• Korean Journal of Optics and Photonics
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• v.30 no.3
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• pp.94-100
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• 2019

The near-field subwavelength squint-less focusing system of a phased array antenna is designed and demonstrated by numerical simulation. The Huygens-Fresnel principle is applied to numerical simulation for calculation of the phased array antenna at microwave frequency. It was shown that beam squinting can be eliminated, utilizing true-time optical delay lines based on a chirped fiber grating in the proposed system. Furthermore, subwavelength focusing with high numerical aperture can be achieved by considering the fact that the array elements of the phased-array antenna can be treated as diffractive elements in an optical lens system. Also, side lobes can be suppressed by decreasing the distance between element antennas to less than half of the wavelength.

• Proceedings of the Optical Society of Korea Conference
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• 2007.07a
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• pp.255-256
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• 2007

We propose a novel method for the beam focusing by a single subwavelength metal slit surrounded by chirped dielectric surface gratings. In the proposed method, the period of each grating is chirped to make a focused beam at the desired position. Design of the grating structures for optimal beam focusing and the analysis of the field distribution are conducted based on the rigorous coupled wave analysis (RCWA). It is shown that the focused beam is formed at 1.5${\mu}m$ from the metal substrate and its full width at half maximum (FWHM) is 411nm.

• Journal of the Optical Society of Korea
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• v.9 no.4
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• pp.162-168
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• 2005

Extraordinary phenomena related to the transmission of light via metallic films with subwavelength holes and grooves are known to be due to resonant excitation and interference of surface waves. These waves make various surface structures to have optically effective responses. Further, a related study subject involves the control of light transmitted from a single hole or slit by surrounding it with diffractive structures. This paper reports on the effects of controlling light with a periodic groove structure with Fresnel-type chirping. In Fresnel-type chirping, diffracted surface waves are coherently converged into a focus, and it is designed considering the conditions of constructive interference and angular spectrum optimization under the assumption that the surface waves are composite diffracted evanescent waves with a well-defined in-plane wavenumber. The focusing ability of the chirped periodic structures is confirmed experimentally by two-beam attenuated total reflection coupling. Critical factors for achieving subwavelength foci and bounds on size of focal spots are discussed in terms of the simulation, which uses the FDTD algorithm.

• Journal of the Optical Society of Korea
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• v.17 no.3
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• pp.262-268
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• 2013

We study the focusing properties of a two-dimensional square-lattice photonic crystal (PC) comprising silica and germanium partitioned cylinders in air background. The finite difference time domain (FDTD) method with periodic boundary condition is utilized to calculate the dispersion band diagram and the FDTD method incorporating the perfectly matched layer boundary condition is employed to simulate the image formation. In contrast to the common square PCs in which the negative refraction effect occurs in the first photonic band without negative phase propagation, in our suggested model system, the frequency with negative refraction exists in the second band and in near-infrared region. In this case, the wave propagates with a negative phase velocity and the evanescent waves can be supported. We also discuss the dependency of the image resolution and its location on surface termination, source location, and slab thickness. According to the simulation results, spatial resolution of the proposed PC lens is below the radiation wavelength.

• Current Optics and Photonics
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• v.2 no.5
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• pp.482-487
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• 2018

We investigate the radiation characteristics of radially polarized light and azimuthally polarized light through plasmonic subwavelength-scale annular slit (PSAS) structures, by means of both theoretical and numerical methods. Effective-medium theory was utilized to analyze the characteristics of PSAS structures, and the corresponding results showed that PSAS structures can function as a metallic medium for azimuthally polarized light, or as a low-loss dielectric medium for radially polarized light. Numerical calculations based on the finite-element method were also performed, to verify the theoretical analyses. It turned out that the numerical results supported the theoretical results. Moreover, we exploited the PSAS structures in novel nanophotonic elements with dual functionalities that could selectively focus or pass/block incident light, depending on its polarization state. For example, if PSAS structures were implemented in the dielectric region of a metallic Fresnel zone plate, the modified zone plate could function as a blocking element to azimuthally polarized light, yet as a focusing element to radially polarized light. On the contrary, if PSAS structures were implemented in the metallic region of a metallic Fresnel zone plate (i.e. the inverted form of the former), it could function as a focusing element to azimuthally polarized light, yet as a simple transparent element to radially polarized light.