Fabrication and Characterization of Monocrystalline Sesquioxide Waveguide Lasers

The development of integrated optical devices based on rare-earth doped sesquioxides is very promising for applications that require lasers with high frequency stability. Thus, the subject of this work is the fabrication of rare-earth doped sesquioxide waveguiding films by pulsed laser deposition (PLD) and their characterization as well as the realization of rib-channel waveguide lasers based on these films. Nd3+ and Er3+ doped sesquioxide films with thicknesses of 1 to 3 µm were deposited on sapphire as well as sesquioxide substrates. The growth was monitored using reflection high-energy electron diffraction. The structure of the films was characterized by use of X-ray diffraction and atomic force microscopy, and their fluorescence lifetimes as well as their absorption and emission cross-sections were determined. Highly-textured polycrystalline Sc2O3 and Y2O3 films with surface roughnesses as low as 2 nm and spectroscopic properties similar to those of bulk crystals were fabricated on sapphire substrates. Epitaxial two-dimensional growth up to a film thickness of 3 µm has been realized for lattice matched (Gd,Lu)2O3 films deposited on Y2O3 substrates. The surface structure of these monocrystalline films consists of nearly atomically flat terraces and step edges with typical heights of a single monolayer. The fluorescence lifetimes of the lattice matched (Gd,Lu)2O3 films are comparable to those of correspondingly doped Y2O3 bulk crystals, whereas their emission and absorption spectra are slightly broadened. Using a newly developed loss-measurement technique, the propagation losses within the waveguiding films have been determined to be between 1.4 dB/cm and 14.8 dB/cm at wavelengths of approximately 800 nm. These relatively high losses can be explained by scattering at parasitic particulates, which typically occur during PLD. Several films were structured by Ar-ion etching, resulting in 2 to 5 µm wide and 6 to 7 mm long rib-channel waveguides. Gain measurements performed with the 0.6 at.% doped Er:(Gd,Lu)2O3 rib-channel waveguides resulted in signal enhancements up to 5.9 dB/cm at 1536 nm upon in-band pumping at 1480 nm. While room-temperature continuous-wave laser emission at 1.58 µm has been demonstrated for a 0.2 at.% doped Er:Sc2O3 bulk crystal pumped at either 975 nm or 1536 nm, laser experiments performed with the Er3+ doped waveguides have not been successful. Continuous-wave laser emission at 1075 nm and 1080 nm has however been realized with a mon