Lithium niobate (LN) is an excellent nonlinear optical material widely deployed for telecommunications and wavelength conversion. While its high χ2 nonlinearity, wide transparency window and low optical loss offer unique advantages, conventional LN devices are bulky and discrete due to the low index-contrast in ion-exchanged waveguides. In this talk, I will provide a summary of our recent results in integrated LN photonics that overcomes this limitation by direct etching thin-film LN. We show that waveguides and resonators with sub-wavelength light confinement and extremely low propagation loss (< 0.03 dB/cm) can be fabricated using standard lithography techniques. Together with the strong electro-optic and nonlinear responses, we demonstrate electro-optic modulators with CMOS-compatible driving voltage of 1.4 V and electro-optic bandwidths up to 300 GHz, promising for future telecommunications and millimeter-wave applications. Leveraging the high nonlinear-optic coefficient, we demonstrate broadband Kerr and electro-optic frequency comb generation, as well as highly efficient nonlinear wavelength conversion, which could open up avenues for high-performance chip-scale quantum photonic integrated circuits.
Dr. Cheng Wang received his B.S. degree in Microelectronics from Tsinghua University in 2012. Afterwards, he joined Harvard University as a Ph.D. student in the School of Engineering and Applied Sciences, advised by Prof. Marko Loncar. He received his S.M. and Ph.D. degrees, both in Electrical Engineering from Harvard University, in May 2015 and May 2017, respectively. From 2017 – 2018, Cheng conducted research as a postdoctoral fellow at Harvard, before joining City University of Hong Kong as an Assistant Professor in June 2018. Dr. Wang’s research focuses on the design and nanofabrication technology of integrated photonic devices and circuits. His current research effort focuses on realizing integrated lithium niobate photonic circuits for applications in optical communications, millimeter-wave/terahertz technologies, nonlinear optics, and quantum photonics. Since joining CityU, Dr. Wang has received a number of awards including the NSFC Excellent Young Scientist Fund (HK & Macau) (2019), the Croucher Innovation Award (2020), and The President’s Award, CityU (2020).