Wide range of color change in nanohole array structure on a metal film have been successfully demonstrated using asymmetric-lattice design of nanoholes and an electrically switching polarization rotator. Recently, some studies have been reported that various color states were obtained in a single unit cell structure using extraordinary optical transmission (EOT) of nanopatterned structure, which could be one of the most important solutions for achieving ultrahigh integration density in optoelectronic devices. However, because they used the interfacial refractive index or dielectric constant as controlling factors for the color tuning, they were not capable of inducing a changeable range of color with different primary color states. To overcome this limitation, in this study, an asymmetric-lattice nanohole array design was integrated with an electrically controlled polarization rotator, employing a twisted nematic (TN) liquid crystal (LC). This simple structure of nanohole arrays with a rectangular lattice enabled mixed color states as well as precisely designed two different primary colors, by modulating the polarization of the incident light. The color-tuning shift was greater than 120 nm. Since the surface plasmonic (SP) modes on both sides, a top and a bottom interface, were matched better by the TN-LC layer assembled on the rectangular-lattice nanohole metal layer, the transmittance at the resonance peak wavelength was increased by 158% compared to that of the bare nanohole structure. The nanohole-array-on-metal-film simultaneously functions as an electrode, and this advantage, coupled with the low driving voltage of the TN-LC layer, can open new possibilities in applications to various optoelectronic device concepts.
Micro size antennas have significant merits due to the small size effect, enabling new device concepts. However, the low-quality factor (Q-factor), the large size of impedance matching components, and the poor selectivity of the multi-array design remain challenging issues. To solve these issues, a floating coil structure stacked on a loop micro-antenna is suggested. Various floating coil designs are prepared with appropriate matching conditions at specific target frequencies, using an easy fabrication process without the need for additional space. A simple one-loop antenna design shows a higher Q-factor than other, more complicated designs. The micro-sized loop antenna with the 80 μm trace width design exhibits the highest Q-factor, around 31 within 7 GHz. The 8 different floating coil designs result in high-frequency selectivity from 1 to 7 GHz. The highest selectivity contrast and WPT efficiency are above 7 and around 1%, respectively. Considering the size of the antenna, the efficiency is not low, mainly due to the good matching effect with the high Q-factor of the floating coil and the loop antenna. This micro-antenna array concept with high integration density can be applied for advanced wireless neural stimulation or in wireless pixel array concepts in flexible displays.
A nanostructure which induces localized surface plasmon resonance (LSPR) can be utilized in visible light and near infrared (NIR) regions and it shows promising features as a bio-detector because LSPR state is changed easily by different bio-related materials. Owing to transparent property of many biomolecules as well as diluted states in base solutions, it is hard to distinguish each other by eye or microscope analysis. However, difference in molecular structure and composition makes difference in optical characteristics such as a refractive index or a dielectric constant. Therefore, our LSPR-based nanohole array structure which has high sensitivity to detect small changes in optical characteristics can be a great candidate for a bio detector. Here, we fabricated structural color filters (SCFs) to detect wavelength shifts for several biomolecules and optimized the nanohole array structures for high sensitivity. Periodic nanohole arrays were designed to present resonance peaks in visible light region for optical analysis and fabricated in Au or Al thin film layer. The spectral shifts were detected caused by biomolecules.
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