Multilayer silicon nitride-on-silicon photonic platforms for three-dimensional integrated photonic devices and circuits

Today, generic foundry silicon photonic platforms use only one waveguide layer, implemented in the top silicon (Si) device layer of a silicon-on-insulator (SOI) wafer. However, very large-scale integrated photonic circuits. comprising of hundreds or even thousands of devices, require complex on-chip optical routing networks that become difficult or impractical to implement using only one Si waveguide layer because of waveguide crossing loss, crossing crosstalk, optical power handling limitations, and/or waveguide loss. Such very large-scale integrated photonic circuits enable applications in, for example, optical switch fabrics and optical phased arrays. Integrated photonic platforms that have several waveguide layers make possible three-dimensional (3D) on-chip optical routing to overcome the limitations of a single layer. For example, multilayer platforms support extraordinarily low loss over/under-pass types of crossings, wherein a waveguide in the topmost (bottommost) layer can pass over (under) many waveguides in the lower (upper) levels. This talk presents our ongoing research in foundry fabricated multilayer silicon nitride (SiN)-on-Si integrated photonic platforms [1, 2]. The platforms have included one or two SiN waveguide layers atop a Si waveguide layer fabricated on 8” SOI at the A*STAR Institute of Microelectronics Si photonic foundry (Fig. 1 and Fig. 2). SiN enables improved passive photonic components compared to Si due to its lower optical absorption, reduced waveguide scattering, and lower index contrast. In our platforms, light is transferred between the Si and SiN layers using adiabatic waveguide tapers, and active devices, such as highly efficient modulators, photodetectors, and potentially hybrid lasers, are implemented in the Si layer. We have demonstrated a number of novel and high performance devices on SiN-on-Si platforms, including highly efficient and broadband fiber-to-chip SiN-on-Si grating couplers; bi-level polarization rotator splitters; ultra-low-loss waveguide crossings; and ultra-efficient U-shaped PN junction for carrier depletion modulators [1-5]. The results and future directions of this research will be discussed.