Yu-Ju Hung

Magnifying Superlens in the Visible Frequency Range

We demonstrate a magnifying superlens that can be integrated into a conventional far-field optical microscope. Our design is based on a multilayer photonic metamaterial consisting of alternating layers of positive and negative refractive index, as originally proposed by Narimanov and Engheta. We achieved a resolution on the order of 70 nanometers. The use of such a magnifying superlens should find numerous applications in imaging.

Two-dimensional metamaterial structure exhibiting reduced visibility at 500 nm.

Metamaterials provide unprecedented freedom and flexibility in the creation of new structures, which control electromagnetic wave propagation in very unusual ways. Very recently various theoretical designs for an electromagnetic cloak were suggested and an experimental realization of a partial cloak operating in a two-dimensional cylindrical geometry were reported in the microwave frequency range. We report on an experimental two-dimensional reduced visibility structure that approximates the distribution of the radial component of the dielectric permittivity necessary to achieve nonmagnetic cloaking in the visible frequency range.

Experimental modeling of cosmological inflation with metamaterials

Abstract Recently we demonstrated that mapping of monochromatic extraordinary light distribution in a hyperbolic metamaterial along some spatial direction may model the flow of time and create an experimental toy model of the big bang. Here we extend this model to emulate cosmological inflation. This idea is illustrated in experiments performed with two-dimensional plasmonic hyperbolic metamaterials. Spatial dispersion which is always present in hyperbolic metamaterials results in scale-dependent (fractal) structure of the inflationary “metamaterial spacetime”. This feature of our model replicates hypothesized fractal structure of the real observable universe.

Rayleigh backscattering induced power penalty on bidirectional wavelength-reuse fiber systems

Intraband crosstalk induced by back reflections, mainly Rayleigh backscattering is experimentally and theoretically studied in a bidirectional system using the same wavelength. Assuming that 1.0 dB of power penalty is an acceptable design criterion, the distance between the adjacent nodes is limited to be 40 km. The derived crosstalk penalties are in excellent agreement with those obtained from experiments.

Impact of repeated uniaxial mechanical strain on p-type flexible polycrystalline thin film transistors

This letter investigates the effect of repeated bending of flexible p-channel low-temperature polycrystalline–silicon thin-film transistors employing an ultra-low-temperature process (<673 K). Experimental results reveal that interface state density (Nit) and grain boundary trap density (Ntrap) after 10 000 width-axis tensile strain bending iterations are more pronounced than after equivalent width-axis compressive strain bending. Extracted interface and grain boundary traps both increase, which elevate trap assisted leakage. Furthermore, the bending distorts the Si–Si bonds in the polycrystalline silicon (Poly-Si) film, which causes more significant negative bias temperature instability (NBTI) degradation because strain-induced weak Si–Si bonds can react with dissociated H during NBTI stress.

Effects of Repetitive Mechanical Bending Strain on Various Dimensions of Foldable Low Temperature Polysilicon TFTs Fabricated on Polyimide

This letter investigates the effect of repeated uniaxial mechanical stress on bias-induced degradation behavior in polycrystalline thin-film transistors (TFTs). After 100 000 iterations of channel-width-direction mechanical compression, serious threshold voltage degradation and an abnormal hump are observed. Simulation indicates that the strongest mechanical stress occurs at both sides of the channel edge, between the polycrystalline silicon and gate insulator. Since these stress points produce oxide traps in the gate insulator, the degradation of threshold voltage shift and parasitic current path can be attributed to electron trapping at these intense mechanical stress points. In addition, the degradation becomes serious with diminishing TFT size.

On the Origin of Anomalous Off–Current Under Hot Carrier Stress in p-Channel DDDMOS Transistors With STI Structure

This letter investigates the abnormal off-current behavior induced by hot carrier stress (HCS) in p-channel double diffused drain metal-oxide-semiconductor transistors with a shallow trench isolation (STI) structure. According to ISE-TCAD simulation, the electric field at the drain-side corners of the high-voltage n-well (HVNW) adjacent to the STI trench is stronger than the electric field in the channel center in width direction. Moreover, because a nitride layer acts as a buffer in STI, the electrons generated by impact ionization at the corners of the HVNW can be easily trapped in the nitride layer or at the liner oxide/nitride layer interface. Furthermore, the extension of electron trapping in STI from drain to source during HCS forms the off-current conductive path. Based on the charge pumping measurements at different operation conditions, this path formation is further demonstrated by the comparisons of charge pumping measurements between initial state and after HCS.

Strong optical coupling effects through a continuous metal film with a surface dielectric grating

We have observed experimentally the anomalously large light transmission through a continuous gold film with various PMMA surface dielectric gratings deposited on top of the film. The spectra of these samples have been measured for different incident and scattered angles. Enhanced transmission through the film is attributed to the excitation of various surface plasmon modes. Both symmetrical and anti-symmetrical surface plasmon dispersion relations have been applied to analyze the transmission spectrum. Similar anomalous transmission effects have been observed in light transmission through gold-chalcogenide glass (As2S3) interfaces after grating formation in the chalcogenide glass using two-beam interference with strong pump light. Enhanced transmission is demonstrated using a weak probe beam. These observations demonstrate the possibility of all-optical signal processing using enhanced anomalous light transmission through metal films.

Enhanced transmission of light through a gold film due to excitation of standing surface-plasmon Bloch waves

We have observed enhanced transmission of light through a gold film due to excitation of standing surface plasmon Bloch waves in a surface Fabry-Perot resonator. Our experimental results strongly contradict the recently suggested model of light transmission via excitation of a composite diffractive evanescent wave.

Super-resolution optics using short-wavelength surface plasmon polaritons

We demonstrate that surface plasmon polaritons can be guided and focused by dielectric optical elements deposited on top of a gold film. Two examples of such devices are demonstrated. In a first set of experiments plasmon polaritons were coupled to dielectric nano-waveguides using a parabolic surface coupler. This experiment demonstrates that using surface plasmon polaritons the scale of optoelectronic devices based on dielectric waveguides can be shrunk by at least an order of magnitude. A parabola-shaped dielectric waveguide may also be used as a mirror in two-dimensional imaging experiments. The optical images formed by the mirror may be enhanced using simple digital filters. As a result, 30 nm resolution has been achieved.