distributed fiber-optic time transfer is composed of a first clock source, a first fiber-optic time transfer unit, N relay and user units, M bidirectional optical amplifying units, a second fiber-optic time transfer unit and a second clock source. Each relay and user unit can obtain timing signals synchronized with the first clock source according to the time interval between the received forward and backward timing signals and realize distributed fiber-optic time transfer while realizing the optical-electric-optical relay of the forward and backward transmitted optical signals. The invention makes the bidirectional time signals pass through the same link to ensure maximum symmetry of the main link bidirectional delay; the effect of multiple optical amplifications of noise such as Rayleigh scattering on the stability of the fiber-optic time transfer is effectively avoided by the optical-electric-optical process; the distributed time transfer is realized by the bidirectional timing signal time interval received by the relay and user units.