To transfer and expand in the optical telecommunication range the accurate 5S1/2(F = 3) – 5D5/2 (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.