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Kim, Teun-Teun,Lee, Sun-Goo,Park, Hae Yong,Kim, Jae-Eun,Kee, Chul-Sik The Optical Society 2010 Optics express Vol.18 No.6
<P>A two-dimensional photonic crystal asymmetric Mach-Zehnder filter (AMZF) based on the self-collimation effect is studied by numerical simulations and experimental measurements in microwave region. A self-collimated beam is effectively controlled by employing line-defect beam splitters and mirrors. The measured transmission spectra at the two output ports of the AMZF sinusoidally oscillate with the phase difference of pi in the self-collimation frequency range. Position of the transmission peaks and dips can be controlled by varying the size of the defect rod of perfect mirrors, and therefore this AMZF can be used as a tunable power filter.</P>
Ring-type Fabry-Pérot filter based on the self-collimation effect in a 2D photonic crystal
Kim, Teun-Teun,Lee, Sun-Goo,Kim, Seong-Han,Kim, Jae-Eun,Park, Hae Yong,Kee, Chul-Sik The Optical Society 2010 Optics express Vol.18 No.16
<P>We propose a ring-type Fabry-Pérot filter (RFPF) based on the self-collimation effect in photonic crystals. The transmission characteristics of self-collimated beams are experimentally measured in this structure and compared with the results obtained with the simulations. Bending and splitting mechanisms of light beams by the line defects introduced into the RFPF are used to control the self-collimated beam. Antireflection structures are also employed at the input and output photonic crystal interfaces in order to minimize the coupling loss. Reflectance of the line-defect beam splitters can be controlled by adjusting the radius of defect rods. As the reflectance of the line-defect beam splitters increases, the transmission peaks become sharper and the filter provides a Q-factor as high as 1037. Proposed RFPF can be used as a sharply tuned optical filter or as a spectrum analyzer based on the self-collimation phenomena of photonic crystals. Furthermore, it is suitable for a building block of photonic integrated circuits, as it does not back reflect any of the incoming self-collimated beams owing to the antireflection structure applied.</P>
Terahertz near-field spectroscopy for various applications
Seo Changwon,Kim Teun-Teun 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.6
Terahertz (THz= 1012 Hz) spectroscopy has been recognized as a promising analytical technique for non-destructive, highly accurate investigation. However, despite its advantages, relatively long-wavelength and weak light-matter interaction limit the potential of these techniques to measure physical phenomena occurring within small areas and molecules, where lots of physical properties have been discovered. In this review, we introduce recent advances in THz near-feld techniques as contact-free and non-invasive methods, particularly scattering-type scanning near-feld optical microscopy (s-SNOM) with atomic force microscope (AFM) tip and transmission-type of photoconductive antenna microprobe (PCAM)-based THz near-feld microscopy. Furthermore, practical applications of these cutting-edge spectroscopic methods are discussed.
Reversibly Stretchable and Tunable Terahertz Metamaterials with Wrinkled Layouts
Lee, Seungwoo,Kim, Seongnam,Kim, Teun‐,Teun,Kim, Yushin,Choi, Muhan,Lee, Seung Hoon,Kim, Ju‐,Young,Min, Bumki WILEY‐VCH Verlag 2012 ADVANCED MATERIALS Vol.24 No.26
<P><B>The use of wrinkling provides a generic route to stretchable metamaterials</B>, with unprecedented terahertz tunability. The wrinkled metamaterial can be stretched reversibly up to 52.5%; the structural integrity can be maintained during at least 100 stretching/relaxing cycles. Importantly, the wrinkling of meta‐atoms offers a deterministic way to achieve controlled broadening of electrical resonance.</P>
Lee, Sun-Goo,Kim, Seong-Han,Kim, Teun-Teun,Kim, Jae-Eun,Park, Hae Yong,Kee, Chul-Sik Optical Society of America 2012 Optics express Vol.20 No.8
<P>The resonant transmission of self-collimated beams through zigzag-box resonators is demonstrated experimentally and numerically. Numerical simulations show that the flat-wavefront and the width of the beam are well maintained after passing through zigzag-box resonators because the up and the down zigzag-sides prevent the beam from spreading out and the wavefront is perfectly reconstructed by the output zigzag-side of the resonator. Measured split resonant frequencies of two- and three-coupled zigzag-box resonators are well agreed with those predicted by a tight binding model to consider optical coupling between the nearest resonators. Slowing down the speed of self-collimated beams is also demonstrated by using a twelve-coupled zigzag-box resonator in simulations. Our work could be useful in implementing devices to manipulate self-collimated beams in time domain.</P>
Switching terahertz waves with gate-controlled active graphene metamaterials
Lee, Seung Hoon,Choi, Muhan,Kim, Teun-Teun,Lee, Seungwoo,Liu, Ming,Yin, Xiaobo,Choi, Hong Kyw,Lee, Seung S.,Choi, Choon-Gi,Choi, Sung-Yool,Zhang, Xiang,Min, Bumki Nature Publishing Group 2012 Nature materials Vol.11 No.11
The extraordinary electronic properties of graphene provided the main thrusts for the rapid advance of graphene electronics. In photonics, the gate-controllable electronic properties of graphene provide a route to efficiently manipulate the interaction of photons with graphene, which has recently sparked keen interest in graphene plasmonics. However, the electro-optic tuning capability of unpatterned graphene alone is still not strong enough for practical optoelectronic applications owing to its non-resonant Drude-like behaviour. Here, we demonstrate that substantial gate-induced persistent switching and linear modulation of terahertz waves can be achieved in a two-dimensional metamaterial, into which an atomically thin, gated two-dimensional graphene layer is integrated. The gate-controllable light??matter interaction in the graphene layer can be greatly enhanced by the strong resonances of the metamaterial. Although the thickness of the embedded single-layer graphene is more than six orders of magnitude smaller than the wavelength (<貫/1,000,000), the one-atom-thick layer, in conjunction with the metamaterial, can modulate both the amplitude of the transmitted wave by up to 47% and its phase by 32.2째 at room temperature. More interestingly, the gate-controlled active graphene metamaterials show hysteretic behaviour in the transmission of terahertz waves, which is indicative of persistent photonic memory effects.