Coherent coupling between an optomechanical membrane and an interacting photon Bose–Einstein condensate

In this paper, we study theoretically the optomechanical interaction of an interacting condensate of photons with an oscillating mechanical membrane in a microcavity. We show that in the Bogoliubov approximation, due to the large number of photons in the condensate, there is a linear strong effective coupling between the Bogoliubov mode of the photonic Bose–Einstein condensate (BEC) and the mechanical motion of the membrane which depends on the photon–photon scattering potential. This coupling leads to the cooling of the mechanical motion, the normal mode splitting (NMS), the squeezing of the output field and the entanglement between the excited mode of the cavity and the mechanical mode. Since the photon condensation occurs at room temperature, this hybrid system can be potentially considered as a room temperature source of squeezed light as well as a suited candidate for exploring the quantum effects. We show that, on one hand, the non-linearity of the photon gas increases the degree of the squeezing of the output field of the microcavity and the efficiency of the cooling process at high temperatures. On the other hand, it reduces the NMS in the displacement spectrum of the oscillating membrane and the degree of the optomechanical entanglement. In addition, the temperature of the photonic BEC can be used to control the above-mentioned phenomena.     

Hybridizing Plasmonic Materials with 2D‐Transition Metal Dichalcogenides toward Functional Applications

Recently, 2D transition metal dichalcogenides (TMDs) have become intriguing materials in the versatile field of photonics and optoelectronics because of their strong light–matter interaction that stems from the atomic layer thickness, broadband optical response, controllable optoelectronic properties, and high nonlinearity, as well as compatibility. Nevertheless, the low optical cross‐section of 2D‐TMDs inhibits the light–matter interaction, resulting in lower quantum yield. Therefore, hybridizing the 2D‐TMDs with plasmonic nanomaterials has become one of the promising strategies to boost the optical absorption of thin 2D‐TMDs. The appeal of plasmonics is based on their capability to localize and enhance the electromagnetic field and increase the optical path length of light by scattering and injecting hot electrons to TMDs. In this regard, recent achievements with respect to hybridization of the plasmonic effect in 2D‐TMDs systems and its augmented optical and optoelectronic properties are reviewed. The phenomenon of plasmon‐enhanced interaction in 2D‐TMDs is briefly described and state‐of‐the‐art hybrid device applications are comprehensively discussed. Finally, an outlook on future applications of these hybrid devices is provided.     

A Nanophotonic Structure Containing Living Photosynthetic Bacteria

Photosynthetic organisms rely on a series of self‐assembled nanostructures with tuned electronic energy levels in order to transport energy from where it is collected by photon absorption, to reaction centers where the energy is used to drive chemical reactions. In the photosynthetic bacteria Chlorobaculum tepidum, a member of the green sulfur bacteria family, light is absorbed by large antenna complexes called chlorosomes to create an exciton. The exciton is transferred to a protein baseplate attached to the chlorosome, before migrating through the Fenna–Matthews–Olson complex to the reaction center. Here, it is shown that by placing living Chlorobaculum tepidum bacteria within a photonic microcavity, the strong exciton–photon coupling regime between a confined cavity mode and exciton states of the chlorosome can be accessed, whereby a coherent exchange of energy between the bacteria and cavity mode results in the formation of polariton states. The polaritons have energy distinct from that of the exciton which can be tuned by modifying the energy of the optical modes of the microcavity. It is believed that this is the first demonstration of the modification of energy levels within living biological systems using a photonic structure.     

Cover Picture: Spontaneous Emission Control in Micropillar Cavities Containing a Fluorescent Molecular Dye (Adv. Mater. 6/2006)

The cover depicts a micropillar microcavity containing a fluorescent organic dye, Lumogen Red, the fabrication of which is described on p. 742 by Lidzey and co‐workers. The optical confinement resulting from the low‐dimensionality of the pillar results in a number of effects, including an enhancement in spontaneous‐emission rate. This process is confirmed using time‐resolved scanning near‐field optical microscopy. Such structures are of interest in the development of new types of low‐threshold lasers and single‐photon light sources for quantum cryptography.     

Subwavelength Artificial Structures: Opening a New Era for Engineering Optics

In the past centuries, the scale of engineering optics has evolved toward two opposite directions: one is represented by giant telescopes with apertures larger than tens of meters and the other is the rapidly developing micro/nano‐optics and nanophotonics. At the nanoscale, subwavelength light–matter interaction is blended with classic and quantum effects in various functional materials such as noble metals, semiconductors, phase‐change materials, and 2D materials, which provides unprecedented opportunities to upgrade the performance of classic optical devices and overcome the fundamental and engineering difficulties faced by traditional optical engineers. Here, the research motivations and recent advances in subwavelength artificial structures are summarized, with a particular emphasis on their practical applications in super‐resolution and large‐aperture imaging systems, as well as highly efficient and spectrally selective absorbers and emitters. The role of dispersion engineering and near‐field coupling in the form of catenary optical fields is highlighted, which reveals a methodology to engineer the electromagnetic response of complex subwavelength structures. Challenges and tentative solutions are presented regarding multiscale design, optimization, fabrication, and system integration, with the hope of providing recipes to transform the theoretical and technological breakthroughs on subwavelength hierarchical structures to the next generation of engineering optics, namely Engineering Optics 2.0.     

On‐Chip Rolling Design for Controllable Strain Engineering and Enhanced Photon–Phonon Interaction in Graphene

On‐chip strain engineering is highly demanded in 2D materials as an effective route for tuning their extraordinary properties and integrating consistent functionalities toward various applications. Herein, rolling technique is proposed for strain engineering in monolayer graphene grown on a germanium substrate, where compressive or tensile strain could be acquired, depending on the designed layer stressors. Unusual compressive strains up to 0.30% are achieved in the rolled‐up graphene tubular structures. The subsequent phonon hardening under compressive loading is observed through strain‐induced Raman G band splitting, while distinct blueshifts of characteristic peaks (G⁺, G^?, or 2D) can be well regulated on an asymmetric tubular structure with a strain variation. In addition, due to the strong confinement of the local electromagnetic field under 3D tubular geometry, the photon–phonon interaction is highly strengthened, and thus, the Raman scattering of graphene in rolled‐up tubes is enhanced. Such an on‐chip rolling approach leads to a superior strain tuning method in 2D materials and could improve their light–matter interaction in a tubular configuration, which may hold great capability in 2D materials integration for on‐chip applications such as in mechanics, electronics, and photonics.     

A Review on Organic–Inorganic Halide Perovskite Photodetectors: Device Engineering and Fundamental Physics

The last eight years (2009–2017) have seen an explosive growth of interest in organic–inorganic halide perovskites in the research communities of photovoltaics and light‐emitting diodes. In addition, recent advancements have demonstrated that this type of perovskite has a great potential in the technology of light‐signal detection with a comparable performance to commercially available crystalline Si and III–V photodetectors. The contemporary growth of state‐of‐the‐art multifunctional perovskites in the field of light‐signal detection has benefited from its outstanding intrinsic optoelectronic properties, including photoinduced polarization, high drift mobilities, and effective charge collection, which are excellent for this application. Photoactive perovskite semiconductors combine effective light absorption, allowing detection of a wide range of electromagnetic waves from ultraviolet and visible, to the near‐infrared region, with low‐cost solution processability and good photon yield. This class of semiconductor might empower breakthrough photodetector technology in the field of imaging, optical communications, and biomedical sensing. Therefore, here, the focus is specifically on the critical understanding of materials synthesis, design, and engineering for the next‐stage development of perovskite photodetectors and highlighting the current challenges in the field, which need to be further studied in the future.     

二维光子晶体微腔的制备及其对硅光学材料的光量子放大

光子晶体(PC)可以增加光物质相互作用和光发射效率,在微纳光子学、量子光学及信息光学等领域中都有着广泛的应用。近年来,二维硅基光子晶体微腔的发光增强效应研究取得了较为重大的突破。本文针对现有二维光子晶体及微腔的制备方法与发光性能的调控展开论述,详细介绍了二维光子晶体微腔的制备进程与温度、泵浦能量、微腔结构对微腔Q因子以及发光性能的影响,并进一步展望了二维光子晶体在硅材料光量子放大领域未来研究所面临的问题及应用前景。     

Room temperature current injection polariton light emitting diode with a hybrid microcavity

The strong light-matter interaction within a semiconductor high-Q microcavity has been used to produce half-matter/half-light quasiparticles, exciton-polaritons. The exciton-polaritons have very small effective mass and controllable energy-momentum dispersion relation. These unique properties of polaritons provide the possibility to investigate the fundamental physics including solid-state cavity quantum electrodynamics, and dynamical Bose-Einstein condensates (BECs). Thus far the polariton BEC has been demonstrated using optical excitation. However, from a practical viewpoint, the current injection polariton devices operating at room temperature would be most desirable. Here we report the first realization of a current injection microcavity GaN exciton-polariton light emitting diode (LED) operating under room temperature. The exciton-polariton emission from the LED at photon energy 3.02 eV under strong coupling condition is confirmed through temperature-dependent and angle-resolved electroluminescence spectra.     

Single Nanoparticle Detection Using Optical Microcavities

Detection of nanoscale objects is highly desirable in various fields such as early‐stage disease diagnosis, environmental monitoring and homeland security. Optical microcavity sensors are renowned for ultrahigh sensitivities due to strongly enhanced light‐matter interaction. This review focuses on single nanoparticle detection using optical whispering gallery microcavities and photonic crystal microcavities, both of which have been developing rapidly over the past few years. The reactive and dissipative sensing methods, characterized by light‐analyte interactions, are explained explicitly. The sensitivity and the detection limit are essentially determined by the cavity properties, and are limited by the various noise sources in the measurements. On the one hand, recent advances include significant sensitivity enhancement using techniques to construct novel microcavity structures with reduced mode volumes, to localize the mode field, or to introduce optical gain. On the other hand, researchers attempt to lower the detection limit by improving the spectral resolution, which can be implemented by suppressing the experimental noises. We also review the methods of achieving a better temporal resolution by employing mode locking techniques or cavity ring up spectroscopy. In conclusion, outlooks on the possible ways to implement microcavity‐based sensing devices and potential applications are provided.     

Recent Advances in Organic One‐Dimensional Composite Materials: Design,Construction, and Photonic Elements for Information Processing

Many recent activities in the use of one‐dimensional nanostructures as photonic elements for optical information processing are explained by huge advantages that photonic circuits possess over traditional silicon‐based electronic ones in bandwidth, heat dissipation, and resistance to electromagnetic wave interference. Organic materials are a promising candidate to support these optical‐related applications, as they combine the properties of plastics with broad spectral tunability, high optical cross‐section, easy fabrication, as well as low cost. Their outstanding compatibility allows organic composite structures which are made of two or more kinds of materials combined together, showing great superiority to single‐component materials due to the introduced interactions among multiple constituents, such as energy transfer, electron transfer, exciton coupling, etc. The easy processability of organic 1D crystalline heterostructures enables a fine topological control of both composition and geometry, which offsets the intrinsic deficiencies of individual material. At the same time, the strong exciton‐photon coupling and exciton‐exciton interaction impart the excellent confinement of photons in organic microstructures, thus light can be manipulated according to our intention to realize specific functions. These collective properties indicate a potential utility of organic heterogeneous material for miniaturized photonic circuitry. Herein, focus is given on recent advances of 1D organic crystalline heterostructures, with special emphasis on the novel design, controllable construction, diverse performance, as well as wide applications in isolated photonic elements for integration. It is proposed that the highly coupled, hybrid optical networks would be an important material basis towards the creation of on‐chip optical information processing.     

Recent Progress of Strong Exciton–Photon Coupling in Lead Halide Perovskites

The semiconductor exciton–polariton, arising from the strong coupling between excitons and confined cavity photon modes, is not only of fundamental importance in macroscopic quantum effects but also has wide application prospects in ultralow‐threshold polariton lasers, slowing‐light devices, and quantum light sources. Very recently, metallic halide perovskites have been considered as a great candidate for exciton–polariton devices owing to their low‐cost fabrication, large exciton oscillator strength, and binding energy. Herein, the latest progress in exciton–polaritons and polariton lasers of perovskites are reviewed. Polaritons in planar and nanowires Fabry–Pérot microcavities are discussed with particular reference to material and photophysics. Finally, a perspective on the remaining challenges in perovskite polaritons research is given.     

Size‐Dependent Control of Exciton–Polariton Interactions in WS2 Nanotubes

Multiwall WS₂ nanotubes (and fullerene‐like nanoparticles thereof) are currently synthesized in large amounts, reproducibly. Other than showing interesting mechanical and tribological properties, which offer them a myriad of applications, they are recently shown to exhibit remarkable optical and electrical properties, including quasi‐1D superconductivity, electroluminescence, and a strong bulk photovoltaic effect. Here, it is shown that, using a simple dispersion‐fractionation technique, one can control the diameter of the nanotubes and move from pure excitonic to polaritonic features. While nanotubes of an average diameter >80 nm can support cavity modes and scatter light effectively via a strong coupling mechanism, the extinction of nanotubes with smaller diameter consists of pure absorption. The experimental work is complemented by finite‐difference time‐domain simulations, which shed new light on the cavity mode–exciton interaction in 2D materials. Furthermore, transient absorption experiments of the size‐fractionated nanotubes fully confirm the steady‐state observations. Moreover, it is shown that the tools developed here are useful for size control of the nanotubes, e.g., in manufacturing environment. The tunability of the light–matter interaction of such nanotubes offers them intriguing applications such as polaritonic devices, in photocatalysis, and for multispectral sensors.     

M‐shaped Grating by Nanoimprinting: A Replicable,Large‐Area,Highly Active Plasmonic Surface‐Enhanced Raman Scattering Substrate with Nanogaps

Plasmonic nanostructures separated by nanogaps enable strong electromagnetic‐field confinement on the nanoscale for enhancing light‐matter interactions, which are in great demand in many applications such as surface‐enhanced Raman scattering (SERS). A simple M‐shaped nanograting with narrow V‐shaped grooves is proposed. Both theoretical and experimental studies reveal that the electromagnetic field on the surface of the M grating can be pronouncedly enhanced over that of a grating without such grooves, due to field localization in the nanogaps formed by the narrow V grooves. A technique based on room‐temperature nanoimprinting lithography and anisotropic reactive‐ion etching is developed to fabricate this device, which is cost‐effective, reliable, and suitable for fabricating large‐area nanostructures. As a demonstration of the potential application of this device, the M grating is used as a SERS substrate for probing Rhodamine 6G molecules. Experimentally, an average SERS enhancement factor as high as 5×10⁸ has been achieved, which verifies the greatly enhanced light–matter interaction on the surface of the M grating over that of traditional SERS surfaces.     

Single photon transport in one-dimensional coupled-resonator waveguide coupling to a whispering gallery resonator interacting with a semiconductor quantum dot

We theoretically investigate the hybrid mechanism for transmission of a single photon in one-dimensional coupled microcavity waveguide coupled to a whispering-gallery resonator interacting with a semiconductor quantum dot (QD). The QD is modeled as a V-type three-level system. The reflection and transmission coefficients for a single photon propagating in the hybrid system are deduced by using the discrete coordinates approach. The resonator–QD coupling strength, intermode backscattering, and the detuning between the resonator and the QD, respectively, which affect the transport properties of the single photon, are analyzed. We also compare the single photon transport properties in the waveguides with sinusoidal, linear, and quadratic form dispersion relations.     

A Flexible High‐Performance Photoimaging Device Based on Bioinspired Hierarchical Multiple‐Patterned Plasmonic Nanostructures

In insect eyes, ommatidia with hierarchical structured cornea play a critical role in amplifying and transferring visual signals to the brain through optic nerves, enabling the perception of various visual signals. Here, inspired by the structure and functions of insect ommatidia, a flexible photoimaging device is reported that can simultaneously detect and record incoming photonic signals by vertically stacking an organic photodiode and resistive memory device. A single‐layered, hierarchical multiple‐patterned back reflector that can exhibit various plasmonic effects is incorporated into the organic photodiode. The multiple‐patterned flexible organic photodiodes exhibit greatly enhanced photoresponsivity due to the increased light absorption in comparison with the flat systems. Moreover, the flexible photoimaging device shows a well‐resolved spatiotemporal mapping of optical signals with excellent operational and mechanical stabilities at low driving voltages below half of the flat systems. Theoretical calculation and scanning near‐field optical microscopy analyses clearly reveal that multiple‐patterned electrodes have much stronger surface plasmon coupling than flat and single‐patterned systems. The developed methodology provides a versatile and effective route for realizing high‐performance optoelectronic and photonic systems.     

High‐Efficiency Nonfullerene Organic Solar Cells with a Parallel Tandem Configuration

In this work, a highly efficient parallel connected tandem solar cell utilizing a nonfullerene acceptor is demonstrated. Guided by optical simulation, each of the active layer thicknesses of subcells are tuned to maximize its light trapping without spending intense effort to match photocurrent. Interestingly, a strong optical microcavity with dual oscillation centers is formed in a back subcell, which further enhances light absorption. The parallel tandem device shows an improved photon‐to‐electron response over the range between 450 and 800 nm, and a high short‐circuit current density (J _SC) of 17.92 mA cm^?2. In addition, the subcells show high fill factors due to reduced recombination loss under diluted light intensity. These merits enable an overall power conversion efficiency (PCE) of >10% for this tandem cell, which represents a ≈15% enhancement compared to the optimal single‐junction device. Further application of the designed parallel tandem configuration to more efficient single‐junction cells enable a PCE of >11%, which is the highest efficiency among all parallel connected organic solar cells (OSCs). This work stresses the importance of employing a parallel tandem configuration for achieving efficient light harvesting in nonfullerene‐based OSCs. It provides a useful strategy for exploring the ultimate performance of organic solar cells.     

Properties of a Strong Coupling Bipolaron in an Asymmetric Quantum Dot

We study a strong coupling bipolaron’s vibrational frequency, self-trapping energy and potential induced by the electron–longitudinal optical (LO) phonon interaction in an asymmetric quantum dot (AQD). The effects of the electron–phonon coupling strength, the transverse and longitudinal effective confinement lengths are taken into account by using linear combination operator and unitary transformation methods. It is found that the vibrational frequency is an increasing function of the electron–phonon coupling strength, whereas it is a decreasing one of the transverse and longitudinal effective confinement lengths. The absolute values of the self-trapping energy and the potential induced by the electron–LO phonon interaction will increase with increasing coupling strength or decreasing effective confinement lengths.     

Interaction between dual cavity modes in a planar photonic microcavity

Abstract

We theoretically study the interaction between dual cavity modes in a planar photonic microcavity structure in the optical communication wavelength range. The merging and splitting of cavity mode is analysed with realistic microcavity structures. The merging of dual cavity resonance into a single cavity resonance is achieved by changing the number of layers between the two cavities. The splitting of single cavity resonance into dual cavity resonance is obtained with an increase in the reflectivity of mirrors in the front and rear side of the microcavity structure. The threshold condition for the merging and splitting of cavity mode is established in terms of structural parameters. The physical origin of the merging of dual cavity modes into a single cavity resonance is discussed in terms of the electric field intensity distribution in the microcavity structure. The microcavity structure with dual cavity modes is useful for the generation of entangled photon pairs, for achieving the strong-coupling regime between exciton and photon and for high-resolution multi-wavelength filters in optical communication.