Abstract: Disclosed is a method of fabricating an optical waveguide device including the steps of forming a mask over a waveguide core material layer so as to leave a portion of the layer exposed, and exposing the structure to an oxidizing environment to form an oxide layer on the waveguide core material layer at least in the exposed portion thereby defining the lateral dimension of the waveguide core. The resulting waveguide core has extremely smooth surfaces for low optical losses.

Abstract: A system for producing an optical gain, the system including a host having a light conducting path doped with thulium, holmium, and at least one rare earth selected from the group consisting of europium and terbium in respective amounts sufficient to produce an optical gain by energizing the thulium to a .sup.3 H.sub.4 state to produce an optical gain by a .sup.3 H.sub.4 -.sup.3 F.sub.4 transition, producing a 1.47 .mu.m wavelength output. There is subsequent energy transfer from the .sup.3 F.sub.4 state of the thulium to a .sup.5 I.sub.7 state of the holmium, and energy transfer from the .sup.5 I.sub.7 state to the rare earth selected from the group consisting of europium and terbium. The system can include oscillator, amplifier, and superluminescence source configurations. A method for making and a method for using the system are included.

Abstract: An optical fiber having a core with a composition consisting essentially of 48 to 60 mole percent ZrF.sub.4, 15 to 25 mole percent BaF.sub.2, 1 to 5 mole percent LaF.sub.3, 1 to 5 mole percent AlF.sub.3, 15 to 22 mole percent NaF, and 1 to 8 mole percent ThF.sub.4 ; and a cladding having an index of refraction lower than that of the core. The glass of the core can be doped, for example, with rare earths. Built-in casting, rotational casting, casting around a rod, and rod-in-tube methods can be used to produce optical fibers having a composition in accordance with the present invention and having improved resistance to crystallization, as compared to ZBLAN glasses, even in the presence of rare earth dopants.