2ND-HARMONIC GENERATION OF A 1560-NM DISTRIBUTED-FEEDBACK LASER BY USE OF A KNBO3 CRYSTAL FOR FREQUENCY LOCKING TO THE RB-87 D(2) LINE AT 780 NM

Second-harmonic generation of a semiconductor distributed-feedback laser at 1560 nm is described. It is produced by use of a 4.8-mm-long KNbO3 crystal at room temperature. As much as 2.2 nW of power at 780 nm is obtained for 11.3 mW of fundamental power incident upon the crystal. This signal is used to interrogate a component of the linear absorption profile of the D2 line in Rb-87 (780.241 nm) and to produce an error signal used to frequency lock the 1560-nm distributed-feedback laser. Such a system can therefore be a candidate for establishing an absolute wavelength standard at 1560 nm.