J. M. Wiesenfeld

40-Gb/s transmission over multiple 120-km spans of conventional single-mode fiber using highly dispersed pulses

We demonstrate the transmission of a 40-Gb/s signal over multiple (up to six) 120-km spans of conventional single-mode fiber (SMF). We use a very low duty cycle return-to-zero (RZ) format which employs optical pulses much shorter than the bit-period. The resulting broad spectrum of these short pulses reduces nonlinear effects and enables the transmission of the signal over long distances.

Electrooptic sampling of a packaged high-speed GaAs integrated circuit

The authors describe the use of electrooptic sampling to characterize the performance of a packaged 1.7-GHz GaAs planar integrated decision circuit. To study the packaged device, it was necessary for the optical probe beam to impinge on the circuit from the front (active) side. This geometry enabled effective evaluation of the circuit, in spite of reduced spatial resolution and voltage sensitivity compared to a backside probing geometry. Using a gain-switched InGaAsP laser source, waveforms have been measured in the D flip-flop within the circuit and propagation delays of about 25 ps in the input buffers. Apparent crosstalk has been measured when the probe is positioned between adjacent active circuit lines and it is found that this crosstalk depends sensitively on the position of the probe beam. >

Dynamic add/drop of 8-of-16 10 Gb/s channels in 4/spl times/40 km semiconductor-optical-amplifier-based WDM system

We demonstrate the benefits of near-linear SOA-amplified 4/spl times/40 km WDM transmission system. Eight out of sixteen 10 Gb/s channels are added or dropped (with only a 0.7 bB penalty in the remaining channels) over a wide range of time scales.

Limitations on Switching Speed in Wideband Semiconductor Lasers

An experimental and theoretical study of large-signal switching transients in directly modulated semiconductor lasers is reported. The main parameters affecting high-speed switching are identified and device-dependent limitations on modulation at multi-gigabit per second data rates are described.

8-Gb/s return-to-zero modulation of a semiconductor laser by gain switching

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.

Measurements of switching transients in high-speed semiconductor lasers

Recent developments in high-speed semiconductor lasers with bandwidths approaching 20 GHz (see, for example, Ref. 1) offer the possibility of digital transmission at data rates in the 10-20Gbit/s range. The modulation characteristics of these high-speed lasers are usually evaluated by small-signal measurements. However, the switching behavior under large-signal conditions determines the ultimate limits on high-speed digital modulation.