Abstract

Return-to-zero (RZ) pulse modulation is necessary in systems using optical time–division multiplexing. This modulation format, however, is more complex than nonreturn-to-zero (NRZ) modulation¹ and makes more demanding requirements on the bandwidth capabilities of the laser and its drive electronics. We demonstrate pseudorandom RZ modulation of an InGaAsP constricted mesa laser² at 8 Gb/s, using pulses which are generated by gain-switching in the laser. The basic principle of gain-switching is that only the first spike of the relaxation oscillation is emitted for each data bit. For this process to be useful in data transmission, it is important that carrier and photon densities return to the same values after each bit. If this condition is not met, pattern effects will result producing intersymbol interference. Gigabit per second RZ modulation using gain-switched pulses has been analyzed in the literature,^3–5 but there has been limited experimental investigation of the technique. In the present work we demonstrate the technique’s practicality at multi-Gb/s rates and investigate the laser operating parameters for minimum pattern effects.

© 1987 Optical Society of America