A small-area light intensity modulator implemented in silicon

The authors demonstrate an optical modulator designed to provide a practical interface between silicon ICs and fiber-optic systems. The device uses the strongest optical effect in silicon, free-carrier optical dispersion, and the mode-filtering properties of single-mode optical fibers as the basis for a 200-mHz bandwidth reflection-type intensity modulator at 1.3- mu m wavelength. In contrast to the more familiar waveguide modulators, this silicon modulator's small size and vertical structure give it a much higher bandwidth (albeit with lower modulation depth) and allow it to be monolithically integrated anywhere on a silicon integrated circuit. The device was demonstrated in a simple fiber experiment using a CW 1.3- mu m laser diode. The modulator achieves 10% optical modulation depth over a 200-MHz bandwidth when under a forward bias of 10 mA and RF root-mean-square current also of 10 mA.