Light funneling from a photonic crystal laser cavity to a nano-antenna: overcoming the diffraction limit in optical energy transfer down to the nanoscale

Local field enhancement using a photonic-plasmonic nanostructure

Over the last few years, optical nanoantennas are continuously attracting interest owing to their ability to efficiently confine, localize resonance, and significantly enhanced electromagnetic fields at a subwavelength scale. However, such strong confinement can be further enhanced by using an appropriate combination of optical nanoantennas and Slanted Bound states in the continuum cavities. Here, we propose to synergistically bridge the plasmonic nanoantennas and high optical quality-factor cavities to numerically demonstrate six orders of magnitude local intensity enhancement without critical coupling conditions. The proposed hybrid system paves a new way for applications requiring highly confined fields such as optical trapping, optical sensing, nonlinear optics, quantum optics, etc.

Flexible transfer of plasmonic photonic structures onto fiber tips for sensor applications in liquids

Plasmonic photonic nanostructuring on the end facets of optical fibers may enable extensive applications of the miniaturized devices in sensors. However, the small area on the fiber tips and the large aspect ratio of the fiber body largely restrict direct fabrication, which is apparently the challenge in most of the nanopatterning techniques. Therefore, efficient and easily applicable transfer techniques are more practical for fabricating plasmonic nanodevices on the fiber tips. In this study, we report the fabrication of plasmonic photonic structures on large-area planar substrates, flexibilization of the structures into thin films, and transfer of these films onto the end facets of optical fibers. This strategy enables high-quality functionalization of fiber tips by plasmonic photonic devices, thus providing new approaches for sensor applications.

Electromagnetic field hugely enhanced by coupling to optical energy focusing structure

In this article, we introduce a new optical energy focusing structure consisting of a circular dielectric Bragg nanocavity and a circular metallic plasmonic lens. Via the hybridization of Bragg cavity modes and surface plasmon modes, optical energy is highly confined in the central region of the Bragg nanocavity under linearly polarized illumination. When either a bowtie nano-antenna (BNA) or a magnetic resonator (MR) is placed on this focusing structure, the energy can be high-efficiently coupled and focused into the BNA or MR. Simulations show that the electric field enhancement (|E|/|E₀|) in the BNA and magnetic field enhancement (|H|/|H₀|) in the MR can be more than 3000 and 200, respectively. This proposed hybrid dielectric-metallic structure opens a new avenue in energy focusing and transferring and provides opportunities for various applications, including single-molecule SERS, optical trapping, photolithography, fluorescent microscopy, magnetic sensors, etc.

Strong coupling in hybrid metal-dielectric nanoresonators

We study resonant photonic-plasmonic coupling between a gold dipole nanoantenna and a silicon nanodisc supporting electric and magnetic dipolar Mie-type resonances. Specifically, we consider two different cases for the mode structure of the silicon nanodisc, namely spectrally separate and spectrally matching electric and magnetic dipolar Mie-type resonances. In the latter case, the dielectric nanoparticle scatters the far fields of a unidirectional Huygens' source. Our results reveal an anticrossing of the plasmonic dipole resonance and the magnetic Mie-type dipole resonance of the silicon nanodisc, accompanied by a clear signature of photonic-plasmonic mode hybridization in the corresponding mode profiles. These characteristics show that strong coupling is established between the two different resonant systems in the hybrid nanostructure. Furthermore, our results demonstrate that in comparison with purely metallic or dielectric nanostructures, hybrid metal-dielectric nanoresonators offer higher flexibility in tailoring the fractions of light which are transmitted, absorbed and reflected by the nanostructure over a broad range of parameters without changing its material composition. As a special case, highly asymmetric reflection and absorption properties can be achieved.This article is part of the themed issue 'New horizons for nanophotonics'.

Pr-based metallic glass films used as resist for phase-change lithography

Metallic glass film of Pr₆₀Al₁₀Ni₁₀Cu₂₀ is proposed to be used as a resist of phase-change lithography (PCL). PCL is a mask-less lithography technology by using laser-direct-writing to create the intended nanopatterns. Thermal distribution in the PrAlNiCu film after exposure is calculated by finite element method (FEM). Thin films are exposed by continuous-wave laser and selective etched by nitric-acid solution, and the patterns are discerned by optical and atomic force microscope. The etching rate of as-deposited PrAlNiCu is thus nearly five times of the crystalline film. These results indicate that PrAlNiCu metallic glass film is a promising resist for phase-change lithography.

Double-way spectral tunability for the control of optical nanocavity resonance

Scanning Near-field Optical Microscopy (SNOM) has been successful in finely tuning the optical properties of photonic crystal (PC) nanocavities. The SNOM nanoprobes proposed so far allowed for either redshifting or blueshifting the resonance peak of the PC structures. In this paper, we theoretically demonstrate the possibility of a redshifting (up to +0.65 nm) and a blueshifting (up to −5 nm) the PC cavity resonance wavelength with a single perturbation element. As an example, a fiber bowtie-aperture nano-antenna (BNA) engraved at the apex of a SNOM tip is proposed to play this role. The double-way tunability is the result of a competition between an induced electric dipole (BNA at resonance) leading to a redshift and an induced magnetic dipole (the tip metalcoating) giving rise to a blueshift of the resonance wavelength. We demonstrate that the sign of the spectral shift can be simply controlled through the tip-to-cavity distance. This study opens the way to the full postproduction control of the resonance wavelength of high quality-factor optical cavities.