Investigation of Germanium-Loaded Slot Waveguides for Mid-Infrared Third Harmonic Generation

In this paper, we propose a metal-semiconductor-metal slot waveguide (MSMSW) for producing mid-infrared (MIR) light from 10.2 mu m by means of third harmonic generation (THG). In this waveguide, the required interaction length is limited by the large Ohmic loss, and therefore, perfect phase-matching condition (PMC) which ensures long coherent length is not necessary. Without the limitation of perfect PMC, the THG interaction mainly occurs between two fundamental modes at pump and harmonic wavelength, respectively leading to high nonlinear coefficient. According to our simulation, the conversion up to similar to 9.1 x 10(-4) can be achieved within micron-scale waveguide under 1 W pump power. Furthermore, the waveguide demonstrates both large fabrication error and wavelength shift tolerance. The proposed waveguide can be a promising candidate for MIR light generation with large integration capability.