A silicon nitride platform by physical vapor deposition for dense wavelength division multiplexing on chip

On-chip and off-chip optical interconnections have been expected to breakthrough the scaling bottleneck of the microprocessors. The missing link is dense-wavelength-division-multiplexed (DWDM) technology. The high index contrast, Si on insulator (SOI) platform, here after referred to as HiDex, is excellent to shrink the footprint of devices and circuits. However, HiDex has a fundamental limit to implement DWDM because of the large thermo-optic (TO) coefficient of Si. Although silica optical bench, i.e., low index contrast (LoDex) is much more stable than HiDex, the large bending radii have made it impossible to integrate on a chip. The present paper proposes mid index contrast (MiDex) platform to implement the DWDM, typically based on silicon nitride (SiN_x) as in Fig. 1. We have demonstrated the capability of MiDex to lock wavelength of multiplexing and demultiplexing (MUX/DEMUX): The shift of the ring resonance was less than 100 GHz at a temperature range from room temperature to 70°C. Since no absorption appears around 1520 nm without any high temperature annealings normally required, it is clear that the SiN_x based MiDex platform would be ready for DWDM application of Si photonics.