Silicon nitride is demonstrated as a high performance and cost-effective solution for dense integrated photonic circuits in the visible spectrum. Experimental results for nanophotonic waveguides fabricated in a standard CMOS pilot line with losses below 0.71dB/cm in an aqueous environment and 0.51dB/cm with silicon dioxide cladding are reported. Design and characterization of waveguide bends, grating couplers and multimode interference couplers (MMI) at a wavelength of 660 nm are presented. The index contrast of this technology enables high integration densities with insertion losses below 0.05 dB per 90° bend for radii as small as 35 µm. By a proper design of the buried oxide layer thickness, grating couplers with efficiencies above 38% for the TE polarization have been obtained.

High-performance silicon nitride focusing grating couplers with AlCu/TiN reflectors for a visible wavelength (660 nm) have been designed and fabricated in a standard complementary metal-oxide-semiconductor pilot line. The influence of the bottom oxide cladding thickness on the grating decay length and efficiency is theoretically and experimentally investigated. It is shown how the metal reflector not only increases the efficiency but also allows reduction of the radiated beam size. Coupling efficiencies above 59% have been measured for compact focusing gratings.

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