Long-distance frequency transfer over an urban fiber link using optical phase stabilization

TL;DR

This paper demonstrates ultra-stable frequency transfer over an 86 km urban fiber link, effectively simulating a 172 km link using a recirculation loop and optical phase stabilization, achieving extremely low phase noise levels.

Contribution

It introduces a practical method for long-distance frequency transfer over urban fibers with phase noise cancellation, without spooled fiber extensions.

Findings

Achieved frequency stability with an Allan deviation of a few 10-16 at 1s.

Successfully doubled fiber link length using a recirculation loop.

Demonstrated effective phase noise cancellation with commercial components.

Abstract

We transferred the frequency of an ultra-stable laser over 86 km of urban fiber. The link is composed of two cascaded 43-km fibers connecting two laboratories, LNE-SYRTE and LPL in Paris area. In an effort to realistically demonstrate a link of 172 km without using spooled fiber extensions, we implemented a recirculation loop to double the length of the urban fiber link. The link is fed with a 1542-nm cavity stabilized fiber laser having a sub-Hz linewidth. The fiber-induced phase noise is measured and cancelled with an all fiber-based interferometer using commercial off the shelf pigtailed telecommunication components. The compensated link shows an Allan deviation of a few 10-16 at one second and a few 10-19 at 10,000 seconds.