Using full-wafer processing, we demonstrate a sophisticated nanotechnology for the realization of an ultrahigh sensitive cavity-coupled plasmonic device that combines the advantages of Fabry-Perot microcavities with those of metallic nanostructures. Coupling the plasmonic nanostructures to a Fabry-Perot microcavity creates compound modes, which have the characteristics of both Fabry-Perot and localized surface plasmon resonance (LSPR) modes, boosting the sensitivity and figure-of-merit of the structure. The significant trait of the proposed device is that the sample to be measured is located in the substrate region and is probed by the compound modes. It is demonstrated that the sensitivity of the compound modes is much higher than that of LSPR of plasmonic nanostructures or the pure Fabry-Perot modes of the optical microcavity. The response of the device is also investigated numerically and the agreement between measurements and calculations is excellent. The key features of the device introduced in this work are applicable for the realization of ultrahigh sensitive plasmonic devices for biosensing, optoelectronics, and related technologies.

The far-field polarization of the optical response of a plasmonic antenna can be tuned by subtly engineering of its geometry. In this paper, we develop design rules for nano antennas which enable the generation of circular polarized light via the excitation of circular plasmonic modes in the structure. Two initially orthogonal plasmonic modes are coupled in such a way that a rotational current is excited in the structure. Modifying this coupling strength from a weak to a strong regime controls the helicity of the scattered field. Finally, we introduce an original sensing approach that relies on the rotation of the incident polarization and demonstrates a sensitivity of 0.23 deg·nm −1 or 33 deg·RIU −1 , related to changes of mechanical dimensions and the refractive index, respectively. KEYWORDS: Plasmonics, antennas, coupling strength, polarization, sensors I n the past few decades, localized plasmon resonances supported by metallic nanostructures have attracted significant attention thanks to their applications in a variety of fields, such as biosensing, 1 photovoltaics, 2 and optoelectronics.3 It is now well-known that, with appropriate tuning of a plasmonic nanostructure, it is possible to engineer both its near and far-field response.4−8 In the optical regime, plasmonic nanostructures react similarly to antennas in the sense that incident light can be collected and stored in the near-field, and conversely, energy stored in the near-field can be radiated into the far-field. The far-field emission pattern of planar plasmonic structures is determined by the near-field distribution. As a consequence, it is possible by engineering the near-field of a plasmonic nanostructure to design its response in a way such that a linearly polarized excitation results in a circular polarized (CP) response.9−18 Recently, nanostructures supporting not only one single plasmon mode but also multiple interacting plasmonic modes have been developed. 19−23 The interaction between such plasmonic modes allows energy transfer between the particular modes within the corresponding wavelength range, and consequently, different modes can indirectly be excited through their near-field. In line with the observed asymmetric scattering spectra, these modes are named Fano resonances. 24 Potential applications of such structures exhibiting Fano line shapes include sensing, energy storage, and spectroscopy enhancement.25−28 Most of those applications rely on the modulation of the intensity of the scattered light induced by the interaction of the plasmonic modes over different spectral regions. It has already been shown that light polarization can be altered using plasmonic nano antennas 29−31 or plasmonic metamaterials. 32−34 In this paper, we show that the polarization of the scattered light can be controlled by introducing a perturbation into a system with initially orthogonal plasmonic modes. Furthermore, we demonstrate that such structures can be used for the generation of CP light from an incident linearly polarized plane wave. ...

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We establish a general method to bridge the gap between full-field electromagnetic calculations and equivalent lumped circuit elements to describe the optical response of plasmonic nanostructures. The exact value of each lumped element is extracted from one single full-field calculation using the Poynting vector and considerations on the energy flow in the system. The equivalent circuit obtained this way describes the complete response of the system at any frequency and can be used to optimize it for specific applications or perform parametric studies. This powerful approach can accurately reproduce the behavior of complex plasmonic nanostructures, such as Fano resonances, retardation effects, and polarization coupling. Furthermore, the influence of coupling parameters within the different modes supported by a given plasmonic structure can be investigated, thus providing new physical insights into its functioning mechanisms.

After providing a detailed overview of nanofabrication techniques for plasmonics, we discuss in detail two different approaches for the fabrication of metallic nanostructures based on e-beam lithography. The first approach relies on a negative e-beam resist, followed by ion beam milling, while the second uses a positive e-beam resist and lift-off. Overall, ion beam etching provides smaller and more regular features including tiny gaps between sub-parts, that can be controlled down to about 10 nm. In the lift-off process, the metal atoms are deposited within the resist mask and can diffuse on the substrate, giving rise to the formation of nanoclusters that render the nanostructure outline slightly fuzzy. Scattering cross sections computed for both approaches highlight some spectral differences, which are especially visible for structures that support complex resonances, such as Fano resonances. Both techniques can produce useful nanostructures and the results reported therein should guide the researcher to choose the best suited approach for a given application, depending on the available technology.

In this paper, a hybrid optical guiding system based on low group velocity offered by photonic crystal (PhC) waveguides and vertical confinement as well as high field enhancement of. Surface lasmon polaritons (SPP) is proposed. We show that for efficient sensing, conventional two-dimensional PhC waveguides with finite height require a high aspect ratio in the order of 30 in order to efficiently confine the guiding mode. The fabrication of devices with such a high aspect ratio is considered too challenging and inefficient for mass production. By combining a PhC waveguide and SPPs, the proposed system efficiently confines the optical mode vertically while benefiting from the lateral confinement enabled by PhC structures. As a result, the required aspect ratio drops to about 4 making the fabrication in large scale feasible. This design provides strong light-matter interaction within small dimensions, which is beneficial for miniaturizing on-chip photonic sensors.

The construction, alignment, and performance of a setup for broadband wide-angle dispersion measurements, with emphasis on surface plasmon resonance (SPR) measurements, are presented in comprehensive detail. In contrast with most SPR instruments working with a monochromatic source, this setup takes advantage of a broadband/white light source and has full capability for automated angle vs. wavelength dispersion measurements for any arbitrary nanostructure array. A cylindrical prism is used rather than a triangular one in order to mitigate refraction induced effects and allow for such measurements. Although seemingly simple, this instrument requires use of many non-trivial methods in order to achieve proper alignment over all angles of incidence. Here we describe the alignment procedure for such a setup, the pitfalls introduced from the finite beam width incident onto the cylindrical prism, and deviations in the reflected/transmitted beam resulting from the finite thickness of the sample substrate. We address every one of these issues and provide experimental evidences on the success of this instrument and the alignment procedure used.