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 differential phase shift between the two arms of the interferometer in the unbiased state. The conventional modulator has a differential phase shift of 0 radians, while the /spl pi/-shift modulator has a differential phase shift of /spl pi/ radians. The nonlinear dependence on the applied voltage of the attenuation and phase constants of the optical signal propagating in the p-i-n waveguide leads to different characteristics for the two modulators. The influence of the splitting ratio of the Y-junctions is considered for single-arm and dual-arm (push-pull) modulation formats. The /spl pi/-shift modulator is shown to yield better transmission performance for 10 Gb/s systems compared to the conventional modulator.