Reconstructing a plasmonic metasurface for a broadband high-efficiency optical vortex in the visible frequency.

Metasurfaces consisting of a two-dimensional metallic nano-antenna array are capable of transferring a Gaussian beam into an optical vortex with a helical phase front and a phase singularity by manipulating the polarization/phase status of light. This miniaturizes a laboratory scaled optical system into a wafer scale component, opening up a new area for broad applications in optics. However, the low conversion efficiency to generate a vortex beam from circularly polarized light hinders further development. This paper reports our recent success in improving the efficiency over a broad waveband at the visible frequency compared with the existing work. The choice of material, the geometry and the spatial organization of meta-atoms, and the fabrication fidelity are theoretically investigated by the Jones matrix method. The theoretical conversion efficiency over 40% in the visible wavelength range is worked out by systematic calculation using the finite difference time domain (FDTD) method. The fabricated metasurface based on the parameters by theoretical optimization demonstrates a high quality vortex in optical frequencies with a significantly enhanced efficiency of over 20% in a broad waveband.

High-resolution plasmonic structural colors from nanohole arrays with bottom metal disks.

We present transmissive plasmonic structural colors from subwavelength nanohole arrays with bottom metal disks for scaled-up manufacturing by nanoimprint lithography (NIL). Comprehensive theoretical and experimental studies are carried out to understand the specific extraordinary optical transmission behavior of the structures with such bottom metal disks. Distinctive colors covering the entire visible spectrum can be generated by changing the structural dimensions of hole arrays in Ag covered by the metal disks. The plasmonic energy hybridization theory is applied to explain the unstable color output with shallow holes so that a large processing window during NIL could be achieved for mass production. A high-resolution of 127,000 dots per inch is demonstrated with potential applications, including color filters and displays, high-resolution color printing, CMOS color imaging, and anti-counterfeiting.

Photon nanojet lens: design, fabrication and characterization.

In this paper, a novel nanolens with super resolution, based on the photon nanojet effect through dielectric nanostructures in visible wavelengths, is proposed. The nanolens is made from plastic SU-8, consisting of parallel semi-cylinders in an array. This paper focuses on the lens designed by numerical simulation with the finite-difference time domain method and nanofabrication of the lens by grayscale electron beam lithography combined with a casting/bonding/lift-off transfer process. Monte Carlo simulation for injected charge distribution and development modeling was applied to define the resultant 3D profile in PMMA as the template for the lens shape. After the casting/bonding/lift-off process, the fabricated nanolens in SU-8 has the desired lens shape, very close to that of PMMA, indicating that the pattern transfer process developed in this work can be reliably applied not only for the fabrication of the lens but also for other 3D nanopatterns in general. The light distribution through the lens near its surface was initially characterized by a scanning near-field optical microscope, showing a well defined focusing image of designed grating lines. Such focusing function supports the great prospects of developing a novel nanolithography based on the photon nanojet effect.

A new chemically amplified resist for high resolution patterning by E-beam lithography.

In this work, we have undertaken evaluation of the lithography property of a recently available chemically amplified resist (CAR) resist, UV1116 supplied by Rohm and Haas Company. Systematic study of the EBL property such as sensitivity, contrast, high resolution limit and dense capability, as well as resistance to plasma dry etching has been carried out. In comparison with the performance of UVIII, we conclude that the UV1116 can be a good alternative with better lithography quality.

Fabrication of 150 nm half-pitch grating templates for nanoimprint lithography.

We present the fabrication of 150 nm half-pitch Si grating templates by reactive ion etch (RIE), which are used in nanoimprint lithography (NIL) for high groove density gratings in SU-8 plastic. The etch properties such as the etch rate, profile and etching selectivity of Si over Cr as etch mask were carefully studied. Under the optimum condition Si gratings with 150 nm in linewidth, 480 nm in height and nearly 90 degree in verticality of the sidewall have been achieved. 150 nm half-pitch gratings on SU-8 were then successfully imprinted using the fabricated templates. The diffraction pattern of zeroth and first order from the SU-8 gratings was observed using a 266 nm laser beam. The developed nanofabrication technique in this work is applicable not only for templates but also for other nanostructures in silicon.