Abstract

To date, lightwave systems’ transmitters have used direct current modulation of the injection laser source. At gigabit/sec modulation rates, spectral control of the laser becomes more difficult and power penalties caused by dispersion become important in long haul applications¹. An alternative approach, which offers the potential for efficient modulation, narrow source linewidth, and flexibility in the choice of laser structure, is the use of an external high-speed modulator². These devices have been made low-loss with low drive voltage and wide bandwidth for the 1.3μm wavelength³ and more recently have been optimized for the 1.55μm region⁴. Below we describe the first use of a Ti:LiNbO₃ traveling-wave directional coupler switch as an external modulator for optical fiber transmission at 4Gb/s. Repeaterless transmission at 1.53μm wavelength over 117km of conventional single-mode fiber was achieved. This result represents the largest capacity x repeater spacing product, ~0.5Tb–km/s, reported for a single-channel optical fiber span.

© 1985 Optical Society of America