Designing an Efficient Silicon Photonics System: Direct Integrating Photonic Crystal Surface Emitting Laser With Inverse-Designed Perfect Vertical Grating Coupler for Optimal Optical Communication Applications

Silicon photonics, merging silicon-based electronics and photonics, offers a transformative leap in optical technologies by providing high-density, high-speed optical interconnects at reduced costs. Central to this progress is the silicon nitride (Si₃N₄) waveguide, recognized for its low propagation losses and compatibility with CMOS manufacturing processes, enabling photonic-electronic integration on a single chip. This paper addresses the critical challenge of cost-efficient packaging in silicon photonics through the direct vertical bonding of photonic-crystal surface-emitting lasers (PCSELs) onto Si₃N₄ grating couplers. PCSELs, known for their high power, coherent vertical emission, and superior beam quality, are optimized here for integration with silicon photonics. This study employs an adjoint shape optimization algorithm to design an inverse-designed vertical grating coupler (VGC) to improve coupling efficiency. Our approach demonstrates significant advancement by achieving a coupling efficiency of 84.4% (−0.74 dB) for the inverse-designed VGC and 75.1% (−1.24 dB) for the combined metagrating and forward-designed grating coupler with direct PCSEL bonding. This efficiency is achieved through meticulous design and optimization of the PCSEL structure, grating coupler parameters, and incorporating a distributed Bragg reflector (DBR) to minimize losses. These findings showcase the potential for high-performance, cost-effective silicon photonic devices, setting a new benchmark for integrated photonic systems. This work presents a holistic and innovative solution, addressing the key challenges in the field and paving the way for future commercialization and broader silicon photonics applications.