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Nanolasers based on emerging dielectric cavities with deep sub‐wavelength confinement of light offer a large light‐matter coupling rate and near‐unity spontaneous emission factor, β$\beta$. These features call for reconsidering the standard approach to identifying the lasing threshold. Here, a new threshold definition is suggested, taking into account the recycling process of photons when β$\beta$ is large. This threshold reduces to the classical balance between gain and loss in the limit of macroscopic lasers, but qualitative as well as quantitative differences emerge for nanolasers. In particular, this new threshold identifies the onset of a transition regime, where the quantum statistics of the emitted light evolve into the Poissonian statistics of a coherent state. It is shown that the threshold with photon recycling consistently marks the onset of the change in the second‐order intensity correlation, g(2)(0)$g^{(2)}(0)$, toward coherent laser light, irrespective of the laser size and down to the case of a single emitter. In contrast, other threshold definitions may well predict lasing in light‐emitting diodes. An overview of different threshold definitions proposed in the literature is provided and their predictions are compared when going from macroscopic to microscopic lasers. [ABSTRACT FROM AUTHOR]

Self‐assembled semiconductor quantum dots face challenges in terms of scalable device integration because of their random growth positions, originating from the Stranski–Krastanov growth mode. Even with existing site‐controlled growth techniques, for example, nanohole or buried stressor concepts, a further lithography and etching step with high spatial alignment requirements is necessary to accurately integrate quantum dots into the nanophotonic devices. Here, the fabrication and characterization of strain‐induced site‐controlled microcavities are reported, where site‐controlled quantum dots are positioned at the antinode of the optical mode field in a self‐aligned manner without the need of any further nano‐processing. It is shown that the cavity properties such as Q‐factor, mode volume, and mode splitting can be tailored by the geometry of the integrated buried stressor, with an opening <4 µm. The experimental results are complemented with theory calculations based on continuum elasticity. Lasing signatures, including super‐linear input‐output response and linewidth narrowing, are observed for a 3.6‐µm self‐aligned cavity with a Q‐factor of 18 000. Furthermore, the quasi‐planar site‐controlled cavities exhibit no detrimental thermal effects. This approach integrates seamlessly with the industrial‐matured manufacturing process and the buried‐stressor technique, paving the way for exceptional scalability and straightforward manufacturing of high‐β microlasers and bright quantum light sources. [ABSTRACT FROM AUTHOR]

The current need for coherent light sources for integrated (nano)photonics motivates the search for novel laser designs emitting at technologically relevant wavelengths with high‐frequency stability and low power consumption. Here, a new monolithic architecture that integrates monolayer MoS2 and chains of silver nanoparticles on a rare‐earth (Nd3+) doped LiNbO3 platform is developed to demonstrate Q‐switched lasing operation at the nanoscale. The localized surface plasmons provided by the nanoparticle chains spatially confine the gain generated by Nd3+ ions at subwavelength scales, and large‐area monolayer MoS2 acts as saturable absorber. As a result, an ultra‐compact coherent pulsed light source delivering stable train pulses with repetition rates of hundreds of kHz and pulse duration of 1 µs is demonstrated without the need of any voltage‐driven optical modulation. Moreover, the monolithic integration of the different elements is achieved without sophisticated processing, and it is compatible with LiNbO3‐based photonics. The results highlight the robustness of the approach, which can be extended to other 2D materials and solid‐state gain media. Potential applications in communications, quantum computing, or ultra‐sensitive sensing can benefit from the synergy of the materials involved in this approach, which provides a wealth of opportunities for light control at reduced scales. [ABSTRACT FROM AUTHOR]

A laser model is formulated in terms of quantum harmonic oscillators. Emitters in the low lasing states are usual harmonic oscillators, and emitters in the upper states are inverted harmonic oscillators. Diffusion coefficients, consistent with the model and necessary for solving quantum nonlinear laser equations analytically, are found. Photon number fluctuations of the lasing mode and fluctuations of the population of the lasing states are calculated. Collective Rabi splitting peaks are predicted in the intensity fluctuation spectra of the superradiant lasers. Population fluctuation mechanisms in superradiant lasers and lasers without superradiance are discussed and compared with each other. [ABSTRACT FROM AUTHOR]

Despite the enormous technological interest in micro and nanolasers, surprisingly, no class‐B quantum density‐matrix model is available to date, capable of accurately describing coherence and photon correlations within a unified theory. In class‐B lasers—applicable for most solid‐state lasers at room temperature—, the macroscopic polarization decay rate is larger than the cavity damping rate which, in turn, exceeds the upper level population decay rate. Here, a density‐matrix theoretical approach for generic class‐B lasers is carried out, and closed equations are provided for the photonic and atomic reduced density matrix in the Fock basis of photons. Such a relatively simple model can be numerically integrated in a straightforward way, and exhibits all the expected phenomena, from one‐atom photon antibunching, to the well‐known S‐shaped input–output laser emission and super‐Poissonian autocorrelation for many atoms (1≤g(2)(0)≤2$1\le {g}^{(2)}(0)\le 2$), and from few photons (large spontaneous emission factors, β≈1$\beta \approx 1$) to the thermodynamic limit (N≫1$N\gg 1$ and β≈0$\beta \approx 0$). Based on the analysis of g(2)(τ)${g}^{(2)}(\tau)$, it is concluded that super‐Poissonian fluctuations are clearly related to relaxation oscillations in the photon number. A strong damping of relaxation oscillations with an atom number as small as N≈10$N \approx 10$ is predicted. This model enables the study of few‐photon bifurcations and nonclassical photon correlations in class‐B laser devices, also leveraging quantum descriptions of coherently coupled nanolaser arrays. [ABSTRACT FROM AUTHOR]

Light sources with ultra‐low energy consumption and high performance are required to realize optical interconnects for on‐chip communication. Photonic crystal (PhC) nanocavity lasers are one of the most promising candidates for this role. In this work, a continuous‐wave PhC nanolaser with an ultra‐low threshold current of 10.2 µA emitting at 1540 nm and operated at room temperature is demonstrated. The lasers are InP‐based bonded on silicon (Si), and comprise a buried heterostructure active region and lateral p–i–n junction, feature CMOS‐compatible drive voltage, and exhibit low self‐heating. Carrier leakage is a fundamental limitation of the lateral pumping scheme that is identified as unwanted spontaneous emission from the InP p–i interface, limiting the injection efficiency to 3% which further decreases at higher current. The effect of fabrication disorder and p‐doping absorption on the Q‐factor is studied experimentally showing that p‐doping limits the Q‐factor to 8000, with a p‐doping absorption coefficient of 120 cm−1. [ABSTRACT FROM AUTHOR]

Surface plasmons exhibit an extraordinary capability to reduce the structural size and improve light−matter interaction. However, for small‐sized plasmonic cavities, the optical diffraction limit makes the near‐field difficult to observe, complicating the analysis of exact lasing characteristics. In this study, a 4f measurement system is used to extract the mode parity from the interference pattern and reconstruct the near‐field of the hybrid plasmonic perovskite nanolasers. In conjunction with other measurements, a series of rigorous methods for determining the exact resonance mode and obtaining the precise lasing characteristics of perovskite nanolasers are described. By applying these methods, the scaling laws for wire‐type hybrid plasmonic perovskite lasers are successfully determined and an appropriate size is selected for achieving outstanding lasing performance with low threshold power consumption and a high group index. These methods can be applied to nanowire plasmon‐based lasers to advance the development of plasmonic devices. [ABSTRACT FROM AUTHOR]

Nanowire lasers are potential light sources that can be used in photonic integrated circuits (PICs) for inter‐chip optical communication. However, due to the size incompatibility between a nanoscale laser and a micrometer‐scale optical waveguide, their integration within a PIC remains challenging. Here, an in situ growth strategy to directly construct perovskite nanolasers inside the long polymethyl methacrylate (PMMA) fibers is explored. As the perovskite nanolasers are embedded inside the PMMA fibers, effective coupling of lasing light to the PMMA fibers is expected. Furthermore, due to the protection of PMMA coating, the perovskite nanolasers exhibit high robustness in water and demonstrate significant improvement in photostability. Stable single‐mode and polarization operations are obtained at room temperature from the lasers with a low excitation threshold. Hence, these results pave the way to realize ultra‐stable perovskite‐based PICs suitable for inter‐chip optical communication. [ABSTRACT FROM AUTHOR]

Lasing at the nanoscale using plasmonic nanoparticles offers the prospect of strong field concentration, hence strong light−matter interactions, low lasing thresholds, and ultrafast operation. However plasmonic nanoparticles suffer from high dissipative and radiative losses, the latter being rigidly tied to the shape of the nanoparticles and symmetry of their localized plasmon resonant modes. To overcome this limitation, recent theoretical work proposes using direct lasing into dark surface states to construct lasers that conceptually allow for independent implementation of the lasing state and its coherent radiation output. Here, lasing in dark resonant states of a metasurface laser and controllable coherent outcoupling of radiation with the aid of a tightly coupled, weakly radiative metasurface are demonstrated experimentally. The laser is implemented using a thin, low‐loss dielectric film supporting surface mode‐like dark dielectric bound states and the coupling metasurface is composed of small non‐resonant scatterers that controllably but weakly perturb the dark mode and turn it partially bright. Distinct far‐field signatures that can be observed experimentally for both dark and bright lasing are identified and demonstrated. The scalability of this design, here implemented for lasing in the near‐infrared, enables large‐aperture ultra‐thin coherent light sources with controllable emission from the infrared to the visible. [ABSTRACT FROM AUTHOR]

Halide perovskite micro‐ and nanolasers have become a novel platform for efficient generation of coherent emission in the whole visible range. However, the laser emission outcoupling from the perovskite microcrystals faces a number of problems related to large divergence angle, light‐soaking by a substrate, and high losses in the case of coupling with nanowaveguides. Here the perovskite nano‐ and microlasers are proposed to be integrated with a photonic crystal supporting Bloch surface waves (BSWs), which are coupled directly from the perovskite lasers with the efficiency of over 16%. The BSWs exciting at 535‐nm wavelength show high in‐plane directivity, down to 9∘${}^{\circ }$, and long‐propagation length, up to 50 μ$\umu$m. Moreover, a pronounced beam steering effect for the generated laser emission is demonstrated by varying the pumping laser beam position, which provides an additional degree of freedom for in‐plane control of the lasing mode outcoupling. [ABSTRACT FROM AUTHOR]

Micro‐ and nanolasers are emerging optoelectronic components with many properties still to be explored and understood. On the one hand, they make it possible to address fundamental physical questions in the border area between classical physics and quantum physics, on the other hand, they open up new application perspectives in many areas of photonics. This progress report provides an overview of the exciting developments from conventional semiconductor lasers toward nanoscale lasers, whose function relies on increased light–matter interaction in low‐mode‐volume resonators and unconventional gain concepts. The latest advances in the physical understanding of light emission from high‐β lasers, in which a large part of the spontaneous emission is coupled into the laser mode, are highlighted. In the limit of β = 1, this leads to thresholdless lasing and it is shown that quantum optical characterization is required to fully explore the underlying emission processes. In addition, emerging nanolaser concepts based on Fano resonators, topological photonics, and 2D materials are presented. Open questions, future prospects, and application scenarios of high‐β lasers in integrated photonics, quantum nanophotonics, and neuromorphic computing are discussed. [ABSTRACT FROM AUTHOR]

Nearly half a century ago, the German physicist Hermann Haken proved that the laser dynamics could be described, under certain conditions, by the Lorenz equations, the paradigm of deterministic chaos. Unfortunately, its experimental realization has remained elusive for conventional laser materials and cavities mostly due to the extreme pumping conditions and the low cavity quality factors ("bad‐cavity condition") required to achieve Lorenz–Haken (L‐H) self‐pulsing dynamics upon continuous wave excitation. In this paper, it is theoretically proved that dielectric and plasmonic nanolasers, that can naturally fulfill the bad‐cavity condition, may overcome the limitations of macroscopic cavities and make the observation of L‐H instabilities in visible‐IR solid‐state materials become a reality. Remarkably, the adequate choice of active material and cavity design enables the generation of trains of ultrashort pulses in the sub‐ps regime and with MHz–GHz repetition rates without the need of resorting to neither mode‐locking nor Q‐switching techniques. Thus, the results reported in this manuscript unveil a new paradigm in the generation of ultrashort pulses at the nanoscale. [ABSTRACT FROM AUTHOR]

The strong electric and magnetic resonances in dielectric subwavelength structures have enabled unique opportunities for efficient manipulation of light–matter interactions. Besides, the dramatic enhancement of nonlinear light–matter interactions near so‐called bound states in the continuum (BICs) has recently attracted enormous attention due to potential advancements. However, the experimental realizations and the applications of high‐Q factor resonances in dielectric resonances in the visible have thus far been considerably limited. In this work, the interplay of electric and magnetic dipoles in arrays of dielectric nanoresonators is explored. The experimental realization of high‐Q factor resonances in the visible through the collective diffractive coupling of electric and magnetic dipoles is reported. It is also shown that coupling the Rayleigh anomaly of the array with the dipoles of the individual nanoresonators can result in the formation of different types of BICs. The resonances in the visible regime is utilized to achieve lasing action at room temperature with high spatial directionality and low threshold. Finally, multi‐mode, directional lasing is experimentally demonstrated and the BIC‐assisted lasing mode engineering in arrays of dielectric nanoresonators is studied. It is believed that the results enable a new range of applications in flat photonics through realizing on‐chip controllable single and multi‐wavelength micro‐lasers. [ABSTRACT FROM AUTHOR]

A hybrid graphene–insulator–metal (GIM) platform is proposed with a supported surface plasmon polariton (SPP) wave that can be manipulated by breaking Lorentz reciprocity. The ZnO SPP nanowire lasers on the GIM platforms are demonstrated up to room temperature to be actively modulated by applying external current to graphene, which transforms the cavity mode from the standing to propagation wave pattern. With applying 100 mA external current, the laser threshold increases by ≈100% and a 1.2 nm Doppler shift is observed due to the nonreciprocal propagation characteristic. The nanolaser performance also depends on the orientation of the nanowire with respect to the current flow direction. The GIM platform can be a promising platform for integrated plasmonic system functioning laser generation, modulation, and detection. [ABSTRACT FROM AUTHOR]

Nanolasers, with small footprint and ultralow threshold, are promising for applications in data communication, on‐chip optical computing, and optical interconnects. In addition to the microcavity design, the choice of gain material is another critical factor determining the optical performance of nanolasers. 2D materials are widely studied and applied in nanoscale optoelectronic devices due to their exceptional electrical, chemical, thermal, and optical properties caused by the unique layered structures. As emerging materials with unique optical properties, 2D materials are selected as effective gain materials for designing of nanolasers. In this review, the recent advances in nanolasers based on 2D materials are comprehensively addressed. [ABSTRACT FROM AUTHOR]

The ongoing miniaturization of semiconductor lasers has enabled ultra‐low threshold devices and even provided a path to approach thresholdless lasing with linear input–output characteristics. Such nanoscale lasers have initiated a discourse on the origin of the physical mechanisms involved and their boundaries, such as the required photon number, the importance of optimized light confinement in a resonator, and mode‐density enhancement. Here, high‐β metal‐clad coaxial nanolasers, which facilitate thresholdless lasing are investigated. Both the conventional lasing characteristics, as well as the photon statistics of the emitted light at 10 K under continuous wave excitation are experimentally and theoretically investigated. While the former lacks adequate information to determine the threshold to coherent radiation, the latter reveals a finite threshold pump power. The work confirms an important aspect of high‐β lasers, namely that a thresholdless laser does have a finite threshold pump power and must not be confused with a hypothetical zero‐threshold laser. Moreover, the results reveal an excitation power dependent β‐factor which needs to be taken into account to correctly describe the experimental data. [ABSTRACT FROM AUTHOR]

Miniaturized and rationally assembled nanostructures exhibit extraordinarily distinct physical properties beyond their individual units. This review will focus on structured small-scale optical cavities, especially on plasmonic nanoparticle lattices that show unique electromagnetic near fields from collective optical coupling. By harnessing different material systems and structural designs, various light-matter interactions can be engineered, such as nanoscale lasing, nonlinear optics, and exciton-polariton coupling. Key device performance of nanoscale lasers will be discussed, including low power threshold, output tunability, and electrical pump. This review will also cover emerging applications of nanoscale optical cavities in quantum engineering. Structured nanoscale cavities can serve as a scalable platform for integrated photonic circuits and hybrid quantum photonic systems. [ABSTRACT FROM AUTHOR]

Spontaneous photon bursts are observed in the output collected from a mesoscale semiconductor-based laser near the lasing threshold. Their appearance is compared to predictions obtained from Laser Rate Equations and from a Stochastic Laser Simulator. While the latter is capable of predicting the observed large photon bursts, the photon numbers computed by the former produces a noisy trace well below the experimentally detectable limit. We explain the discrepancy between the two approaches on the basis of an incorrect accounting of the onset of stimulated emission by the Rate Equations, which instead are capable of complementing the physical description through topological considerations. [ABSTRACT FROM AUTHOR]

Rubidium lead halides (RbPbX3), an important class of all‐inorganic metal halide perovskites, are attracting increasing attention for photovoltaic applications. However, limited by its lower Goldschmidt tolerance factor t≈0.78, all‐inorganic RbPbBr3 has not been reported. Now, the crystal structure, X‐ray diffraction (XRD) pattern, and band structure of perovskite‐phase RbPbBr3 has now been investigated. Perovskite‐phase RbPbBr3 is unstable at room temperature and transforms to photoluminescence (PL)‐inactive non‐perovskite. The structural evolution and mechanism of the perovskite–non‐perovskite phase transition were clarified in RbPbBr3. Experimentally, perovskite‐phase RbPbBr3 was realized through a dual‐source chemical vapor deposition and annealing process. These perovskite‐phase microspheres showed strong PL emission at about 464 nm. This new perovskite can serve as a gain medium and microcavity to achieve broadband (475–540 nm) single‐mode lasing with a high Q of about 2100. [ABSTRACT FROM AUTHOR]

Rubidium lead halides (RbPbX3), an important class of all‐inorganic metal halide perovskites, are attracting increasing attention for photovoltaic applications. However, limited by its lower Goldschmidt tolerance factor t≈0.78, all‐inorganic RbPbBr3 has not been reported. Now, the crystal structure, X‐ray diffraction (XRD) pattern, and band structure of perovskite‐phase RbPbBr3 has now been investigated. Perovskite‐phase RbPbBr3 is unstable at room temperature and transforms to photoluminescence (PL)‐inactive non‐perovskite. The structural evolution and mechanism of the perovskite–non‐perovskite phase transition were clarified in RbPbBr3. Experimentally, perovskite‐phase RbPbBr3 was realized through a dual‐source chemical vapor deposition and annealing process. These perovskite‐phase microspheres showed strong PL emission at about 464 nm. This new perovskite can serve as a gain medium and microcavity to achieve broadband (475–540 nm) single‐mode lasing with a high Q of about 2100. [ABSTRACT FROM AUTHOR]

Simultaneous suppression of time delay (TD) signature in all observables of optical chaos emission, i.e. in both intensity and phase, has been achieved using two or more semiconductor laser (SL) sources or using two independent polarization components of single vertical cavity surface-emitting laser (VCSEL). In this paper, we examine for the first time the simultaneous TD feature suppression using a single nanolaser of single polarization state. The influence of hybrid optical/electrooptic feedback schemes employing either conventional, phase-conjugate, or grating mirror is evaluated. The concealment of TD signature is then investigated by means of the autocorrelation function. The results reveal the operational regions in each case with well eliminated TD signature in all observables. A secure communications system utilizing chaotic nanolaser is presented. Security analysis for a message transmitted in the form of a colored image is carried out which verifies the immunity of the system against possible statistical, brute force and differential attacks. [ABSTRACT FROM AUTHOR]

Nanoscale semiconductor lasers have been developed recently using either metal, metallo-dielectric, or photonic crystal nanocavities. While the technology of nanolasers is steadily being deployed, their expected performance for on-chip optical interconnects is still largely unknown due to a limited understanding of some of their key features. Specifically, as the cavity size is reduced with respect to the emission wavelength, the stimulated and the spontaneous emission rates are modified, which is known as the Purcell effect in the context of cavity quantum electrodynamics. This effect is expected to have a major impact in the "threshold-less" behavior of nanolasers and in their modulation speed; but its role is poorly understood in practical laser structures, characterized by significant homogeneous and inhomogeneous broadening and by a complex spatial distribution of the active material and cavity field. In this paper, we investigate the role of the Purcell effect in the stimulated and spontaneous emission rates of semiconductor lasers taking into account the carriers' spatial distribution in the volume of the active region over a wide range of cavity dimensions and emitter/cavity linewidths, enabling the detailed modeling of the static and dynamic characteristics of either micro- or nano-scale lasers using single-mode rate-equations analysis. The ultimate limits of scaling down these nanoscale light sources in terms of Purcell enhancement and modulation speed are also discussed showing that the ultrafast modulation properties predicted in nanolasers are a direct consequence of the enhancement of the stimulated emission rate via reduction of the mode volume. [ABSTRACT FROM AUTHOR]

Coherent light sources have been demonstrated based on a wide range of nanostructures, however, little effort has been devoted to probing their underlying coherence properties. Here, we report long-range spatial coherence of lattice plasmon lasers constructed from a periodic array of gold nanoparticles and a liquid gain medium at room temperature. By combining spatial and temporal interferometry, we demonstrate millimeter-scale (~1 mm) spatial coherence and picosecond (~2 ps) temporal coherence. The long-range spatial coherence occurs even without the presence of strong coupling with the lattice plasmon mode extending over macroscopic distances in the lasing regime. This plasmonic lasing system thus provides a platform for understanding the emergence of long-range coherence from collections of nanoscale resonators and points toward novel types of distributed lasing sources. [ABSTRACT FROM AUTHOR]

Metastable structural polymorphs can have superior properties and applications to their thermodynamically stable phases, but the rational synthesis of metastable phases is a challenge. Here, a new strategy for stabilizing metastable phases using surface functionalization is demonstrated using the example of formamidinium lead iodide (FAPbI3) perovskite, which is metastable at room temperature (RT) but holds great promises in solar and light-emitting applications. We show that, through surface ligand functionalization during direct solution growth at RT, pure FAPbI3 in the cubic perovskite phase can be stabilized in nanostructures and thin films at RT without cation or anion alloying. Surface characterizations reveal that long-chain alkyl or aromatic ammonium (LA) cations bind to the surface of perovskite structure. Calculations show that such functionalization reduces the surface energy and plays a dominant role in stabilizing the metastable perovskite phase. Excellent photophysics and optically pumped lasing from the stabilized single-crystal FAPbI3 nanoplates with low thresholds were demonstrated. High-performance solar cells can be fabricated with such directly synthesized stabilized phase-pure FAPbI3 with a lower bandgap. Our results offer new insights on the surface chemistry of perovskite materials and provide a new strategy for stabilizing metastable perovskites and metastable polymorphs of solid materials in general. [ABSTRACT FROM AUTHOR]

Unique features of graphene have motivated the development of graphene-integrated photonic devices. In particular, the electrical tunability of graphene loss enables high-speed modulation of light and tuning of cavity resonances in graphene-integrated waveguides and cavities. However, efficient control of light emission such as lasing, using graphene, remains a challenge. In this work, we demonstrate on/off switching of single- and double-cavity photonic crystal lasers by electrical gating of a monolayer graphene sheet on top of photonic crystal cavities. The optical loss of graphene was controlled by varying the gate voltage Vg, with the ion gel atop the graphene sheet. First, the fundamental properties of graphene were investigated through the transmittance measurement and numerical simulations. Next, optically pumped lasing was demonstrated for a graphene-integrated single photonic crystal cavity at Vg below -0.6 V, exhibiting a low lasing threshold of ∼480 μW, whereas lasing was not observed at Vg above -0.6 V owing to the intrinsic optical loss of graphene. Changing quality factor of the graphene-integrated photonic crystal cavity enables or disables the lasing operation. Moreover, in the double-cavity photonic crystal lasers with graphene, switching of individual cavities with separate graphene sheets was achieved, and these two lasing actions were controlled independently despite the close distance of ∼2.2 μm between adjacent cavities. We believe that our simple and practical approach for switching in graphene-integrated active photonic devices will pave the way toward designing high-contrast and ultracompact photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Semiconductor micro/nano-cavities with high quality factor (Q) and small modal volume provide critical platforms for exploring strong light-matter interactions and quantum optics, enabling further development of coherent and quantum photonic devices. Constrained by exciton binding energy and thermal fluctuation, only a handful of wide-band semiconductors such as ZnO and GaN have stable excitons at room temperature. Metal halide perovskite with cubic lattice and well-controlled exciton may provide solutions. In this work, high-quality single-crystalline cesium lead halide CsPbX3 (X = Cl, Br, I) whispering-gallery-mode (WGM) microcavities are synthesized by vapor-phase van der Waals epitaxy method. The as-grown perovskites show strong emission and stable exciton at room temperature over the whole visible spectra range. By varying the halide composition, multi-color (400-700 nm).WGM excitonic lasing is achieved at room temperature with low threshold (~ 2.0 μJ cm−2) and high spectra coherence (~0.14-0.15 nm). The results advocate the promise of inorganic perovskites towards development of optoelectronic devices and strong light-matter coupling in quantum optics. [ABSTRACT FROM AUTHOR]

Leaky modes are below-cutoff waveguide modes that lose part of their energy to the continuum of radiation modes during propagation. In photonic nanowire lasers, leaky modes have to compete with almost lossless above-cutoff modes and are therefore usually prevented from crossing the lasing threshold. The situation is drastically different in plasmonic nanowire systems where the above-cutoff plasmonic modes are very lossy because of their strong confinement to the metal surface. Due to gain guiding, the threshold gain of the hybrid electric leaky mode does not increase strongly with reduced wire diameter and stays below that of all other modes, making it possible to observe leaky-mode lasing. Plasmonic ZnO nanowire lasers operating in the gain-guided regime could be used as coherent sources of surface plasmon polaritons at the nanoscale or as surface plasmon emitting diodes with an emission angle that depends on the nanowire diameter and the color of the surface plasmon polariton. [ABSTRACT FROM AUTHOR]

Abstract: Novel plasmonic nanolaser structures are proposed by leveraging the efficient guiding properties of hybrid plasmonic modes of nanowire based waveguides. Theoretical investigations reveal that the coupling between the metal nanowire and the high-index dielectric nanostructure with optical gain results in strong field enhancement in the low-index gap region, sufficient modal overlap with the gain medium and low propagation loss, which could enable lasing at the subwavelength scale with low pump threshold. The proposed nanowire-based plasmonic nanolasers are also compatible with standard fabrication technology and could be appealing candidates for active photonic systems. [Copyright &y& Elsevier]

We generalize the semiclassical model of the dipole nanolaser (DNL) based on the Heisenberg-Langevin approach, taking into account spontaneous emission of plasmons into the generation mode, nonlinearity of generation, and noises. We find a 'thresholdless' smooth transition from the spontaneous emission to the stimulated emission and the threshold conditions for such a transition and determine the spectrum of generation and its linewidth. We show that, in spite of the very low quality of the DNL generation mode, the linewidth of a DNL with many M ∼ 10 − 10 emitters decreases, with the pump increase, to quite small values ~ 10 of the width 2Γ of the lasing transition at modest pump rates, about 30 times larger that the decay rate of the emitter upper lasing state. This fact confirms the practical possibilities of realizing DNLs with narrow-line stimulated emission. Otherwise, the linewidth of DNLs with small M ∼ 1 number of emitters is larger than 2Γ and increases with the pump rate. In addition our results on DNLs can be applied to other lasers, such as nanolasers, microlasers, and LEDs for lighting, also with a low-quality cavity and strong spontaneous emission into the generation mode. [ABSTRACT FROM AUTHOR]

A subwavelength plasmonic indented waveguide with an active In GaAsP core is proposed. The characteristics of the gap plasmon mode and gain required for lossless propagation are investigated and analyzed by the finite element method. We numerically calculate the normalized mode areas and percentages of energy confined in In GaAsP and metal for plasmonic nanolaser applications. It is shown that the indentation of the sidewalls has an optimal value for which the lasing threshold gain is minimal. The structure could enable low-threshold subwavelength lasing and applications for optoelectronic integrated circuits. [ABSTRACT FROM AUTHOR]

Abstract: We show that careful preparation conditions enable the preparation of high quality nanoribbons capable of room-temperature lasing covering the complete spectral range from near infrared (NIR) to ultraviolet (UV). Two ternary compound II-VI semiconductors, CdS1−X Se X and Zn Y Cd1−Y S, can be grown on single c-Si substrates to achieve this task. High-resolution transmission electron microscopy and x-ray diffraction showed that the ternary nanoribbons were single phase and single crystal. Room-temperature optical measurements showed that band-gap engineering could be realized via composition modulation in X and Y, with fine tuning of the lasing wavelength via composition changes (ΔX and ΔY) capable of overlapping thermally induced tuning, demonstrating the possibility of continuous tuning in the lasing wavelength throughout the complete 340–710 nm spectral range. We further demonstrate that it is possible to control the spatial composition gradient with sub-mm resolution thus opening the possibility for the fabrication of devices with full spectral optimization. [Copyright &y& Elsevier]

Owing to their ultrahigh optical confinement, plasmonic nanolasers with cavity sizes beyond the diffraction limit of light, are attracting increasing attention for pursuing extreme lasing conditions on nanoscale including ultracompact cavity mode, ultrafast lasing modulation, significantly enhanced light–matter interaction, and Purcell effect. In this review, the recent progress on plasmonic nanolasers from both theoretical and experimental aspects is introduced, with emphases on plasmonic nanolasers with subdiffraction‐limit cavity‐mode confinement. Starting from a theoretical model and key parameters of a plasmonic nanolaser, general concerns of materials for both plasmonic cavities and gain media are summarized. Then, experimental efforts on realization of plasmonic nanolasers with cavity‐mode confinement increased from 1 to 3 dimensions are reviewed, followed by a brief introduction of some novel designs of plasmonic nanolasers and plasmon‐assisted nanolasers. Finally, future prospects and challenges in pursuing extreme lasing conditions of plasmonic nanolasers are discussed, and the identification of lasing threshold in these tiny lasers is revisited. [ABSTRACT FROM AUTHOR]

Lead halide perovskites are considered as very promising photovoltaic materials due to their tunable direct bandgaps, large absorption coefficients, long carrier diffusion lengths, and ultralow trap state densities, etc. With these unique properties, the lead halide perovskites have also demonstrated great potential for use as semiconductor gain materials. In this review, a snapshot on the recent advances of lead halide perovskite micro‐ and nanolasers is given. The dependence of lasing performance on the perovskite dimensionality, crystal size, and operation temperature is systematically discussed. Furthermore, the development of continuous wave (cw) pumped perovskite lasers and lead‐free perovskite lasers is also summarized. In the final section, the challenges and future prospects of metal halide perovskite lasers are provided. These pieces of knowledge would help advancing the development of perovskite on‐chip coherent light sources. [ABSTRACT FROM AUTHOR]

Organic micro/nanolasers hold a promising potential in advancing the fields of photonics and optoelectronics. Recently, great progress has been made in designing and controlling the output characteristics of organic micro/nanolasers, which significantly expands the capabilities and improves the performance of micro/nanolasers. In this Progress Report, the design philosophy, research progress, and further research directions in manipulating the output behaviors of organic micro/nanolasers are presented. A brief introduction to the fundamentals of the organic micro/nanolasers is given with an emphasis on the basic principle for laser output control. Various organic micro/nanolasers with desired output are discussed in detail, including wavelength tunable lasers, multiwavelength lasers, mode controllable lasers, and directional lasers. Special emphasis is put on gaining insight into the structure–property relationship in the controllable organic micro/nanolasers. Finally, future research directions and challenges toward more advanced control strategies of organic micro/nanolasers are provided to give an outlook on this emerging field. [ABSTRACT FROM AUTHOR]

Integration of ultracompact light sources on silicon platforms is regarded as a crucial requirement for various nanophotonic applications. In this work, InGaAs/InP core/shell nanowire array photonic crystal lasers are demonstrated on silicon‐on‐insulator substrates by selective‐area epitaxy. 9 × 9 square‐lattice nanowires forming photonic crystal cavities with a footprint of only 3.0 × 3.0 μm2, and a high Q factor of 23 000 are achieved by forming these nanowires on two‐dimensional silicon gratings. Room‐temperature lasing is observed from a fundamental band‐edge mode at 1290 nm, which is the O‐band of the telecommunication wavelength. Optimized growth templates and effective in‐situ passivation of InGaAs nanowires enable the nanowire array to lase at a low threshold of 200 μJ cm−2, without any signature of heating or degradation above the threshold. These results represent a meaningful step toward ultracompact and monolithic III–V lasers on silicon photonic platforms. InGaAs/InP core/shell nanowire array photonic crystal lasers are demonstrated, which are monolithically integrated on pre‐patterned silicon‐on‐insulator substrates. 9 × 9 square‐lattice nanowire arrays form high‐Q photonic crystal cavities with an extremely small footprint of 3.0 × 3.0 μm2, and room‐temperature lasing is observed from the fundamental band‐edge mode at 1290 nm. [ABSTRACT FROM AUTHOR]