Wook-Jae Lee

Optical constants of evaporated gold films measured by surface plasmon resonance at telecommunication wavelengths

We report the first measurement of the optical constants of evaporated goldfilms by using the surface plasmon resonance curve fitting method with an attenuated total reflection device from 16 to 70 nm thickness at telecommunication wavelengths. The results that were obtained by surface plasmon resonance measurement are in good agreement with those obtained by ellipsometry. Until now, optical constants of thin metalfilms are known to change according to the thickness due to the variation of the electrical resistivity. This phenomenon is also verified in this study by a simple surface plasmon resonance measurement. It is observed that for the goldfilms of thicknesses of less than 20 nm, the real part of the refractive index increases and the imaginary part decreases with decreasing film thickness.

Multiband perfect absorbers using metal-dielectric films with optically dense medium for angle and polarization insensitive operation

The cavity resonant properties of planar metal-dielectric layered structures with optically dense dielectric media are studied with the aim of realizing omnidirectional and polarization-insensitive operation. The angle-dependent coupling between free-space and cavity modes are revealed to be a key leverage factor in realizing nearly perfect absorbers well-matched to a wide range of incidence angles. We establish comprehensive analyses of the relationship between the structural and optical properties by means of theoretical modeling with numerical simulation results. The presented work is expected to provide a simple and cost-effective solution for light absorption and detection applications that exploit planar metal-dielectric optical devices.

Silver superlens using antisymmetric surface plasmon modes

Silver lenses having super-resolution are analyzed in terms of antisymmetric modes of surface plasmon which have the ability to amplify evanescent waves in UV region. Antisymmetric surface plasmon modes excited by subwavelength grating enhances the resolution and contrast of silver superlens. By using a 20 nm-thick silver superlens, the half-pitch resolution of approximately lambda(0)/8 can be achieved with good contrast at a free space wavelength of 435 nm. The resolution of silver superlens can also be improved using shorter illumination wavelength. We show that the thinner the lens, the better the imaging ability of the silver superlens due to the excitation of antisymmetric surface plasmon modes of higher propagation wave vectors. The thickness of lens is varied from 20 to 40 nm in a three layer system, SiO(2)-Ag-SiO(2). Obtained results illustrate that practical application for patterning periodic structures with good contrast and penetration depth can be achieved by using antisymmetric surface plasmon modes.

Enhanced Transmission in a Fiber-Coupled Au Stripe Waveguide System

We experimentally demonstrated the enhanced transmission in a fiber-coupled Au stripe waveguide system using a linearly tapered (LT) structure at a telecommunication wavelength of 1.55 ¿m. The LT structure consists of two 100- ¿m-long tapered regions connecting various widths of input and output waveguides with a waist region. The lowest insertion loss of the 1-cm-long LT-Au stripe waveguide is ~ 4.3 dB, when it has 6-¿m -wide input and output waveguides and a 4- ¿m-wide waist waveguide. The insertion loss is reduced by ~ 2 dB compared to the 4-¿m-wide and 1-cm-long straight Au stripe waveguide, which is achieved by decreasing the coupling loss. The losses of the LT region, which has a tapered angle of less than 0.3° between the input-output waveguides and the waist waveguide, are smaller than 0.4 dB. We showed that the insertion loss of the Au stripe waveguide can be reduced by introducing the LT structure, which can also provide efficient mode conversion.

Lasing in hybrid metal-Bragg nanocavities

We report room-temperature lasing from an optically pumped subwavelength-scale cylindrical InGaAsP pillar surrounded by circular Bragg reflectors on a metal substrate with a dielectric spacer layer. By taking advantage of wide in-plane photonic bandgaps and proper vertical antiresonances, three dielectric Bragg pairs produce a sufficient optical feedback capable of low threshold lasing from the fundamental TE011 mode. A large spontaneous emission coupling into the lasing mode is obtained from the cavity-enhanced Purcell effects and effective suppression of nonlasing modes.

Room-temperature lasing of a circular Bragg cavity laser with a bottom metal plane

We demonstrate room-temperature operation of a metallodielectric semiconductor laser with circular Bragg reflectors and a bottom metal plane. Experimental results show that the quality factor of ~1300 and the effective threshold of 12 μW.

Open nanopatch cavity with annular Bragg reflector and bottom metal plane

We propose an open nanopatch cavity with radial Bragg reflectors and a bottom metal plane. Numerical simulations show that high Q-factor of ∼2800 and a small physical volume of ∼0.86 cubic wavelength can be achieved.

Metallodielectric nanopatch cavity with extended metal shields

We report that the radial extension of parallel metal plates can significantly suppress the radiation losses from the cylindrical metallodielectric nanopatch cavities. The improved quality factor can be obtained analytically, and therefore systematically optimized.