Integrated Lithium-Niobate Photonics
Lithium niobate (LN) is an “old” material with many applications in optical and microwave technologies, owing to its unique properties that include large second order nonlinear susceptibility, large piezoelectric response, and wide optical transparency window. Conventional LN components, including modulators and periodically polled frequency converters, have been the workhorse of the optoelectronic industry. They are reaching their limits, however, as they rely on weakly guiding ion-diffusion defined optical waveguides in bulk LN crystal. I will discuss our efforts aimed at the development of integrated LN platform [1, 2], featuring sub-wavelength scale light confinement and dense integration of optical and electrical components. Examples of devices to be discussed include integrated LN electro-optic modulators that can be driven directly by a CMOS circuit  and ultra-high Q LN optical cavities  with application in electro-optic and Kerr frequency combs. Finally, various approaches to perform nonlinear wavelength conversion in LN waveguides will be discussed [5-6].
1. C. Wang, M. J. Burek, Z. Lin, H. A. Atikian, V. Venkataraman, I. Huang, P. Stark, and M. Lončar, “Integrated high quality factor lithium niobate microdisk resonators”, Opt. Express, 22, 30924 (2014)
2. C. Wang, M. Zhang, B. Stern, M. Lipson, and M. Loncar, “Nanophotonic Lithium Niobate Electro-optic Modulators.” Optics Express, 26, 1547 (2017).
3. M. Zhang, C. Wang, X. Chen, M. Bertrand, A. Shams-Ansari, S. Chandrasekhar, P. Winzer, and M. Lončar, “Ultra-High Bandwidth Integrated Lithium Niobate Modulators with Record-Low Vπ”, OFC, San Diego, CA (11–15 March 2018), post-deadline paper Th4A.5 (DOI: 10.1364/OFC.2018.Th4A.5)
4. M. Zhang, C. Wang, R. Cheng, A. Shams-Ansari, and M. Loncar, “Monolithic Ultrahigh-Q Lithium Niobate Microring Resonator.” Optica, 4, 1536 (2017).
5. C. Wang, Z. Li, M. H. Kim, X. Xiong, X. F. Ren, G. C. Guo, N. Yu, and M. Loncar, “Metasurface-assisted phase-matching-free second harmonic generation in lithium niobate waveguides”, Nature Communications, 8, 2098, (2017)
6. C. Wang, X. Xiong, N. Andrade, V. Venkataraman, X. F. Ren, G. C. Guo, and M Lončar, “Second harmonic generation in nano-structured thin-film lithium niobate waveguides”, Optics Express, 6, 6963 (2017)