Distributed Bragg Reflector Microcavity Research Articles

Positronium density measurements using polaritonic effects

Recent experimental advances in Positronium (Ps) physics have made it possible to produce dense Ps ensembles in which Ps-Ps interactions may occur, leading to the production of Ps$_2$ molecules and paving the way to the realization of a Ps Bose-Einstein Condensate (BEC). In order to achieve this latter goal it would be advantageous to develop new methods to measure Ps densities in real-time. Here we describe a possible approach to do this using polaritonic methods: using realistic experimental parameters we demonstrate that a dense Ps gas can be strongly coupled to the photonic field of a distributed Bragg reflector microcavity. In this strongly coupled regime, the optical spectrum of the system is composed of two hybrid positronium-polariton resonances separated by the vacuum Rabi splitting, which is proportional to the square root of the Ps density. Given that polaritons can be created on a sub-cycle timescale, a spectroscopic measurement of the vacuum Rabi splitting could be used as an ultra-fast Ps density measurement in regimes relevant to Ps BEC formation. Moreover, we show how positronium-polaritons could potentially enter the ultrastrong light-matter coupling regime, introducing a radically novel platform to explore its non-perturbative phenomenology.

Detection and amplification of spin noise using scattered laser light in a quantum-dot microcavity

Fundamental properties of the spin-noise signal formation in a quantum-dot microcavity are studied by measuring the angular characteristics of the scattered light intensity. A distributed Bragg reflector microcavity was used to enhance the light-matter interaction with an ensemble of n-doped (In,Ga)As/GaAs quantum dots, which allowed us to study subtle effects of the noise signal formation. Detecting the scattered light outside of the aperture of the transmitted light, we measured the basic electron spin properties, like g-factor and spin dephasing time. Further, we investigated the influence of the microcavity on the scattering distribution and possibilities of signal amplification by additional resonant excitation.

Engineering Optical Absorption in Graphene and Other 2D Materials: Advances and Applications

Abstract2D materials are promising but remain to be further explored, with respect to their usage in various optoelectronic devices. Generally, 2D materials exhibit far less than ideal absorption due to their thickness, limiting their deployment in practical optoelectronic applications. To address this challenge, extensive research has been performed utilizing different designs, such as distributed Bragg reflector microcavities, metallic reflectors, photonic crystal nanocavities, and plasmonic nanostructures, to confine light within 2D materials and increase light absorption. Recent progresses in enhancing light absorption in graphene and other 2D materials such as transition metal dichalcogenides and phosphorene are reviewed. Some physical mechanisms that realize enhanced absorption in 2D materials, as well as their potential applications are also discussed.

Design and realization of one-dimensional double hetero-structure photonic crystals for infrared-radar stealth-compatible materials applications

In this paper, a new type one-dimensional (1D) double hetero-structure composite photonic crystal (CPC) for infrared-radar stealth-compatible materials applications was proposed and studied numerically and experimentally. First, based on transfer matrix method of thin-film optical theory, the propagation characteristics of the proposed structure comprising a stack of different alternating micrometer-thick layers of germanium and zinc sulfide were investigated numerically. Calculation results exhibit that this 1D single hetero-structure PC could achieve a flat high reflectivity gradually with increasing the number of the alternating media layers in a single broadband range. Then, based on principles of distributed Bragg reflector micro-cavity, a 1D double hetero-structure CPC comprising four PCs with thickness of 0.797 μm, 0.592 μm, 1.480 μm, and 2.114 μm, respectively, was proposed. Calculation results exhibit that this CPC could achieve a high reflectance of greater than 0.99 in the wavelength ranges of 3–5 μm and 8–14 μm and agreed well with experiment. Further experiments exhibit that the infrared emissivity of the proposed CPC is as low as 0.073 and 0.042 in the wavelength ranges of 3–5 μm and 8–12 μm, respectively. In addition, the proposed CPC can be used to construct infrared-radar stealth-compatible materials due to its high transmittance in radar wave band.

Optical anisotropy of m ‐plane nitride air‐gap distributed Bragg reflector microcavities

AbstractWe investigated the optical anisotropy properties of m‐plane air/AlGaN distributed Bragg reflector microcavities fabricated by the thermal decomposition of GaN. Micro‐photoluminescence measurements were performed at room temperature. From the recorded spectrum, two cavity modes with different polarization direction (parallel to a and c) were observed, which are attributed to the birefringence properties of the non‐polar nitride structure.In addition, the mode with E ‖ a has a higher PL intensity than that of the mode with E ‖ c. Based on k · p Hamiltonians, the matrix elements were calculated around the Γ point, revealing the origin of the mode intensity difference. These results would be very helpful for exciton‐cavity coupling research in non‐polar microcavities. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication and optical properties of non-polar III-nitride air-gap distributed Bragg reflector microcavities

Using the thermal decomposition technique, non-polar III-nitride air-gap distributed Bragg reflector (DBR) microcavities (MCs) with a single quantum well have been fabricated. Atomic force microscopy reveals a locally smooth DBR surface, and room-temperature micro-photoluminescence measurements show cavity modes. There are two modes per cavity due to optical birefringence in the non-polar MCs, and a systematic cavity mode shift with cavity thickness was also observed. Although the structures consist of only 3 periods (top) and 4 periods (bottom), a quality factor of 1600 (very close to the theoretical value of 2100) reveals the high quality of the air-gap DBR MCs.

Laser and infrared compatible stealth from near to far infrared bands by doped photonic crystal

Photonic crystals can realize broadband thermal infrared stealth based on its high-reflection photon forbidden band. By forming a “hole-digging” reflection spectrum of doped photonic crystals at military laser wavelength of 1.06μm and 10.6μm, compatible stealth of laser and infrared can be achieved. We selected lead telluride (PbTe) and cryolite (Na3AlF6), and designed a one-dimensional two-defect-mode photonic crystal based on principles of distributed Bragg reflector micro-cavity. The reflection and transmission spectra of the photonic crystals were calculated by transfer matrix method of thin-film optical theory. The calculation results show that the designed multi-cycle dual-hetero-junction photonic crystal has a high spectral reflectance in the near, middle and far infrared band, whose spectral reflectance is greater than 99% in 1∼5μm and 8∼14μm infrared bands, and spectral transmittance at 1.06μm and 10.6μm is greater than 96%. This will satisfy the laser and infrared compatible stealth in the near, middle and far infrared bands

Three-Dimensional FDTD Simulation of Micro-Pillar Microcavity Geometries Suitable for Efficient Single-Photon Sources

We present the results of calculations of the microcavity mode structure of distributed-Bragg-reflector (DBR) micro-pillar microcavities of group III-V semiconductor materials. These structures are suitable for making single photon sources when a single quantum dot is located at the center of a wavelength scale cavity. The 3-D finite difference time domain (FDTD) method is our primary simulation tool and results are validated against semi-analytic models. We show that high light extraction efficiencies can be achieved (>90%) limited by sidewall scattering and leakage. Using radial trench DBR microcavities or 2-D photonic crystal structures, we can further suppress sidewall emission, however, light is then redirected into other leaky modes

Fabrication and characterization of InGaN resonant‐cavity light‐emitting diodes on silicon substrates

AbstractGaN‐based resonant‐cavity light‐emitting diodes (RCLEDs) have been fabricated on Si substrates by a combination of laser lift‐off and wafer bonding techniques. The RCLED structure consisted of an InGaN/GaN multiple‐quantum‐well active layer between the top (5‐pairs) and bottom (7.5‐pairs) dielectric TiO2/SiO2 distributed Bragg reflector (DBR) with an optical reflectance of 85 and 99.9%, respectively. The cavity mode of the RCLED shows a linewidth of 5.5 nm at a main emission peak at 525 nm. The emission full width at half maximum can decrease from 48 to 35 nm, indicating the effect of the DBR microcavity. The quality factor for this resonant cavity structure was estimated to be approximately 100. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Dynamics of a high-Q vertical-cavity organic laser

We investigate the dynamics of the organic laser guest-host composite of tris-(8-hydroxy quinoline) aluminium and 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran embedded in a high-Q (Q≈4500) double distributed Bragg reflector microcavity using subpicosecond up-conversion techniques. Lasing is observed at a threshold of 0.4nJ∕20μJcm−2 with a linewidth of 0.05 nm (resolution limit). We observe a strongly nonlinear intensity-dependent delay of the emitted radiation burst. All experimental results are successfully modeled by a set of nonlinear rate equations, emphasizing the importance of a feedback mechanism for lasing.

Optimization of three-dimensional micropost microcavities for cavity quantum electrodynamics

This article presents a detailed analysis, based on the first-principles finite-difference time-domain method, of the resonant frequency, quality factor (Q), mode volume (V), and radiation pattern of the fundamental (HE11) mode in a three-dimensional distributed-Bragg-reflector (DBR) micropost microcavity. By treating this structure as a one-dimensional cylindrical photonic crystal containing a single defect, we are able to push the limits of Q/V beyond those achievable by standard micropost designs, based on the simple rules established for planar DBR microcavities. We show that some of the rules that work well for designing large-diameter microposts (e.g., high-refractive index contrast) fail to provide high-quality cavities with small diameters. By tuning the thicknesses of mirror layers and the spacer, the number of mirror pairs, the refractive indices of high and low refractive index regions, and the cavity diameter, we are able to achieve Q as high as 10^4, together with a mode volume of 1.6 cubic wavelengths of light in the high-refractive-index material. The combination of high Q and small V makes these structures promising candidates for the observation of such cavity quantum electrodynamics phenomena as strong coupling between a quantum dot and the cavity field, and single-quantum-dot lasing.

Modification of Spontaneous Emission of a Single Quantum Dot

Modification of spontaneous emission of a single InAs quantum dot is demonstrated using an epitaxial distributed Bragg reflector microcavity that has been post-growth processed into microposts. The micropost structure isolates single quantum dots within the microcavity resonance, and creates a three-dimensionally (3D) confined photonic cavity. Discrete mode structure from the 3D cavity is observed, as well as the coupling of a single quantum dot to one of these modes in the weak coupling cavity QED regime.

Cavity-Induced Changes of Spontaneous Emission Lifetime in One-Dimensional Semiconductor Microcavities.

Spontaneous emission lifetime in a one-dimensional AlGaAs distributed Bragg reflector microcavity has been systematically measured as a function of emission wavelength tuned by the quantum-confined Stark effect in order to confirm the cavity-induced alteration of the SE lifetime. The result manifests a substantial cavity-induced fractional change of the exciton decay times, $\ensuremath{\sim}$30% around the on-axis resonant wavelength, despite the relatively large broadening of the excitonic emission being comparable to the cavity resonance width in the low- $Q$ cavity.