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The 40th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), was held over 23–28 August 2015 at the Chinese University of Hong Kong. The scope of the conference included all scientific and technological activities from millimeter-waves to the Terahertz (THz) regime and on to the far-infrared region of the electromagnetic spectrum. This covers a very wide range of disciplines, encompassing everything from micro- and nano-scale devices and structures to large-scale accelerators and tokamaks and their applications.
Presentations at this conference addressed issues ranging from basic physics, chemistry, electrical engineering and materials science to problems in high frequency circuits and systems, communications, antennas and optics, imaging and spectroscopy, and much, much more.
THz Communications
“We now have many enabling technologies thanks to the recent progress of semiconductor devices and integrated circuits operating at THz frequencies,” Nagatsuma of Osaka University told Nature Photonics. “In addition to the data rate, other expected advantages of THz communications over microwave communications are low power consumption and smaller transceiver size, particularly coming from a reduction in the antenna size,” he added.
He says that scientists are turning to the development of photonic, rather than electronic, devices for THz communications because it is easier to achieve higher data rates using photonic components. “In addition, photonics-based systems might be deployed in the future convergence of fibre optic and wireless communications networks,” commented Nagatsuma. He believes that ultrawideband amplifiers and antennas are the most crucial components needed to make full use of the bandwidth. “Even for photonics-based systems, amplifiers are necessary to boost the output power in the transmitter and to increase the sensitivity in the receiver,” he stressed.
THz communication devices will require innovation in integration and packaging to be practical. Guillermo Carpintero of Universidad Carlos III de Madrid in Spain described how he and his co-workers are tackling this challenge and have developed integrated photonics-based sources of millimetre and THz waves.
“Although we tried to use available generic integration-platform building blocks, there is no building block for Bragg mirrors,” said Carpintero. As a result, the team developed the concept of integrated multimode interference reflector mirrors for mode-locked lasers. The optical spectrum of the optical heterodyne source based on the mode-locked photonic integrated circuit around 1,560 nm showed a carrier wave frequency of 90 GHz. The team has used this on-chip optical heterodyne source to perform broadband wireless data transmission.
High Power Pulsed Terahertz Radiation from Large Area Plasmonic Photoconductive Emitters
The paper High Power Pulsed Terahertz Radiation From Large Area Plasmonic Photoconductive Emitters, co-authored by Shang-Hua Yang and his advisor, Prof. Mona Jarrahi received Best Student Paper Award (3rd place). This paper presents a novel photoconductive terahertz emitter that offers a dramatic increase in output power over current emitters, by more than one order of magnitude.
The improved performance results from the use of a large area plasmonic photoconductive emitter configuration that can offer high optical-to-terahertz conversion efficiencies while handling high optical pump power levels.
Fabrication of terahertz wave absorber based on dielectric spheres
Researchers from Institute of Laser Engineering, Osaka University and others, presented a paper “Fabrication of a terahertz wave absorber based on dielectric spheres”.
Very thin absorbers can be fabricated by using metamaterials, by designing the distances between the first and second layers so that the phases of the reflected waves from the first and second layers are canceled. The large phase shift and localized fields caused by the resonances make the absorber thinner and more efficient.
Researchers have fabricated a compact near perfect terahertz wave absorber by distributing TiO2 microspheres (53.3 mm) on the aluminum tape. The resonant wavelength of the spheres is smaller than that of the incident terahertz waves so it is efficient to design very thin absorber.
The distance between resonator and substrate (d) is critical parameter in absorption and by adjusting d , the large absorption coefficient over 99% can be achieved.
THz scanning tunneling microscopy (STM)
Frank Hegmann of the University of Alberta in Canada talked about imaging ultrafast dynamics of a single InAs nanodot on GaAs with THz scanning tunnelling microscopy (STM). In THz STM, free-space-propagating THz pulses with picosecond duration are antenna-coupled to the tip of a scanning tunnelling microscope, producing a transient rectified tunnel current signal that depends on the shape of the current–voltage (I–V) curve of the tunnel junction.
Excitations of the sample may affect local electric fields and the local density of states, which can modify the I–V response. The THz-STM, which is sensitive to the local I–V response of the tunnel junction, can provide information on the transient dynamics of excitations on surfaces with 0.5 ps time resolution and 2 nm spatial resolution.
LongWave Photonics and NEC Demonstrate a Real-Time Imaging Microscopy System
LongWave Photonics and NEC demonstrate a real-time imaging microscope system at IRMMW-THz in Mainz, Germany. THz illumination was provided by QCLs at 4.3 THz and 3.1 THz (software selectable) and were mounted in LongWave’s EasyQCL-HP system. Real-time images were taken using a microscopy system developed by NEC using the Terahertz Imager.
Lake Shore’s THz materials characterization system
Lake Shore showcased their high-frequency material and device measurement technology. Their Model 8501 as a fully integrated platform for exploring phenomena in emerging electronic and magnetic materials over a range of temperature and fields using non-contact THz-frequency energy. The system uses uniquely designed continuous wave THz (CW-THz) emitter and detector components for measuring at 200 GHz to 1.5 THz frequencies and spectral resolution of better than 500 MHz.
Because the system includes a high-field cryostat and superconducting magnet, spectroscopic responses of material properties can be measured across a range of temperatures and field strengths.
Tydex’s THz Scanning Fabry-Perot Interferometer
Terahertz scanning Farby-Perot interferometer (TSFPI) is designed for measuring wavelength and intensity of narrowband THz radiation. TSFPI may be used with pulsed as well as continuous sources of narrowband THz radiation. TSFPI is comprised of two semi-transparent parallel silicon mirrors; one of those is mounted on a motor-driven linear actuator. Measuring of THz radiation parameters is performed by means of translation (scanning) of the moving mirror.
THz Scanning Fabry-Perot Interferometer is also capable of measuring wavelength and intensity of wideband THz sources, as well as filtering THz radiation as per Fabry-Perot interferometer transmission spectrum.
SFPI may be used with the following sources: Gyrotrons; Optically pumped submillimeter wave lasers; Backward wave oscillators; Free-electron lasers; Difference-frequency THz generators; Photomixing THz generators; Quantum cascade lasers; p-Ge lasers and Novel THz sources.
The next IRMMW-THz will be held in Copenhagen, Denmark over 26–30 September 2016.
