Glass Integrated Optics: 50 Years and Still Growing Strong

Glass is a ubiquitous material, which has proven to be fundamental also for the development of photonics and in particular of fiber and integrated optics. Figure 1 shows what is (at least at authors' knowledge) the first photo of the mode pattern of a planar waveguide, constituted by a liquid core in between two glass optical plates [1]. Even a few years before the appearance of the September 1969 issue of the Bell System Technical Journal which included seminal papers containing the word "integrated optics" in their title [2,3], planar optical waveguides had been demonstrated by using thermal tempering (namely, ion exchange) of an optical glass [4] and proton irradiation of fused silica |5|.