Ultra-stable long distance optical frequency distribution using the Internet fiber network

Area of Science:

• Physics
• Optical Engineering
• Telecommunications

Background:

• Accurate frequency distribution is crucial for scientific research and next-generation networks.
• Existing methods face limitations in distance and stability over standard fiber infrastructure.

Purpose of the Study:

• To demonstrate a long-distance, ultrastable optical frequency distribution link.
• To enhance the robustness and performance of optical frequency transfer over existing fiber networks.

Main Methods:

• Utilized a 540 km internet fiber network for signal propagation.
• Implemented a cost-effective, automated optoelectronic station for signal regeneration and stabilization.
• Employed heterodyne optical phase locking and polarization tracking for signal integrity.
• Used a fibered optical interferometer for round-trip phase detection.

Main Results:

• Achieved a fractional frequency instability of 5 × 10(-15) at 1 second and 2 × 10(-19) at 30,000 seconds.
• Demonstrated uninterrupted signal propagation in both directions.
• Maintained stable beat note amplitudes despite polarization variations.

Conclusions:

• The developed system represents a significant advancement in wide-area ultrastable optical frequency distribution.
• The technology is a key step towards building a sustainable network for precise frequency comparison.
• The cost-effective and automated approach enhances the practicality of long-distance frequency transfer.