MODULATION CHARACTERISTICS OF SEMICONDUCTOR MACH-ZEHNDER OPTICAL MODULATORS

The transmission and chirp characteristics are described for two types of semiconductor Mach-Zehnder modulators, distinguished by the differ ential phase shift between the two arms of the interferometer in the u nbiased state. The conventional modulator has a differential phase shi ft of 0 radians, while the pi-shift modulator has a differential phase shift of pi radians. The nonlinear dependence on the applied voltage of the attenuation and phase constants of the optical signal propagati ng in the p-i-n waveguide leads to different characteristics for the t wo modulators. The influence of the splitting ratio of the Y-junctions is considered for single-arm and dual-arm (push-pull) modulation form ats. The pi-shift modulator is shown to yield better transmission perf ormance for 10 Gb/s systems compared to the conventional modulator.