Improving the response of optical phase modulators in SOI by computer simulation

This paper reports on the simulation of a low-loss single-mode optical phase modulator fabricated in silicon-on-insulator (SOI) material. The device operates by injecting free carriers to change the refractive index in the guiding region, and has been modeled using the two-dimensional (2-D) device simulation package SILVACO. SILVACO has been employed to optimize the overlap between the injected free carriers in the intrinsic region and the propagating optical mode. Attention has been paid to both the steady state and transient properties of the device. In order to produce quantitative results, a particular p-i-n device geometry has been employed in the optimization, but the trends in the results are general enough to be of help in the design of many modulator geometries. The specific example device we have used is designed to support a single optical guided mode and is of multimicrometer dimensions thus simplifying fabrication and allowing efficient coupling to-from single-mode fibers (SMF´s) or other single-mode devices. The modeling indicates that increased dc device performance results from an increase in the doping concentrations and the contact diffusions of the p/sup +/ and n/sup +/ regions. The transient performance of the device in terms of switching times depends on the separation of the p/sup +/ and n/sup +/ regions. The optimizations are applicable to large (multimicrometer size) modulators. Phase modulators with low driving currents (<8 mA) and modulators with transient rise times of 39 ns and fall times of 6 ns are predicted.