Design and optimization of integrated photonic grating couplers for on-chip applications

Integrated photonics has emerged as a transformative technology, enabling the monolithic integration and large-scale integration of optical components on a single chip. This advancement has facilitated significant progress in fields such as telecommunications, biomedical sensing, quantum computing, and precision metrology. Unlike traditional electronic circuits, integrated photonics leverages light for information transmission and processing, offering distinct advantages such as high bandwidth, ultra-fast data transfer, and low power consumption. However, one of the major challenges in integrated photonics is the efficient coupling of light between optical fibers and on-chip waveguides. In optical communication and sensing applications, standard optical fibers used for light transmission typically have core diameters of around 10 μm, whereas photonic waveguides on a chip can have dimensions smaller than 1 μm. This significant mode size mismatch results in substantial coupling losses, which directly affect the overall efficiency of integrated photonic devices. Various coupling techniques have been developed to address this issue, with grating couplers and edge couplers being the most widely used solutions. Grating couplers provide a vertical coupling mechanism by redirecting incident light from a fiber into a waveguide through a diffraction-based structure. They offer key advantages such as relaxed alignment tolerances, compatibility with wafer-scale testing, and compact footprint, making them particularly attractive for high-density integrated photonic systems. In contrast, edge couplers provide higher coupling efficiency but require precisely polished facets, making fabrication and packaging more challenging. Silicon (Si) and silicon nitride (SiN) are the two most commonly used materials in photonic integration. Silicon photonics, with its high refractive index contrast, enables strong optical confinement and is CMOS-compatible, making it suitable for large-scale integration. Silicon nitride, on the other hand, offers lower propagation losses and broader spectral operation, making it ideal for nonlinear and quantum applications. Despite the extensive research on grating couplers, most studies focus on a single material. This thesis proposes optimized grating coupler designs utilizing both Si and SiN materials at 1550 nm wavelength. By optimizing design parameters such as grating period, etch depth, and coupling angle, we aim to enhance coupling efficiency while maintaining a compact footprint. The results of this study contribute to the development of high-performance integrated photonic systems by improving fiber-to-chip coupling efficiency across multiple wavelengths, thereby expanding the applicability of photonic platforms.