Nonlinear response of SiGe waveguides in the mid-infrared

The linear and nonlinear optical response of SiGe waveguides in the mid-infrared are experimentally measured. By cutback measurements we find the linear losses to be less than 1.5dB/cm between 3µm and 5µm, with a record low loss of 0.5dB/cm at a wavelength of 4.75µm. By launching picosecond pulses between 3.25µm and 4.75µm into the waveguides and measuring both their self-phase modulation and nonlinear transmission we find that nonlinear losses can be significant in this wavelength range due to free-carrier absorption induced by multi-photon absorption. This should be considered when engineering SiGe photonic devices for nonlinear applications in the mid-IR.