Center for Subwavelength Optics

Seoul, South Korea

Center for Subwavelength Optics

Seoul, South Korea
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Keun Yoo H.,Gwangju Institute of Science and Technology | Lee S.-G.,Gwangju Institute of Science and Technology | Kang C.,Gwangju Institute of Science and Technology | Kee C.-S.,Gwangju Institute of Science and Technology | And 2 more authors.
Applied Physics Letters | Year: 2013

The characteristics of terahertz (THz) modulation in organic copper phthalocyanine thin films deposited on a Si wafer were investigated by angle-dependent photoexcitation. We reveal that the efficiency of THz modulation reflects not only the angle-dependent reflectivity of the organic thin films that undergo a change of complex refractive index due to photoexcitation but also the laser-induced birefringence induced by a charge density grating in the direction normal to the polarization of the excitation beams. © 2013 AIP Publishing LLC.


Lee S.-G.,Gwangju Institute of Science and Technology | Kim S.-H.,KAIST | Kim T.-T.,KAIST | Kim J.-E.,KAIST | And 3 more authors.
Optics Express | Year: 2012

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. © 2012 Optical Society of America.


Kim S.-H.,KAIST | Kim T.-T.,KAIST | Oh S.,Imperial College London | Kim J.-E.,KAIST | And 2 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We demonstrate experimentally and theoretically that spoof surface plasmons (SSPs) can propagate without diffraction, i.e., self-collimation (SC) of SSPs. To excite and detect SSPs on a structured brass surface, we employed a pair of monopole antennas. The scanned horizontal and vertical field intensity distributions of the SSPs reveal a narrow Gaussian envelope at the SC frequency. While the Gaussian SSP is well maintained, being prevented from spreading during lengthy propagation, SSPs with frequencies below or above the SC frequency diverge. We examine the possibility of steering self-collimated SSPs. © 2011 American Physical Society.


Lee S.-G.,Electronics and Telecommunications Research Institute | Park J.-M.,Korea Aerospace Research Institute | Kee C.-S.,Gwangju Institute of Science and Technology | Kee C.-S.,Center for Subwavelength Optics
Optics Express | Year: 2014

We report that the Fano resonance of self-collimated beams can be achieved in a two-dimensional photonic crystal by introducing a Fano resonator that is composed of zigzag line defects. An asymmetric Fano line shape in a transmission spectrum is generated by the interference between radiated light beams from the resonator and self-collimated beams that directly pass through the resonator without resonance. It is shown that the Fano profile increases in sharpness as the number of zigzag line defects increases because the phase values of the radiated light beams change more rapidly when the number of defects increases. The Fano resonance of self-collimated beams could provide an efficient approach to manipulate light propagation and increase the possibility of application of self-collimated beams. © 2014 Optical Society of America


Yang J.-K.,Kongju National University | Kee C.-S.,Gwangju Institute of Science and Technology | Kee C.-S.,Center for Subwavelength Optics | Lee J.W.,Gwangju Institute of Science and Technology
Optics Express | Year: 2011

We report on the three-dimensional subwavelength confinement of the electromagnetic waves at a coupled metallic slit structure beyond diffraction limit in terahertz region. Lateral confinement behavior, leading to the three-dimensional confinement, is caused by a strong funneling effect of the light which occurs at the intersection of slits with a sharp metal geometry. Tunability of the resonant frequency and the position of the light confinement is achieved by controlling the slit length and the position of the intersection of slits, respectively. © 2011 Optical Society of America.


Lee E.S.,Korea University | Jeon T.-I.,Korea University | Jeon T.-I.,Center for Subwavelength Optics
Optics Express | Year: 2012

A single groove in a parallel-plate waveguide (PPWG) has been applied to a tunable terahertz (THz) notch filter with a transverseelectromagnetic (TEM) mode. When the air gap between the metal plates of the PPWG is controlled from 60 to 240 μm using a motor controlled translation stage or a piezo-actuator, the resonant frequency of the notch filter is changed from 1.75 up to 0.62 THz, respectively. Therefore, the measured tunable sensitivity of the notch filter increases to 6.28 GHz/μm. The measured resonant frequencies were found to be in good agreement with the calculation using an effective groove depth. Using a finitedifference time-domain (FDTD) simulation, we also demonstrate that the sensitivity of a THz microfluidic sensor can be increased via a small air gap, a narrow groove width, and a deep groove depth. © 2012 Optical Society of America.


Lee E.S.,Korea University | Lee S.-G.,Gwangju Institute of Science and Technology | Kee C.-S.,Gwangju Institute of Science and Technology | Kee C.-S.,Center for Subwavelength Optics | And 2 more authors.
Optics Express | Year: 2011

We present a tunable notch filter having a wide terahertz (THz) frequency range and a low-pass filter (LPF) having a 0.78 THz cutoff frequency. Single slit and multiple slits are positioned at the center of air gaps in tapered parallel-plate waveguides (TPPWG) to obtain the notch filter and LPF, respectively. The notch filter has a dispersion-free and lowloss transverse magnetic (TM) mode. The Q factor was proved to be 138, and the resonant frequency is easily tunable by adjusting the air gaps between TPPWG. On the other hand, the cut off frequency of the LPF was determined using a Bragg stop band, which depends on slit period. The LPF has a transition width of 68 GHz at the cutoff frequency and a dynamic range of 35 dB at stop bands. In addition, the characteristics of such filters were analyzed using finite-difference time-domain (FDTD) simulations. © 2011 Optical Society of America.


Lee S.-G.,Gwangju Institute of Science and Technology | Kee C.-S.,Gwangju Institute of Science and Technology | Kee C.-S.,Center for Subwavelength Optics
Applied Optics | Year: 2013

We report that self-collimated beams from a photonic crystal can be refracted to any direction in air by introducing an additional layer composed of dielectric rods at a photonic crystal surface. The refraction angle can be tuned from negative to positive value by adjusting the period of the additional layer. The refracted beam power can be also controllable by varying the radii of rods in the layer and the distance between the layer and the surface. The grating-induced omnidirectional refraction of self-collimated beams could provide an efficient way to manipulate light propagation and increase the possibility of application of self-collimated beams. © 2013 Optical Society of America.


Kim S.E.,Gwangju Institute of Science and Technology | Kim B.H.,Gwangju Institute of Science and Technology | Lee C.G.,Chosun University | Lee S.,Yonsei University | And 3 more authors.
Optics Express | Year: 2012

We propose a novel design of photonic crystal fiber (PCF) using an elliptical air hole in the core as a defected core in order to enhance the performance of modal birefringence and to control the properties of chromatic dispersion at the same time. From the simulation results, it is shown that the proposed fiber has high birefringence up to the order of 10-2, negative flattened chromatic dispersion in a broad range of wavelengths, and low confinement loss less than that of the single mode fiber. The outstanding advantage of the proposed PCF is that high birefringence, negative flattened dispersion, and low confinement loss can be achieved just by adding a small sized elliptical air hole in the core to the elliptical air hole PCF, especially at the same time. © 2012 Optical Society of America.


Lee E.S.,Korea University | So J.-K.,Seoul National University | Park G.-S.,Seoul National University | Kim D.,Seoul National University | And 5 more authors.
Optics Express | Year: 2012

We report experimental and finite-difference time-domain simulation studies on terahertz (THz) characteristics of band gaps by using metal grooves which are located inside the flare parallel-plate waveguide. The vertically localized standing-wave cavity mode (SWCM) between the upper waveguide surface and groove bottom, and the horizontally localized SWCM between two groove side walls (groove cavity) are observed. The E field intensity of the horizontally localized SWCM in grooves is very strongly enchanced which is three order higher than that of the input THz. The 4 band gaps except the Bragg band gap are caused by the π radian delay (out of phase) between the reflected THz field by grooves and the propagated THz field through the air gap. The measurement and simulation results agree well. © 2012 Optical Society of America.

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