Silicon Nitride Building Blocks in the Visible Range of the Spectrum

In this study, a platform guiding single-moded light at wavelengths of 480 nm, 520 nm and 633 nm (blue, green and red) is proposed and designed with several components being fabricated and characterised for the specific wavelength of 633 nm. A waveguide with propagation losses of 3.6 dB/cm is obtained, with a high confinement factor of 90.5% and a tight bending radius of 60 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m with 0.2 dB losses per bend, offering a good trade-off between losses, confinement factor and compactness. Also, a 1 × 2 MMI is demonstrated, with a footprint of 5 × 161 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m², and losses of 0.2 dB. Finally, a silicon nitride single-layer grating coupler has been validated to allow the fibre-to-chip coupling, with losses smaller than 11.7 dB. A comparison of the proposed platform with other state-of-the-art stoichiometric silicon nitride technologies performing in the range of the spectrum of 630–660 nm is shown. The present platform demonstrates losses in the order of the state-of-the-art single-mode waveguides, but with an enhancement of the confinement factor from 61% to 90.5%, which allows to decrease the bending radius by 20 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m or more compared with other state-of-the-art technologies.