Ultra-subwavelength phase-sensitive Fano-imaging of localized photonic modes

Abstract

Photonic and plasmonic devices rely on nanoscale control of the local density of optical states (LDOS) in dielectric and metallic environments. The tremendous progress in designing and tailoring the electric LDOS of nano-resonators requires an investigation tool that is able to access the detailed features of the optical localized resonant modes with deep-subwavelength spatial resolution. This scenario has motivated the development of different nanoscale imaging techniques. Here, we prove that a technique involving the combination of scanning near-field optical microscopy with resonant scattering spectroscopy enables imaging the electric LDOS in nano-resonators with outstanding spatial resolution (l/19) by means of a pure optical method based on light scattering. Using this technique, we investigate the properties of photonic crystal nanocavities, demonstrating that the resonant modes appear as characteristic Fano line shapes, which arise from interference. Therefore, by monitoring the spatial variation of the Fano line shape, we locally measure the phase modulation of the resonant modes without the need of external heterodyne detection. This novel, deep-subwavelength imaging method allows us to access both the intensity and the phase modulation of localized electric fields. Finally, this technique could be implemented on any type of platform, being particularly appealing for those based on non-optically active material, such as silicon, glass, polymers, or metals.

Near-field speckle imaging of light localization in disordered photonic systems

“…In addition, since the proportionality between the mode shift and the mode electric field intensity at the position of the nanometric perturbation (the SNOM tip) is an exact result, the perturbation imaging is a more sensitive and high fidelity tool to retrieve the mode electric field intensity. Moreover, the resolution in perturbation imaging is generally increased with respect to the PL imaging [25,28]. All these considerations lead us to exploit the spectral shift for a direct mapping of individual localized random modes.…”

Coupled Photonic Crystal Nanocavities as a Tool to Tailor and Control Photon Emission

“…Finally, we want to stress here that a deterministic integration of QDs in PC systems might also be achieved using the spatially selective hydrogen-removal approach presented in [54,57]. In this case, indeed, the SNOM ability to "see" the electromagnetic field of a PC cavity as we have seen before [29,64] can be used to map the field distribution of the fundamental cavity mode of a fully hydrogenated GaAsN/GaAs PC cavity, and, eventually, using near field illumination, to fabricate a Figure 11. (a) Sketch of the processing steps leading to the deterministic integration of a single Ga(AsN) quantum dot (QD) with a PC cavity.…”

“…Finally, we want to stress here that a deterministic integration of QDs in PC systems might also be achieved using the spatially selective hydrogen-removal approach presented in [54,57]. In this case, indeed, the SNOM ability to "see" the electromagnetic field of a PC cavity as we have seen before [29,64] can be used to map the field distribution of the fundamental cavity mode of a fully hydrogenated GaAsN/GaAs PC cavity, and, eventually, using near field illumination, to fabricate a quantum emitter coupled with the cavity mode. Although, within this further approach the spatial accuracy is worse than that achievable with the EBL-based method presented above (only a spatial precision of~100 nm can be reached by this fabrication approach [55]), the overall process flexibility is improved by the possibility to tailor the QD emission energy to that of the cavity mode, simply by varying the QD fabrication parameters.…”

Site-Controlled Quantum Emitters in Dilute Nitrides and their Integration in Photonic Crystal Cavities

“…We want to stress here that a QD-PhC integrated system might also be realized by using the spatially selective hydrogen-removal approach presented in Section 3.2. In this case, indeed, the SNOM ability to "see" the electromagnetic field of a PhC cavity [88] can be used to map the field distribution of the fundamental cavity mode of a fully hydrogenated GaAsN/GaAs PhC cavity and, eventually, to fabricate by near field illumination a quantum emitter coupled with the cavity mode. Although within this further approach the spatial accuracy is worse than that achievable with the EBL-based method presented above (only a spatial precision of ~100 nm can be reached by conventional SNOM's stages), the overall process flexibility is improved by the possibility to tailor the emission energy of the QD to that of the cavity mode simply by varying the QD fabrication parameters (see Figure 5).…”