Illuminating a plasmonic nanoantenna by a set of coherent light beams should tremendously modify its scattering, absorption and polarization properties, thus enabling all-optical dynamic manipulation. However, diffraction inherently makes coherent control of isolated subwavelength-sized nanoantennas highly challenging when illuminated from free-space. Here, we overcome this limitation by placing the nanoantenna at a subwavelength distance of the output facet of silicon waveguides that provide monolithically-defined paths for multibeam coherent illumination. Inspired by coherent perfect absorption (CPA) concepts, we demonstrate experimentally modulation of the nanoantenna scattering by more than one order of magnitude and of the on-chip transmission by >50% over a ~200 nm bandwidth at telecom wavelengths by changing the phase between two counter-directional coherent guided beams. Moreover, we demonstrate coherent synthesis of polarization of the radiated field by illuminating the nanoantenna from orthogonal waveguides. Our finding paves the way towards coherent manipulation of nanoantennas and all-optical processing without nonlinearities in an integrated platform.

A photonic bandgap (PBG) biosensor has been developed for the label-free detection of proteins. As the sensing in this type of structures is governed by the interaction between the evanescent field going into the cladding and the target analytes, scanning near-field optical microscopy has been used to characterize the profile of that evanescent field. The study confirms the strong exponential decrease of the signal as it goes into the cladding. This means that biorecognition events must occur as close to the PBG structure surface as possible in order to obtain the maximum sensing response. Within this context, the PBG biosensor has been biofunctionalized with half-antibodies specific to bovine serum albumin (BSA) using a UV-induced immobilization procedure. The use of half-antibodies allows one to reduce the thickness of the biorecognition volume down to ca. 2.5 nm, thus leading to a higher interaction with the evanescent field, as well as a proper orientation of their binding sites towards the target sample. Then, the biofunctionalized PBG biosensor has been used to perform a direct and real-time detection of the target BSA antigen.

Invisibility cloaks have become one of the most outstanding developments among the wide range of applications in the field of metamaterials. So far, most efforts in invisibility science have been devoted to achieving practically realizable cloak designs and to improving the effectiveness of these devices in reducing their scattering cross-section (SCS), a scalar quantity accounting for the total electromagnetic energy scattered by an object. However, little attention has been paid to the opposite side of the technology: the development of more efficient techniques for the detection of invisibility devices. For instance, the SCS ignores the phase change introduced by the cloak, as well as the angular dependence of the incident and scattered waves. Here, a different path is proposed, which takes advantage of the smarter way in which diffraction tomography processes all this overlooked information to improve the efficiency in unveiling the presence of invisibility devices. This approach not only results in a considerable sensitivity enhancement in the detection of different kinds of cloaks based on both scattering cancellation and transformation optics, but also enables us to obtain images depicting the approximate shape and size of the cloak. The proposed method can be extended to the detection of sound cloaks.

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