Effect of Particle-Induced Voids on Evanescent Coupling in Silicon Photonics Heterogeneous Integration

Abstract

Supporting increasingly complex on-chip functionalities necessitates efficient heterogeneous integration of active components (e.g., InP lasers, LiNbO3 modulators) in silicon photonics. However, deep-submicrometer particles and the resulting voids at the bonding interface of the integrated components can severely degrade evanescent coupling efficiency. In this paper, we combine an elastomechanical model and coupled-mode theory to quantify void-induced loss in two representative architectures: InP-on-Si lasers and LiNbO3-on-Si3N4 modulators. For lasers, the impact is strongly location dependent: a 100 nm particle in a taper region incurs a 0.913 dB coupling loss versus 0.058 dB mid-device (>15× increase). Increasing the separate confinement heterostructure (SCH) thickness from 25/25 nm to 100/100 nm suppresses higher-order mode excitation and flattens the loss response. Optoelectronic modeling confirms that this optical robustness far outweighs the marginal penalty in carrier injection efficiency. For modulators, replacing a slab LiNbO3 film with a rib waveguide and employing a compact adiabatic Si3N4/LiNbO3 taper confines the mode away from the electrodes and maintains low void-induced loss for particles up to sub-micrometer sizes. These results underscore the need for robust interfaces achieved through coordinated optimization of the layer stack, coupling scheme, and device geometry. Based on these insights, we propose design guidelines for void-tolerant evanescent interfaces on the silicon photonics platform, enabling higher yield in densely integrated heterogeneous photonic systems.