25 GHz operation of silicon optical modulator with projection MOS structure

We report a high-speed and compact silicon optical modulator based on the free carrier plasma dispersion in a silicon rib waveguide with a MOS (metal-oxide-semiconductor) junction structure. To achieve high-speed and high-efficiency performance, an improved structure of a very small rib waveguide including a projection MOS junction was studied. We demonstrated high speed of 25 GHz operation in case of 120-200 μm phase-shift length and high optical modulation efficiency of 0.5-0.67 Vcm for V π L by using a projection MOS junction structure. According to the carrier-density simulation, higher operation bandwidth up to 40 GHz can be realized.