Abstract

Frequency stabilization of laser diodes is of vital importance to the exploitation of frequency division multiplexing coherent transmission systems. In particular, frequency stabilization in the 1.5- μm region, ideally at 1.55 μm of importance for present optical transmission systems, is now required. For frequency stabilization of 1.5-μm DFB lasers, several schemes have been investigated which involve use of an ammonia absorption line¹ at 1.519 μm, a krypton optogalvanic effect² at 1.533 μm, or second harmonic generation of 1.56-μm laser diode radiation and an atomic rubidium line.³ Another method using acetylene (C₂H₂) absorption lines as a frequency reference has been investigated in the region from 1.52 to 1.54 μm^4,5 However, since the absorption of C₂H₂ molecules in the wavelength region longer than 1.54 μm is rather weak,^4,5 it is difficult to use this molecule for practical frequency stabilization at these longer wavelengths. In fact, to date, no frequency references suitable for stabilization in the regions of 1.54 and 1.55 μm have been proposed, and no demonstration of frequency stabilization has been reported.

© 1990 Optical Society of America