Chunlei Du

Surface plasmon polariton propagation and combination in Y-shaped metallic channels

The propagation and combination of surface plasmon polaritons (SPPs) in Y-shaped metallic nanochannels are investigated numerically via finite difference time domain (FDTD). It is shown that the behavior of SPPs in nano-size channels resembles that of light guiding in conventional waveguides, and SPPs can also be combined effectively with appropriately designed structures. The loss associated with metal absorption and scattering with the multiple reflections between slit openings on the bend angle are analyzed numerically. The Fabry-Perot cavity effect displayed by SPPs traveling in channels with finite length is discussed as well.

Directional excitation of surface plasmons with subwavelength slits

We propose a method to manipulate the excitation direction of surface plasmons using subwavelength slits fabricated in a metallic film. By designing the specific effective index for each slit, the relative phase of plasmonics generated at the slit exit aperture can be tailored. Therefore, the electromagnetic field intensity along one direction on the metal surface can be enhanced or suppressed by surface plasmon interference. Numerical calculations performed by the finite-difference time-domain method illustrate our theoretical design.

Focal length modulation based on a metallic slit surrounded with grooves in curved depths

According to the numerical calculation, the relative phase of emitting light scattered by surface plasmon in a single subwavelength metallic groove can be modulated by the groove depth. The focal length of the slit-groove-based focusing structures can be adjusted in certain value if the groove depths are arranged in traced profile. With the regulation of the groove depth profile, it is possible to modify the focus position in the precision of nanoscale without increasing the size of the nanodevice. The simulation results verify that the method is effective for the design of nano-optical devices such as optical microprobes.

Design of electromagnetic refractor and phase transformer using coordinate transformation theory

We designed an electromagnetic refractor and a phase transformer using form-invariant coordinate transformation of Maxwells equations. The propagation direction of electromagnetic energy in these devices can be modulated as desired. Unlike the conventional dielectric refractor, electromagnetic fields at our refraction boundary do not conform to the Snells law in isotropic materials and the impedance at this boundary is matched which makes the reflection extremely low; and the transformation of the wave front from cylindrical to plane can be realized in the phase transformer with a slab structure. Two dimensional finite-element simulations were performed to confirm the theoretical results.

Subwavelength imaging with anisotropic structure comprising alternately layered metal and dielectric films

Subwavelength imaging can be obtained with alternately layered metallodielectric films structure, even when the permittivity of metal and dielectric are not matched. This occurs as the effective transversal permittivity tends to be zero or the vertical one approaches infinity, depending on the permittivity value of the utilized dielectric and metal material. Evanescent waves can be amplified through the structure, but not in a manner of fully compensating the exponentially decaying property in dielectric. Numerical illustration of subwavelength imaging is presented for variant configuration of anisotropic permittivity with finite layer number of metallodielectric films.

Design of oblate cylindrical perfect lens using coordinate transformation.

A circular cylindrical and an oblate cylindrical perfect lens are designed by using coordinate transformation theory. Theoretical analyses are performed to give an insight into the variant angular magnification in the oblate cylindrical perfect lens. We further take advantage of the oblate cylindrical coordinate system to make the object surface flat for future practical imaging and lithography applications. We also for the first time make systematical simulations of various kinds of perfect lens, including numerical confirmation of Mankei Tsangs statement about the magnification of the planar perfect lens and the imaging and magnifying performance beyond the diffraction limit of our designed perfect lens. All the calculated results agree well with our mathematical derivations, thus verifying the coordinate transformation method in designing perfect lenses.

Plasmonic beam deflector

The authors theoretically demonstrate a plasmonic beam deflector based on the particular properties of surface plasmon polaritons in metallic nanoslits. Beam deflection ranging from 0 degrees to 90 degrees can be achieved by designing the deflector with appropriate structural parameters. Numerical illustrations of deflectors for variant deflection angles are presented through finite-difference time-domain simulation, showing good agreement with theoretical analysis. The efficiency and some factors influencing the deflection behavior are also discussed.

Wearable temperature sensor based on graphene nanowalls

We demonstrate an ultrasensitive wearable temperature sensor prepared using an emerging material, graphene nanowalls (GNWs), and its ease of combination with polydimethylsiloxane (PDMS). Fabrication of the sensor allows for a polymer-assisted transfer method making it considerably facile, biocompatible and cost effective. The resultant device exhibits a positive temperature coefficient of resistivity (TCR) as high as 0.214 °C−1, which is three fold higher than that of conventional counterparts. We attribute this to the excellent stretchability and thermal sensitivity of GNWs together with the large expansion coefficient of PDMS. Moreover, the sensor is capable of monitoring body temperature in real time, and it presents a quite fast response/recovery speed as well as long term stability. Such wearable temperature sensors could constitute a significant step towards integration with the next frontier in personalized healthcare and human–machine interface systems.

Sub-diffraction-limited interference photolithography with metamaterials

We present that an interference lithography technique beyond the diffraction limit can be theoretically achieved by positing an anisotropic metamaterial under the conventional lithographic mask. Based on the special dispersion characteristics of the metamaterial, only the enhanced evanescent waves with high spatial frequencies can transmit through the metamaterial and contribute to the lithography process. Rigorous coupled wave analysis shows that with 442nm exposure light, one-dimensional periodical structures with 40nm features can be patterned. This technique provides an alternative method to fabricate large-area nanostructures.

Electromagnetic Concentrators with Reduced Material Parameters Based on Coordinate Transformation

Omni-directional electromagnetic field concentrators have been recently reported by Marco Rahm et al. [Photon. Nanostruct.: Fundam. Appl. 6, 87 (2008)] based on form-invariant coordinate transformations related to its Jacobi transformation matrix. Using transverse-electric wave illumination, we reduced the complex material parameters of the concentrator for future practical implementation. Concentrators with different set of permittivity and permeability tensors are proposed. The electromagnetic concentrating performance and the scattering properties at the inner and outer boundary of these concentrators are theoretically and numerically analyzed. Finally we obtain a set of material tensors for a concentrator that simultaneously has perfect matched interior and exterior interfaces.