arXiv subjects

Jussi Kelavuori

Publications and source records attributed to Jussi Kelavuori.

5 recordsLinked to original sources

arXiv2025

Photonic Doping of Epsilon-Near-Zero Bragg Microcavities

Epsilon-near-zero (ENZ) photonics provides a powerful route to extreme dispersion engineering, strong field confinement, and unconventional wave phenomena. A closely related concept is \textit{photonic doping}, where subwavelength nonmagnetic dielectric materials embedded in ENZ media enable exotic responses such as perfect-magnetic-conductor behavior and simultaneous epsilon- and mu-near-zero states. However, photonic doping has remained limited to microwave and far-infrared regimes due to the intrinsic losses of optical ENZ materials. Here, photonic doping is demonstrated at optical frequencies by embedding a periodic array of dielectric Mie resonators into an ultralow-loss, all-dielectric ENZ platform based on near-cutoff Bragg microcavities. The resulting structures support spectrally isolated, quasi-singular coupled Bragg--Mie resonances spanning electric and magnetic multipolar orders and their overtones. These modes exhibit effective near-zero-index dispersion with fields confined either within or between the nanoparticles. A representative $14\,μ\mathrm{m}$-scale doped structure exhibits quality factors approaching $10^{4}$ and magnetic-dipole Purcell enhancements exceeding $5\times10^{3}$ in the near-infrared. The demonstrated platform elevates the photonic doping from a microwave-only concept to a fully optical, low-loss, and multipole-resolved platform, enabling ultra-narrowband Mie-like resonances, enhanced magnetic-light interactions, and new opportunities in multipolar-selective spectroscopy and lasing, low-threshold nonlinear optics and efficient single-photon emission.

physics.optics↗

arXiv2025

Purcell Effect in Epsilon-Near-Zero Microcavities

Epsilon-near-zero (ENZ) photonics presents a powerful platform for integrated photonic systems, enabling a range of novel and extraordinary functionalities. However, the practical implementation of ENZ-based systems is often constrained by high material losses and severe impedance mismatch, limiting the efficient interaction of light with ENZ media. To overcome these challenges, we introduce all-dielectric Bragg reflection microcavities operating at their cutoff frequency as a high-figure-of-merit ENZ resonant platform, providing an ultra-low-loss alternative for studying emission processes in ENZ media. While Bragg cavities are well-established, their potential as ENZ resonant microcavities remains largely unexplored. We investigate the Purcell effect and quality factor in these structures, comparing their performance with those of the perfect-electric-conductor and metallic counterparts. Through analytical derivations based on Fermi's golden rule and field quantization in lossless dispersive media, we establish scaling laws that distinguish these ENZ cavities from conventional resonators. Frequency-domain simulations validate our findings, demonstrating that in all-dielectric ENZ Bragg-reflection microcavities, the Purcell and quality factors scale as $L/λ_0$ and $(L/λ_0)^3$, respectively, where $L$ is the cavity length and $λ_0$ is the resonance wavelength. Our results offer key insights into the design of ENZ-based photonic systems, paving the way for enhanced light-matter interactions in nonlinear optics and quantum photonics.

physics.optics↗

arXiv2024

Dispersion-induced $Q$-factor enhancement in waveguide-coupled surface lattice resonances

Diffractively coupled nanoparticle arrays are promising candidates for helping to flatten many photonic devices such as lasers, lenses, and metrology instruments. Their performance, however, is directly linked with the size of the metasurfaces, limiting their applicability in nanophotonic applications. Here, we dramatically reduce array sizes of high-$Q$-factor metasurfaces by utilizing strongly dispersive media. The effect is demonstrated by theoretically and numerically studying periodic arrays of plasmonic nanoparticles embedded inside Bragg-reflector waveguides. We demonstrate array dimensions reduction up to two orders of magnitude while still achieving ultra-high $Q$-factors in excess of 10$^4$.

physics.optics↗

arXiv2021

Thermal Control of Plasmonic Surface Lattice Resonances

Plasmonic metasurfaces exhibiting collective responses known as surface lattice resonances (SLRs) show potential for realizing tunable and flat photonic components for wavelength-selective processes, including lasing and optical nonlinearities. However, post-fabrication tuning of SLRs remains challenging, limiting the applicability of SLR-based components. Here, we demonstrate how the properties of high quality factor SLRs are easily modified by breaking the symmetry of the nanoparticle surroundings. We break the symmetry by changing the refractive index of the overlying immersion oil simply by controlling the ambient temperature of the device. We show that already modest temperature changes of 10°C can increase the quality factor of the investigated SLR from 400 to 750. Our results demonstrate accurate and reversible modification of the properties of the SLRs, paving the way towards tunable SLR-based photonic devices. On a more general level, our results demonstrate how symmetry breaking of the surrounding dielectric environment can be utilized for efficient and potentially ultrafast modification of the SLR properties.

physics.optics↗

arXiv2020

Transient perturbative nonlinear responses of plasmonic materials

Recent investigations on optical nonlinearities of plasmonic materials suggest their responses may be even beyond the usual perturbative description. To better understand these surprisingly strong responses, we develop here a simple but general approach to describe the nonlinear optical response of plasmonic materials up to $n$th perturbation order. We apply the approach to understand spectral broadening occurring in resonant metasurfaces and investigate the enhancement of high-harmonic generation from multiply-resonant metasurfaces, predicting an over million-fold enhancement of higher harmonics.

physics.optics↗