Topology optimized photonic components towards higher integration density

Abstract

This thesis explores the design and experimental validation of inverse-designed passive Nano-photonic components for compact and high-throughput photonic integrated circuits (PICs) on the Silicon-on-Insulator (SOI) platform. Topology optimization is employed to analyze the advantages and limitations of this optimization method. The study focuses on the design of waveguide bends, crossings, wavelength demultiplexers, and asymmetric transmission structures for densely packed photonic chips. Sharp L, U, and T bends are successfully demonstrated, with footprint sizes ranging from 2.5µm x 2.5µm to 1µm x 1µm. Utilizing the adjoint method, highly efficient and broad-band bends are achieved. A compact wavelength division multiplexer is implemented, separating 1300nm and 1500nm wavelengths within a 3µm x 2µm footprint. The device exhibits an extinction ratio of approximately 20dB for TE mode and 9dB for TM mode on both ports. A waveguide crossing with a size of 4µm x 4µm demonstrates low insertion loss (<0.18dB) and excellent cross-talk performance (-41dB) across the wavelength range of 1250-1550nm.The thesis also presents an inverse design approach for an asymmetric light transmission device. This miniaturized device has size of 3µm x 3.6µm and achieves a rejection ratio exceeding 14dB for transmission in two directions. Operating over a broadband wavelength range of 1450-1650nm, the device utilizes only Silicon and Silicon dioxide, ensuring compatibility with CMOS fabrication processes. This research contributes to the advancement of loss-tolerant passive inverse designed photonic components. Experimental validation of waveguide bends, crossings, wavelength demultiplexers, and asymmetric transmission structures confirms their functionality and highlights their potential for integration into future photonic systems.