Phase Matching for Difference Frequency Generation in GaAs Via an Artificial Birefringence Technique Using Silver Nanowires

The lack of anisotropic properties in GaAs prevents the use of birefringence as a phase matching technique in three-wave mixing with GaAs as a nonlinear medium. When metallic nanowires are embedded in GaAs, the composite structure is characterized as a metamaterial with anisotropic properties, if the separation distance between the nanowires is less than the wavelengths of the mixed waves. The effective permittivity is used to investigate this metamaterial structure with its anisotropic properties theoretically in terms of phase matching for difference frequency generation. The resultant difference frequencies, which are in the mid-infrared region, are broadly tunable from 2.8 to 11 μm. This tuning is performed by varying the pump and the signal wavelengths in the range between 1 to 2 μm. The losses of the structure due to absorption are included using the transfer matrix method.