Welcome to the Glass Age

85 excellent control of the microsphere diameter. Another field that has emerged rapidly in recent years to become a hot topic in photonics research is flexible photonics. Its growth has mirrored the rapid development of flexible components and devices (LEDs, OLEDs, displays, wearable sensors) in the area of consumer electronics. At first sight, organic materials would appear the most convenient fabrication platform, due to their mechanical flexibility, low cost and large-scale manufacturing potential; inorganic materials, however, remain the long- term choice for making stable and high-performance photonic devices. Thus, glasses may play an important role even in this area, both as highly transparent, and mechanically, thermally and chemically robust substrates which can also be bent, and as a material platform for optical interconnects and sensor applications. Very thin glasses are now marketed by major glass producers worldwide, with thicknesses in the range 30-200 μm, and are widely used in solar panels and in cellular phones (including foldable phones). There is strong interest in the development of monolithic glass integrated photonic circuits, made in these very thin glasses by direct laser writing, ensuring novel mechanical properties suitable for easier three- dimensional integration of electronic and photonic components. On the other hand, chalcogenide glass waveguides made by thin films thermally evaporated onto polymeric substrates from As 2 S 3 binary system or Ge 23 Sb 7 S 70 ternary alloy have already exhibited excellent characteristics, namely their low deposition temperature, tunability of their refractive index (from 2 to 3.5, depending on composition) and very low propagation loss (less than 1 dB/m) in the band around the 1.5 μm wavelength [9]. This approach appears very promising for new applications such as high-bandwidth-density optical interconnects, conformal wearable sensors and ultrasensitive strain gauges. Figure 5.5. Principle of optical amplification with electronic energy levels and some emission bands of active lanthanoid ions in comparison with optical fiber loss spectrum. Source: S. Tanabe.