Abstract

Optical frequency standards operating at 1.55 µm are required for fiber-optic wavelength division multiplexed communication systems and for 'cold start' coherent optical communication. Unfortunately, transitions near 1.55 µm are rare and difficult to probe. One may overcome the difficulties associated with frequency references at 1.55 µm by second harmonic generation (SHG) and locking to Rb D₂ line near 780 nm. This reference was already used to stabilize 1560 nm laser diodes using the internally generated second harmonic of diode lasers and by bulk external SHG in KNbO₃, however the SHG power levels were in the pW range and the nW range, respectively, hence locking to Doppler broadened line was possible, but the power level was not sufficient for locking to sub-Doppler lines.

© 1996 IEEE