Utilizing Symmetry Breaking in Slot Nano-Antenna Arrays for achieving Outstanding Figure of Merit Values in Refractive Index Sensor

Michal Eitan-Wiener Department of Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel Zeev Iluz -, CST AG, Darmstadt, Germany Yuval Yifat Department of Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel Amir Boag Department of Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel Yael Hanein Department of Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel Jacob Scheuer Department of Physical Electronics, School of Electrical Engineering, Tel Aviv University, Tel Aviv, Israel

Localized surface plasmon resonance (LSPR) is a promising alternative for the realization of label-free biosensors based on refractive index (RI) sensing. Such sensors are attractive thanks to their simplicity, low-cost, and compact dimensions and have been demonstrated for applications ranging from medical diagnosis to environmental monitoring. The main challenge in exploiting LSPR for sensing is in increasing their sensitivity and, more importantly, their figure of merit (FOM). Furthermore, a major technological challenge involves the development of a simple platform such as the use of an optical fiber in which several materials, macro- and nano-structures are integrated, embedded and connected all together to provide the necessary physical connections and light-matter interactions.

In this work we demonstrate a new concept for RI plasmonic sensing utilizing nano slot-antenna arrays (NSAAs) which are fabricated over a gold backplane reflector. Such array is illuminated by a linearly polarized beam at an angle which deviates slightly from the normal to the array plane. Utilizing the Wood’s anomaly (WA) phenomenon, the antenna array attains high sensitivities exceeding 1020 nm/RIU and record level FOMs of up to 210, i.e. approaching the theoretically estimated limit. The large FOM is obtained due to the symmetry breaking caused by the non-perpendicular illumination, which lifts the degeneracy of the left- and right-propagating surface waves corresponding to the WA. Owing to the non-perpendicular illumination employed here, the spectral notch in the scattered power associated with the WA occurs at two separated wavelengths, thus forming a narrow (~5 nm FWHM) peak.

We will also present some recent advances in implementing this scheme on an optical fiber configuration and establishing highly sensitive label free detection of bio-molecules, as well as utilizing the slot antenna for real time detection of nano-particle trapping.

michale1@tauex.tau.ac.il