ALD high-k layer grating couplers for single and double slot on-chip SOI photonics

State of the art grating couplers for horizontal single and double slot waveguides are presented; in these devices the input signal is transmitted from a single mode optical fiber to silicon on insulator slot waveguides. In the waveguides, atomic layer deposited (ALD) high-k dielectrics form the low refractive index slot. It is demonstrated that the new fully etched design combined with precision of ALD result in highly reproducible devices with efficiency variations less than 1%. Devices have a peak coupling efficiency of 24% at 1.55 μm. In order to achieve the optimal design, optical properties of high-k films are studied with spectroscopic ellipsometry. Measured refractive indices show variations from reference values, originated from film densities.