Sub-wavelength grating silicon to silicon nitride interlayer couplers in commercial foundry silicon photonics

The development of silicon photonics platforms has played a pivotal role in enabling large-scale photonic integrated circuits (PICs). Most of today's silicon photonics processes incorporate silicon nitride to realize devices requiring ultra-low loss and to leverage its unique material properties. Efficient light transport between the silicon and silicon nitride layers necessitates a compact and high-performance interlayer coupler. In this work, we utilize the tunable refractive index and dispersion properties of subwavelength grating (SWG) waveguides in the silicon layer to design compact and broadband interlayer couplers. We present analytical modeling, supported by simulations, of interlayer coupling and experimentally demonstrate proof-of-concept interlayer transitions using the GlobalFoundries 45SPCLO process.