All ALD TiO2-Al2O3-TiO2 horizontal slot waveguides for optical sensing

We report for the first time on the use of Atomic Layer Deposition (ALD) to produce TiO₂-AlO₃-TiO₂ horizontal slot waveguides optical sensors. The propagation losses of the waveguides are measured and found to be 18 dB/cm for the quasi-TM mode. These losses are better than the losses reported in slot waveguides made using PECVD techniques (for materials like SiC of similar refractive index as TiO₂) with the advantage of a very accurate layer thickness control thanks to the ALD process and the possibility to decrease by a factor 3 the slot size. The field being so confined in the slot we investigated allows the implementation of these slots in a cantilever based sensor. A sensitivity of 0.5 dB/nm is reported.