Photon Extraction Research Articles

Exciton Fine Structure in InAs Quantum Dots with Cavity-Enhanced Emission at Telecommunication Wavelength and Grown on a GaAs (111) A Vicinal Substrate

The effcient generation of entangled photons at telecom wavelength is crucial for the success of many quantum communication protocols and the development of fiber-based quantum networks. Entangled light can be generated by solid state quantum emitters with naturally low fine structure splitting, such as highly symmetric InAs quantum dots (QDs) grown on (111)-oriented surfaces. Incorporating this kind of QDs into optical cavities is critical to achieve sufficient signal intensitiesfor applications, but has so far shown major complications. In this work we present droplet epitaxy of telecom-wavelength InAs QDs within an optical cavity on a vicinal (2{\deg} miscut) GaAs(111)A substrate. We show a remarkable enhancement of the photon extraction efficiency compared to previous reports together with a reduction of the density that facilitates the isolation of single spectral lines. Moreover, we characterise the exciton fine structure splitting and employ numerical simulations under the framework of the empirical pseudopotential and configuration interaction methods to study the impact of the miscut on the optical properties of the QDs. We demonstrate that the presence of miscut steps influences the polarisation of the excitonic states and introduces a preferential orientation in the $C_{3v}$ symmetry of the surface.

Optimization of photonic crystal structure by FDTD method to improve the light extraction efficiency in silicon

Silicon photonics technology is on its last hurdle to complete the system with active research on enhancing the light extraction efficiency of silicon. Silicon has a very poor radiative emission efficiency due to its indirect bandgap, thus making the probability of radiative recombination to be very low. The periodic quantum confinement structures such as photonic crystals (PhCs) can be tailored to increase the radiative recombination probability at the desired wavelengths. In this paper, we have optimized the silicon photonic crystal (Si PhCs) parameters to obtain luminescence at silicon bandgap and telecommunication wavelength using FDTD method. The extraction of photons is mostly conquered in the silicon structure that has lattice constant, a: 480 nm with radius, r: 140 nm and a: 500 nm with r: 160 nm. We have also observed the emissive photon luminescence that emerges in the most stable state of optical communication wavelength at 1310 nm.

Band-Edge Effect-Induced Electrochemiluminescence Signal Amplification Based on Inverse Opal Photonic Crystals for Ultrasensitive Detection of Carcinoembryonic Antigen.

Photonic crystals (PCs) have emerged as a promising electrochemiluminescence (ECL) matrix in the domain of immunoassay. Making maximum use of light manipulation properties of PCs is highly desired for improving the sensitivity. In this work, we proposed a band-edge effect-induced ECL enhancement strategy based on silica inverse opal PCs (SIOPCs). By fine-tuning the lattice constant and carefully calibrating the stopband position, we found that the band edge of the stopband exerted significant influences on the ECL intensity and spectral distribution. The high density of states at the blue edge of the photonic band gap increased the radiative transition probability of ECL emitters and enhanced the photon extraction during propagation, giving rise to ∼20-fold ECL signal amplification accompanied by a redistributed ECL spectrum for the Ru(bpy)32+-TPrA system. In combination with the intrinsic structural superiority, like large specific surface area and interconnected macropores, the developed SIOPC electrode was successfully applied in constructing a sandwich-type immunosensor. The fabricated immunosensor displayed a very low detection limit of 0.032 pg/mL and a wide linear range of 0.1 pg/mL-150 ng/mL for a carcinoembryonic antigen assay, showing its potential application in disease diagnosis.

Bright Quantum Dot Single-Photon Emitters at Telecom Bands Heterogeneously Integrated on Si.

Whereas the Si photonic platform is highly attractive for scalable optical quantum information processing, it lacks practical solutions for efficient photon generation. Self-assembled semiconductor quantum dots (QDs) efficiently emit photons in the telecom bands (1460–1625 nm) and allow for heterogeneous integration with Si. In this work, we report on a novel, robust, and industry-compatible approach for achieving single-photon emission from InAs/InP QDs heterogeneously integrated with a Si substrate. As a proof of concept, we demonstrate a simple vertical emitting device, employing a metallic mirror beneath the QD emitter, and experimentally obtained photon extraction efficiencies of ∼10%. Nevertheless, the figures of merit of our structures are comparable with values previously only achieved for QDs emitting at shorter wavelength or by applying technically demanding fabrication processes. Our architecture and the simple fabrication procedure allows for the demonstration of high-purity single-photon generation with a second-order correlation function at zero time delay, g(2)(τ = 0) < 0.02, without any corrections at continuous wave excitation at the liquid helium temperature and preserved up to 50 K. For pulsed excitation, we achieve the as-measured g(2)(0) down to 0.205 ± 0.020 (0.114 ± 0.020 with background coincidences subtracted).

Enhanced Ultraviolet Spontaneous and Lasing Emission Through Interface Engineering of Patterned Vertically Aligned ZnO Nanowires

AbstractDue to optical radiation losses, a high pumping threshold or low temperature is necessary for driving ultraviolet (UV) light emission devices, and surface/interface engineering method is one of the alternatives for tailoring photon behavior. Here, a fully integrated nanowire (NW) laser device is thus constructed, resulting in suppressed interface light loss. Enhanced UV spontaneous and lasing emission is observed due to adequate gain to compensate for the optical loss. Applying well‐aligned ZnO NW cavities, optimized UV spontaneous and lasing emission is realized, supporting an effective optical path through interface engineering for photon extraction. As proven by experimental results, through interface integration with Pt metal for ZnO NWs, 170% photoluminescence (PL) emission enhancement accompanied by 145% broaden emission spectra width in the UV region is obtained. It is also observed that more lasing modes appeare when excitation density is high enough, lasing modes interspacing of around 3 nm, and full width at half maximum of the modes &lt;0.003 eV for the lasing device could be observed. The detailed optical simulation is proposed to understand the physical origin of internal mechanisms contributing to the optimized spontaneous and stimulated lasing emission behaviors.

57‐4: Invited Paper: Progress on Key Innovations in Direct‐View μLED Display Manufacturing

Applied Materials reported earlier on an innovative approach to μLED‐based front plane technology using a single wavelength GaN LED emitter with Cd‐free quantum dots for color conversion. This proprietary μLED front plane technology incorporates several key innovations such as the use of high external quantum efficiency dice in ultraviolet wavelength spectrum (vs. red/green/blue), highest photon extraction efficiency at small die‐size, fewer number of mass transfer steps with high yield, and a four‐subpixel backplane architecture to allow for a simple, cost‐effective repair strategy. A picture of this display is shown below.

Micro‐Nano Structure Functionalized Perovskite Optoelectronics: From Structure Functionalities to Device Applications

AbstractMetal halide perovskite, an emerging photosensitive semiconductor, has been widely employed in solar cells, light‐emitting diodes, photodetectors, and lasers owing to its excellent photophysical properties and simple solution preparation processing. However, as a photoactive layer, the higher refractive index and thinner thickness of perovskite film can cause reflection and transmission at the interface, and confine the emitted light within devices, resulting in the poor incident photon absorption and emitted photon extraction. In addition, the intrinsic brittleness of perovskite material restricts its potential applications in flexible optoelectronics. Therefore, great effort has been put into micro‐nano structured perovskite optoelectronics, and the reported reviews mainly focus on the fabrication process of micro‐nano patterned perovskite. Herein, the functionalities of micro‐nano structures in optoelectronics, including improving the light trapping, light extraction, light modulation, carrier dynamics, mechanical robustness, and other novel functionalities, are comprehensively reviewed. The specific applications of these functionalities in perovskite‐based optoelectronic devices are then discussed in detail to provide a better understanding of the photophysical properties of micro‐nano structure functionalized optoelectronics. Finally, promising strategies to promote the multifunctional commercial applications of micro‐nano structured perovskite optoelectronics are provided.

Numerical optimization of single-mode fiber-coupled single-photon sources based on semiconductor quantum dots.

We perform extended numerical studies to maximize the overall photon coupling efficiency of fiber-coupled quantum dot single-photon sources emitting in the near-infrared and O-band and C-band. Using the finite element method, we optimize the photon extraction and fiber-coupling efficiency of quantum dot single-photon sources based on micromesas, microlenses, circular Bragg grating cavities and micropillars. The numerical simulations which consider the entire system consisting of the quantum dot source itself, the coupling lens, and the single-mode fiber, yield overall photon coupling efficiencies of up to 83%. Our work provides objectified comparability of different fiber-coupled single-photon sources and proposes optimized geometries for the realization of practical and highly efficient quantum dot single-photon sources.

On the excitation and radiative decay rates of plasmonic nanoantennas

Abstract Plasmonic nanoantennas have the ability to confine and enhance incident electromagnetic fields into very sub-wavelength volumes, while at the same time efficiently radiating energy to the far-field. These properties have allowed plasmonic nanoantennas to be extensively used for exciting quantum emitters—such as molecules and quantum dots—and also for the extraction of photons from them for measurements in the far-field. Due to electromagnetic reciprocity, it is expected that plasmonic nanoantennas radiate energy as efficiently as an external source can couple energy to them. In this paper, we adopt a multipole expansion (Mie theory) and numerical simulations to show that although reciprocity holds, certain plasmonic antennas radiate energy much more efficiently than one can couple energy into them. This work paves the way towards designing plasmonic antennas with specific properties for applications where the near-to-far-field relationship is of high significance, such as: surface-enhanced Raman spectroscopy, strong coupling at room temperature, and the engineering of quantum states in nanoplasmonic devices.

Time Resolution Studies of Thallium Based Cherenkov Semiconductors

In the context of improving the detector performance of time-of-flight positron emission tomography (TOF-PET), the combination of charge induction readout and prompt Cherenkov photon production in semiconductor materials can lead to an outstanding detector performance in energy, timing, and spatial resolution. Energy resolutions as good as 1.2% at 662 keV and 5% at 122 keV are reported for pixel thallium bromide (TlBr) detectors. The high refractive index of Tl-based materials, between 2.3 and 2.6, leads to a high Cherenkov photon generation yield but can also challenge photon extraction, potentially affecting the time performance. In this work, the timing properties of TlBr and thallium chloride (TlCl) crystals of different geometries are measured using an optimized test setup with high-frequency readout electronics. A coincidence time resolution (CTR) value of 167 ± 6 ps FWHM is achieved using a 3 × 3 × 3 mm3black-painted TlBr crystal. In order to assess potential improvements, a Geant4-based simulation tool kit is developed and validated against experimental measurements. The simulation tool kit is used to predict the contributions limiting the time resolution regarding the crystal and photodetector properties, highlighting the potential of such materials. Finally, paths to further improve the detector performance in TOF-PET are discussed.

Ground Photon Extraction From Photon-Counting LiDAR Data Using Adaptive Cloth Simulation With Terrain Index

Photon-counting light detection and ranging (LiDAR) Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) enables the drafting of global elevation maps. However, vegetation cover, terrain undulation, and residual noise in signal photons substantially reduce the accuracy of ground photon extraction. Existing ground photon extraction algorithms do not consider the factors influencing photon extraction, and the threshold setting lacks a theoretical basis. This study proposed a photon-extraction algorithm with scenario adaptability. First, the cloth simulation was adapted with a terrain index to extract ground photons; based on this, the cloth breakage concept was proposed to remove residual noise. We tested the algorithm in Denali National Park and compared its results with those of other extraction algorithms. The results showed that the terrain index was robust and consistent with the actual terrain; the adaptive cloth simulation achieved the best accuracy and precision under different canopy heights and terrains. The mean absolute error and root mean square error of extracted photons were 0.95 and 3.41 m, respectively. This study provides a solution to estimate ground elevation using photon-counting LiDAR data.

Transferable room-temperature single-photon emitters in hexagonal boron nitride grown by molecular beam epitaxy

The solid-state single-photon source is the core of applications such as quantum cryptography, quantum sensing, and quantum computing. Recently, the point defects in two-dimensional (2D) hexagonal boron nitride (h-BN) have become excellent candidates for next-generation single-photon sources due to their chemical and physical stability and ultra-high brightness at room temperature. The 2D layered structure of h-BN allows the single-photon emitters (SPEs) in it to have high photon extraction efficiency and be integrated into photonic circuits easily. However, most of the SPEs found in h-BN flakes are present at the edges or wrinkles. Here, we report on the room-temperature SPEs in h-BN film grown by molecular beam epitaxy followed by a high-temperature post-annealing process and their deterministic transfer. Using the all-dry viscoelastic stamping method, the h-BN film grown on the Al2O3 substrate can be transferred to other substrates. The transferred SPEs are discretely distributed among the continuous h-BN flakes, and the SPE density is as high as ∼0.17 μm−2. After identification, the determined SPE can be deterministically transferred to other structures by the all-dry transfer method. The deterministic transfer of SPEs distributed on the h-BN flakes promises the potential to integrate SPEs into many quantum technology applications.

Optical Quality of InAs/InP Quantum Dots on Distributed Bragg Reflector Emitting at 3rd Telecom Window Grown by Molecular Beam Epitaxy.

We present an experimental study on the optical quality of InAs/InP quantum dots (QDs). Investigated structures have application relevance due to emission in the 3rd telecommunication window. The nanostructures are grown by ripening-assisted molecular beam epitaxy. This leads to their unique properties, i.e., low spatial density and in-plane shape symmetry. These are advantageous for non-classical light generation for quantum technologies applications. As a measure of the internal quantum efficiency, the discrepancy between calculated and experimentally determined photon extraction efficiency is used. The investigated nanostructures exhibit close to ideal emission efficiency proving their high structural quality. The thermal stability of emission is investigated by means of microphotoluminescence. This allows to determine the maximal operation temperature of the device and reveal the main emission quenching channels. Emission quenching is predominantly caused by the transition of holes and electrons to higher QD’s levels. Additionally, these carriers could further leave the confinement potential via the dense ladder of QD states. Single QD emission is observed up to temperatures of about 100 K, comparable to the best results obtained for epitaxial QDs in this spectral range. The fundamental limit for the emission rate is the excitation radiative lifetime, which spreads from below 0.5 to almost 1.9 ns (GHz operation) without any clear spectral dispersion. Furthermore, carrier dynamics is also determined using time-correlated single-photon counting.

A cavity-based optical antenna for color centers in diamond

An efficient atom–photon interface is a key requirement for the integration of solid-state emitters, such as color centers in diamond, into quantum technology applications. As other solid-state emitters, however, their emission into free space is severely limited due to the high refractive index of the bulk host crystal. In this work, we present a planar optical antenna based on two silver mirrors coated on a thin single crystal diamond membrane, forming a planar Fabry–Pérot cavity that improves the photon extraction from single tin vacancy (SnV) centers and their coupling to an excitation laser. Upon numerical optimization of the structure, we find theoretical enhancements in the collectible photon rate by a factor of 60 as compared to the bulk case. As a proof-of-principle demonstration, we fabricate single crystal diamond membranes with sub-μm thickness and create SnV centers by ion implantation. Employing off-resonant excitation, we show a sixfold enhancement of the collectible photon rate, yielding up to half a million photons per second from a single SnV center. At the same time, we observe a significant reduction of the required excitation power in accordance with theory, demonstrating the functionality of the cavity as an optical antenna. Due to its planar design, the antenna simultaneously provides similar enhancements for a large number of emitters inside the membrane. Furthermore, the monolithic structure provides high mechanical stability and straightforwardly enables operation under cryogenic conditions as required in most spin–photon interface implementations.

Point Defects in Monolayer h-AlN as Candidates for Single-Photon Emission.

A single-photon emission (SPE) system based on a solid state is one of the fundamental branches in quantum information and communication technologies. The traditional bulk semiconductors suffered limitations of difficult photon extraction and long radiative lifetime. Two-dimensional (2D) semiconductors with an entire open structure and low dielectric screening can overcome these shortcomings. In this work, we focus on monolayer h-AlN due to its wide band gap and the successful achievement of SPE compared to its bulk counterpart. We systematically investigate the properties of point defects, including vacancies, antisites, and impurities, in monolayer h-AlN by employing hybrid density functional theory calculations. The -1 charged Al vacancy (VAl-) and +1 charged nitrogen antisite (NAl+) are predicted to achieve SPE with the zero-phonon lines of 0.77 and 1.40 eV, respectively. Moreover, the charged point-defect complex CAlVN+, which is composed of vacancies and carbon substitutions, also can be used for SPE. Our results extend the avenue for realizing SPE in 2D semiconductors.

InP-based single-photon sources operating at telecom C-band with increased extraction efficiency

In this work, we demonstrate a triggered single-photon source operating at the telecom C-band with photon extraction efficiency exceeding any reported values in this range. The non-classical light emission with low probability of the multiphoton events is realized with single InAs quantum dots (QDs) grown by molecular beam epitaxy and embedded directly in an InP matrix. Low QD spatial density on the order of 5 × 108 cm−2 to ∼2 × 109 cm−2 and symmetric shape of these nanostructures together with spectral range of emission make them relevant for quantum communication applications. The engineering of extraction efficiency is realized by combining a bottom distributed Bragg reflector consisting of 25 pairs of InP/In0.53Ga0.37Al0.1 As layers and cylindrical photonic confinement structures. Realization of such a technologically non-demanding approach even in a non-deterministic fashion results in photon extraction efficiency of (13.3 ± 2) % into 0.4 numerical aperture detection optics at approximately 1560 nm emission wavelength, i.e., close to the center of the telecom C-band.

Bright Electrically Controllable Quantum‐Dot‐Molecule Devices Fabricated by In Situ Electron‐Beam Lithography

AbstractSelf‐organized semiconductor quantum dots represent almost ideal two‐level systems, which have strong potential to applications in photonic quantum technologies. For instance, they can act as emitters in close‐to‐ideal quantum light sources. Coupled quantum dot systems with significantly increased functionality are potentially of even stronger interest since they can be used to host ultra‐stable singlet‐triplet spin qubits for efficient spin‐photon interfaces and for deterministic photonic 2D cluster‐state generation. An advanced quantum dot molecule (QDM) device is realized and excellent optical properties are demonstrated. The device includes electrically controllable QDMs based on stacked quantum dots in a pin‐diode structure. The QDMs are deterministically integrated into a photonic structure with a circular Bragg grating using in situ electron beam lithography. A photon extraction efficiency of up to (24 ± 4)% is measured in good agreement with numerical simulations. The coupling character of the QDMs is clearly demonstrated by bias voltage dependent spectroscopy that also controls the orbital couplings of the QDMs and their charge state in quantitative agreement with theory. The QDM devices show excellent single‐photon emission properties with a multi‐photon suppression of . These metrics make the developed QDM devices attractive building blocks for use in future photonic quantum networks using advanced nanophotonic hardware.

Nitrogen-Vacancy Center Coupled to an Ultrasmall-Mode-Volume Cavity: A High-Efficiency Source of Indistinguishable Photons at 200 K

Solid state atom-like systems have great promise for linear optic quantum computing and quantum communication but are burdened by phonon sidebands and broadening due to surface charges. Nevertheless, coupling to a small mode volume cavity would allow high rates of extraction from even highly dephased emitters. We consider the nitrogen vacancy centre in diamond, a system understood to have a poor quantum optics interface with highly distinguishable photons, and design a silicon nitride cavity that allows 99 % efficient extraction of photons at 200 K with an indistinguishability of > 50%, improvable by external filtering. We analyse our design using FDTD simulations, and treat optical emission using a cavity QED master equation valid at and beyond strong coupling and which includes both ZPL broadening and sideband emission. The simulated design is compact (< 10 um), and owing to its planar geometry, can be fabricated using standard silicon processes. Our work therefore points towards scalable fabrication of non-cryogenic atom-like efficient sources of indistinguishable photons.

Signal Photon Extraction Method for Weak Beam Data of ICESat-2 Using Information Provided by Strong Beam Data in Mountainous Areas

The Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) can measure the elevations of the Earth’s surface using a sampling strategy with unprecedented spatial detail. In the daytime of mountainous areas where the signal–noise ratio (SNR) of weak beam data is very low, current algorithms do not always perform well on extracting signal photons from weak beam data (i.e., many signal photons were missed). This paper proposes an effective algorithm to extract signal photons from the weak beam data of ICESat-2 in mountainous areas. First, a theoretical equation of SNR for ICESat-2 measured photons in mountainous areas was derived to prove that the available information provided by strong beam data can be used to assist the signal extraction of weak beam data (that may have very low SNR in mountainous areas). Then, the relationship between the along-track slope and the noise level was used as the bridge to connect the strong and weak beam data. To be specific, the along-track slope of the weak beam was inversed by the slope–noise relationship obtained from strong beam data, and then was used to rotate the direction of the searching neighborhood in the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm. With the help of this process, the number of signal photons included in the searching neighborhood will significantly increase in mountainous areas and will be easily detected from the measured noisy photons. The proposed algorithm was tested in the Tibetan Plateau, the Altun Mountains, and the Tianshan Mountains in different seasons, and the extraction results were compared with the results from the ATL03 datasets, the ATL08 datasets, and the classical DBSCAN algorithm. Based on the ground-truth signal photons obtained by visual inspection, the parameters of the classification precision, recall, and F-score of our algorithm and three other algorithms were calculated. The modified DBSCAN could achieve a good balance between the classification precision (93.49% averaged) and recall (89.34% averaged), and its F-score (more than 0.91) was higher than that of the other three methods, which successfully obtained a continuous surface profile from weak beam data with very low SNRs. In the future, the detected signal photons from weak beam data are promising to assess the elevation accuracy achieved by ICESat-2, estimate the along-track and cross-track slope, and further obtain the ground control points (GCPs) for stereo-mapping satellites in mountainous areas.

Controllable photon extraction based on a single-photon Raman interaction

A target whispering-gallery-mode microresonator (WGMM) directly coupled to a waveguide with an auxiliary side-coupled WGMM is proposed to deterministically extract both the resonant and non-resonant single incident photons from a waveguide. Based on the single-photon Raman interaction (SPRINT) between an Λ-type three-level atom and the target WGMM, a full quantum theory in real space is adopted to calculate the extraction efficiencies at the single-photon level. The results show that the extraction efficiencies can be significantly improved by appropriately tuning the frequencies of the auxiliary WGMM and the coupling strength between the two WGMMs, even when the atom and WGMMs have dissipations. Since mode redistribution is only externally imposed on the auxiliary WGMM, the population and phase of the atom are not directly affected. The nonlocal control, which ensures that the SPRINT takes place, results in high extraction efficiencies. We also find that the transmission probabilities of both the resonant and non-resonant incident photons can be controlled in a range from 0 to 100%, so that the proposed double-WGMM system has the potential to be used as a single-photon switch.