Ge-on-insulator Platform for Mid-infrared Photonic Integrated Circuits

Since mid-infrared (MIR) wavelengths have a great potential for optical communication, sensing, and quantum information, Si-based MIR photonic integrated circuits (PICs) have been developed by leveraging Si photonics technology for near-infrared wavelengths. However, the transparency wavelength window of Si is from 1.2 μm to 8 μm, limiting the available wavelengths in the MIR spectrum. Ge is emerging as a waveguide material to overcome this difficulty because Ge is transparent in the entire MIR spectrum. We have developed a Ge-on-insulator (GeOI) platform for MIR integrated photonics. The strong optical confinement in a GeOI waveguide enables an ultracompact MIR PIC. Using wafer bonding and Smart-cut, a GeOI wafer was successfully fabricated. As a result, we have demonstrated various Ge passive devices, thermo-optic phase shifters, modulators, and photodetectors on a GeOI platform.