Double-layered wide-bandgap photonic materials for efficient nonlinear applications without periodic poling

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Title: Double-layered wide-bandgap photonic materials for efficient nonlinear applications without periodic polingDeveloping efficient, scalable nonlinear nanophotonics platforms would enable a host of classical and quantum applications including wavelength conversion, image restoration, quantum-enhanced sensing and hacker-proof quantum communication. Currently, efficient second-order nonlinear processes are predominantly realized by applying the so-called quasi-phase-matching (QPM) technique in ferroelectric materials such as lithium niobate, where the polarity of the material is periodically poled (inverted) to achieve constructive interaction between different waves. However, fabrication of QPM is challenging in thin-film nanophotonics platforms such as lithium niobate-on-insulator, as the poling period is significantly reduced compared to their bulky counterparts due to stronger waveguide dispersion. In addition, given that QPM is customarily designed for one specific nonlinear process, it is practically difficult to implement multiple different nonlinear processes on the same chip, thus severely limiting the scaling potential of integrated photonics. Finally, the QPM technique cannot be easily generalized to non-ferroelectric materials such as silicon carbide and aluminum nitride, as there is no known method to alter their domain polarity other than during the growth period. This project aims to develop a novel double-layered nanophotonics platform for efficient nonlinear applications without periodic poling, which provides an elegant solution to some of the most pressing issues faced by the broad integrated photonics community, including tunability, efficiency and scalability. The double-layered device concept can be generalized to most of second-order nonlinear materials such as lithium niobate, silicon carbide, aluminum nitride, gallium nitride, gallium phosphide, etc., potentially transforming the way of nonlinear optical processes being implemented on these materials and improving the overall efficiency significantly.Finally, this project also trains undergraduate and graduate students in the area of optics and quantum photonics, and the research findings will be integrated into relevant courses and outreach programs. The core idea of this research is to stack two layers of second-order nonlinear materials with opposite polarity and employ the second-order transverse-magnetic mode as one of the interacting modes waves. This configuration allows achieving phase matching and good modal overlap simultaneously, which greatly simplifies the fabrication process and enables scalable implementation of various nonlinear processes on the same chip. The team of researchers will focus on two wide-bandgap photonic materials, i.e., lithium niobate and silicon carbide, which have generated a lot of recent interests due to their unique material properties. Such double-layered nanophotonics materials will be investigated for several important applications, including efficient second-harmonic generation, sum-frequency generation, and optical parametric oscillation in lithium niobate, and quantum frequency conversion for converting single photons in the visible band to the telecom band in silicon carbide.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.