Yung Chiang Lan

GaN Metalens for Pixel-Level Full-Color Routing at Visible Light

Metasurface-based components are known to be one of the promising candidates for developing flat optical systems. However, their low working efficiency highly limits the use of such flat components for feasible applications. Although the introduction of the metallic mirror has been demonstrated to successfully enhance the efficiency, it is still somehow limited for imaging and sensing applications because they are only available for devices operating in a reflection fashion. Here, we demonstrate three individual GaN-based metalenses working in a transmission window with extremely high operation efficiency at visible light (87%, 91.6%, and 50.6% for blue, green, and red light, respectively). For the proof of concept, a multiplex color router with dielectric metalens, which is capable of guiding individual primary colors into different spatial positions, is experimentally verified based on the design of out-of-plane focusing metalens. Our approach with low-cost, semiconductor fabrication compatibility and high working efficiency characteristics offers a way for establishing a complete set of flat optical components for a wide range of applications such as compact imaging sensors, optical spectroscopy, and high-resolution lithography, just named a few.

Manipulation of tunneling frequencies using magnetic fields for resonant tunneling effects of surface plasmons

This work investigates the manipulation of terahertz surface plasmons (SPs) on a semiconductor surface by applying an external static magnetic field. The dispersion relations of the coupled surface magnetoplasmon under the Voigt configuration in the semiconductor-insulator-semiconductor structure are derived. For a TM-polarized wave that is normally incident onto a semiconductor film with periodic narrow grooves on both surfaces, the applied external static magnetic field with the Voigt configuration redshifts the frequencies of the SP-induced resonant tunneling. This phenomenon is attributable to the reduction in the effective plasma frequency by the applied magnetic field.

Effects of surface plasmon resonant scattering on the power conversion efficiency of organic thin-film solar cells

The power conversion efficiencies of organic solar cells fabricated with Ag and Ti nanoparticle arrays using nanosphere lithography are studied. The Ag nanoparticle array exhibits a broad absorption spectrum peaked at 420nm, which spectrally overlaps with the absorption band of the organic absorbing layer centered at 520nm, while no peak presented for the Ti nanoparticle array. Power conversion efficiencies by the solar cells with Ag and Ti nanoparticle arrays are 2.42% and 1.68%, respectively. This efficiency improvement is proposed to originate from the strong surface plasmon resonant scattering of visible light by Ag nanoparticle arrays.

Three‐Dimensional Plasmonic Micro Projector for Light Manipulation

photovoltaics, [ 5 ] super-resolution imaging, [ 6 ] and various twodimensional plasmonic lens. [ 7 ] Besides, using nanostructures to project SPP plane waves into the adjacent free space is also an important issue. The interactions of plasmonic nanostructure on SPP wave involve not only the in-plane behavior, but also out-of-plane scattering which is captured as the far-fi eld radiated light. [ 8 ] A few theoretical approaches to convert the confi ned surface plasmons into radiated waves have been proposed. [ 9 ] It is highly desirable to extend the application range of plasmonic devices into the domain of three-dimensional light manipulation. [ 10 ] Recently, three-dimensional focusing and diverging of SPP waves by a quarter circular structure composed of gold (Au) nanobumps were studied. [ 11 ] The forward and backward scattering from individual Au nanobump are observed above and below Au surface, respectively. Hence, the Au nanobumps confer additional three-dimensional propagating wave vectors ( k x , k y , k z ) on SPP wave for departing from surface. Therefore, it is possible to manipulate the three-dimensional plasmonic scattering into specifi c geometry by arranging the Au nanobumps, which is schematically depicted in Figure 1 a. In this paper, we manipulate the scattering of SPP waves by various plasmonic structures composed of arranged nanobumps on a gold thin fi lm. Upon controlling the geometry of the plasmonic structures, the height, position, and pattern of scattered light can be modifi ed as desired. It provides a simple and effi cient way to project a specifi c light pattern into free space, and demonstrate the capability of three-dimensional light manipulation.

Gain-assisted Hybrid-superlens Hyperlens for Nano Imaging

We propose an innovative active imaging device named gain-assisted hybrid-superlens hyperlens and examine its resolving power theoretically. This semi-cylindrical device consists of a core of semi-cylindrical super-lens and a half cylindrical outer shell of hyperlens. Both the superlens and hyperlens parts of the device are appropriately designed multi-layered metal-dielectric structures having indefinite eigenvalues of dielectric tensors. The dielectric layers of the hyperlens are doped with Coumarin, which play the role of gain medium. The gain medium is analyzed thoroughly using a generic four-level system model, and the permittivity of the gain medium is extracted from this analysis for simulating the imaging characteristics of the device. According to our simulation at wavelength of 365 nm, an excellent resolution power much better than the diffraction limit value can be achieved.

Surface plasmon-like modes on structured perfectly conducting surfaces

Surface plasmon-like (SPL) modes are the electromagnetic surface eigenmodes supported by the structured perfectly conducting surfaces. The standard eigenvalue-solving method is adopted to solve these SPL modes. The field patterns of the SPL modes in the square holes for in-plane wavevectors k(x) = 2pi / 2d and k(x) = 2pi /d are TE(10)-like and TE(11), respectively. However, the field patterns can no longer be identified as any particular waveguide mode for other in-plane wavevectors. The dispersion relations of the SPL modes are obtained numerically. The change in mode character with wavevector prevents the dispersion relation from being derived by assuming only the fundamental mode in the holes. On a thin perfect conductor perforated with structures, the SPL mode splits into a high-frequency anti-symmetric mode and a low-frequency symmetric mode, which is caused by the mutual interaction of the electromagnetic evanescent fields on both sides.

Resonant tunneling effects on cavity-embedded metal film caused by surface-plasmon excitation

We investigate cavity-modulated resonant tunneling through a silver film with periodic grooves on both surfaces. A strip cavity embedded in the film affects tunneling frequencies via a coupling mode and waveguide mode. In the coupling mode, both the resonant tunneling through the gap between the groove and the cavity and the cavity itself form an entire resonant structure. In the waveguide mode, however, the cavity functions as a surface-plasmon waveguide. Hence, tunneling frequencies are close to resonant absorption frequencies of the groove structure and are irrelevant to cavity properties.

Simulation study of carbon nanotube field emission display with under-gate and planar-gate structures

Recently, two new CNTs-based triode structures, i.e., under-gate and planar-gate structures, for field emission display were proposed and exhibited good characteristics. In this paper, we will investigate how the current density distributed on anode plate and how the display’s resolution affected by the bias conditions of the emitter and the gate electrode via computer simulation. Our simulation results exhibit that the gate voltage has a strong effect on display’s resolution. For the planar triode structure, the good resolution is achieved when the gate voltage is adjusted to converge the electron beams on an anode plate. For the under-gate structure, the display has a good resolution provided that the gate voltage is not too large to pull the electrons striking on other pixels. In general, the under-gate structure has a wider gate-biased operating condition, but the planar triode structure has a higher light efficiency under the same resolution. Due to the lack of field effect in the y-direction, the spot size of the current density on anode plate looks like strips instead of points. And the resolution of the display will be affected by this factor.

Plasmonic Zener tunneling in metal-dielectric waveguide arrays.

We elucidate in this Letter plasmonic Zener tunneling (PZT) in metal-dielectric waveguide arrays (MDWAs) by using numerical simulations and theoretical analyses. PZT in MDWAs occurs at the waveguide entrance and wherever the beam completes Bloch oscillations, because the bandgap between the first and second bands is minimal at the center of the first Brillouin zone. This feature significantly differs from that of optical Zener tunneling in dielectric waveguide arrays. The dependence of the simulated tunneling rate on the gradient of the relative permittivity of the dielectric layers correlates with the tunneling theory, thus confirming the occurrence of PZT in MDWAs.

Actively controlled super-resolution using graphene-based structure

A super-resolution (with λ/50 resolution ability at mid-infrared region) device that consists of a monolayer graphene sandwiched between two dielectric materials with two alternate chemical potentials in graphene (which can be obtained by alternately applying two biased voltages to graphene) is proposed and analyzed. When the subwavelength resolution is achieved, the graphene-based device can be viewed as an effective optical medium with alternate arrangement of positive and negative refractive indices. And the isofrequency dispersion curves of the effective optical medium have the hyperbolic form. Furthermore, the super-resolution at different desired frequencies can be reached by merely changing the chemical potentials of graphene. The proposed devices have potential applications in multi-functional material, real-time subwavelength imaging, and high-density optoelectronic components for using the abnormal diffraction feature.