Erbium-doped oxide films and devices prepared by sputtering for optoelectronic applications

Stimulated by the rapid development of Er-doped fiber amplifiers, rare-earth doped oxide films are drawing increasing attention for amplifiers and lasers suitable for integrated optics. Thin-film waveguide devices require high rare-earth concentration in order to obtain a certain amount of optical gain in a relatively short length. In this study, we have developed highly Er-doped {dollar}({lcub}sim{rcub}{dollar}1 mole %) silicate glass films using rf-magnetron sputtering techniques. Er-doped films show a strong, room-temperature luminescence at 1.54 {dollar}rmmu m{dollar} wavelength, corresponding to the {dollar}rmsp4Isb{lcub}13/2{rcub}to{lcub}sp4{rcub}Isb{lcub}15/2{rcub}{dollar} transition of {dollar}rm Ersp{lcub}3+{rcub}{dollar} ions. Fluorescence decay lifetime over 9 msec were obtained, indicating that Er atoms are homogeneously distributed without forming many clusters. Using the Er-doped glass films as an active guiding layer, we have designed and fabricated ridge waveguide structure for optical amplifiers. A novel fabrication process was developed and used in forming the ridge structures. The process does not involve etching of the Er-doped silicate glass films, therefore it is simple and reliable, and yet produces well defined ridges with low propagation loss. The amplifier performance of the fabricated devices was characterized using a 980 nm laser diode as a pump source and a 1.54 {dollar}rmmu m{dollar} DFB laser as a signal source. A 1.7-cm long waveguide shows a signal enhancement of 15.4 dB with a pump power of 40 mW. This enhancement fully compensates for both Er absorption and waveguide losses and results in a net gain of 7.2 dB. The measured gain performance is compared with the simulation result, which was obtained by solving the propagation-rate equations of Er-doped waveguides.; Resonant microcavities have also received much attention because of their capability of controlling spontaneous emission properties within the cavity. We have investigated enhancement of Er luminescence in a resonant microcavity. A cavity structure resonant at 1.54 {dollar}rmmu m{dollar} was designed and fabricated by sandwiching an Er-doped layer between multilayer dielectric Bragg mirrors. Luminescence enhancement of over 10 times was observed from the fabricated structure. We also developed Er-doped conducting oxide films using rf-sputtering. The Er-doped films show a clear room-temperature photoluminescence at 1.54 {dollar}rmmu m.{dollar} The Er-doped films are conducting with a resistivity of down to {dollar}10sp{lcub}-3{rcub} Omega{dollar}-cm. The Er-doped conducting oxides are promising as a material that may allow electrical excitation of rare-earth ions as well as optical excitation.