Nonlinear Metasurface for Simultaneous Control of Spin and Orbital Angular Momentum in Second Harmonic Generation.

The spin and orbital angular momentum (SAM and OAM) of light is providing a new gateway toward high capacity and robust optical communications. While the generation of light with angular momentum is well studied in linear optics, its further integration into nonlinear optical devices will open new avenues for increasing the capacity of optical communications through additional information channels at new frequencies. However, it has been challenging to manipulate the both SAM and OAM of nonlinear signals in harmonic generation processes with conventional nonlinear materials. Here, we report the generation of spin-controlled OAM of light in harmonic generations by using ultrathin photonic metasurfaces. The spin manipulation of OAM mode of harmonic waves is experimentally verified by using second harmonic generation (SHG) from gold meta-atom with 3-fold rotational symmetry. By introducing nonlinear phase singularity into the metasurface devices, we successfully generate and measure the topological charges of spin-controlled OAM mode of SHG through an on-chip metasurface interferometer. The nonlinear photonic metasurface proposed in this work not only opens new avenues for manipulating the OAM of nonlinear optical signals but also benefits the understanding of the nonlinear spin-orbit interaction of light in nanoscale devices.

Controlling interface states in 1D photonic crystals by tuning bulk geometric phases.

There is no known simple rule that assures the existence of interface states in photonic crystals (PCs). We show here that one can control the existence or absence of interface states in 1D PCs through engineering the bulk geometrical phase such that interface states can be guaranteed in some or all photonic bandgaps. We verify experimentally the interface state design paradigm in 1D multilayered PCs fabricated by electron beam vapor deposition. We obtain the geometrical phases by measuring the reflection phases at the bandgaps of the PCs and achieve good agreement with the theory. Our approach could provide a platform for generating a PC interface state for various applications.

Diameter Dependence of Planar Defects in InP Nanowires.

In this work, extensive characterization and complementary theoretical analysis have been carried out on Au-catalyzed InP nanowires in order to understand the planar defect formation as a function of nanowire diameter. From the detailed transmission electron microscopic measurements, the density of stacking faults and twin defects are found to monotonically decrease as the nanowire diameter is decreased to 10 nm, and the chemical analysis clearly indicates the drastic impact of In catalytic supersaturation in Au nanoparticles on the minimized planar defect formation in miniaturized nanowires. Specifically, during the chemical vapor deposition of InP nanowires, a significant amount of planar defects is created when the catalyst seed sizes are increased with the lower degree of In supersaturation as dictated by the Gibbs-Thomson effect, and an insufficient In diffusion (or Au-rich enhancement) would lead to a reduced and non-uniform In precipitation at the NW growing interface. The results presented here provide an insight into the fabrication of "bottom-up" InP NWs with minimized defect concentration which are suitable for various device applications.

High-Performance Wrap-Gated InGaAs Nanowire Field-Effect Transistors with Sputtered Dielectrics.

Although wrap-gated nanowire field-effect-transistors (NWFETs) have been explored as an ideal electronic device geometry for low-power and high-frequency applications, further performance enhancement and practical implementation are still suffering from electron scattering on nanowire surface/interface traps between the nanowire channel and gate dielectric as well as the complicated device fabrication scheme. Here, we report the development of high-performance wrap-gated InGaAs NWFETs using conventional sputtered Al2O3 layers as gate dielectrics, instead of the typically employed atomic layer deposited counterparts. Importantly, the surface chemical passivation of NW channels performed right before the dielectric deposition is found to significantly alleviate plasma induced defect traps on the NW channel. Utilizing this passivation, the wrap-gated device exhibits superior electrical performances: a high ION/IOFF ratio of ~ 2 × 10(6), an extremely low sub-threshold slope of 80 mV/decade and a peak field-effect electron mobility of ~ 1600 cm(2)/(Vs) at VDS = 0.1 V at room temperature, in which these values are even better than the ones of state-of-the-art NWFETs reported so far. By combining sputtering and pre-deposition chemical passivation to achieve high-quality gate dielectrics for wrap-gated NWFETs, the superior gate coupling and electrical performances have been achieved, confirming the effectiveness of our hybrid approach for future advanced electronic devices.

Optical properties of silver nanoprisms and their influences on fluorescence of europium complex.

The optical properties of truncated triangular silver nanoprisms and their influences on the fluorescence of europium complex Eu(TTFA)(3) were investigated in theory and experiment separately. In theory, we found that the fluorescence of Eu ions would be greatly enhanced by these nanoprisms, the enhancement factor of the fluorescence depended on the concentrations of nanoprisms. They were verified in the experiment. The influence of silver nanoprisms on the radiative and nonradiative decay rates of Eu ions were also deduced, and found that the silver nanoprisms greatly reduced the energy loss caused by the nonradiative decay.

Fabrication of low-loss, single-mode-channel waveguide with DNA-CTMA biopolymer by multistep processing technology.

A multistep processing and reactive ion etching technique has been developed to fabricate optical channel waveguides based on deoxyribonucleic acid-cetyltrimethylammonium biopolymer material. The channel waveguides exhibit excellent single-mode output and high confinement of light because of the sharp waveguide profile with very smooth surfaces and vertical sidewalls. The measurement results show that these channel waveguides have low propagation losses and small polarization dependent losses at 633, 1310, and 1550 nm wavelengths.