The objective of this research is to develop planar transmission-line metamaterials integrated with active quantum-cascade gain material for novel terahertz photonic and electronic devices. The approach is to use terahertz quantum-cascade laser metal-metal waveguide (similar to microstrip transmission line) that is fabricated using a wafer-bonding process as a platform for the implementation of transmission-line metamaterials. Research will proceed via (i) a comprehensive program of metamaterial electromagnetic design and modeling, microfabrication, experimental characterization, and (ii) design of advanced quantum-cascade gain material and its growth by molecular beam epitaxy by the industrial collaborator.
The intellectual merit is the development of active terahertz planar metamaterials that provide photonic gain from stimulated emission to balance losses, and the demonstration of novel active metamaterial devices, such as zero-index lasers, sub-wavelength lasers, and phased array terahertz emitters. The terahertz spectral range is ideally situated to allow integration of metamaterial and gain concepts from both electronic and photonic frequencies.
The broader impact is the development of terahertz technology for eventual applications in sensing, imaging, communications, and spectroscopy applications, and the transfer of this technology to the industrial partner to support its programs in high-speed electronics for defense and space science. Outreach to underrepresented groups will occur by working with UCLA's Center for Excellence in Engineering and Diversity program to recruit undergraduate students for research. Educational exchange will occur via students directly interacting with industry, and industrial employees performing research at UCLA. The PI will develop a graduate course "Terahertz Technology" that will be informed by this research.
The terahertz (THz) frequency range consists of frequencies from 300 GHz – 10 THz, and remains one of the least developed regions of the electromagnetic spectrum. One of the reasons for this is the difficulty of generating and manipulating THz electromagnetic waves with the power levels and degree of integration that has been achieved in the neighboring microwave and infrared frequency ranges. This project focused upon the development of a particular source of THz radiation, the THz quantum-cascade laser, combined with waveguides, laser cavities, and antennas inspired by transmission-line metamaterials that originate in the microwave frequency range. We have proposed novel structures and concepts for laser cavities, such as a so called "zero-index laser", which has the potential for a more efficient extraction of THz power from the laser. We have also demonstrated that it is possible to create terahertz metamaterial waveguides in which wave fronts propagate both forwards and backwards while the energy flows forward. Such a waveguide was demonstrated as an antenna that radiates a beam in the forward and backwards direction. This work lays the foundation for new THz laser antennas which can rapidly steer a beam in different directions, which will prove useful for THz imaging and radar applications. Also, this work lays the foundation for a THz laser with widely and dynamically tunable wavelength, which will prove useful for spectroscopy using THz radiation for chemical and biological material identification. This project fostered a university/industry collaboration between UCLA and Northrop Grumman Aerospace Systems. It also led to development of material for undergraduate and graduate classes by the PIs, training and presentation of research results at conferences by graduate students, participation of several undergraduate students through summer research experiences. Also, PI and several graduate students participated in an outreach to underrepresented minority undergraduate students by hosting teams of freshman students in a research project course. Report for General Public on Diversity Antenna As more and more wireless devices are used, the available electromagnetic resources such as frequency spectrum becomes overloaded unless more efficient use of spectrum is activated. Toward such a goal, this project executed development of diversity antennas. Such antennas are capable of simultaneously handling different electromagnetic characteristics such as polarization of the air waves and as radiation properties for a given frequency. In a sense, several antennas that sense different electromagnetic properties are combined into a single element. Specifically, we have developed several antennas with polarization diversity and pattern diversity that are planar, low cost and integrable with the wireless communication front ends. Initial effort has been expended for high frequency antennas covering 20 GHz and above. More recently, we have realized low frequency versions for 825 MHz to 2200 MHz. Designed antennas have excellent agreement between electromagnetic simulation and measurement and are believed useful toward realization of efficient communication requirements.
