4-Gb/s Optical Time-Division Multiplexed System Experiments Using Ti:LiNbO₃ Switch/Modulators

Abstract

Optical time-division multiplexing (OTDM) is a useful technique for increasing the bit rate of lightwave systems beyond the bandwidth capabilities of drive electronics. We report here a novel optical multiplexing and demultiplexing scheme using mode-locked extended cavity injection lasers as sources of optical pulses, and Ti:LiNbO₃ waveguide switch/modulators for modulation and demultiplexing operations. An OTDM experiment is described in which two separate lasers are mode-locked and externally modulated at 2 Gb/s, and then optically multiplexed to a bit rate of 4 Gb/s. The 4-Gb/s multiplexed signal is transmitted over 8 km of fiber, demultiplexed with a Ti:LiNbO₃ waveguide switch, and received at low error rate. The experiments reported here extend our previous work on external modulation [1], OTDM using gain-switched lasers [2], and our work on mode-locking of extended-cavity injection lasers [3]. The mode-locked lasers provide an excellent means of generating short pulses at high repetition rates, using only narrow-band electronics. In addition, they offer the potential of good spectral purity — a key requirement for low distortion, high bit-rate transmission over long fiber lengths.