Kristof Lodewijks

Tuning plasmonic interaction between gold nanorings and a gold film for surface enhanced Raman scattering

We investigate the plasmonic properties of gold nanorings in close proximity to a gold film. The rings have been fabricated using nanosphere lithography and are optimized to boost their near-infrared surface enhanced Raman scattering (SERS) effects. A SERS enhancement factor as large as 1.4×107 has been achieved by tuning the separation between the gold nanorings and the gold film. In addition, we have numerically and experimentally demonstrated an enhanced tunability of the plasmon resonance wavelength and a narrowing of the plasmon linewidth for increasing ring-film interaction.

Groove-gratings to optimize the electric field enhancement in a plasmonic nanoslit-cavity

We study the spectral properties of a triangular plasmonic nanoslit-cavity with periodic triangular grooves to optimize the field enhancement inside the nanoslit. This work is mainly based on numerical calculations and also partly supported by experimental evidence. In the nanoslit-cavity, we can distinguish following three main contributions to the field enhancement: electrostatic interaction in the nanoslit, surface plasmon polariton standing waves in the cavity and excitation, and reflection of surface plasmon polaritons by the grating. The importance of phase matching between surface plasmons generated at the nanoslit and the gratings is also investigated in order to optimize the local field intensity in the nanoslit.

Nb2O5 as waveguide material for visible light photonic integrated circuits (Conference Presentation)

Photonic Integrated Circuits (PICs) in the visible wavelength range have been extensively used for life science applications. Silicon Nitride has been the most widely used material, as it allows to fabricate low loss waveguides with the refractive index ranging from 1.9 to 2.1. For downscaling of PICs, many investigations into Titanium Oxide (TiO2) have been studied. The refractive index of TiO2 ranges from 2.3 to 2.6. Despite a high refractive index, TiO2 tends to crystallize at temperatures above 300oC, limiting its potential for CMOS compatible fabrication. In addition, the presence of oxygen vacancies in TiO2 results into photon absorption in the visible range, leading to high propagation losses. We investigate Niobium Oxide (Nb2O5) as an alternative waveguide material, focusing on material and optical properties for light propagation in the visible wavelength range. Physical vapor deposition of the Nb target in Oxygen atmosphere results in stoichiometric Nb2O5. On a 200mm wafer, a 90nm Nb2O5 is deposited on 2.3µm bottom clad (SiO2). The extracted refractive index is above 2.3, while the extinction coefficient is 0 for visible wavelengths. From X-ray diffraction, the as-deposited layers were amorphous, while the surface roughness was below 0.3 nm. Waveguides were patterned using 193 nm lithography and etched using chlorine based chemistry. In the visible range, optical losses for un-cladded waveguides were below 5 dB/cm, comparable to our in-house SiN platform. There were no significant changes in optical losses after 400oC anneal, signifying its potential for improved propagation after top-cladding deposition.