Low-loss optical waveguides for the near ultra-violet and visible spectral regions with Al2O3 thin films from atomic layer deposition

In this work, we report low-loss single-mode integrated optical waveguides in the near ultra-violet and visible spectral regions with aluminum oxide (Al2O3) films using an atomic layer deposition (ALD) process. Alumina films were deposited on glass and fused silica substrates by the ALD process at substrate/chamber temperatures of 200 oC and 300 oC. Transmission spectra and waveguide measurements were performed in our alumina films with thicknesses in the range of 210-380 nm for the optical characterization. Those measurements allowed us to determine the optical constants (nw and kw), propagation loss, and thickness of the alumina films. The experimental results from the applied techniques show good agreement and demonstrate a low-loss optical waveguide. Our alumina thin-film waveguides are well transparent in the whole visible spectral region and also in an important region of the UV; the measured propagation loss is below 4 dB/cm down to a wavelength as short as 250 nm. The low propagation loss of these alumina guiding films, in particular in the near ultra-violet region which lacks materials with high optical performance, is extremely useful for several integrated optic applications.