The design, fabrication, and characterization of an upconversion-luminescence enhancer based on a two-dimensional plasmonic crystal are described. Full-wave finite-difference time domain analysis was used for optimizing the geometrical parameters of the plasmonic crystal for maximum plasmon activity, as signified by minimum light reflection. The optimum design produced >20× enhancement in the average electromagnetic field intensity within a one-micron-thick dielectric film over the plasmonic crystal. The optimized plasmonic upconverter was fabricated and used to enhance the upconversion efficiency of sodium yttrium fluoride: 3% erbium, 17% ytterbium nanocrystals dispersed in a poly(methylmethcrylate) matrix. A thin film of the upconversion layer, 105 nm in thickness, was spin-coated on the surface of the plasmonic crystal, as well as on the surfaces of planar gold and bare glass, which were used as reference samples. Compared to the sample with a planar gold back reflector, the plasmonic crystal showed an enhancement of 3.3× for upconversion of 980-nm photons to 655-nm photons. The upconversion enhancement was 25.9× compared to the same coating on bare glass. An absorption model was developed to assess the viability of plasmonically enhanced upconversion for photovoltaic applications.
Enhancement of electromagnetic field by two dimensional arrays of rectangular and cylindrical nanopillars of both gold
and silver metals arranged in either square or triangular lattices was investigated. We simulated these gratings by 3D
Finite Difference Time Domain (3D-FDTD) method in visible and near infrared (NIR) wavelengths regime and
investigated field enhancement by exciting surface plasmon polaritons (SPPs) as a function of geometrical parameters of
grating. It was found that the geometrical grating parameters such as period, shape, thickness and size can be tuned for
excitation of SPPs at particular frequency of interest. The tuned grating would lead to an electric field intensity
enhancement by greater than 100× near the grating surface due to excitation of SPPs. Cylindrical gratings tuned for 750
nm at zero degree incident angle showed that the thickness of grating is the most sensitive geometrical parameter of
resonance. Furthermore, triangular lattice gratings have wider bandwidth of resonance than square lattice gratings.
Meanwhile, wavelength versus incident angle diagram showed that the enhancement was highly sensitive with angle of
incidence.
We have designed and simulated compact photonic crystal (PC) slab waveguide based wave plate. We have numerically
investigated the optical path of the TE-like and TM-like waves propagating through a triangular based photonic crystal
(PC) slab waveguide. The PC slab waveguide is formed by removing one row of the air holes along &Ggr;K direction. The
plane wave expansion and three-dimensional finite-difference time domain (3D-FDTD) methods were employed for the
design and simulation of the PC slab waveguide. The thickness of 0.75a, a is the lattice constant, for the PC slab
waveguide provides both TE-like and TM-like modal guiding within the normalized frequency band of 0.26-0.268.
Spatial Fourier transform (SFT) of the electromagnetic field distribution in the propagation direction was used for the
analysis of the dispersion properties of the guided modes of the PC slab waveguide. It was found that the effective
refractive indices of the TM-like modes were substantially larger than that of the TE-like modes. The large birefringence
of this structure suggests that the PC slab waveguide is useful for the construction of compact wave plates. The
birefringence larger than 12.6 % within the modal guiding frequency band was achieved for the PC slab waveguide.
Thus, the PC slab waveguide with the length of 6 &mgr;m provides first-order half wave plate within the normalized
frequency band of 0.26-0.268.
One of the main problems in modeling guided wave devices in silica is the determination of the proper input parameters to the model. In this paper, we propose a method to determine five critical parameters: the depth, the length, the refractive index, the loss, and the thermo-optic coefficient of the silica waveguide. The finite difference method is used for the calculation of the optical modes in waveguides with a step index profile. The Beam Propagation Method (BPM) is used to analyze the test structures of the test-chip. The test set includes a planar waveguide, a symmetric Mach-Zehnder structure, an asymmetric Mach-Zehnder structure, and a series of planar waveguides with different lengths. This test-set is designed based on 1um Optical Integrated Circuit (OIC) technology.
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