In the late eighties, a new class of materials, known as photonic crystals (PCs), emerged enabling the propagation and generation of light to be potentially manipulated with unprecedented control. PCs consist of a periodic modulation of dielectric constant in one, two, or three dimensions, which can result in the formation of directional or omni-directional photonic band gaps (PBGs), spectral regions where light propagation is forbidden, and more remarkably, novel dispersion characteristics. Since PC properties scale with the dimension of the wavelength of interest, significant technological constraints must be fully addressed to manufacture 3D PBG materials for optical or infrared applications such as displays, lightning, and communications. PCs enable the unraveling of unique optical phenomena such as PBGs, spontaneous emission rate manipulation, sub-wavelength focusing, and superprism effects. This research focuses on the feasibility to achieve omni-directional PBGs in synthetic opal-based 3D PCs through precise nanoscale control to the original dielectric architecture. In particular, the optical response to the conformal deposition of dielectric layers using atomic layer deposition (ALD) within the porous template is strongly emphasized. Geometrical models were developed to faithfully model the manipulation of the synthetic opal architecture by ALD and then used in electromagnetic algorithms to predict the resulting optical properties. From these results, this research presents and investigates a scheme used to greatly enhance and adjust the PBG width and position, as well as simultaneously reducing the dielectric contrast threshold at which the PBG forms. This Thesis demonstrates that the unique opal architectures offered by ALD not only supports the formation of larger PBGs with high index materials; but also enables the use of optically transparent materials with reduced refractive index. Additionally, slight alteration of these structures facilitates the incorporation of non-linear (NL) electro-optical (EO) material for dynamic tuning capabilities and potentially offers a pathway for fabricating multi-functional photonic devices. Finally, low-temperature ALD was investigated as a means to manipulate band gaps and dispersion effects in 2D PC silicon slab waveguides and 3D organic biologically-derived templates. The results indicate the unique ability of ALD to achieve composite structures with desirable (large PBGs) or novel (slow light) optical properties.