Design of mid-infrared nonlinear silicon–germanium waveguides for broadband/discrete-band wavelength conversion

Abstract

A dispersion-engineered silicon–germanium (Si0.8Ge0.2) waveguide is designed for mid-infrared (MIR) broadband or discrete-band wavelength conversion by using its advantages of high nonlinearity and tight mode-field confinement. The dispersion of this waveguide is engineered by optimizing the waveguide geometry. The zero-dispersion wavelength is tuned to about 2 μm, and the dispersion curve is flattened to reduce the dispersion slope. In the MIR band, the 3 dB bandwidth for the four-wave mixing effect reaches 795 nm, and the peak conversion efficiency is −25.0 dB when the pump power is 500 mW, which can support the broadband all-optical wavelength conversion for next-generation MIR optical communications. Discrete-band wavelength conversion between the MIR (2.5–3.8 μm) and telecommunication (1.30–1.72 μm) bands is realized by using the pair of phase-matching wavelengths far away from the pump. Moreover, by choosing proper waveguide geometries, the signals in the band of 2.0–3.8 μm can be efficiently converted to the idler with fixed wavelength of 1.55 μm, which exhibits the potential to realize indirect detection by using telecommunication-band detectors to detect MIR signals.