Optical Nanocavities Research Articles

Sandwich-typed resonator cavity based on a regular photonic crystal nanobeam

The authors propose and numerically examine a two-component design of an optical nanocavity. The design utilizes the effective medium theory. Such a nanocavity consists, first, of a photonic crystal nanobeam, in which the photonic crystal unit cell is not changed. Second, the cavity contains a fragment of some supplementary material of the size of several or several tens of photonic crystal unit cells. This paper describes the cavity model in which the both components have an equal thickness and can be fabricated from the same silicon wafer. While combining the two components, the defect has formed, in which the resonant mode can be excited. The advantages of the proposed cavity model are reported, particularly the easiness with which the cavities array can be fabricated and the possibility of implementing electrically pumped light sources and amplifiers. The fabrication tolerances of the proposed nanocavity were investigated. It has been found that existing structural layers alignment technologies can be used for fabricating the suggested cavity.

Overcoming Auger recombination in nanocrystal quantum dot laser using spontaneous emission enhancement

We propose a method to overcome Auger recombination in nanocrystal quantum dot lasers using cavity-enhanced spontaneous emission. We derive a numerical model for a laser composed of nanocrystal quantum dots coupled to optical nanocavities with small mode-volume. Using this model, we demonstrate that spontaneous emission enhancement of the biexciton transition lowers the lasing threshold by reducing the effect of Auger recombination. We analyze a photonic crystal nanobeam cavity laser as a realistic device structure that implements the proposed approach.

Engineering of metal-clad optical nanocavity to optimize coupling with integrated waveguides

We propose a cladding engineering method that flexibly modifies the radiation patterns and rates of metal-clad nanoscale optical cavity. Optimally adjusting the cladding symmetry of the metal-clad nanoscale optical cavity modifies the modal symmetry and produces highly directional radiation that leads to 90% coupling efficiency into an integrated waveguide. In addition, the radiation rate of the cavity mode can be matched to its absorption rate by adjusting the thickness of the bottom-cladding layer. This approach optimizes the energy-flow rate from the waveguide and maximizes the energy confined inside the nanoscale optical cavity.

Two-component cavity based on a regular photonic crystal nanobeam

The authors propose and numerically examine a two-component design for an optical nanocavity. Such a nanocavity consists, first, of a photonic crystal (PC) nanobeam, in which the PC unit cell is not changed. Second, the cavity contains a fragment of some supplementary material of the size of several or several tens of PC unit cells. When the two components are combined, a defect forms in which the resonant mode can be excited. The advantages of the proposed cavity model are reported, particularly the possibility of implementing electrically pumped light sources and amplifiers and the simplification of development of nanocavities with nonlinear properties. The fabrication tolerances of the proposed nanocavity were investigated. It has been found that existing structural layer alignment technologies can be used for fabricating the suggested cavity.

Proposed Coupling of an Electron Spin in a Semiconductor Quantum Dot to a Nanosize Optical Cavity

We propose a scheme to efficiently couple a single quantum dot electron spin to an optical nano-cavity, which enables us to simultaneously benefit from a cavity as an efficient photonic interface, as well as to perform high fidelity (nearly 100%) spin initialization and manipulation achievable in bulk semiconductors. Moreover, the presence of the cavity speeds up the spin initialization process beyond the GHz range.

Simulations of high-Q optical nanocavities with a gradual 1D bandgap

High-quality cavities in hybrid material systems have various interesting applications. We perform a comprehensive modeling comparison on such a design, where confinement in the III-V material is provided by gradual photonic crystal tuning, a recently proposed method offering strong resonances. The III-V cavity couples to an underlying silicon waveguide. We report on the device properties using four simulation methods: finite-difference time-domain (FDTD), finite-element method (FEM), bidirectional eigenmode propagation (BEP) and aperiodic rigorous coupled wave analysis (aRCWA). We explain the major confinement and coupling effects, consistent with the simulation results. E.g. for strong waveguide coupling, we find quantitative discrepancies between the methods, which establishes the proposed high-index-contrast, lossy, 3D structure as a challenging modeling benchmark.

Two-component nanocavity based on a regular photonic crystal nanobeam

I propose and numerically examine a two-component design of an optical nanocavity. Such a nanocavity consists, first, of a photonic crystal nanobeam, in which the period of the structure is not changed. Second, the cavity contains a piece of additional (supplementary) material with the area of several periods of the photonic crystal. When combining the two components the defect has formed, in which the resonant mode can be excited. The advantages of the proposed model of the cavity has been considered. In particular, the easiness of formation of cavities arrays and of development of dynamic nanophotonic elements. The proposed nanocavity fabrication tolerances have been calculated. It is shown that existing structural layers alignment technologies can be used for fabrication.

A three-dimensional silicon photonic crystal nanocavity with enhanced emission from embedded germanium islands

We report the realization of a silicon three-dimensional photonic crystal nanocavity containing self-assembled germanium-island emitters. The three-dimensional woodpile photonic crystal was assembled layer by layer by micromanipulation using silicon plates grown by molecular beam epitaxy. An optical nanocavity was formed in the center of the photonic crystal by introducing a point defect into one of the plates. Measurements of the filtered spontaneous emission from the Ge islands in the active plate through the localized modes of the structure directly reveal information on the evolution of the frequency and Q-factor as upper cladding plates are sequentially added. An exponential increase of the cavity-Q is observed when the number of upper cladding plates is increased up to a maximum of ten. The emission of germanium-islands within the cavity reveals several strongly polarized cavity modes with quality-factors up to ≈13 600. The emission intensity of the cavity modes is enhanced by large factors up to ≈58× as compared with the active plate outside the photonic environment.

Polarization-sensitive cathodoluminescence Fourier microscopy

Determining the emission polarization properties of sub-wavelength structures like optical nanoantennas, nanocavities and photonic crystals is important to understand their physical properties and to optimize their use in applications. Recently we have shown that angle-resolved cathodoluminescence imaging spectroscopy (ARCIS), which uses a 30 keV electron beam as an excitation source, is a useful technique to study the far-field properties of such structures. Here we extend the technique with polarization-sensitive angular detection. As proof-of-principle, we experimentally probe the emission polarization properties of three orthogonal dipolar emitters of which the polarization is well-known and find excellent agreement between experiment and theory. We access these dipole orientations by exciting an unstructured gold surface and a ridge nanoantenna with an in-plane dipolar plasmon resonance. The light emission is collected with an aluminum half paraboloid mirror. We show how to take the effect of the paraboloid mirror on the emission polarization into account and how to predict the polarization-filtered pattern if the emission polarization is known. Furthermore, we calculate that by introducing a slit in the beam path the polarization contrast in cathodoluminescence spectroscopy can be strongly enhanced. Finally, we reconstruct the emission polarization from the experimental data and show that from these field patterns we can infer the orientation of the induced dipole moment. The ability to measure the emission polarization, in combination with the sensitivity to the local density of optical states, broad spectral range and high excitation resolution, can be employed to study photonic nanostructures in great detail.

Double resonance 1-D photonic crystal cavities for single-molecule mid-infrared photothermal spectroscopy: theory and design

We propose and theoretically examine a novel mid-infrared (mid-IR) photothermal spectroscopic sensing technique capable of detecting a single small molecule. Our conceptual design attains such high sensitivity by leveraging dramatically amplified photothermal effects in an optical nanocavity doubly resonant at both mid-IR pump and near-IR probe wavelengths. Unlike conventional mid-IR spectroscopy, the technique eliminates the need for cryogenically cooled mid-IR photodetectors, as optical detection is performed solely at the near-IR probe wavelength. A device design based on nested one-dimensional nanobeam photonic crystal cavities is numerically analyzed to demonstrate the technique's potential for single small gas molecule detection.

A chip-scale integrated cavity-electro-optomechanics platform

We present an integrated optomechanical and electromechanical nanocavity, in which a common mechanical degree of freedom is coupled to an ultrahigh-Q photonic crystal defect cavity and an electrical circuit. The system allows for wide-range, fast electrical tuning of the optical nanocavity resonances, and for electrical control of optical radiation pressure back-action effects such as mechanical amplification (phonon lasing), cooling, and stiffening. These sort of integrated devices offer a new means to efficiently interconvert weak microwave and optical signals, and are expected to pave the way for a new class of micro-sensors utilizing optomechanical back-action for thermal noise reduction and low-noise optical read-out.

Shaking optical nanocavities

Surface acoustic waves can actively modulate the optical mode of a photonic crystal defect cavity. Fast tuning rates, compared with the typical lifetimes of optical emitters and photons inside the cavity, pave the way for deeper insights into cavity quantum electrodynamics.

One-dimensional polaritons with size-tunable and enhanced coupling strengths in semiconductor nanowires

Strong coupling of light with excitons in direct bandgap semiconductors leads to the formation of composite photonic-electronic quasi-particles (polaritons), in which energy oscillates coherently between the photonic and excitonic states with the vacuum Rabi frequency. The light-matter coherence is maintained until the oscillator dephases or the photon escapes. Exciton-polariton formation has enabled the observation of Bose-Einstein condensation in the solid-state, low-threshold polariton lasing and is also useful for terahertz and slow-light applications. However, maintaining coherence for higher carrier concentration and temperature applications still requires increased coupling strengths. Here, we report on size-tunable, exceptionally high exciton-polariton coupling strengths characterized by a vacuum Rabi splitting of up to 200meV as well as a reduction in group velocity, in surface-passivated, self-assembled semiconductor nanowire cavities. These experiments represent systematic investigations on light-matter coupling in one-dimensional optical nanocavities, demonstrating the ability to engineer light-matter coupling strengths at the nanoscale, even in non-quantum-confined systems, to values much higher than in bulk.

Hybrid Photonic−Plasmonic Crystal Nanocavities

We propose a hybrid optical nanocavity consisting of photonic crystals coupled to a metal surface with a nanoscale air gap between. The hybridization of photonic crystal modes and surface plasmons across the gap forms hybrid cavity modes, which are highly confined in the low-loss air gap region. Deep subwavelength mode volume and high quality factor are demonstrated at telecommunication wavelength, resulting in an extremely large Q/V(m) ratio of 60,000 λ(-3). This new type of high-Q/V(m) broad-band hybrid nanocavity opens up opportunities for various applications in enhanced light-matter interactions.

Exciton–polariton light–semiconductor coupling effects

The integrated absorption of an excitonic resonance is a measure of a semiconductor's coupling to an optical field. The concept of an exciton–polariton expresses the non-perturbative coupling between the electromagnetic field and the optically induced matter polarization. Ways to alter this coupling include confining the light in optical cavities and localizing the excitonic wavefunction in quantum wells and dots, which is illustrated by quantum strong coupling between a single dot and an optical nanocavity. Positioning quantum wells in periodic or quasiperiodic lattices with spacing close to a half wavelength results in pronounced modifications to the light transmission. Light–matter coupling can also be used to generate and interrogate an exciton population, for example by the recently developed technique of absorbing terahertz radiation.

Mutual coupling of two semiconductor quantum dots via an optical nanocavity

We present an experimental and theoretical study of a system consisting of two spatially separated self-assembled InGaAs quantum dots strongly coupled to a single optical nanocavity mode. Due to their different size and compositional profiles, the two quantum dots exhibit markedly different DC Stark shifts. This allows us to tune them into mutual resonance with each other and a photonic crystal nanocavity mode as a bias voltage is varied. Photoluminescence measurements show a characteristic triple peak during the double anticrossing, which is a clear signature of a coherently coupled system of three quantum states. We fit the entire set of emission spectra of the coupled system to theory and are able to investigate the coupling between the two quantum dots via the cavity mode, and the coupling between the two quantum dots when they are detuned from the cavity mode. We suggest that the resulting quantum V-system may be advantageous since dephasing due to incoherent losses from the cavity mode can be avoided.

An Optical Nanocavity Incorporating a Fluorescent Organic Dye Having a High Quality Factor

We have fabricated an L3 optical nanocavity operating at visible wavelengths that is coated with a thin-film of a fluorescent molecular-dye. The cavity was directly fabricated into a pre-etched, free-standing silicon-nitride (SiN) membrane and had a quality factor of Q = 2650. This relatively high Q-factor approaches the theoretical limit that can be expected from an L3 nanocavity using silicon nitride as a dielectric material and is achieved as a result of the solvent-free cavity-fabrication protocol that we have developed. We show that the fluorescence from a red-emitting fluorescent dye coated onto the cavity surface undergoes strong emission intensity enhancement at a series of discrete wavelengths corresponding to the cavity modes. Three dimensional finite difference time domain (FDTD) calculations are used to predict the mode structure of the cavities with excellent agreement demonstrated between theory and experiment.

Nonlinear Optical Properties of Core-Shell Nanocavities for Enhanced Second-Harmonic Generation

A nonlinear optical plasmonic core-shell nanocavity is demonstrated as an efficient, subwavelength coherent light source through second-harmonic generation. The nonlinear optical plasmonic nanocavity incorporates a noncentrosymmetric medium, which utilizes the entire mode volume for even-order nonlinear optical processes. In previous plasmonic nanocavities, enhancement of such processes was only possible at the interface but symmetry prohibited in the body. We measured an enhancement of over 500 times in the second-harmonic radiation power. Calculations show that an enhancement of over 3500 times is achievable.

Enhanced photoluminescence emission from two-dimensional silicon photonic crystal nanocavities

We present a temperature-dependent photoluminescence study of silicon optical nanocavities formed by introducing point defects into two-dimensional photonic crystals. In addition to the prominent TO-phonon-assisted transition from crystalline silicon at ∼1.10 eV, we observe a broad defect band luminescence from ∼1.05 to ∼1.09 eV. Spatially resolved spectroscopy demonstrates that this defect band is present only in the region where air holes have been etched during the fabrication process. Detectable emission from the cavity mode persists up to room temperature; in strong contrast, the background emission vanishes for T⩾150 K. An Arrhenius-type analysis of the temperature dependence of the luminescence signal recorded either in resonance with the cavity mode or weakly detuned suggests that the higher temperature stability may arise from an enhanced internal quantum efficiency due to the Purcell effect.

Generation of nonclassical states of light via photon blockade in optical nanocavities

The generation of nonclassical states of light via photon blockade with time-modulated input is analyzed. We show that improved single-photon statistics can be obtained by adequately choosing the parameters of the driving laser pulses. An alternative method, where the system is driven via a continuous-wave laser and the frequency of the dipole is controlled (e.g., electrically) at very fast time scales is presented.