Design issues for high-speed electro-optic modulators

The effect of velocity matching, impedance matching, conductor loss and dielectric loss on the optical bandwidth is reported for Lithium Niobate and GaAs electro-optic modulators by using rigorous numerical techniques. It is shown that by etching Lithium Niobate the switching voltage and bandwidth can be improved and similarly by using a higher aluminium content in the buffer layer the device length for a given optical loss can be shortened. It is also observed that the dielectric loss and impedance matching play a key role in velocity matched high-speed modulators with low conductor loss. Finally it is indicated that by using tantalium pentoxide coating, velocity matching can be achieved for GaAs modulators.