Nonsymmetric Mach-Zehnder interferometers used as low-drive-voltage modulators

Optical communications systems require fast optical modulators which are compatible with existing microwave-frequency drive circuits and which have low voltage requirements. The authors have designed and demonstrated a novel type of integrated optical modulator: a nonsymmetric Mach-Zehnder interferometer, which has both low switching voltage and efficient coupling to microwave-frequency drive circuits. In 2-cm-long devices, made in z-cut LiNbO₃, switching voltages of 3.2 V and better than 20-dB extinction ratio were measured at λ=1.3 μm. Device performance in the nonsymmetric devices was independent of the asymmetry, which indicates that devices of this kind are tolerant of fabrication variations