First industrial-grade coherent fiber link for optical frequency standard dissemination

Area of Science:

• Physics
• Metrology
• Optical Communications

Background:

• Coherent optical fiber links are crucial for high-precision frequency transfer.
• Existing links are often established by national metrology institutes.
• Industrial involvement is key to scaling metrology infrastructure.

Purpose of the Study:

• To establish and characterize a fully bidirectional 680 km fiber link for metrology.
• To demonstrate industrial consortium management of such a link.
• To assess the feasibility of a national optical fiber network for frequency standards.

Main Methods:

• Utilized an active telecommunication fiber network with parallel data traffic.
• Employed three repeater laser stations and four remote bidirectional erbium-doped fiber amplifiers.
• Characterized short-term and long-term frequency stability and transfer accuracy.

Main Results:

• Achieved short-term stability of 5.4×10⁻¹⁶ at 1s integration time (0.5 Hz bandwidth).
• Reported long-term stability of 1.7×10⁻²⁰ at 65,000s integration time.
• Demonstrated frequency transfer accuracy of 3×10⁻²⁰ with no observed shift and 99.93% uptime over five days.

Conclusions:

• The link's performance is comparable to state-of-the-art metrology links.
• This represents a significant step towards a French optical fiber network for metrology.
• The network will provide broad access to ultrahigh-performance frequency standards for scientific users.