Photonic Chip Optical Mixing for Sub-Picosecond Clock Synchronization
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Solution Overview
Problem
Current two-way optical time transfer systems face challenges in achieving sub-picosecond accuracy due to jitter in electronics and sensitivity to optical dispersion, especially in long optical fiber links and temperature fluctuations, which complicates clock synchronization between remote sites.
Innovation Solution
The use of photonic chips to optically combine received and locally generated optical pulses with different repetition rates, reducing electronic jitter and minimizing optical path lengths, thereby enabling femtosecond accuracy in clock synchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If photodetectors are used to detect optical pulse arrival times, then clock synchronization can be performed, but electronic jitter limits accuracy to picosecond level
Solution Approach 1:
The patent replaces electronic detection with optical detection. Instead of converting optical pulses to electrical signals and suffering from electronic jitter, the system uses optical mixing to combine received pulses with local oscillator pulses, then detects the optical beat signal directly. This substitution of electronic system with optical system eliminates the electronic jitter limitation and enables sub-picosecond timing accuracy.
2Length of stationary object
If long optical fiber links are used for remote communication, then distance coverage is improved, but optical dispersion increases and degrades signal quality
Solution Approach 1:
The patent uses periodic optical pulses with different repetition rates from master and slave stations. By operating in the periodic domain and using optical mixing of these periodic signals, the system can achieve synchronization without being degraded by dispersion effects that accumulate over long fiber links. The periodic nature allows for continuous phase comparison rather than single-shot measurements.
3Stability of the object's composition
If temperature stabilization systems are implemented to reduce thermal effects, then measurement stability is improved, but system complexity and power consumption increase
Solution Approach 1:
The patent replaces thermal management systems with an optical reference approach. Instead of actively stabilizing temperatures to prevent thermal drift, the system uses optical pulses from a stable laser source as a reference. The optical frequency and phase serve as the stable reference, eliminating the need for complex temperature control hardware and reducing power consumption while maintaining measurement stability.
4Measurement precision
If optical pulse trains with different repetition rates are combined, then clock synchronization accuracy is improved to femtosecond level, but optical combining complexity increases
Solution Approach 1:
The patent combines optical pulse trains from master and slave stations using optical couplers or beam splitters to merge the two optical signals. This physical merging of optical paths allows direct optical interference and mixing, enabling precise phase and timing comparison. The combining operation is performed in the optical domain before detection, achieving femtosecond-level synchronization accuracy through straightforward optical components rather than complex electronic processing.
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 allows for sub-picosecond accurate clock synchronization by reducing electronic interference and temperature sensitivity, improving the system's precision and reducing the complexity and power consumption associated with temperature stabilization.
Implementation Method 1
a first optical combiner coupled to the optical interface and the second optical interface where the first optical combiner is configured to combine the first pulse train and the second pulse train into a combined optical signal
Data Source
AI summary
Embodiments herein describe sub-picosecond accurate two-way clock synchronization by optically combining received optical pulses with optical pulses generated locally in a photonic chip before the optical signals are then detected by a photodetector to obtain an interference measurement. That is, the optical pulses can have different repetition rates so that the offset between the received and local optical pulses constantly changes, thereby resulting in different interference measurements. Optically combining the pulses in the photonic chip avoids much of the jitter introduced by the electronics. Further, the sites can obtain multiple interference measurements which can be evaluated to accurately determine when the optical pulses arrive at the site with femtosecond accuracy.