Orientation-patterned gallium arsenide for quasi-phasematched infrared nonlinear optics

Devices using nonlinear optical frequency conversion in the infrared have many applications, ranging from generation of coherent radiation for spectroscopy and military applications, to wavelength conversion in optical communication systems. Semiconductors such as GaAs have excellent properties for frequency conversion, in particular large nonlinear coefficients and transparency throughout the mid-infrared, but lack birefringence, limiting their usefulness so far. Quasi-phasematching (QPM) provides an alternative solution that requires a modulation of the sign of the nonlinear coefficient in the material. In this work we have developed an all-epitaxial orientation-patterning fabrication process for both bulk-like and waveguide devices in the GaAs material system and have demonstrated various nonlinear optical interactions which show that orientation-patterned GaAs is a promising candidate for QPM infrared applications.; Our orientation template is fabricated in three steps: polar-on-nonpolar growth of GaAs/Ge/GaAs heterostructures in a molecular beam epitaxy system (MBE) to control lattice inversion; photolithography and selective chemical etching steps to expose surfaces of different orientations; MBE regrowth to complete the template. Orientation-patterned AlGaAs films fabricated in this fashion exhibit vertical propagation of the antiphase domains under all MBE conditions tested. QPM periods short enough to phasematch any interaction in the transparency range of AlGaAs have been demonstrated.; Using this technique, we fabricated QPM waveguide devices and achieved second harmonic generation from a pump laser at 1.55 mum. However, the conversion efficiency in these devices was limited by large propagation losses at both fundamental and harmonic wavelengths that we attributed to corrugation at the core/cladding interfaces. We also grew 0.5 mm thick films of orientation-patterned GaAs in a hydride vapor phase epitaxy reactor using the orientation template as a seed. Antiphase domain boundaries propagated vertically throughout the films for QPM periods as short as 20 m, sufficient to phasematch nonlinear interactions pumped at 1.3 mum. The thick films exhibited very low attenuation at near-infrared wavelengths, and good long-range homogeneity. 8 mum radiation was generated from the difference frequency mixing of two near-infrared lasers at 1.3 and 1.55 muM. These results show that orientation-patterned GaAs is a very attractive solution for nonlinear frequency conversion in the infrared.