Whispering gallery germanium-on-silicon photodetector.

We design and demonstrate, to the best of our knowledge, the first whispering gallery germanium-on-silicon photodetector with evanescent coupling from a silicon bus waveguide in a CMOS-compatible process. The small footprint (63.6  μm2), high responsivity (∼1.04  A/W at 1530 nm), low bias voltage (-1  V), low dark current (2.03 nA), and large optoelectric bandwidth (32.9 GHz) of the detector enable simultaneous wavelength filtering and power detection, ideal for handling large network data traffic. In addition, with the resonant nature of the detector, we also optimize the design to enable long-wavelength detection, achieving a separate device with a detection range of up to 1630 nm with a >0.45  A/W responsivity, making it an important building block for optical communication networks.