Optical Time Distributor for Sub-Femtosecond Clock Synchronization
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Solution Overview
Problem
Current time distribution methods, particularly over free-space links, face challenges in achieving sub-femtosecond synchronization between distant clocks due to atmospheric turbulence and motion, and existing RF-based techniques are limited in precision and stability.
Innovation Solution
An optical time distributor using frequency combs and phase-modulated laser signals for two-way time-frequency transfer (O-TWTFT) over a single-mode free-space link, enabling real-time synchronization and frequency comparison between distant clocks with sub-femtosecond accuracy, despite turbulence and motion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If RF-based time distribution methods are used over free-space links, then device complexity is reduced, but measurement precision deteriorates due to atmospheric turbulence and motion
Solution Approach 1:
The patent replaces RF-based time distribution with optical frequency comb-based time distribution. The optical frequency comb acts as a bridge between optical and RF domains, enabling precise time-frequency transfer while avoiding the limitations of direct RF transmission through turbulent atmosphere. The optical comb's ultra-stable frequency references and coherent detection capabilities provide sub-femtosecond synchronization precision that RF methods cannot achieve.
Solution Approach 2:
The patent introduces an optical frequency comb as an intermediary between the optical domain and RF domain. The comb's multiple harmonics serve as intermediate frequency references that enable precise time transfer. The comb's phase-coherent structure allows it to mediate the conversion of optical phase information into measurable RF signals, achieving high precision without direct RF transmission through the atmosphere.
2Measurement precision
If optical frequency combs are used for time distribution, then measurement precision improves to sub-femtosecond level, but device complexity increases due to multiple combs and phase modulation requirements
Solution Approach 1:
The patent divides the time distribution system into separate functional modules: master clock with master comb, remote clock with remote comb, and transfer comb for signal transmission. Each comb serves a specific function (generation, transmission, or local reference), allowing independent optimization and simplifying the overall system architecture while maintaining high precision frequency comparison capabilities.
Solution Approach 2:
The patent employs periodic phase modulation of the optical frequency comb at specific harmonics. This periodic action creates a phase-coherent pulse train that carries precise timing information. The regular periodic structure enables coherent detection and simplifies the extraction of time-frequency information, reducing the complexity of signal processing while achieving sub-femtosecond precision.
3Measurement precision
If phase-modulated laser signals are transmitted over free-space links, then measurement precision improves, but reliability deteriorates due to atmospheric turbulence and link instability
Solution Approach 1:
The patent implements a two-way time-frequency transfer scheme where phase information is exchanged bidirectionally between master and remote clocks. The phase modulation depth and frequency are carefully controlled to maximize the feedback signal strength while minimizing sensitivity to atmospheric turbulence. This feedback mechanism enables real-time compensation for link instabilities while maintaining high precision time transfer.
Solution Approach 2:
The patent optimizes key parameters including phase modulation depth, modulation frequency, and optical power to achieve the best balance between precision and reliability. By carefully selecting the modulation frequency to match the detection bandwidth and adjusting the phase modulation depth to maximize signal-to-noise ratio while avoiding non-linear effects, the system achieves robust performance under varying atmospheric conditions.
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
The system achieves sub-femtosecond synchronization and frequency stability, overcoming limitations of traditional methods by utilizing optical combs and phase-modulated signals to maintain clock synchronization across turbulent and moving platforms, with fractional frequency uncertainty reaching 2×10−19 and synchronization bandwidths of 100 Hz or lower.
Implementation Method 1
an optical time distributor includes a master clock that includes a master comb that produces a master clock coherent optical pulse train output; a transfer comb that produces a transfer coherent optical pulse train
Implementation Method 2
produces the phase-modulated laser signal in response to receipt of the remote coherent optical pulse train
Data Source
AI summary
An optical time distributor includes: a master clock including: a master comb; a transfer comb; and a free-space optical terminal; and a remote clock in optical communication with the master clock via a free space link and including: a remote comb that produces: a remote clock coherent optical pulse train output; a remote coherent optical pulse train; a free-space optical terminal in optical communication: with the remote comb; and with the free-space optical terminal of the master clock via the free space link, and that: receives the remote coherent optical pulse train from the remote comb; receives the master optical signal from the free-space optical terminal of the master clock; produces the remote optical signal in response to receipt of the remote coherent optical pulse train; and communicates the remote optical signal to the free-space optical terminal of the master clock.