The study of the resonant behavior of silicon nanostructures provides a new route for achieving efficient control of both electric and magnetic components of light. We demonstrate experimentally and numerically that enhancement of localized electric and magnetic fields can be achieved in a silicon nanodimer. For the first time, we experimentally observe hotspots of the magnetic field at visible wavelengths for light polarized across the nanodimer's primary axis, using near-field scanning optical microscopy.

Optical bound states in the continuum (BIC) are localized states with energy lying above the light line and having infinite lifetime. Any losses taking place in real systems result in transformation of the bound states into resonant states with finite lifetime. In this Letter, we analyze properties of BIC in CMOS-compatible one-dimensional photonic structure based on silicon-on-insulator wafer at telecommunication wavelengths, where the absorption of silicon is negligible. We reveal that a high-index substrate could destroy both off-Γ BIC and in-plane symmetry protected at-Γ BIC turning them into resonant states due to leakage into the diffraction channels opening in the substrate. We show how two concurrent loss mechanisms, scattering due to surface roughness and leakage into substrate, contribute to the suppression of the resonance lifetime and specify the condition when one of the mechanisms becomes dominant. The obtained results provide useful guidelines for practical implementations of structures supporting optical bound states in the continuum.

Enhancement of optical response with high-index dielectric nanoparticles is attributed to the excitation of their Mie-type magnetic and electric resonances. Here we study Raman scattering from crystalline silicon nanoparticles and reveal that magnetic dipole modes have much stronger effect on the scattering than electric modes of the same order. We demonstrate experimentally a 140−fold enhancement of Raman signal from individual silicon spherical nanoparticles at the magnetic dipole resonance. Our results confirm the importance of the optically-induced magnetic response of subwavelength dielectric nanoparticles for enhancing light-matter interactions.

Optical bound states in the continuum (BICs) provide a way to engineer resonant response in photonic crystals with giant quality factors. The extended interaction time in such systems is particularly promising for enhancement of nonlinear optical processes and development of a new generation of active optical devices. However, the achievable interaction strength is limited by the purely photonic character of optical BICs. Here, 1 arXiv:1905.13505v1 [cond-mat.mes-hall] 31 May 2019 we mix optical BIC in a photonic crystal slab with excitons in atomically thin transition metal dichalcogenide MoSe 2 via strong coupling to form exciton-polaritons with Rabi splitting exceeding 27 meV. We experimentally show BIC-like behavior of both upper and lower polariton branches, with complete suppression of radiation into far-field at the BIC wavevector and strongly varying Q-factor in its vicinity. Owing to an effective disorder averaging through motional narrowing, we achieve small polariton linewidth of 2 meV and demonstrate linewidth control via angle and temperature tuning. Our results pave the way towards developing tunable BIC-based polaritonic devices for sensing, lasing, and nonlinear optics. Optical bound states in the continuum (BICs), supported by photonic crystal structures of certain geometries, have received much attention recently as a novel approach to generating extremely spectrally narrow resonant responses. 1,2 Since BICs are uncoupled from the radiation continuum through symmetry protection 3 or resonance trapping, 4 their high quality factors, while reaching 10 5 − 10 6 , can be robust to perturbations of photonic crystal geometric parameters. This enables a broad range of practical applications, including recently demonstrated spectral filtering, 5 chemical and biological sensing, 6,7 and lasing. 4Providing an efficient light-trapping mechanism, optical BICs are particularly attractive for enhancing nonlinear optical effects, with recent theoretical proposals discussing enhanced bistability 8 and Kerr-type focusing nonlinearity. 9 However, for practical realization of these proposals, a significantly stronger material nonlinear susceptibility is needed than generally available in dielectric-based photonic crystals.An attractive approach to the enhancement of effective nonlinearity is through the use of exciton-polaritons -hybrid quasi-particles that inherit both the coherent properties of photonic modes and interaction strength of excitons. 10,11 Hybrid nanophotonic systems incorporating atomically thin transition metal dichalcogenides (TMDs) have proven to be a particularly promising platform owing to their ease of fabrication and possibility of room temperature operation. [12][13][14] In addition to conventional microcavity-based designs, TMD

We reveal unusually strong polarization sensitivity of electric and magnetic dipole resonances of high‐index dielectric nanoparticles placed on a metallic film. By employing dark‐field spectroscopy, we observe the polarization‐controlled transformation from high‐Q magnetic‐dipole scattering to broadband suppression of scattering associated with the electric dipole mode, and show numerically that it is accompanied by a strong enhancement of the respective fields by the nanoparticle. Our experimental data for silicon nanospheres are in an excellent agreement with both analytical calculations based on Green's function approach and the full‐wave numerical simulations. Our findings further substantiate dielectric nanoparticles as strong candidates for many applications in enhanced sensing, spectroscopy and nonlinear processes at the nanoscale.