In less than a decade, the mid-infrared (mid-IR) spectral range (2.5-12 μm) has become a key application for innovative silicon photonic devices because of the growing potential in spectroscopy, materials processing, chemical and biomolecular sensing, security and industry applications. We review the latest developments of emitters (GeSn lasers or heterogeneous quantum cascade laser on Si), passive devices (Silicon on Insulator, suspended Si or Ge waveguides, and SiGe/Si waveguides, Ge/SiGe waveguides), highly efficient nonlinear devices as well as integrated detectors for mid-IR applications. Perspectives for potential applications will also be discussed.

The evolution of silicon optical modulators is recalled, from the first effect demonstrations to the characterization of high-performance devices integrated in optical waveguides. Among possibilities to achieve optical modulation in silicon-based materials, the carrier depletion effect has demonstrated good capacities. Carrier depletion in Si and SiGe/Si structures has been theoretically and experimentally investigated. Large phase modulation efficiency, low optical loss, and large cutoff frequency are obtained by considering simultaneously optical and electrical structure performances. Integrated Mach-Zehnder interferometers and resonators are compared to convert phase modulation into intensity modulation. Finally, recent results on high-speed and low-loss silicon optical modulator using an asymmetric Mach-Zehnder interferometer are presented. It is based on a p-doped slit embedded in the intrinsic region of a lateral pin diode integrated in a silicon-on-insulator waveguide. This design allows a good overlap between the optical mode and carrier density variations. An insertion loss of 5 dB has been measured with a -3 dB bandwidth of 15 GHz.