Frequency stabilization of a frequency-doubled 1556-nm source to the 5S(1/2)-> 5D(5/2) two-photon transitions of rubidium

Improvements in the power level of sources near 1550 nm and in the efficien cy of waveguide frequency doublers enabled us to lock a frequency-doubled s ource directly to the 5S(1/2) --> 5D(5/2) two-photon transitions near 778 n m. We obtained a sufficiently powerful second-harmonic signal, exceeding 2 mW, by doubling an external-cavity diode laser that was amplified by an erb ium-doped fiber amplifier ina periodically poled LiNbO3 channel waveguide. Our experimental scheme can be used for realizing compact, high-performance frequency standards near 1550 nm for fiber-optic communication and sensing applications. (C) 2000 Optical Society of America OCIS codes: 230.7370, 19 0.4360.