Nanoplasmonic approach for Raman spectroscopy on siliconnitride waveguides
Main Researcher: Frederic Peyskens
The use of Raman spectroscopy has several advantages for biosensing applications. First of all it offers a unique fingerprint of the analyte under study since Raman signals probe the internal vibrational and rotational levels of the particle. Besides that no labeling of the analyte nor the detecting surface is required. Despite these major advantages Raman spectroscopy suffers from the fact that it is extremely weak. Therefore enhancement mechanisms are necessary for an efficient detection.
It is well established that small metallic nano-antennas exhibit a plasmonic resonance with concomitant large field enhancements. The resonance strongly depends on the surrounding medium and can be tuned by adjusting the geometry of the metallic nanostructures. Efficient excitation of the resonance requires an optimal alignment between the excitation polarization and the antenna axis.
In order to determine the Raman enhancement due to nanoplasmonics we theoretically studied the structure depicted in Fig.1: a silicon nitride waveguide patterned with a nano-plasmonic antenna (Fig. 2). A few important conclusions were drawn from this study. First of all the structure allows for an efficient coupling between the dipole radiation and the fundamental TE-mode. Secondly we found that Raman enhancements up to 10^10 compared to the unpatterned waveguide can be achieved (Fig.3). Furthermore we can (by fabrication) align the nano-antenna optimally with the excitation polarization and excite and collect the Raman signal through the same waveguide. Because of these interesting properties we are investigating different nano-antenna designs integrated on the silicon nitride platform in order to develop efficient and improved Raman sensors.
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