Photonic Chip Time Transfer Using CW Phase Comparison
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Solution Overview
Problem
Existing two-way optical time transfer methods face challenges in achieving high accuracy clock synchronization due to jitter in electronics, complexity, power consumption, and limited signal-to-noise ratio, particularly in systems using frequency combs and continuous wave lasers.
Innovation Solution
A photonic integrated circuit (PIC) that combines and separates continuous wave optical signals using waveguides, multiplexers, and demultiplexers, along with a digital backend for phase extraction and phase locked loops, to determine timing deviation between remote clocks without requiring high power lasers or multiple frequency combs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pulse-based frequency comb methods are used for optical time transfer, then timing information can be extracted, but the duty cycle limitation reduces signal-to-noise ratio and measurement sensitivity
Solution Approach 1:
The patent changes the fundamental parameter of the optical signal from pulsed to continuous wave (CW) to eliminate duty cycle limitations. By using CW lasers instead of pulsed frequency combs, the system maintains continuous optical power transmission, thereby improving signal-to-noise ratio while still enabling precise timing deviation measurements through phase comparison of the exchanged CW signals
2Measurement precision
If two frequency combs are used at each link site for synchronization, then clock synchronization can be achieved, but system complexity, power consumption, and expense increase
Solution Approach 1:
The patent extracts and eliminates the unnecessary second frequency comb from each link site. By using only a single CW laser per site instead of two frequency combs, the system achieves clock synchronization through phase comparison of exchanged CW signals, thereby reducing component count, system complexity, and power consumption while maintaining synchronization accuracy
Solution Approach 2:
The patent replaces expensive, complex frequency comb systems with simpler, lower-cost continuous wave lasers. This substitution reduces the overall system expense and complexity while achieving the same clock synchronization function through a more economical optical source
3Device complexity
If a single CW laser is used for time transfer, then system complexity is reduced, but power requirements increase significantly due to squared link loss
Solution Approach 1:
The patent inverts the traditional single-ended time transfer approach by implementing a two-way symmetric exchange of CW signals between sites. Each site transmits a CW signal to the other and simultaneously receives and compares the returned signal, enabling timing deviation measurement without requiring excessive power to overcome squared link loss, as the bidirectional exchange balances the power requirements
4Measurement precision
If photodetectors are used to detect optical pulse arrival, then pulse detection is achieved, but electronic jitter limits timing accuracy to picosecond level
Solution Approach 1:
The patent substitutes electronic pulse detection with optical phase comparison. Instead of using photodetectors to detect pulse arrivals (which suffer from electronic jitter), the system uses CW lasers and compares the optical phases of transmitted and received signals, thereby achieving femtosecond-level timing accuracy without being limited by electronic jitter
Data Source
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AI summary
A photonic platform (e.g., a photonic chip) is described which can include integrated components such as laser cavities, modulators, optical multiplexers/demultiplexers, photodiodes, and supercontinuum generators that are connected using optical waveguides and splitters/combiners to perform two-way optical time transfer. Integrating various combinations of these optical components onto the same photonic chip (e.g., photonic integrated circuit (PIC)) can reduce the size of the device, reduce noise, improve assembly by reducing the amount of fiber connections, and the like. A digital processing system is also described for performing two-way optical time transfer.