Photonic Integrated Circuits for Nonlinear Devices, Ranging Techniques, and Sensing Applications

Advancements in volume manufacturing have significantly boosted the potential of photonic integrated circuits (PICs), positioning them to replace bulk optics across numerous applications. Among the fields experiencing the greatest benefits from this progress is nonlinear photonics, which enables the highly confined manipulation of light within on-chip dimensions. This development paves the way for a diverse array of applications, including frequency combs, LiDARs, sensing and biomedical technologies, photonic computing, and RF photonics. The inherent advantages of PICs, such as their compact size and stable performance facilitated by integration, make them particularly appealing for these applications.

Among the different materials, lithium niobate (LN) has attracted considerable attention from researchers due to its outstanding properties. Creating nonlinear optical frequency converter devices using LN necessitates quasi-phase matching (QPM) achieved through periodic poling. Additionally, efficiently coupling nonlinearly generated light, such as fundamental and second harmonic spots, to an output fiber demands an optimized edge coupler. This thesis introduces an edge coupler design for x-cut thin-film LN specifically tailored to optimize the simultaneous coupling of spots at different wavelengths resulting from nonlinear processes.

Nonlinear photonics finds applications in autonomous vehicles as well. Light detection and ranging (LiDAR) has emerged as a robust technique for swiftly detecting and classifying objects even in rapidly changing and low-visibility conditions. However, conventional LiDAR systems are often limited by the speed of their 2D scanning process across the entire scene. In this thesis, a ranging technique is proposed, leveraging dual frequency combs with slightly different repetition rates. This approach facilitates parallel ranging in one direction, reducing the scanning process to a single dimension and offering the promise of high-speed LiDAR systems.

Beyond these applications, the rapid expansion of modern technologies, such as the Internet of Things (IoT), has driven demand for highly sensitive, compact, and cost-effective optical sensors. PIC-based optical sensors offer advantages such as high sensitivity, broad dynamic range, cost efficiency, and high throughput. This thesis introduces a design for a linear and fully passive refractive index (RI) sensor on the silicon-on-insulator (SOI) platform. The sensor maintains a constant figure of merit (FOM) across the entire range of refractive index variations in the cover medium, addressing the limitations of conventional RI sensors, which exhibit nonlinear responses.