Rare-earth activated glasses in integrated optical devices with different geometric shapes: Fibers, planar waveguides and microspheres

Glasses activated by rare-earths in optical devices is a potentially important area of research in developing effective optical means for the propagation of light and luminescence enhancement. Applications involving optical glasses have grown considerably in recent years focused on the development of new shapes of optical devices and improved glass compositions, but also in new processes for their preparation. The confinement of light in small objects has become an essential requirement for optical devices. Examples of this trend are provided by optical fibers, optical integrated circuits (planar waveguides or slab) and, more recently, optical dielectric resonators supporting the Whispering Gallery Modes (glass microspheres). To demonstrate the technological importance of optical devices with unique properties exhibited by glasses activated by rare earths, we review some functional aspects of such devices, where light is confined in different volumes or shapes, particularly fibers, monoliths, films/coatings and microspheres. Glasses activated by rareearths are often used as components in optical integrated circuits for optical communication and sensor applications. Optical waveguides (planar, strip, or fiber waveguides) and spherical microresonators are some current examples of integrated glass-based optical devices.