Development of an optical frequency comb around 1556 nm referenced to an Rb frequency standard at 778 nm

BNM-SYRTE, Bureau national de métrologie, Systèmes de Références Temps et Espace, Observatoire de Paris/CNRS-UMR 8630, 61 avenue de l'Observatoire, 75014 Paris, France

Corresponding author: ouali.acef@obspm.fr

Received: 7 February 2002
Revised: 17 June 2002
Accepted: 27 August 2002
Published online: 15 November 2002

Abstract

To transfer and expand in the optical telecommunication range the accurate 5S_1/2(F = 3) – 5D_5/2 (F = 5) rubidium frequency reference at 778 nm (385.285 THz), we employ a second harmonic generation (SHG) process coupled to an optical frequency comb (OFC) both based on the use of a low power and narrow linewidth laser diode operating around 1556 nm. The Rb optical frequency reference is known with an accuracy of 2.6 × 10⁻¹² and exhibits a frequency stability of 4 × 10⁻¹³τ^−1/2, with a Flicker plateau of 2 × 10⁻¹⁴ for τ > 200 s. With 20 mW of laser power at 1556 nm, we perform a SHG process in a periodically poled lithium niobate (PPLN) crystal and we obtain 6.5 μW of harmonic radiation at 778 nm, used to phase lock the IR laser against a Rb optical frequency standard (OFS). This Rb-referenced fundamental radiation at 1556 nm is duplicated as 34 lines spaced by 10 GHz using an electro-optic phase modulator (EOM). This preliminary result is mainly limited by unexpected high optical losses in the Fabry Perot cavity, which comprises the EOM.