Photonic integrated circuits (PICs) hold significant promise in applications such as data center networks, artificial intelligence, high-performance computing, quantum computing, and LiDAR, thanks to their energy efficiency and large communication bandwidth. By leveraging the infrastructure and technologies of conventional CMOS foundries, the development and manufacturing costs of PIC chips are significantly reduced. However, the commercialization of PIC products faces a critical challenge in optical packaging, which currently accounts for three times the cost of the PIC itself. Among these challenges, fiber-to-PIC coupling—a key step in optical packaging—remains particularly difficult due to the need for precise optical alignment and costly fabrication processes.
In this dissertation, I introduce a novel fiber-to-PIC coupling method designed to address these challenges, utilizing an innovative optical coupling device known as the integrated microlens (IMC). Integrated microlens couplers effectively enlarge the mode size of the outgoing beam from the PIC (up to 80 µm), facilitating efficient mode-matching to optical fibers and enabling a coupling method that is both efficient and alignment-tolerant. Experimentally, we demonstrate state-of-the-art optical coupling performance with IMCs, achieving a chip-to-fiber coupling loss of 0.6 dB per coupler, a polarization-dependent loss of 0.2 dB, and a wavelength-dependent loss of 0.2 dB. Additionally, these couplers exhibit exceptional fiber-to-chip alignment tolerance of up to 10 µm in the transverse direction.
More importantly, integrated microlens couplers are fully compatible with wafer-level fabrication processes, ensuring excellent dimensional and quality control. This compatibility positions IMCs as a highly scalable and manufacturable solution for optical packaging, making them a promising candidate for addressing the challenges of commercial photonic product development.
This work will first present the operating principle of an IMC, along with the design and simulation of IMCs featuring mode field diameters (MFD) of 10 µm, 20 µm, and 80 µm. Subsequently, the fabrication process and measurement results of the IMC will be discussed. Finally, the integration of the IMC onto a photonic platform will be discussed.