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Conference on Lasers and Electro-Optics

Frequency Measurement of a Sr Optical Lattice Clock Using a Coherent Optical Link over a 120-km Fiber

Feng-Lei Hong, M. Musha, Masao Takamoto, Hajime Inaba, Shinya Yanagimachi, Akifumi Takamizawa, Ken-ichi Watabe, Takeshi Ikegami, Michito Imae, Y. Fujii, M. Amemiya, K. Nakagawa, Kenji Ueda, Hidetoshi Katori

Published Jan 1, 2009• 0 citations
Publisher

Abstract

We demonstrate a precision frequency measurement using a phase-stabilized 120-km optical fiber link over a physical distance of 50 km. The absolute frequency of the 87Sr optical lattice clock is measured to be 429228004229874.1(2.4) Hz.
DOI
10.1364/cleo.2009.cmb2

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We report a system of two independent strontium optical lattice standards with88Sr probed with a single shared ultra-narrow laser. We achieved frequency stability (frequency between two standards) of 7 × 10-17. The absolute frequency of the clock transition can be measured by the use of an optical frequency comb referenced to the UTC(AOS) and UTC(PL) via the 330-km stabilized fibre optic link of the OPTIME network. The 15.5-km stabilized fibre optic link between National Laboratory for Atomic, Molecular, and Optical Physics (KL FAMO) and Toruń Centre for Astronomy made it possible to use the optical clocks as a frequency reference for the 32-metre precise parabolic antenna of the radio telescope in the Toruń Centre for Astronomy participating in the VLBI networks. We report the world's first astronomical VLBI measurements referenced to an optical atomic clock.
Abstract Two 87Sr optical lattice clocks (OLCs) are being developed and operated at the National Institute of Metrology (NIM), located on different campuses that are 40 km apart. In order to compare the optical frequencies of these two Sr OLCs, a 58-km noise canceled fiber link is built to transfer both a 1542-nm transfer laser and a microwave reference from Changping campus to Hepingli campus. Two commercial optical frequency combs (OFCs) with adapted single-branch 698/1542 nm outputs coherently unite the two 698-nm clock lasers and the 1542-nm transfer laser. The fractional instability of the comparison yields 3.1 × 10−17 at 10000 s averaging time. The measured fractional frequency difference between these two Sr OLCs was evaluated to be 1.9(3.2) × 10−17, which is within their claimed uncertainties. This result demonstrates the consistency of their frequencies when they serve as optical frequency standards. Our remote comparison demonstrates the feasibility of optical clock comparison through a long-distance fiber link and contributes to the progress of redefinition of the SI second.
Laser frequency stabilization and atom manipulation are important techniques for optical frequency metrology. We report on the development of an ytterbium (171Yb) and a strontium (87Sr) optical lattice clock at the National Metrology Institute of Japan (NMIJ). The result of absolute frequency measurement of the171Yb lattice clock is shown. We also report on narrow-linewidth fiber-based frequency combs that are used not only to measure the absolute frequency of the optical lattice clocks but also to servo control the frequency of the lasers for cooling and trapping Yb and Sr atoms.