We investigate the transmission properties of arrays of three-dimensional (3-D) gold patches having one- and two-dimensional
(1- and 2-D) periodicities, and describe the interaction of cavity and surface plasmon modes. We vary the
main geometrical parameters to assess similarities and emphasize differences between 1-D and 2-D periodic patterns.
We analyze the spectral response as a function of incident angle and polarization to corroborate our findings. We will
also consider form and air filling factors of the grating to assess our ability to control the transmission spectrum. In
particular, we observe strong inhibition of the transmission when the impinging wave-vector parallel to the surface of the
metal matches the surface plasmon wave-vector of the unperturbed air-gold interface when added to the grating lattice
wave-vector. This phenomenon favors the opening of a plasmonic band gap, featuring the suppression of transmission
and simultaneous coupling to back-radiation (reflections) of the unperturbed surface plasmon. High-Q, resonating modes
occur at the edges of the forbidden band, boosting the energy transfer across the grating thus providing enhanced
transmission and broadside directivity at the exit side of the grating.
Recent scientific publications have highlighted the possibility of enhancing solar conversion efficiency in thin
film solar cells using surface plasmon (SP) waves and resonances. One main strategy is to deposit layers of
metal nanoparticles on the top of a thin film silicon solar cell which can increase light absorption and
consequently the energy conversion in the frequency range where the silicon intrinsic absorptance is low. In
this paper, we investigate the effects produced on the light absorption and scattering by silver nanoparticles,
arranged in a periodic pattern, placed on the top of amorphous silicon (α-Si) thin layer. We propose different
geometry of metal objects, quantifying the scattering (back and forward) determined by the nanoparticles in
dependence of their shapes and Si thickness. The analysis reveals that the thickness of the substrate has huge
influence on the scattering, in particular on the back one, when the nanoparticles have corners, whereas it
seems less dramatic when rounded profiles are considered (nanospheres).
In this paper we propose the design and the fabrication of 90° bend ridge waveguide (WG) assisted by a two-dimensional photonic crystal (2D-PC). 2D-PCs act as efficient mirrors along the boundaries of the bend ridge thus reducing the in-plane losses. The ridge waveguide consists of a 3 μm x 0.75 μm titanium dioxide core on a silica bottom cladding. The 2D-PC structure surrounding the bend waveguide is composed of a triangular array of circular dielectric pillars having a height of 0.75 μm. The titanium dioxide waveguiding core layer is covered with PMMA in order to create a quasi-symmetric structure. A photonic band gap centered around 1.3 μm is obtained by a PC radius r = 0.33a and lattice period a = 0.450 μm. The design of the whole structure is subsequently optimized by using a 3D Finite Difference Time Domain based computer code. The ridge waveguide assisted by a 2D-PC has been fabricated by using electron beam lithography and reactive ion etching. For the pattern transfer we have used about 50 nm thin layer Cr metal etch mask obtained by means of a lift-off technique based on the use of bi-layer resist (PMMA/MMA).
The presence of the 2D-PC around the bend waveguide leads to a sharp increase of the transmission efficiency around 1.3 μm for curvature radius of 2.5 μm. The bend transmission results to be in the range between 0.76 and 0.85 when the thickness of the ridge WG and of the 2D-PC pillars is between 0.75 and 1.3 μm. This value is more than twice with respect to the bend waveguide without 2D-PC.