Amplification in epitaxially grown Er:(Gd,Lu)₂O₃ waveguides for active integrated optical devices

Monocrystalline lattice matched $Er(0.6$ $at.$ %):$(Gd,Lu)_2O_3$ films with nearly atomically flat surfaces and thicknesses up to 3 μm have been grown on $Y_2O_3$ substrates using pulsed laser deposition. The emission cross sections were comparable with the ones of $Er:Y_2O_3$ bulk crystals, showing only a marginal spectral broadening. Rib channel waveguiding could be demonstrated after structuring the films with reactive ion etching. Gain measurements have been performed and the results compared with a theoretical gain spectrum. A gain of 5.9 dB/cm could be measured at 1535.5 nm through in-band pumping at 1480 nm. The scattering losses in such a 7 mm long rib waveguide have been determined to be below 4.4 dB at 632.8 nm. An extrapolation to the gain wavelength with the $λ^{−4}$-Rayleigh law of scattering resulted in losses of 0.2 dB/cm at 1.5 μm.