Tsung Sheng Kao

Study of a Super-Resolution Optical Structure: Polycarbonate/ZnS–SiO2/ZnO/ZnS–SiO2/Ge2Sb2Te5/ZnS–SiO2

A new super-resolution near-field optical structure was demonstrated. The structure, polycarbonate/ZnS–SiO2(130 nm)/ZnO(15 nm)/ZnS–SiO2(30 nm)/Ge2Sb2Te5(15 nm)/ZnS–SiO2(20 nm), has the ability in recording the small marks beyond the diffraction limit. At a readout power of 5 mW, the carrier to noise ratio (CNR) of more than 33 dB was measured for the recorded marks with the size of 100 nm by a digital versatile disc (DVD) tester. Transmission electron microscope (TEM) images of such structure displayed local orderly nanograins in 15 nm ZnO thin film. Ensemble effects of these ZnO nanostructures of the active layer are the key of the near-field super-resolution.

Toward Omnidirectional Light Absorption by Plasmonic Effect for High-Efficiency Flexible Nonvacuum Cu(In,Ga)Se2 Thin Film Solar Cells

We have successfully demonstrated a great advantage of plasmonic Au nanoparticles for efficient enhancement of Cu(In,Ga)Se2(CIGS) flexible photovoltaic devices. The incorporation of Au NPs can eliminate obstacles in the way of developing ink-printing CIGS flexible thin film photovoltaics (TFPV), such as poor absorption at wavelengths in the high intensity region of solar spectrum, and that occurs significantly at large incident angle of solar irradiation. The enhancement of external quantum efficiency and photocurrent have been systematically analyzed via the calculated electromagnetic field distribution. Finally, the major benefits of the localized surface plasmon resonances (LSPR) in visible wavelength have been investigated by ultrabroadband pump-probe spectroscopy, providing a solid evidence on the strong absorption and reduction of surface recombination that increases electron-hole generation and improves the carrier transportation in the vicinity of pn-juction.

Study of the optical response of phase-change recording layer with zinc oxide nanostructured thin film.

Recently, use of nanostructured materials as a near‐field optical active layer has attracted a lot of interest. The non‐linear optical properties and strong enhancements of metallic oxide nanostructured thin films are key functions in applications of promising nanophotonics. For the importance of ultra‐high density optical data storage, we continue investigating the ultra‐high density recording property of near‐field optical disk consisting of zinc oxide (ZnOx) nanostructured thin film. A carrier‐to‐noise ratio above 38 dB at a recording mark size of 100 nm can be obtained in the ZnOx near‐field optical disk by a DVD driver tester directly. In this article, we use an optical pump‐probe system (static media tester) to measure the optical response of a phase‐change recording layer (Ge2Sb2Te5) and demonstrate the high contrast of optical recording with a ZnOx nanostructured thin film in short pulse durations. Also, we investigate the dependence of writing power and the optical response in conventional re‐writable recording layers and the phase‐change material with ZnOx nanostructured thin film.

Imaging of Recording Marks and Their Jitters With Different Writing Strategy and Terminal Resistance of Optical Output

The relation between recording mark formation and jitter value with radial orient spot (ROS) type laser spot recording was investigated by using a new imaging method of conductive-atomic force microscopy (C-AFM). The readout performances of recording marks were studied by changing the terminal resistance of optical pickup head and writing strategies. The results of clear C-AFM images showed that is possible to adjust the conditions of terminal resistance and writing strategies to have better readout signal performance.

Evanescent field enhancement due to plasmonic resonances of a metamaterial slab

The characteristics of plasmonic resonance in a dielectric‐sandwiched metamaterial film at visible wavelengths of 650 and 568 nm have been investigated (for both p‐ and s‐polarized light). Our calculated results demonstrate that each mode of plasmonic resonance has maximum resonance strength at a particular film thickness of the metamaterial. We also demonstrated that the effect of evanescent field enhancement is due to plasmonic resonances of the sandwiched metamaterial system. And the stronger the plasmonic resonance strength the larger the evanescent field is enhanced at the interfaces of the metamaterial film. Also we see that the plasmonic resonances in a sandwiched metamaterial are influenced not only by the materials that constitute the interfaces but also by the thickness of surrounding dielectrics or distance between evanescent light source and metamaterial film. Finally, our results show that there might be an effective light propagation length that will let the coupling efficiency between evanescent light source and SPs resonance become a maximum. These properties of plasmonic resonances to structure parameters of metamaterial film and its surrounding dielectrics provide a useful way to control the optical responses of an optoelectronic device when the wavelength of light source is fixed. That is, by suitably choosing light polarizations, thickness of the metamaterial thin film or the surrounding dielectrics and the position of evanescent light source, it is possible to modulate the plasmonic resonance wavenumber or resonance strength of the system. Therefore, the optical responses of the system can be modulated. Our results will be helpful for the structure design to control the behaviours of coupled plasmonic resonances and consequently the optical properties of the dielectric‐sandwiched metamaterial film.

Implementation of a short-tip tapping-mode tuning fork near-field scanning optical microscope

We present the implementation of a short‐tip tapping‐mode tuning fork near‐field scanning optical microscope. Tapping frequency dependences of the piezoelectric signal amplitudes for a bare tuning fork fixed on the ceramic plate, a short‐tip tapping‐mode tuning fork scheme and an ordinary tapping‐mode tuning fork configuration with an 80‐cm optical fibre attached are demonstrated and compared. Our experimental results show that this new short‐tip tapping‐mode tuning fork scheme provides a stable and high Q factor at the tapping frequency of the tuning fork and will be very helpful when long optical fibre probes have to be used in an experiment. Both collection and excitation modes of short‐tip tapping‐mode tuning fork near‐field scanning optical microscope are applied to study the near‐field optical properties of a single‐mode telecommunication optical fibre and a green InGaN/GaN multiquantum well light‐emitting diode.

Time-resolved phase-change recording mark formation with zinc oxide near-field optical active layer

In this paper, an optical active thin film of zinc oxide (ZnOx) nano-composites exploited for the enhancement of optical signals in an ultra-high density recording scheme has been demonstrated. Via the electron microscope investigation, the results display randomly distributed crystalline nanograins in the ZnOx thin films. Optical disks with the ZnOx nanostructured thin films show that the carrier-to-noise ratio (CNR) above 25 dB can be obtained at the mark trains of 100 nm, while the optimal writing power is reduced as a function of the increasing thickness of the ZnOx films. Furthermore, by conducting a series of the optical pump–probe experiments, the optical responses of recording marks on as-deposited phase-change Ge2Sb2Te5 (as-GST) recording layers present that the highly contrast bright recording bits can be acquired with the existence of the ZnOx nanostructured thin films, providing prospective potentials in future data storage and optoelectronic devices.

Nano Recording and Readout on Optical Disk

Nano recording and readout on optical disk are investigated by a novel characterization method with ultrahigh resolution. Optical and thermal mechanisms of nano recording and readout on phase-change disk are discussed and proposed

Short fiber probe scheme for tapping-mode tuning fork near-field scanning optical microscopy

Construction of a tapping-mode tuning fork with a short fiber probe as the force sensing element for near-field scanning optical microscopy is reported. This type of near-field scanning optical microscopy provides stable and high Q factor at the tapping frequency of the tuning fork, and thus gives high quality NSOM and AFM images of samples. We present results obtained by using the short tip tapping-mode tuning fork near-field scanning optical microscopy measurements performed on a single mode telecommunication optical fiber and a silica based buried channel waveguide.