Abstract

Direct intensity modulation (IM) of a semiconductor laser is used for most fiber-optic communications experiments and demonstrations. Some of the major problems or research directions in this approach are (1) laser chirping (dispersion penalty), (2) limitations on the 0 and 1 levels caused by mode partitioning or excessive chirping (extinction ratio penalty), (3) higher-frequency operation, and (4) generation of the large high-frequency modulation currents. We propose and demonstrate an approach which at least partially solves each of these four problems. In our approach, the frequency modulation (FM) from a directly modulated semiconductor laser is converted to intensity modulation using a fiber-optic FM discriminator. This approach is more complicated than direct IM but is considerably simpler than heterodyne frequency-shift-keyed or phase-shift-keyed systems.

© 1985 Optical Society of America