Welcome to the Glass Age

82 and attention in two main areas. The first is microstructuring including photonic bandgap and microstructured fibers. Though outside the scope of this Chapter, such fibers generally rely on conventional glasses, primarily silica, and performance results typically from periodic structures in the glass(es), or air channels created by stacking rods and tubes together. The second area is in the materials from which fibers are made. Indeed, there has been a renaissance in optical fiber materials, not just in the range of new materials but also in the length scales and interconnectivities ranging from nano-scale engineered structures, including glass-ceramic, phase-separated and nanoparticle infused cores, to multimaterial fibers where glasses, plastics, and metals run the full length [2]. Glass integrated optics In the mid-1960s it became clear that optical fibers had the capability of winning the competition with metal pipes for long-distance high-capacity communication. Correspondingly, the need emerged for optical connecting elements analogous to existing parallel- plate metal microwave waveguides. Thus, optical thin-film waveguides were designed and fabricated, where light was trapped due to total internal reflections at upper and lower surfaces, i.e., by the same mechanism operating in optical fibers but in a planar geometry rather than a cylindrical one. Shortly thereafter, the new field of integrated optics arose, providing a complete tool for locally manipulating the light coming from a laser source or carried by an optical fiber [4]. Once again, glass immediately emerged as a very convenient material, which had the advantage of full compatibility with optical fibers and provided an easy and low-cost tool to develop technological processes that later could also be transferred to other optical materials. The fundamental requirement for confining the light is that the guiding layer has a refractive index higher than the surrounding media; this goal, in glass integrated optics, is easily achieved Figure 5.3. An example of a photonic device (1 x 8 power splitter for optical fiber communication systems) made in glass by ion-exchange: (a) laboratory demonstration in 1986; (b) qualified pigtailed and packaged device produced some twenty years later by Teem Photonics. Source: Reprinted from Ref. [6] under a Common Creative license.