Integrated Sources on Thin-Film Lithium Niobate

Abstract

Photonic integrated circuits have played a crucial role in the miniaturization and efficiency improvement of many optical components. While many material platforms have played host to excellent photonic devices, in recent years, thin-film lithium niobate (TFLN) on insulator has emerged as a promising photonic platform, owing to its large electro-optic effect, low-loss waveguides, and wafer scalability. Devices on TFLN have witnessed remarkable developments over the past decade, most notably in the realization of high-bandwidth, high-efficiency, and low-loss electro-optic modulators. However, the excellent material properties of the TFLN platform extend beyond EO modulation, making it a candidate platform for many high performance chip-scale optical systems. This dissertation presents work in bringing various functionalities of sources typically realized in bulk systems onto the TFLN platform. Among those included are on-chip pulse and frequency comb generation in lieu of bulk mode-locked lasers, high performance optical isolators using electro-optic modulation in lieu of bulk magneto-optic isolators, and an on-chip, narrow-linewidth extended cavity laser. Included is work involving an emerging technology known as photonic wire bonding, which shows promise as a future integration method to bridge platforms and functionalities. The first half of the thesis concerns the manipulation of continuous-wave light for frequency comb sources. I start by presenting ultrashort pulse generation using cascaded electro-optic amplitude and phase modulators combined with off-chip dispersion, realized using two designs, the second of which is packaged using the novel photonic wire bonding scheme. I then show how, by interfacing the pulse generation chip with a high-Q resonator with matched free spectral range, broadband spectrum generation can occur with relatively low average on-chip power. An outstanding challenge for future integrated photonic systems is in the implementation of on-chip gain, which usually involves integration of III-V semiconductor materials to realize integrated lasers and detectors. The second half of the thesis concerns the integration of high-performance lasers onto the TFLN platform. I show how an electro-optic TFLN phase modulator can be used to realize a high-performance, broadband, and low-loss optical isolator, which is a necessary component for any future work with on-chip lasers. Finally, I show the demonstration of a narrow-linewidth, high-power, tunable extended cavity diode laser using InP and TFLN and integrated using photonic wire bonding.