The extinction ratio(ER) of a Mach-Zehnder-interference(MZI) based silicon optical modulator can be strongly influenced by carrier absorption.Moreover,different doping positions can induce different distributions of injected carriers,leading to different ERs.This effect has been experimentally investigated based on the devices fabricated on silicon-on-insulator(SOI) by using a 0.18μm CMOS process.Our experiments indicate that a device with a doping position of about 0.5μm away from the edge of the rib waveguide has optimal ER.
