Terahertz(THz) wave technology is expected to create new functions that can not be replaced by electromagnetic wave technology of different frequency bands in high-speed wireless communication, medical imaging, biosensor, etc. However, due to the immaturity of component technology, Industrial applications are delayed. Demand for various components such as THz signal sources, modulators, and detectors is increasing. Particularly, as the demand for characteristics such as portability, room temperature operation and low power consumption is increasing, development of semiconductor-based terahertz component technology is socially required. In MIDAS group, various terahertz components are being developed based on a two-dimensional electron fluid platform such as III-V HEMT and Graphene.
In the development of terahertz signal sources and detectors, plasma instabilities occurring in two-dimensional electron fluids are exploited to overcome the limitations of the prior art. In the case of a terahertz control device, the polarization, amplitude, and frequency response characteristics of a terahertz wave are electrically controlled through integration with an artificial material structure, so called, metamaterials.
The THz signal source, which is currently in commercial use, usually uses a separate femtosecond laser to generate a THz wave in the form of a time-domain pulse by irradiating the optical beam into the semiconductor, so that a separate laser device is required, which reduces portability and is expensive. Low efficiency and high efficiency can be achieved with QCL, which does not require laser excitation, but it has a drawback that it has a very high technology barrier and operates only at extremely low temperatures.
In MIDAS group, we develop all electronic small THz signal sources that do not require separate laser equipment. In particular, we have developed a small THz signal source that can emit high output and narrow THz signals at room temperature. We also develop THz measurement system which can analyze frequency characteristics of THz signal source according to temperature in wide frequency range and imaging system that can acquire THz image by using developed signal source.
Terahertz waves have limitations in applying control methods commonly used in “Electronics” and “Photonics”. The method used in “Electronics” has a large energy loss in the frequency conversion process and the method used in “Photonics” has very difficult optical control because the terahertz wave has very small energy (~ meV). Therefore, a metamaterial-based terahertz wave control technology capable of directly modulating a terahertz wave with little energy loss is attracting attention. In addition, electrical control via integration with nanoelectronic device platforms can also be extended to programmable modulators by combining with advanced digital technology.
In MIDAS group, we are developing a modulator capable of controlling the characteristics of terahertz waves through the integration of two-dimensional electron fluid platforms such as III-V HEMT and Graphene and THz metamaterials. We have developed a modulator that can control the characteristics of terahertz imaging system.
The THz imaging system is one of the most technologically advanced technologies using terahertz waves, and its use in airport security search is limited, but it is expected to expand into defense, aerospace, and logistics. However, the research on the THz light source, which is a key element of the THz imaging system, is still insufficient. Therefore, studies are being conducted to develop a high efficiency high power THz light source. In MIDAS group, we are conducting research on THz light source based on photoconductive antenna(PCA).
The basic operation principle of PCA is optical pumping method. In order to develop a high efficiency PCA, it is necessary to construct a structure capable of efficiently performing phase matching of an external laser and a surface, which can maximize the light conversion efficiency. the research is being conducted to minimize the reflection of laser by forming a plasmonic structure on the surface of PCA and to minimize the loss of metal electrode by forming a diffraction lens on the interdigital-type antenna structure.