Efficient Terahertz Generation in Nanophotonic Lithium Niobate Waveguides

Description

Terahertz (THz) frequencies ranging from 0.3 to 10 THz are of particular interest for chemical identification and non-destructive imaging, since a wide variety of molecules have their “fingerprint” absorption lines lying in the THz range. The global THz technology market size is expected to grow at an annual rate of 25% and reach 1 billion USD by 2024. The THz range, however, is often referred to as the “THz gap”, since it lies just between the frequencies of mature electronic and optical technologies. As a result, THz waves cannot be efficiently produced using either the electronic or the optical methods. The lack of efficient and low-cost THz sources has become the major bottleneck for THz technologies to further into our daily life. This project aims to tackle this bottleneck by developing an efficient and compact THz source based on a nanophotonic coupled-waveguide system. The system generates continuous-wave THz emission by mixing two optical lasers via nonlinear optical interactions. The key challenge here is the large wavelength mismatch between optical waves (~ 1 micrometer) and THz waves (~ 100 micrometers), making it difficult to achieve strong optical/THz confinement and large mode overlap simultaenously. The proposed device uses a novel hybrid system consisting of a micrometer-scale periodically poled lithium-niobate (PPLN) waveguide and a Si-based THz waveguide. The PPLN waveguide provides a strong optical confinement and a quasi-phase matched nonlinear interaction, while the Si waveguide allows the generated THz waves to be guided with low losses. PI is an expert in integrated lithium-niobate (LiNbO3, LN) photonics and has previously demonstrated a number of nonlinear photonic devices based on the thin-film LN platform, including nanophotonic PPLN waveguides with ultra-high nonlinear conversion efficiencies. In order to efficiently generate THz waves that are two orders of magnitude away from optical frequencies, this project will involve innovative co-design of integrated LN photonics and THz photonics on the same photonic-THz chip. The hybrid devices will be fabricated and characterized leveraging the photonic, THz and nanofabrication infrastructure and expertise available at CityU to ensure the successful delivery of the project. The successful accomplishment of this project will deliver a chip-based continuous-wave THz source that is frequency tunable and highly efficient. Such a compact low-cost solution could enable a range of applications including trace-chemical detection, medical imaging, security screening and beyond-5G wireless communications, and could benefit the broad academic and industrial communities both in Hong Kong and across the globe.