J. H. Woo

Optical switching of near infrared light transmission in metamaterial-liquid crystal cell structure

A metamaterial-liquid crystal cell structure is fabricated with the metamaterial as one of the liquid crystal alignment layers. Nano-sized double-split ring resonator in the metamaterial accommodates two distinct resonances in the near infrared regime. By adopting an azo-nematic liquid crystal in a twisted nematic liquid crystal cell structure, a photo-isomerization process is utilized to achieve an optical switching of light transmissions between two resonances. A single device of the metamaterial-liquid crystal cell structure has a potential application in the photonic switching in optical fiber telecommunications.

Polarization angle control of coherent coupling in metamaterial superlattice for closed mode excitation

A superlattice structure of planar metamaterial is fabricated, where the orientation of double-split ring resonators is altered in a periodic way. A time-domain terahertz transmission spectrum shows an enhanced Q-factor resonance appears when a closed mode is selectively excited by angular tuning of polarization direction. The polarization-angle selective resonance in metamaterial superlattice has a potential application in the selective field enhancement for spectroscopy.

Anisotropic change in THz resonance of planar metamaterials by liquid crystal and carbon nanotube

THz metamaterials are employed to examine changes in the meta-resonances when two anisotropic organic materials, liquid crystal and carbon nanotubes, are placed on top of metamaterials. In both anisotropic double split-ring resonators and isotropic four-fold symmetric split-ring resonators, anisotropic interactions between the electric field and organic materials are enhanced in the vicinity of meta-resonances. In liquid crystal, meta-resonance frequency shift is observed with the magneto-optical coupling giving rise to the largest anisotropic shift. In carbon nanotube, meta-resonance absorptions, parallel and perpendicular to nanotube direction, experience different amount of broadening of Lorentzian oscillator of meta-resonance. Investigation reported here opens the application of metamaterials as a sensor for anisotropic materials.

Cryogenic temperature measurement of THz meta-resonance in symmetric metamaterial superlattice

We investigated a change in the Q-factor of THz meta-resonance as a function of temperature in a symmetric metamaterial superlattice composed by double-split ring resonators (DSRR). THz time-domain spectroscopy is carried out to measure the transmission spectra. At low temperatures, we could analyze the impact factor for determining the Q-factor of the trapped mode compared with open-mode meta-resonance where radiative damping is still dominant.

Near infrared spectroscopic characterization of metamaterials fabricated by focused ion beam milling

Nano-scaled metamaterials are fabricated by a focused ion beam milling under the fine control of process factors. The meta-resonances are studied in NTR regime and they show the polarization-angle dependence coming from their meta-structures.

Control of meta-resonance in metamaterial by dopant carrier density of silicon substrate

Doping level of dopant carrier density of substrates is varied to control the meta-resonances in terahertz metamaterials. Resonance peak position and quality factor exhibit a red shift and broadening when doping level is lowered.

Control of linear dichroism in metamaterial-twisted nematics structure via photo-isomerization

Linear dichroism in metamaterial-twisted nematics structure of nano meta surface is controlled via photoisomerization process. Azo twisted nematic cell structure enables the switching on-off of meta-induced resonance by trans-cis-trans isomerization when irradiated by UV light.

Electric field control of Berry phase in an optical interferometer

We observed a Pancharatnams phase of light using liquid crystal cell. Changes in the interference pattern are analyzed in terms of the geometric phase change. The electric field dependence of the interference pattern change exhibits the occurrence of geometric phase jump.