Cascaded optical fiber link using the internet network for remote clocks comparison

Area of Science:

• Physics
• Optical Engineering
• Network Communications

Background:

• Ultra-stable optical frequency standards are crucial for scientific advancements.
• Distributing these frequencies over long distances, especially via existing fiber networks, presents significant challenges due to noise and signal degradation.

Purpose of the Study:

• To develop and demonstrate a cascaded optical link for ultra-stable frequency distribution over a long-haul internet fiber network.
• To achieve high fractional frequency instability over extended periods and distances.

Main Methods:

• A 1100 km cascaded optical link comprising four spans with active noise compensation.
• Utilized five automated optoelectronic stations for signal regeneration via heterodyne optical phase locking.
• Employed low-noise fibered optical interferometers for beat-note signal detection and laser locking.

Main Results:

• Demonstrated 3.5 days of continuous operation with fractional frequency instability of 4x10⁻¹⁶ at 1-s and 1x10⁻¹⁹ at 2000 s.
• Extended the link to 1480 km while maintaining similar performance levels.
• Successfully compensated for propagation noise across multiple fiber spans.

Conclusions:

• The developed cascaded optical link enables ultra-stable frequency distribution over existing internet fiber infrastructure.
• This technology represents a significant advancement towards sustainable wide-area optical frequency distribution and comparison networks.
• The system's robustness and high performance pave the way for next-generation metrology and communication systems.