The demand for reconfigurable components in neuromorphic computing, quantum computing and nanophotonics has led to a growing interest in active integrated photonic components. Phase change materials change their physical properties through reversible phase transitions, making them ideal for light manipulation. By altering the material's phase near a localized electromagnetic element, it is possible to achieve non-volatile, reconfigurable, and programmable functionality. However, this results in time-dependent inhomogeneous changes of physical properties, requiring a self-consistent description of electromagnetic, carrier transport, thermal, and phase transition processes. This presentation covers recent developments and applications of multiphysics simulations for phase change material-based nanophotonics.
Phase change materials (PCMs) are materials in which phase transitions can be induced quickly and reversibly, resulting in pronounced changes in their physical properties. PCMs have a diverse technological potential ranging from neuromorphic devices and efficient high-frequency electronics and opto-electronics to (re)programmable optical meta-materials. In this presentation we review our recent results on self-consistent multi-physics description of PCM based photonics including meta-surfaces for mid-infrared and infrared spectral ranges and integrated optics elements.
The high optical losses of metal-based plasmonic materials have driven an extensive search for alternative lower-loss materials that can support plasmonic-like effects, such as sub-diffraction confinement of optical fields. One such alternative employs phonon-mediated collective-charge oscillations (surface phonon polaritons, SPhPs) that can be optically excited in nanostructured polar dielectric materials. Similar to plasmonics, tailoring the geometry of polar-dielectric resonators results in resonances that can be spectrally tuned throughout the spectral range between the LO and TO phonons. However, generally, the spectral position and amplitude of these resonances remain fixed after sample fabrication. In this presentation, we discuss recent advancements made by our group in achieving actively tunable localized SPhP resonances in the long-wave- and far-infrared spectral regimes. In particular, we focus on three experiments that demonstrate active modulation of resonances. The first and second experiments focus on tuning the spectral position of localized SPhP resonances in cylindrical nanopillars that are etched into indium phosphide and silicon carbide substrates. In both of these cases we are able to induce resonance shifts as large as 15 cm-1 by optically injecting free-carriers into the pillars. The optical injection introduces a reversible, free-carrier perturbation to the dielectric permittivity that results in a spectral shift of the resonances. While the effects investigated for both the InP and SiC systems are similar, each material allows us to explore a different aspect of the phenomena. For InP we investigate the effects in the far-infrared (303-344 cm-1) with steady-state carrier photoinjection, while for SiC we investigate the dynamics of frequency modulated resonances in the long-wave infrared (797-972 cm-1) via transient reflection spectroscopy. Lastly, in the third experiment we demonstrate the ability to modulate the amplitude of resonances by coating SiC nanopillars with vanadium dioxide, a well-known phase change material that undergoes a metal-to-insulator transition near a temperature of 70 C. As such, we show that by exploiting this phase change we are able to modulate the reflectance and thermal emission of nanopillar arrays. The results described in this work may open the door to tunable, narrow-band thermal sources that operate in the long-wave to far-infrared spectral regimes.
Today it is possible to engineer the building blocks of artificial materials (meta-materials) with feature sizes smaller than the wavelength of light. The ability to design meta-atoms in a largely arbitrary fashion adds a new degree of freedom in material engineering, allowing to create artificial materials with unusual electromagnetic properties rare or absent in nature. Achieving tunable, switchable and non-linear functionalities of meta-materials at individual meta-atom level could potentially lead to additional flexibility in designing active photonic devices. These include among others, meta-materials based on phase-change materials, whose properties could be altered by thermal or photo-thermal means. In this presentation, our recent results on developing appropriate numerical methods to study hybrid meta-material structures containing phase-change materials will be discussed. Meta-atoms based on plasmon polaritonic materials are considered. We develop appropriate phenomenological models of phase transition and self-consistently couple them with the full wave electromagnetic and heat transfer solvers. Developed methods are used to design meta-surface based tunable components. We demonstrate an importance of the multiphysical modelling and discuss deficiencies of the commonly used purely electromagnetic simulations approaches.
KEYWORDS: Quenching (fluorescence), Magnetism, Nanoparticles, Near field, Near field optics, Metals, Transition metals, Current controlled current source
Emission quenching is analysed at nanometer distances from the surface of an absorbing nanoparticle. It is demonstrated that emission quenching at small distances to the surface is much weaker for magnetic-dipole (MD) than for electric-dipole (ED) transitions. This difference is explained by the fact that the electric field induced by a magnetic dipole has a weaker distance dependence than the electric field of an electric dipole. It is also demonstrated that in the extreme near-field regime the non-locality of the optical response of the metal results in additional emission quenching for both ED and MD transitions.
In this work, we show theoretically and confirm experimentally that thin metal membranes patterned with an array of
slot dimers (or their Babinet analogue with metal rods) can function as a versatile spectral and polarization filter. We
present a detailed covariant multipole theory for the electromagnetic response of an arbitrary dimer based on the Green
functions approach. The theory confirms that a great variety of polarization properties, such as birefringence, chirality
and elliptical dichroism, can be achieved in a metal layer with such slot-dimer patterning (i.e. in a metasurface). Optical
properties of the metasurface can be extensively tuned by varying the geometry (shape and dimensions) of the dimer, for
example, by adjusting the sizes and mutual placement of the slots (e.g. inter-slot distance and alignment angle). Three
basic shapes of dimers are analyzed: II-shaped (parallel slots), V-shaped, and T-shaped. These particular shapes of
dimers are found to be sensitive to variations of the slots lengths and orientation of elements. Theoretical results are well
supported by full-wave three-dimensional simulations. Our findings were verified experimentally on the metal
membranes fabricated using UV lithography with subsequent Ni growth. Such metasurfaces were characterized using
time-domain THz spectroscopy. The samples exhibit pronounced optical activity (500 degrees per wavelength) and high
transmission: even though the slots cover only 4.3 % of the total membrane area the amplitude transmission reaches 0.67
at the resonance frequency 0.56 THz.
We propose a general approach to the design of directional couplers in photonic-crystals operating in the slowlight
regime. We predict, based on a general symmetry analysis, that robust switching of slow-light pulses is
possible between antisymmetrically coupled photonic crystal waveguides. We demonstrate, through numerical
Bloch mode frequency-domain and finite-difference time-domain (FDTD) simulations that, for all pulses with
strongly reduced group velocities at the photonic band-gap edge, complete switching occurs at a fixed coupling
length of just a few unit cells of the photonic crystal.
In this paper we review basic properties of nanopillar coupled periodic waveguides. A nanopillar coupled periodic
waveguide consists of several rows of periodically placed dielectric cylinders. In such a waveguide, light confinement is
due to the total internal reflection, while guided modes dispersion is strongly affected by waveguide periodicity. We
present a systematic analysis of the dispersion and transmission efficiency of nanopillar coupled periodic waveguides
and discusses their possible applications for integrated optics.
Experimental and theoretical studies of the emission directionality diagrams of a perylene dye covering the inner surface of three-dimensional opal-based photonic crystals with incomplete photonic bandgap are reported. Directionality diagram of emission intensity is interpreted in terms of the spontaneous emission suppression by photonic band gap and the emission enhancement due to photon focusing phenomenon. A theoretical model is based on the classical analysis of an angular distribution of the radiated power of a point dipole.
A heterojunction between two 3-dimensional photonic crystals has been realized by interfacing two opal films of different lattice constants. The interface-related transmission minimum has been observed in the frequency range between two directional lowest-order bandgaps of the hetero-opal constituents. The interface transmission minimum has been modelled numerically and tentatively explained by formation of the standing wave across the photonic hetero-crystal due to matching of group velocities of optical modes in both parts at this frequency.
Dielectric periodic media can possess a complex photonic band structure with allowed bands displaying strong dispersion and anisotropy. We show that for some frequencies the form of iso-frequency contours mimics the form of the first Brillouin zone of the crystal. A wide angular range of flat dispersion exists for such frequencies. The regions of iso-frequency contours with near zero curvature cancel out diffraction of the light beam, leading to a self-guided (self-collimated) beam.
A theoretical study of two-wave polarization spectroscopy signal dependencies on crossing angle is presented. The quantitative expressions are obtained, which are in good agreement with the experimental data. The advantages of free-coordinate operator method are illustrated under treatment of band-gap formation in anisotropic stratified periodic structure problems. A method for radiation control based on pumping wave polarization tuning is proposed.
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