Fibre phase noise cancellation for long baseline optical networks

Abstract

We demonstrate a technique for the stable transfer of an optical frequency reference over a kilometre scale optical fibre link. This technique implements phase measurements and laser feedback to cancel out phase fluctuations that are introduced to an optical frequency standard as it passes through the fibre. The resulting differential optical frequency noise reaches 0.5 mHz/√Hz for Fourier frequencies between 5 Hz and 20 Hz. This represents a fractional frequency stability of 1.7 × 10-18 /√Hz, at our measurement frequency of ~300 THz (1064nm).