Optical frequency standard for optical fiber communication based on the Rb 5s --> 5d two-photon transition.

We report an optical frequency standard based on the 5s --> 5d two-photon transition in Rb atoms. The frequency of a lambda = 778 nm diode laser was locked to the two-photon transition. Second-harmonic generation and an optical phase-locked loop were used to transfer the frequency stability to lambda = 1.556 mum for use in optical fiber communication applications.