A Vertical Germanium Thermooptic Modulator For Optical Interconnects

We proposed and demonstrated a novel vertical thermooptic modulator. A Ge-on-insulator device with bottom metal reflector utilizes a self-heating structure to change the temperature-dependent absorption coefficient and refractive index near the absorption edge, thus modulating the light intensity through its asymmetric Fabry-Perot cavity. The peak contrast ratio is 6.1 dB (and 8.7 dB) at 1561.8 nm (and 1563 nm) under 0.8-V (and 1.2-V) bias with 1.6-mW (and 3.6-mW) power consumption. This approach provides efficient vertical thermooptic modulators requiring smaller temperature change and lower operation voltage for optical interconnects.