Optical frequency conversion is important nonlinear process for generating coherent radiation in spectral regions where there are no convenient laser sources. For example, nonlinear processes are... Show moreOptical frequency conversion is important nonlinear process for generating coherent radiation in spectral regions where there are no convenient laser sources. For example, nonlinear processes are used to generate ultraviolet radiation for biomedical applications or mid-infrared radiation in the wavelength range of 3–12 μm for remote sensing of atmosphere. Besides these practical applications, frequency conversion can be used to create entangled photon pairs in quantum optics experiments to test the fundamental laws of quantum mechanics. This thesis describes an experimental investigation of second harmonic generation in III-V semiconductor photonic structures. These nanostructures have both wavelength and subwavelength dimensions. In particular, ensembles of aligned gallium phosphide nanowires and two-dimensional aluminum gallium arsenide photonic crystal slabs with a square lattice of holes are studied. In both cases, the III-V semiconductor material provides a large second-order nonlinearity, while the special arrangement of dielectric material of the nanostructure introduces additional dispersion. This extra dispersion can be used to phase match the nonlinear process in order to make frequency conversion efficient. We demonstrate that it is possible to resonantly couple to leaky modes of a photonic crystal slab at both the fundamental and second harmonic frequency and enhance the second harmonic signal ~10,000 times. Show less