Semiconductor lasers frequency-locked to an absolute reference in the 1.3- and 1.5-μm wavelength regions are needed in many applications of coherent optical communication systems. However, most of the previous reports on frequency-locked semiconductor lasers are limited to GaAIAs lasers operating at ~0.8 μm. This is mainly due to the difficulties of finding any useful atomic or molecular absorption lines at longer wavelengths. A few experiments have been reported at longer wavelengths, which used molecular absorption lines of NH3 (Ref. 1) or HF (Ref. 2) as their references.
© 1989 Optical Society of AmericaPDF Article