Defect Nanocavity Research Articles

High-performance dielectric nano-cavities for near- and mid-infrared frequency applications

We present a judicious design approach for optimizing semiconductor nanocavities, starting from single photonic atoms to build photonic molecules functioning as high-performance nanocavities. This design approach is based on exact analytical solutions to the Maxwell equations for collective Mie resonances. Conceptually, we distinguish different concepts of cavity modes including Mie mode, collective Mie mode, photonic-crystal (PC) band-edge mode, and Feshbach-type bound states in the continuum (BIC) mode. Using the design approach, we present a unique structure of nanocavity supporting the Feshbach-type BIC mode, capable of enhancing the emission rate of a dipolar emitter by orders of magnitude. This high-performance nanocavity suppresses radiative loss channels strongly via destructive interference and consequently channels the emission light efficiently into an in-plane bi-directional beam with a divergence angle of 10°. Engineering the geometrical parameters of the nanocavity for near-infrared frequency applications requires a fabrication tolerance of ±5 nm. This high accuracy is challenging for the mass production of devices. The fabrication accuracy can be relaxed greatly for mid-infrared frequency devices. As a showcase, we analyze and optimize the well-known PC L3 defect nanocavity for mid-infrared frequency applications in the framework of Feshbach resonance. We show that the optimal structure of this defect nanocavity requires a fabrication tolerance of ±50 nm. Our nanocavity design approach may be useful for near- and mid-infrared frequency applications.

Tunable non-Hermiticity in Coupled Photonic Crystal Cavities with Asymmetric Optical Gain

We report a rationally designed coupled photonic crystal (PhC) cavity system that comprises two identical linear defect nanocavities, and we numerically investigate the controllable non-Hermitian optical properties of the eigenmodes of the nanocavities. Three different coupling schemes, namely, the tuning of the sizes of shared airholes, vertical shifting of one of the nanocavities, and lateral shifting of one of the nanocavities, are proposed. We examined the ability of these schemes to control the coupling strength between component cavities, which is a key factor that determines the non-Hermiticity of the system. Moreover, we introduce controlled levels of spatially asymmetric optical gain to the coupled PhC cavity by employing the vertical shifting scheme and independently tuning the gain and loss of individual nanocavities. Consequently, we successfully achieve the correspondingly tuned non-Hermitian behaviors of complex eigenfrequencies, such as the controlled emergence of phase transitions at exceptional points and the asymmetric development of amplified and decayed eigenmodes.

High-Performance Plasmonic Nanolasers with a Nanotrench Defect Cavity for Sensing Applications

Recent developments in small footprint plasmonic nanolasers show promise for active optical sensing with potential applications in various fields, including real-time and label-free biochemical sensing, and gas detection. In this study, we demonstrate a novel hybrid plasmonic crystal nanolaser that features a ZnO nanowire placed on Al grating surfaces with a nanotrench defect nanocavity. The lasing action of gain-assisted defect nanocavity overcomes the ohmic loss parasitically in the plasmonic nanostructures. Therefore, the plasmonic nanolaser exhibits an extremely small mode volume, a narrow linewidth Δλ, and a high Purcell factor that can facilitate the strong interaction between light and matter. This can be used as a refractive index sensor and is highly sensitive to local changes in the refractive indices of ambient materials. By careful design, the near-ultraviolet nanolaser sensors have significant sensing performances of glucose solutions, revealing a high sensitivity of 249 nm/RIU and high resol...

Tuning the Fano resonances in a single defect nanocavity coupled with a plasmonic waveguide for sensing applications

A novel surface plasmon polaritons (SPPs) refractive index sensor based on a single defect nanocavity coupled with a metal–insulator–metal (MIM) waveguide is proposed and numerically simulated by using the finite difference time domain (FDTD) method with perfectly matched layer absorbing boundary condition. It is found that the defect structure can realize two Fano resonances and these two Fano resonances originate from two different mechanisms. The results demonstrate the liner correlation between the resonance wavelengths of the device and the refractive index of the material under sensing. Through the optimization of structural parameters, we achieve a theoretical value of the refractive index sensitivity as high as 1800.4 nmRIU[Formula: see text]. It could be utilized to develop ultra-compact nanodevice for high-resolution biological sensing.

Tuning the Fano resonances in a single defect nanocavity coupled with a plasmonic waveguide for sensing applications

A novel surface plasmon polaritons (SPPs) refractive index sensor based on a single defect nanocavity coupled with a metal-insulator-metal (MIM) waveguide is proposed. The refractive index sensing characteristics of this structure are analyzed by the finite difference time domain (FDTD) meth. The results show that there exist two Fano resonances in the transmission spectra, and both of which have a linear relationship with the refractive index of the detected sample. By optimizing the proposed structure parameters, we achieve a theoretical value of the refractive index sensitivity as high as 1800.4nmRIU−1. It could be utilized to develop ultracompact nanodevice for high-resolution biological sensing.

Fano resonances in a single defect nanocavity coupled with a plasmonic waveguide

Two Fano resonances are theoretically predicted in a single defect nanocavity, consisting of a rectangular cavity with a small stub defect, side-coupled with a plasmonic waveguide. These two Fano resonances are found to originate from two different mechanisms. One is caused by the excitation of a high-order resonant mode in the rectangular cavity owing to the structural breaking, and the other is attributed to the inherent resonant mode in the small stub defect. The narrow high-order mode and inherent mode couple with the broad low-order resonant mode in the rectangular cavity, giving rise to two Fano resonances. Because of the different origins, these two Fano resonances exhibit quite different responses to the variations of the structural dimensions. This has important applications in highly sensitive and multiparameter sensing in the complicated environments.

Electrical properties of GaAs photonic crystal cavity lateral p-i-n diodes

We investigate conduction and free-carrier injection in laterally doped GaAs p-i-n diodes formed in one and two-dimensional photonic crystal (PC) nanocavities. Finite element simulations show that the lateral geometry exhibits high conductivity for a wide range of PC parameters and allows for precise control over current flow, enabling efficient carrier injection despite fast surface recombination. Thermal simulations indicate that the temperature increase during steady-state operation is only 3.3 K in nanobeams and 0.29 K in L3 defect nanocavities. The results affirm the suitability of lateral doping in PC devices and indicate criteria for further design optimization.

Correlation between emission intensity of self-assembled germanium islands and quality factor of silicon photonic crystal nanocavities

We present a comparative micro-photoluminescence study of the emission intensity of self-assembled germanium islands coupled to the resonator mode of two-dimensional silicon photonic crystal defect nanocavities. The emission intensity is investigated for cavity modes of L3 and Hexapole cavities with different cavity quality factors. For each of these cavities many nominally identical samples are probed to obtain reliable statistics. As the quality factor increases we observe a clear decrease in the average mode emission intensity recorded under comparable optical pumping conditions. This clear experimentally observed trend is compared with simulations based on a dissipative master equation approach that describes a cavity weakly coupled to an ensemble of emitters. We obtain evidence that reabsorption of photons emitted into the cavity mode is responsible for the observed trend. In combination with the observation of cavity linewidth broadening in power dependent measurements, we conclude that free carrier absorption is the limiting effect for the cavity mediated light enhancement under conditions of strong pumping.

Outcoupling of Light Generated in a Monolithic Silicon Photonic Crystal Nanocavity through a Lateral Waveguide

We report the design, fabrication and optical investigation of silicon nanocavity light sources based on silicon on insulator photonic crystal nanocavities. The planar geometry of the two-dimensional photonic crystal allows light to be efficiently out-coupled into a planar photonic circuit and our results demonstrate enhanced light transmission from a defect nano-cavity into a W1 photonic crystal waveguide. When compared to the sample without the cavity, we observe an 11-fold enhancement of the luminescence emitted from the cleaved facets of the waveguide measured at the cavity wavelength. The emission exhibits a characteristically strong spatial dependence, confirming that it indeed arises from light generated in the cavity and out-coupled via the waveguide. The obtained cavity mode frequency and spatial dependence are in excellent agreement with finite-difference time-domain simulations and their dependence on the photonic crystal structural properties.

Room temperature continuous wave operation and characterization of photonic crystal nanolaser on a sapphire substrate

A compact photonic crystal defect nanocavity was fabricated on a sapphire substrate. Continuous wave lasing at room temperature was achieved with a low threshold power. We characterized the operated mode, quality factor and radiative efficiency for the compact laser. The thermal properties of the nanolaser were also investigated.

Electrical control of spontaneous emission and strong coupling for a single quantum dot

We report the design, fabrication and optical investigation of electrically tunable single quantum dots—photonic crystal defect nanocavities operating in both the weak and strong coupling regimes of the light–matter interaction. Unlike previous studies where the dot–cavity spectral detuning was varied by changing the lattice temperature, or by the adsorption of inert gases at low temperatures, we demonstrate that the quantum-confined Stark effect can be employed to quickly and reversibly switch the dot–cavity coupling simply by varying a gate voltage. Our results show that exciton transitions from individual dots can be tuned by ∼4 meV relative to the nanocavity mode before the emission quenches due to carrier tunneling escape. This range is much larger than the typical linewidth of the high-Q cavity modes (∼100 μeV) allowing us to explore and contrast regimes where the dots couple to the cavity or decay by spontaneous emission into the two-dimensional photonic bandgap. In the weak-coupling regime, we show that the dot spontaneous emission rate can be tuned using a gate voltage, with Purcell factors ⩾7. New information is obtained on the nature of the dot–cavity coupling in the weak coupling regime, and electrical control of zero-dimensional polaritons is demonstrated for the highest-Q cavities (Q⩾12 000). Vacuum Rabi splittings up to ∼120 μeV are observed, larger than the linewidths of either the decoupled exciton (γ⩽40 μeV) or cavity mode. These observations represent a voltage switchable optical nonlinearity at the single photon level, paving the way towards on-chip dot-based nano-photonic devices that can be integrated with passive optical components.

Silicon photonic crystal nanostructures for refractive index sensing

The authors present the fabrication and optical investigation of silicon on insulator photonic crystal drop filters for use as refractive index sensors. Two types of defect nanocavities (L3 and H1−r) are embedded between two W1 photonic crystal waveguides to evanescently route light at the cavity mode frequency between input and output waveguides. Optical characterization of the structures in air and various liquids demonstrates detectivities in excess of Δn/n=0.018 and Δn/n=0.006 for the H1−r and L3 cavities, respectively. The measured cavity frequencies and detector refractive index responsivities are in good agreement with simulations, demonstrating that the method provides a background free transducer signal with frequency selective addressing of a specific area of the sensor chip.

Design and Characterization of Optofluidic Photonic Crystal Structures for the Detection of Fluorescent-Labeled Biomolecules

The combination of optics and microfluidics into optofluidic systems has provided a means of creating portable integrated platforms for performing fluorescence emission analyses in fieldable systems. We present here the design of a photonic crystal transducer for highly sensitive and selective fluorescence-based biomolecule detection using a reduced-size lattice nanocavity tuned for resonance at emission wavelengths. This novel approach to biosensing is based upon photonic crystal defect structures that are engineered to act as waveguides, optical resonant cavities, and nanofluidic flow channels. This paper will discuss modeling, design, and nanofabrication of optofluidic photonic crystal (PhC) transducers in silicon and GaN materials. First-order results of PhC optical property characterization will be provided. Preliminary simulations indicate that fluorescence emission intensity inside of a PhC resonant defect nanocavity is enhanced to a level 26 times greater than emission outside of a defect due to resonant optical confinement and the Purcell effect.

Prerequisites of nanocavities for single artificial atom laser

AbstractPrerequisites of nanocavities for single quantum dot laser have been theoretically studied by a fully quantum‐mechanical treatment. Numerical simulations are performed by solving master equations for single four‐level electronic system and single cavity electric field mode. Experimentally obtained parameters are used in the simulations to predict prerequisites of the cavity quality factor Q and allowable range of the relative position control of the cavity and a target quantum dot. In the case of a photonic crystal defect nanocavity with a modal volume of 0.04 μm3, the required Q for lasing is 65,000 assuming the atom‐field coupling strength g = 40 GHz. The dephasing effect is also taken into account in the simulation. The results indicate that the dephasing effect can be negligible when the transverse relaxation time is longer than ∼ 100 ps. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electrically probing photonic bandgap phenomena in contacted defect nanocavities

We demonstrate an electrically tunable two dimensional photonic crystal nanocavity containing InAs self-assembled quantum dots (QDs). Photoluminescence and electroluminescence measurements are combined to probe the cavity mode structure and demonstrate a local electrical contact to the quantum dots. Measurements performed as a function of the electric field enable us to probe the capture, relaxation, and recombination dynamics of photogenerated carriers inside the quantum dots emitting into a modified photonic environment. Furthermore, the two dimensional photonic crystal is probed by spatially dependent photocurrent spectroscopy indicating a 3.5× enhancement of the local radiative lifetime of the QDs inside the photonic crystal environment.

Lasing characteristics of a GaN photonic crystal nanocavity light source

Lasing characteristics from photonic crystal defects fabricated on bulk GaN are investigated. The device demonstrates multimode lasing with linewidths as narrow as 2–3Å, and an enhanced spontaneous emission factor β∼0.045. The emission spectra indicate that the laser emission is initiated horizontally in the defect nanocavity and then coupled to the vertical radiation, possibly via photonic crystal Bloch modes or by scattering.

Polarized quantum dot emission from photonic crystal nanocavities studied under moderesonant enhanced excitation

We study the linear polarization of the emission from single quantum dots embedded in an "L3" defect nanocavity in a two-dimensional photonic crystal. By using narrow linewidth optical excitation in resonance with higher-order modes, we are able to achieve strong quantum dot emission intensity whilst reducing the background from quantum dots in the surrounding lattice. We find that all the dots observed emit very strongly linearly polarized light of the same orientation as the closest mode, despite the fact that these quantum dots may be spectrally detuned by several times the mode linewidth. We discuss the coupling mechanisms which may explain this behavior.

Enhancement of light emission from single quantum dot in photonic crystal nanocavity by using cavity resonant excitation

The authors demonstrate highly efficient selective excitation of a single InGaAs self-assembled quantum dot (QD) embedded in a photonic crystal defect nanocavity. A single QD, whose first excited state is resonant with the cavity mode resonance, shows strong light emission from the ground state under cavity resonant excitation. The light emission is nearly ten times stronger than that of a single QD located at an unpatterned area. This result is attributed to the local enhancement of the effective absorption by the cavity resonant effect. This highly efficient excitation technique can be useful for single photon sources.

Observation of fast spontaneous emission decay in GaInAsP photonic crystal point defect nanocavity at room temperature

The spontaneous emission decay in a photonic crystal slab nanocavity with a GaInAsP quantum well active region was measured at room temperature. Even far below lasing threshold, the decay was much faster than that for the as-grown wafer. A consideration including the enhanced spontaneous emission rate by the Purcell effect, intraband relaxation of carriers, nonradiative surface recombination, spatial hole burning, and carrier diffusion enabled us to explain different decay lifetime between on- and off-resonant conditions and between different size cavities. As a result, >16-fold shorter spontaneous emission lifetime was estimated, which strongly suggests the existence of a large Purcell effect.

Characteristics of single defect laser modes in a two-dimensional square lattice photonic crystal slab

Square lattice photonic crystal single defect nanocavity structures are formed in free-standing slab InGaAsP materials emitting near 1.55 μm. Laser operations are achieved from two types of resonant modes, a degenerate dipole mode and a nondegenerate whispering-gallery-like mode. Each laser mode is identified by the measurement of mode shapes, quality factors, and polarization. The threshold absorbed pump power is estimated to be less than 0.2 mW for the whispering gallery mode. It is found, by rate equation analyses, that nonradiative surface recombination, which takes >60% of carrier recombination near threshold, is one of the main limiting factors for the low-threshold operation of photonic crystal single defect lasers.