Keynote speech 1: THz research at State Key Laboratory of Millimeter Waves, Partner Laboratory in City University of Hong Kong

Abstract

In this presentation, we discuss some of the recent THz research activities conducted by faculty members at the State Key Laboratory of Millimeter Waves (SKLMW), Partner Laboratory in City University of Hong Kong. As advised by Academician Shenggang Liu, President of University of Electronic Science and Technology of China from 1986 to 2001 and with support allocated from the Innovation and Technology Commission of Hong Kong SAR and City University of Hong Kong, we started to build up our THz measurement infrastructure in 2012. We are now equipped with facilities for full-range of frequency-domain characterization of circuits, ICs and antennas from 10 MHz to 1.1 THz and time-domain reflection, transmission and spectroscopy up to 3.5 THz. Through access to other departmental facilities, we have micro- and nano-fabrication capabilities for making THz circuits and devices. With fabrication and measurement capabilities in hand, we pursued the investigation of both passive and active frequency selective surfaces (FSSs). We have demonstrated a THz frequency tunable fishnet metamaterial using an electrically controlled polymer dispersed liquid crystal matrix. A tuning range of 10GHz was achieved with the resonance at 0.86 THz. Research on improving the tuning range is on-going. We investigated high-selectivity bandpass FSS in THz band using multilayered FSS screen with systematic introduction of transmission zeros. The metallic and dielectric materials are aluminum and Benzocyclobutene (BCB) polymer, respectively. The FSS resonates at 0.85 THz with an insertion loss of 3.82 dB. For FSS, all the unit cells are identical in size and geometrical shape. In contrast, metasurfaces, with designated electromagnetic responses, are formed by controlling the scattering amplitude and phase of individual unit cells. Again, multilayered screens are employed to provide the needed design degrees of freedom. We have realized frequency scanning metasurfaces with angular and lateral scanning capabilities. Similarly, we have realized metasurfaces for 2D scanning for frequency band between 0.225 to 0.3 THz. On the other hand, we have manipulated the reflection, transmission and polarization of THz waves through metasurfaces in the forms of reflectarrays, transmitarrays and orthomode transducers. New fabrication technologies in 3D printing and nanoimprinting allow us to scale our antenna research to new heights. We developed lens antennas using 3D printing up to 0.3 THz and 1 THz 2-by-2 antenna array using nanoimprinting technology. Electrical properties of the 3D printing materials are retrieved from THz time-domain spectroscopy measurement. The 1-THz array has an ultra-wide bandwidth of 260 GHz, benefitting from the magneto-electric dipole implementation. THz IC design is also a major research thrust in SKLMW. Our first THz source IC at 0.32 THz using 65 nm technology from TSMC yields an output of 0dBm (1mW) and 6dBm (4mW) EIRP when integrated with an LTCC antenna. All the aforementioned devices are characterized in SKLMW and we will also present our tailor made THz near-field scanning system and various probes that we have designed for our THz Mueller matrix imaging system.