Highly nonlinear polariton materials and nanostructures are essential components for resonant optoelectronic devices with enhanced bandwidth and sensitivity, such as nonlinear optical biosensors, photodetectors, and ultrafast optical switches. In this context, the ability to engineer nonlinear interactions in epsilon-near-zero (ENZ) and phonon-polariton media provides exciting opportunities. In this talk, I will discuss our recent work on the development of polariton and ENZ materials with tailored optical dispersion for resonant nanostructures with non-perturbative Kerr-type nonlinear responses on the silicon chip. In particular, I will present the design and characterization of polariton nanostructures for enhanced infrared photon detection on the Si platform.
In this talk I will discuss the design and engineering of novel diffractive devices for light focusing and directional control with applications to light emission, imaging spectroscopy, and photodetection from the visible to the infrared spectral range.
The ability to manipulate light-matter interactions using complex, aperiodic electromagnetic media is at the heart of current nanoplasmonics and metamaterials technologies. Efficient approaches for multiscale electromagnetic field enhancement, concentration and manipulation of fields with designed spatial-frequency spectra in complex media enable the control of propagating and non-propagating electromagnetic modes in optical nanostructures with broadband/multi-band enhanced responses. Besides its fundamental interest, photonic-plasmonic coupling in complex aperiodic environments is also of great importance for a number of device applications such as nano-antennas, ultrafast optical switchers, nanoscale energy concentrators, laser nano-cavities, and optical biochemical sensors.
In this talk, I will discuss our work on the engineering of light scattering and resonance phenomena in low-loss dielectric nanostructures with designed aperiodic geometries for active devices integrated atop the widespread and inexpensive silicon platform. In particular, I will discuss applications to the optical beam shaping of partially coherent radiation and absorption enhancement in thin-film optical photodetectors and solar cells. To this purpose, a new class of aperiodic media generated from prime numbers in complex quadratic fields will be introduced, and their distinctive scattering properties will be discussed within the rigorous Green's matrix spectral method.
The presented work will focus on the design, fabrication and characterization of novel photonic nanostructures that enables the control of anomalous light transport phenomena in silicon-compatible low-loss materials, such as the recently demonstrated logarithmic photon sub-diffusion, thus defining a novel approach to tailor light-matter interactions for technologically relevant applications to optical sensing, light emission, and energy conversion on a chip.
Light emission from metal nanoparticles has potential appications as a highly sensitive refractive index detector. In order for this protential to be realized the mechanics of plasmon enhanced photoluminescence (PL) in planar nanoparticle arrays must be understude. We present an experimental exploreation of emission spectra and realitive efficiency of gold PL in nanoplasmonic arrays. We demonstrate tunability of metal PL by nanoparticle size and discover the critical role of near-field interparticle coupling on emission efficiency. We show that direct excition of plasmon resonances by photoexcited electron-hole pairs is the primary contributer to the metalic nanoparticle emission spectrum. We additionally show that emission is quenched by near-field interactions between nanoparticles leading to spectral broading by increased non-radiative plasmon decay. Finally, we show a correlation between plasmon life-time and PL efficiency. We explore this phenominan for both linear and nonlinear PL. Experimental results are supported by numerical simulations of plasmon life-time.
Scattering by plasmon resonances of metallic nanoparticles can be tailored by particle material, size, shape, and local as well as long-range order. In this presentation we discuss a series of experiments in which long-range Fano-type coupling between grating resonances and localized surface palsmon (LSP) resonances were studied using second harmonic excitation (SH-E) spectroscopy. By tuning the excitation wavelength of a femtosecond laser and measuring the relative second harmonic (SH) signal we demonstrated that when long-range grating resonances spectrally overlap with those of the LSPs, electromagnetic field enhancement occurs on the surface of the nanoparticles leading to an increase in nonlinear scattering. This effect has been demonstrated for periodic arrays of monomers and dimers, bi-periodic antenna arrays for multi-spectral focusing to a single point, and chirped nanoparticle structures for broadband field enhancement. Results are supported by finite difference time domain simulations showing that electromagnetic fields are enhanced close on the surface of the nanoparticles when long-range structural resonances are excited. These studies have revealed design principles for engineering the interplay of photonic and plasmonic coupling for future linear and nonlinear plasmonic devices.
The ability to design and to control light matter interactions on the nanoscale represents the core aspect of the rapidly
growing fields of nanophotonics and nanoplasmonics. Efficient schemes for electromagnetic field localization and
enhancement over broad frequency spectra are essential requirements for the engineering of novel optoelectronic
technologies that leverage on enhanced optical cross sections. In particular, the study of deterministic arrays of resonant
nanostructures without translational invariance offers an enormous potential for the manipulation of localized optical
states and broad frequency spectra. Deterministic Aperiodic Nano Structures (DANS), are generated by mathematical
rules with spectral features that interpolate in a tunable fashion between periodic crystals and disordered random media.
In this paper, we will focus on the optical properties and device applications of planar DANS in relation to plasmon-enhanced
light emission, Surface Enhanced Raman Scattering, and optical biosensing.
We demonstrated lasing in localized optical resonances of deterministic aperiodic structures
with pseudo-random morphologies. The localized lasing modes in the Rudin-Shapiro arrays of air
nanoholes in GaAs membranes occur at reproducible spatial locations and their frequencies are
only slightly affected by the structural fluctuations in different samples. Numerical study on the
resonances of the passive systems and optical imaging of lasing modes enabled us to interpret the
observed lasing behavior in terms of distinctive localized resonances in the two-dimensional Rudin-
Shapiro structures. The deterministic aperiodic media with controllable structural and optical
properties provide a novel platform, alternative to random lasers and different from photonic crystals
lasers, for the engineering of multi-frequency coherent light sources suitable for technological
integration.
The ability to reproducibly and accurately control light matter interaction on the nanoscale is at the core of the field of
optical biosensing enabled by the engineering of nanophotonic and nanoplasmonic structures. Efficient schemes for
electromagnetic field localization and enhancement over precisely defined sub-wavelength spatial regions is essential to
truly benefit from these emerging technologies. In particular, the engineering of deterministic media without translational
invariance offers an almost unexplored potential for the manipulation of optical states with vastly tunable transport and
localization properties over broadband frequency spectra. In this paper, we discuss deterministic aperiodic plasmonic and
photonic nanostructures for optical biosensing applications based on fingerprinting Surface Enhanced Raman Scattering
(SERS) in metal nanoparticle arrays and engineered light scattering from nanostructured dielectric surfaces with low
refractive index (quartz).
Light emission at 1.54 μm from an Er-doped amorphous silicon nitride layer coupled to photonic crystal resonators
and plamonic arrays is studied. We observe the cavity resonances at cryogenic and room temperatures and under
varying optical pump powers. The results demonstrate that small mode volume, high quality factor resonators
enhance Er absorption rates dramatically at the cavity resonance. Photonic crystal cavity resonances exhibit
linewidth narrowing with pump power at cryogenic temperatures, signifying absorption bleaching and partial
inversion of the Er ions. In addition, we fabricate periodic metal-insulator-metal plasmonic structures with a
simple bottom-up fabrication technique. We observe a factor of 10 increase of Er emission coupled to plasmonic
structures.
We present the design of a novel, CMOS compatible, waveguide structure capable of multifrequency transmission bands
with strongly enhanced band-edge states. The concept of the structure is based on the aperiodic Thue-Morse fractal
ordering of dielectric scattering subunits combined with a traditional channel-waveguide scheme. The design of the
waveguide has been carefully optimized in order to ensure its manufacturability within standard CMOS processing. Due
to the lack of translational symmetry, the proposed Thue-Morse waveguide is characterized by multiple photonic
pseudoband-gaps and quasi-localized field states exhibiting large field enhancement effects.
Optical gain has been recently observed in ion implanted Si nanocrystals (nc). Critical issues to the observation of optical gain are the formation of a waveguide structure to improve the mode confinement and a large nanocrystal area den-sity in the samples. Here we confirm these results by measuring optical gain by the variable stripe length (VSL) method on a set of silicon nanocrystals (nc) formed by plasma enhanced chemical vapor deposition (PECVD) and annealing treatments. Time resolved VSL measurements with ns pulses at high pumping fluencies have revealed fast component in the recombination dynamics under gain conditions. Lifetime shortening and superlinear emission have been unambi-guously observed. The spectral shape of the fast luminescence is consistent with the amplified spontaneous emission lineshape (ASE) observed under CW pumping conditions and overlaps the gain spectral band. The observation of light amplification is critically dependent on a very delicate balance among the nc gain cross sections, the optical mode losses of the waveguide structure, and the fast non radiative Auger processes. Within a four levels model we quantify the strong competition among all these processes and we obtain a satisfactory agreement with the experiments.
Silicon nanocrystals, formed by ion implantation and subsequent thermal annealing, show positive optical gain under intense laser excitation. Gain has been measured by the variable strip length method where the amplified spontaneous emission intensity, which is emitted from the sample edge, is measured as a function of the excitation volume. Exponential increase, line narrowing and directionality of stimulated emission have been measured. In addition, by growing silicon nanocrystals in a quartz substrate, single pass gain in pump and probe transmission experiments has been measured. Material gain values as high as those typically found in III-V semiconductors quantum dots have been measured. We claim that population inversion is realized between the fundamental and the recently identified Si equals O interface state. This model explains the gain observations and could account for the lack of auger saturation, free carrier absorption and size dispersion. Critical issues to obtain sizable gain are (1) high oxide quality, (2) high areal density of silicon nanocrystals, and (3) nanocrystals placed in the core region of a waveguide.
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