Direct phase-locking of a Ti:Sapphire optical frequency comb to a remote optical frequency standard.

Eunmi Chae,Kota Nakashima,Takuya Ikeda,Kosuke Yoshioka,Kei Sugiyama

doi:10.1364/oe.27.015649

Abstract

We report on an ultralow noise optical frequency transfer from a remotely located Sr optical lattice clock laser to a Ti:Sapphire optical frequency comb through telecom-wavelength optical fiber networks. The inherent narrow linewidth of the Ti:Sapphire optical frequency comb eliminates the need for a local reference high-finesse cavity. The relative fractional frequency instability of the optical frequency comb with respect to the remote optical reference was 6.7(1) × 10-18 at 1 s and 1.05(3) × 10-19 at 1,000 s including a 2.9 km-long fiber network. This ensured the optical frequency comb had the same precision as the optical standard. Our result paves the way for ultrahigh-precision spectroscopy and conversion of the highly precise optical frequency to radio frequencies in a simpler setup.

Highlights

Optical frequencies have been the most precisely measured quantities since the development of optical frequency combs (OFCs) [1]
We demonstrate a coherent transfer of the remote optical reference at 698 nm directly to a Ti:Sapphire OFC through a 2.9 km-long commercial optical fiber network
The power spectrum of the phase-locked heterodyne beat between the copy of the clock laser and a tooth of the Ti:Sapphire optical frequency comb was measured by a spectrum analyzer (Fig. 4)

Summary

Introduction

Optical frequencies have been the most precisely measured quantities since the development of optical frequency combs (OFCs) [1]. It is possible to directly phase-lock the local OFCs against the remote optical reference without using the local ultranarrow CW laser, provided that the employed fiber length is moderate and that the optical linewidth of the free-running optical frequency comb is sufficiently narrow. This can greatly reduce the complexity accompanied by the use of a high-finesse cavity at the receiver site. We envision the extension of this demonstration to a future setup that enables us to conduct ultrahigh-precision spectroscopy in the visible and ultraviolet regions just by connecting a telecommunication fiber to a Ti:Sapphire OFC

Optical fiber link

Conclusion

Findings

Estimation of the residual one-way fiber phase noise in PLLs