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

摘要

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~(-13)τ~(-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.