A silicon guided-wave optical modulator using free-carrier dispersion effect and radiation loss mechanism

Research and development on silicon optical modulators has been going on for a while. It is because of its mature processing technology and its potential impact on optoelectronic integration, integrated optics, and communication technology. However, silicon optical modulators have its intrinsic limitations in high power (300mA to 800mA), low speed (more than {dollar}mu{dollar}s switching time) and long interaction length (500{dollar}mu{dollar}m-3000{dollar}mu{dollar}m). This dissertation explores a new modulation scheme aiming at compensating these shortcomings.; A combination of free-carrier dispersion effect and radiation loss mechanism is the new modulation scheme. Radiation loss occurs when optical wave propagates through a refractive index discontinuity step. Optical modulation is present when this step discontinuity is eliminated by free-carrier injection.; A combination of the free-carrier conversion, FDTD simulation, SUPREM IV process simulator, and PISCES IIB device simulator is used to simulate a silicon optical modulator and its performance. The simulation indicates that it is possible to have a 50{dollar}mu{dollar}m-long active-length radiation-loss-modulation device with a 43% modulation depth at a 120mA injection current. The device switching time can be up to 30ns-50ns in dc-biasing mode. The simulated radiation-loss-modulator performance suppresses the other types of silicon modulator cited in chapter one.; The simulated silicon modulator is implemented and fabricated. The device is realized as an integration of a p-i-n diode and a ridge wave guide. There are vertical and lateral p-i-n diodes, and p+ buried layer and p+ bulk substrate wave guides. Both types of modulators are conventional bipolar or BiCMOS process compatible. More than 300 individual devices can be produced in a 4" silicon wafer.; Fabricated devices are tested. They show acceptable p-i-n diode electrical and optical wave mode guiding characteristics. The radiation-loss-modulation mechanism is demonstrated as a leaky-radiation loss suppression in the vertical p-i-n diode modulators. Evanescent-wave absorption loss is also seen as a modulation mechanism in the lateral p-i-n diode modulators, and p-i-p diode substrate-biased modulator.; The modulation depth of vertical p-i-n modulators varies from 20% (with a 50{dollar}mu{dollar}m long device) to 30% (with a 500{dollar}mu{dollar}m long device) at 12kA/cm{dollar}sp2{dollar} to 2kA/cm{dollar}sp2{dollar} respectively. The most remarkable feature of this type of modulator is it's small in size. A 50{dollar}mu{dollar}m long active area vertical p-i-n modulator shows a 20% modulation depth at a current of 160mA.; In addition, the radiation loss phenomenon is modeled by using Coupled Mode Theory. Model predicts well the 100{dollar}mu{dollar}m, 200{dollar}mu{dollar}m and 500{dollar}mu{dollar}m long active area devices and lower injection current regime of the 50{dollar}mu{dollar}m long active area device. The simulation only uses one parameter to do the data fitting: the step discontinuity of 5{dollar}mu{dollar}m and 6{dollar}mu{dollar}m height. All of this fit well to the original idea: a radiation loss modulation scheme using virtual refractive index step discontinuity created by free-carrier injection.