An integrated Si-based electro-optical modulator

Optical interconnects are, nowadays, considered a promising alternative to electrical ones and monolithic integration in Si is the only choice when high volumes, low fabrication costs and reduced spaces are needed. We fabricated an electro-optic Si-based modulator working at 1.5 mum using a Bipolar Mode Field-Effect transistor integrated within a Si rib waveguide. The principle of operation is the light absorption by a plasma of free carrier that can be opportunely moved inside or outside the device optical channel by properly changing the bias. The optical channel of the modulator is embodied within its vertical electrical channel. The devices were fabricated using epitaxial Si wafers and standard clean room processing. The optical characterization in static conditions shows a modulation depth, defined as M=(P-Off -P-On)/P-Off - 90 %. It was measured at 1.48 gm using a laser diode source coupled with the modulator through a silica optical fiber. The dynamic electrical characterization provides an electrical switching time of approximate to10 ns. A modulation depth of 72 % is observed at 100kHz electrical modulation frequency.