Integrated lithium niobate photonics and applications

Abstract

The past decade has witnessed a surge in research of photonic integrated circuits (PICs). Novel devices, modules, and system architectures have been realized on several integrated photonics platforms including silicon, silicon dioxide, and silicon nitride, to name a few. In particular, silicon PICs have emerged as promising solutions for data center interconnects due to their scalable fabrication as well as compact size and low operating power. However, as the data traffic in the world is increasing, the community is actively searching for other material platforms to provide lower-power and higher-bandwidth solutions. In particular, for quantum applications, the performance and metrics required of PICs is more demanding than in the case of classical applications. Combination of low optical loss, fast switching (e.g. through $\chi^{(2)}$ nonlinearity), and wide transparency window (e.g. into the visible and UV regions) are crucial for a quantum photonics platform.

Lithium niobate (LN), plays a significant role in our daily life as it has been the workhorse of the telecommunication industry for decades. Over the last decade, the availability of high-quality thin-film lithium niobate (TFLN) and breakthroughs in nanofabrication techniques have enabled numerous integrated, efficient, and high-performance components with unique functionalities. Nowadays devices made on this platform such as electro-optical modulators, nonlinear wavelength converters, and optical parametric amplifiers have already outperformed all existing technologies. More importantly, new functionalities such as cavity-based electro-optic comb sources, frequency shifters, and microwave-to-optical transducers, and non-magnetic based isolators have been realized on thin-film lithium niobate.

In this thesis, I demonstrate high-performance, and ultra-low loss devices in the thin-film lithium niobate platform for applications such as gas spectroscopy and data communication. First, we build a dual-comb interferometer based on cavity-based electro-optic frequency combs. With this we perform a proof-of-concept spectrally-tailored multiplexed sensing benefits from the frequency stability of the comb sources. Next, we design an integrated electro-optic comb with ultra-dense comb spacing down to hundreds of MHz. The third chapter introduces a modification to convectional thin-film lithium niobate fabrication, which improves the minimum achievable loss on this platform by almost an order of magnitude. Our response measurement (self-calibrated via the Kerr nonlinearity) reveals that the intrinsic absorption-limited Q-factor on TFLN platform can be as high as 180 million. In the end, we demonstrate a fully-integrated electrically-driven high-power laser transmitter on lithium niobate with more than 50 GHz bandwidth. This method allows for coupling more than 115 mW of optical power into thin-film lithium niobate waveguides. Finally, I show the path towards devices in the visible range, scalable laser integration and THz generation in TFLN platform.