The period from 1969 to 1998 saw a shift toward engineering light via periodic dielectric media, culminating in the explicit realization of photonic band gaps in structured materials. A major thrust consolidated two- and three-dimensional photonic crystals and introduced photonic-crystal fibers, enabling guided light with tailored dispersion and confinement. The research patterns merged theoretical band-structure concepts with microfabrication advances to translate band-gap physics into functional devices. Historical Significance: The theoretical identification of photonic band gaps in dielectric lattices created a unifying paradigm that parallels electronic crystals, providing a new toolkit for light control. Experimental milestones, including three-dimensional photonic crystals and high-Q microcavities, demonstrated practical regimes where light could be inhibited or channeled, reshaping approaches in communications, sensing, and integrated photonics. The emergence of novel fiber and macroporous materials, such as all-silica photonic-crystal fibers and TiO2 air-sphere crystals, marked a turning point that catalyzed subsequent decades of photonic design.