Formation of Lead Halide Perovskite Based Plasmonic Nanolasers and Nanolaser Arrays by Tailoring the Substrate

Ultracompact and Uniform Nanoemitter Array Based on Periodic Scattering

As emerging gain materials, lead halide perovskites have drawn considerable attention in coherent light sources. With the development of patterning and integration techniques, a perovskite laser array has been realized by distributing perovskite microcrystals periodically. Nevertheless, the packing density is limited by the crystal size and the channel gap distance. More importantly, the lasing performance for individual laser units is quite random due to variation of size and crystal quality. Herein an ultracompact perovskite nanoemitter array with uniform emission has been demonstrated. Individual emitters are formed via scattering evanescent components from a shared Fabry-Perot laser, ensuring uniform lasing emission in a unit cell with a side length of 160 nm and lattice constant of 400 nm. And the periodic silicon scatterers do not deteriorate the lasing threshold dramatically. In addition, the surface emitting efficiency increased significantly. The direct integration of a densely packed nanoemitter array with a silicon platform promises high-throughput sensing and high-capacity optical interconnects.

Microstructure-Assisted Wafer-Scale Fabrication of Perovskite Microlaser Arrays

All inorganic lead halide perovskites exhibit fascinating optical and optoelectronic characteristics for on-chip lasing, but the lack of precise control of wafer-scale fabrication for perovskite microstructure arrays restricts their potential applications in on-chip-integrated devices. In this work, a microstructure-template assisted crystallization method is demonstrated via a designed chemical vapor deposition process, achieving the controllable fabrication of homogeneous perovskite micro-hemispheroid (PeMH) arrays spanning the entire surface area of a 4-inch wafer. Benefiting from the low-loss whispering gallery resonance and plasmon-enhanced light-matter interactions in well-confined hybrid cavities, this CsPbX3/Ag (X = Cl, Br) plasmonic microlasers exhibit quite low thresholds below 10 µJ cm-2. Interestingly, these thresholds can be efficiently modulated through the manipulation of plasmonic resonance and electromagnetic field mode in PeMHs owning various diameters. This strategy not only provides a valuable methodology for the large-scale fabrication of perovskite microstructures but also endorses the potential of all-inorganic perovskite nanostructures as promising candidates for on-chip-integrated light sources.

Metal-Halide Perovskite Lasers: Cavity Formation and Emission Characteristics

Hybrid metal-halide perovskites (MHPs) have shown remarkable optoelectronic properties as well as facile and cost-effective processability. With the success of MHP solar cells and light-emitting diodes, MHPs have also exhibited great potential as gain media for on-chip lasers. However, to date, stable operation of optically pumped MHP lasers and electrically driven MHP lasers-an essential requirement for MHP laser's insertion into chip-scale photonic integrated circuits-is not yet demonstrated. The main obstacles include the instability of MHPs in the atmosphere, rudimentary MHP laser cavity patterning methods, and insufficient understanding of emission mechanisms in MHP materials and cavities. This review aims to provide a detailed overview of different strategies to improve the intrinsic properties of MHPs in the atmosphere and to establish an optimal MHP cavity patterning method. In addition, this review discusses different emission mechanisms in MHP materials and cavities and how to distinguish them.

High-Q lasing via all-dielectric Bloch-surface-wave platform

Controlling the propagation and emission of light via Bloch surface waves (BSWs) has held promise in the field of on-chip nanophotonics. BSW-based optical devices are being widely investigated to develop on-chip integration systems. However, a coherent light source that is based on the stimulated emission of a BSW mode has yet to be developed. Here, we demonstrate lasers based on a guided BSW mode sustained by a gain-medium guiding structure microfabricated on the top of a BSW platform. A long-range propagation length of the BSW mode and a high-quality lasing emission of the BSW mode are achieved. The BSW lasers possess a lasing threshold of 6.7 μJ/mm2 and a very narrow linewidth reaching a full width at half maximum as small as 0.019 nm. Moreover, the proposed lasing scheme exhibits high sensitivity to environmental changes suggesting the applicability of the proposed BSW lasers in ultra-sensitive devices.

Advances in the Application of Perovskite Materials

Nowadays, the soar of photovoltaic performance of perovskite solar cells has set off a fever in the study of metal halide perovskite materials. The excellent optoelectronic properties and defect tolerance feature allow metal halide perovskite to be employed in a wide variety of applications. This article provides a holistic review over the current progress and future prospects of metal halide perovskite materials in representative promising applications, including traditional optoelectronic devices (solar cells, light-emitting diodes, photodetectors, lasers), and cutting-edge technologies in terms of neuromorphic devices (artificial synapses and memristors) and pressure-induced emission. This review highlights the fundamentals, the current progress and the remaining challenges for each application, aiming to provide a comprehensive overview of the development status and a navigation of future research for metal halide perovskite materials and devices.

Ultrafast Antisolvent Growth of Single-Crystalline CsPbCl3 Microcavity for Low-Threshold Room Temperature Blue Lasing

All-inorganic perovskite CsPbCl₃ has recently attracted considerable attention due to its great potentials for the development of high-efficiency, deep-blue optoelectronic devices. Particularly, single-crystalline CsPbCl₃ planar microstructures provide good platforms for both fundamental studies and nanophotonics applications from lasers and detectors to amplifiers. In this study, we report an ultrafast antisolvent deposition route to fabricate single-crystalline CsPbCl₃ microplatelets (MPs). The as-grown MPs exhibit uniform morphology, strong emission, and outstanding gain property. Room temperature photoluminescence lasing is realized at 428 nm with a low threshold of 11.5 μJ cm^-2 and high net optical gain up to 720 cm^-1. These findings advance fundamental understanding on the fabrication and optoelectronic applications of low-dimensional CsPbCl₃ perovskite structures.

High-efficiency (>20%) planar carbon-based perovskite solar cells through device configuration engineering

Carbon-based perovskite solar cells (C-PSCs) have attracted widespread research interest because of their excellent stability. However, the power conversion efficiency (PCE) of C-PSCs, especially planar C-PSCs, lags far behind the certified efficiency (25.5%) of metal-based PSCs. The simple architecture of planar C-PSCs imparts stringent requirements for device configuration. In this study, we fabricated high-performance planar C-PSCs through device configuration engineering in terms of the perovskite active layer and carbon electrode. Through the combination of component and additive engineering, the crystallization and absorption profiles of perovskite active layer have been improved, which afforded sufficient photogenerated carriers and decreased nonradiative recombination. Furthermore, the mechanical and physical properties of carbon electrode were evaluated comprehensively to regulate the back-interface contact. Based on the compromise of the flexibility and conductivity of carbon film, an excellent back-interface contact has been formed, which promoted fast interface charge transfer, thereby decreasing interface recombination and improving carrier collection efficiency. Finally, the as-prepared devices achieved a remarkable PCE of up to 20.04%, which is a record-high value for planar C-PSCs. Furthermore, the as-prepared devices exhibited excellent long-term stability. After storage for 1000 h at room temperature and 25% relative humidity without encapsulation, the as-prepared device retained 94% of its initial performance.

Plasmonic-perovskite solar cells, light emitters, and sensors

The field of plasmonics explores the interaction between light and metallic micro/nanostructures and films. The collective oscillation of free electrons on metallic surfaces enables subwavelength optical confinement and enhanced light-matter interactions. In optoelectronics, perovskite materials are particularly attractive due to their excellent absorption, emission, and carrier transport properties, which lead to the improved performance of solar cells, light-emitting diodes (LEDs), lasers, photodetectors, and sensors. When perovskite materials are coupled with plasmonic structures, the device performance significantly improves owing to strong near-field and far-field optical enhancements, as well as the plasmoelectric effect. Here, we review recent theoretical and experimental works on plasmonic perovskite solar cells, light emitters, and sensors. The underlying physical mechanisms, design routes, device performances, and optimization strategies are summarized. This review also lays out challenges and future directions for the plasmonic perovskite research field toward next-generation optoelectronic technologies.

Directional Lasing from Nanopatterned Halide Perovskite Nanowire

Halide perovskite nanowire-based lasers have become a powerful tool for modern nanophotonics, being deeply subwavelength in cross-section and demonstrating low-threshold lasing within the whole visible spectral range owing to the huge gain of material even at room temperature. However, their emission directivity remains poorly controlled because of the efficient outcoupling of radiation through their subwavelength facets working as pointlike light sources. Here, we achieve directional lasing from a single perovskite CsPbBr₃ nanowire by imprinting a nanograting on its surface, which provides stimulated emission outcoupling to its vertical direction with a divergence angle around 2°. The nanopatterning is carried out by the high-throughput laser ablation method, which preserves the luminescent properties of the material that is typically deteriorated after processing via conventional lithographic approaches. Moreover, nanopatterning of the perovskite nanowire is found to decrease the number of the lasing modes with a 2-fold increase of the quality factor of the remaining modes.

Submicrometer perovskite plasmonic lasers at room temperature

Plasmonic lasers attracted interest for their ability to generate coherent light in mode volume smaller than the diffraction limit of photonic lasers. While nanoscale devices in one or two dimensions were demonstrated, it has been difficult to achieve plasmonic lasing with submicrometer cavities in all three dimensions. Here, we demonstrate submicrometer-sized, plasmonic lasers using cesium-lead-bromide perovskite (CsPbBr3) crystals, as small as 0.58 μm by 0.56 μm by 0.32 μm (cuboid) and 0.79 μm by 0.66 μm by 0.18 μm (plate), on polymer-coated gold substrates at room temperature. Our experimental and simulation data obtained from more than 100 plasmonic and photonic devices showed that enhanced optical gain by the Purcell effect, large spontaneous emission factor, and high group index are key elements to efficient plasmonic lasing. The results shed light on the three-dimensional miniaturization of plasmonic lasers.

Oriented Halide Perovskite Nanostructures and Thin Films for Optoelectronics

Oriented semiconductor nanostructures and thin films exhibit many advantageous properties, such as directional exciton transport, efficient charge transfer and separation, and optical anisotropy, and hence these nanostructures are highly promising for use in optoelectronics and photonics. The controlled growth of these structures can facilitate device integration to improve optoelectronic performance and benefit in-depth fundamental studies of the physical properties of these materials. Halide perovskites have emerged as a new family of promising and cost-effective semiconductor materials for next-generation high-power conversion efficiency photovoltaics and for versatile high-performance optoelectronics, such as light-emitting diodes, lasers, photodetectors, and high-energy radiation imaging and detectors. In this Review, we summarize the advances in the fabrication of halide perovskite nanostructures and thin films with controlled dimensionality and crystallographic orientation, along with their applications and performance characteristics in optoelectronics. We examine the growth methods, mechanisms, and fabrication strategies for several technologically relevant structures, including nanowires, nanoplates, nanostructure arrays, single-crystal thin films, and highly oriented thin films. We highlight and discuss the advantageous photophysical properties and remarkable performance characteristics of oriented nanostructures and thin films for optoelectronics. Finally, we survey the remaining challenges and provide a perspective regarding the opportunities for further progress in this field.

Whispering Gallery Mode Lasing from Perovskite Polygonal Microcavities via Femtosecond Laser Direct Writing

Organic-inorganic halide perovskites have excellent intrinsic properties, such as long carrier lifetime, high photoluminescence quantum yield, and high gain, in whispering gallery mode (WGM) cavities by facile vapor self-assembly or solution process, which make them competitive for high-performance microlasers. However, the performance of perovskite-based microlasers is severely limited by the fabrication of microcavities, which results in poor reproducibility and uncontrolled morphology. Herein, we explore a reproducible method which combined thermal co-evaporation with femtosecond (fs) laser direct writing for formamidinium lead iodide (FAPbI₃) perovskite polygon-shaped WGM microcavities. The microlasers pumped with the fs laser had a low threshold of 4.0-12.3 μJ/cm² and narrow full width at half-maximum of 0.62-1.05 nm. Moreover, size- and shape-dependent WGM lasing performances are also investigated systematically. The results prove that FAPbI₃ polygonal microcavities can serve as promising WGM lasers and have great potential for practical optoelectronic applications.

Light Engineering in Nanometer Space

Significant advances have been made in photonic integrated circuit technology, similar to the development of electronic integrated circuits. However, the miniaturization of cavity resonators, which are the essential components of photonic circuits, still requires considerable improvement. Over the past decades, various optical cavities have been utilized to implement next-generation light sources in photonic circuits with low energy, high data traffic, and integrable physical sizes. Nevertheless, it has been difficult to reduce the size of most commercialized cavities beyond the diffraction limit while maintaining high performance. Herein, recent advancements in subwavelength metallic cavities that can improve performance, even with the use of lossy plasmonic modes, are reviewed. The discussion is divided in three parts according to light engineering methods: subwavelength metal-clad cavities engineered using intermediate dielectric cladding; implementation of plasmonic cavities and waveguides using plasmonic crystals; and development of deep-subwavelength plasmonic waveguides and cavities using geometric engineering. A direction for further developments in photonic integrated circuit technology is also discussed, along with its practical application.

Large-Scale Thin CsPbBr3 Single-Crystal Film Grown on Sapphire via Chemical Vapor Deposition: Toward Laser Array Application

Single-crystal perovskites with excellent photophysical properties are considered to be ideal materials for optoelectronic devices, such as lasers, light-emitting diodes and photodetectors. However, the growth of large-scale perovskite single-crystal films (SCFs) with high optical gain by vapor-phase epitaxy remains challenging. Herein, we demonstrated a facile method to fabricate large-scale thin CsPbBr₃ SCFs (∼300 nm) on the c-plane sapphire substrate. High temperature is found to be the key parameter to control low reactant concentration and sufficient surface diffusion length for the growth of continuous CsPbBr₃ SCFs. Through the comprehensive study of the carrier dynamics, we clarify that the trapped-related exciton recombination has the main effect under low carrier density, while the recombination of excitons and free carriers coexist until free carriers plays the dominate role with increasing carrier density. Furthermore, an extremely low-threshold (∼8 μJ cm^-2) amplified spontaneous emission was achieved at room temperature due to the high optical gain up to 1255 cm^-1 at a pump power of 20 times threshold (∼20 P_th). A microdisk array was prepared using a focused ion beam etching method, and a single-mode laser was achieved on a 3 μm diameter disk with the threshold of 1.6 μJ cm^-2. Our experimental results not only present a versatile method to fabricate large-scale SCFs of CsPbBr₃ but also supply an arena to boost the optoelectronic applications of CsPbBr₃ with high performance.

Plasmonic Nanolasers in On-Chip Light Sources: Prospects and Challenges

The plasmonic nanolaser is a class of lasers with the physical dimensions free from the optical diffraction limit. In the past decade, progress in performance, applications, and mechanisms of plasmonic nanolasers has increased dramatically. We review this advance and offer our prospectives on the remaining challenges ahead, concentrating on the integration with nanochips. In particular, we focus on the qualifications for electrical pumping, energy consumption, and ultrafast modulation. At last, we evaluate the strategies for on-chip source construction design and further threshold reduction to achieve a long-term room-temperature electrically pumped plasmonic nanolaser, the ultimate goal toward practical applications.

Lead halide perovskite vortex microlasers

Lead halide perovskite microlasers have been very promising for versatile optoelectronic applications. However, most perovskite microlasers are linearly polarized with uniform wavefront. The structured laser beams carrying orbital angular momentum have rarely been studied and the applications of perovskites in next-generation optical communications are thus hindered. Herein, we experimentally demonstrate the perovskite vortex microlasers with highly directional outputs and well−controlled topological charges. High quality gratings have been experimentally fabricated in perovskite film and the subsequent vertical cavity surface emitting lasers (VCSELs) with divergent angles of 3^o are achieved. With the control of Archimedean spiral gratings, the wavefront of the perovskite VCSELs has been switched to be helical with topological charges of q = −4 to 4. This research is able to expand the potential applications of perovskite microlasers in hybrid integrated photonic networks, as well as optical computing.

Integration of III-V semiconductor microlasers into modern Si or Si3N4 based photonic integrated circuits remains a challenge. Here, the authors demonstrate a perovskite vortex microlaser with highly directional outputs and well-controlled topological charges that is highly compatible with most materials.

Perovskite Quantum Dot Lasing in a Gap-Plasmon Nanocavity with Ultralow Threshold

Lead halide perovskite materials have recently received considerable attention for achieving an economic and tunable laser owing to their solution-processable feature and promising optical properties. However, most reported perovskite-based lasers operate with a large lasing-mode volume, resulting in a high lasing threshold due to the inefficient coupling between the optical gain medium and cavity. Here, we demonstrate a continuous-wave nanolasing from a single lead halide perovskite (CsPbBr₃) quantum dot (PQD) in a plasmonic gap-mode nanocavity with an ultralow threshold of 1.9 Wcm^-2 under 120 K. The calculated ultrasmall mode volume (∼0.002 λ³) with a z-polarized dipole and the significantly large Purcell enhancement at the corner of the nanocavity inside the gap dramatically enhance the light-matter interaction in the nanocavity, thus facilitating lasing. The demonstration of PQD nanolasing with an ultralow-threshold provides an approach for realizing on-chip electrically driven lasing and integration into on-chip plasmonic circuitry for ultrafast optical communication and quantum information processing.

Ten years of spasers and plasmonic nanolasers

Ten years ago, three teams experimentally demonstrated the first spasers, or plasmonic nanolasers, after the spaser concept was first proposed theoretically in 2003. An overview of the significant progress achieved over the last 10 years is presented here, together with the original context of and motivations for this research. After a general introduction, we first summarize the fundamental properties of spasers and discuss the major motivations that led to the first demonstrations of spasers and nanolasers. This is followed by an overview of crucial technological progress, including lasing threshold reduction, dynamic modulation, room-temperature operation, electrical injection, the control and improvement of spasers, the array operation of spasers, and selected applications of single-particle spasers. Research prospects are presented in relation to several directions of development, including further miniaturization, the relationship with Bose-Einstein condensation, novel spaser-based interconnects, and other features of spasers and plasmonic lasers that have yet to be realized or challenges that are still to be overcome.

Light-Emitting Nanophotonic Designs Enabled by Ultrafast Laser Processing of Halide Perovskites

Nanophotonics based on resonant nanostructures and metasurfaces made of halide perovskites have become a prospective direction for efficient light manipulation at the subwavelength scale in advanced photonic designs. One of the main challenges in this field is the lack of large-scale low-cost technique for subwavelength perovskite structures fabrication preserving highly efficient luminescence. Here, unique properties of halide perovskites addressed to their extremely low thermal conductivity (lower than that of silica glass) and high defect tolerance to apply projection femtosecond laser lithography for nanofabrication with precise spatial control in all three dimensions preserving the material luminescence efficiency are employed. Namely, with CH₃ NH₃ PbI₃ perovskite highly ordered nanoholes and nanostripes of width as small as 250 nm, metasurfaces with periods less than 400 nm, and nanowire lasers as thin as 500 nm, corresponding to the state-of-the-art in multistage expensive lithographical methods are created. Remarkable performance of the developed approach allows to demonstrate a number of advanced optical applications, including morphology-controlled photoluminescence yield, structural coloring, optical- information encryption, and lasing.

Full-Spectrum Analysis of Perovskite-Based Surface Plasmon Nanolasers

We systematically studied the characteristics of hybrid perovskite-based surface plasmon nanolasers. If one changes the anion composition of perovskites, the emission wavelength can be easily tuned. We conducted in full-spectrum modeling that featured hybrid perovskite nanowires placed on different SiO₂-coated metallic (Au, Ag, and Al) plates. The proposed nanocavities that supported plasmonic gap modes exhibited distinguished properties of nanolasers, such as low-transparency threshold-gain and low lasing threshold. The corresponding experimental results for the MAPbBr₃ nanolaser on Ag revealed the low-threshold operation. These superior features were attributed to enhanced light-matter interaction with strong coupling. Therefore, the proposed scheme, integrated with hybrid perovskite as gain material, provides an excellent platform for nanoscale plasmon lasing in the visible to near-infrared spectra.

Materials chemistry and engineering in metal halide perovskite lasers

The invention and development of the laser have revolutionized science, technology, and industry. Metal halide perovskites are an emerging class of semiconductors holding promising potential in further advancing the laser technology. In this Review, we provide a comprehensive overview of metal halide perovskite lasers from the viewpoint of materials chemistry and engineering. After an introduction to the materials chemistry and physics of metal halide perovskites, we present diverse optical cavities for perovskite lasers. We then comprehensively discuss various perovskite lasers with particular functionalities, including tunable lasers, multicolor lasers, continuous-wave lasers, single-mode lasers, subwavelength lasers, random lasers, polariton lasers, and laser arrays. Following this a description of the strategies for improving the stability and reducing the toxicity of metal halide perovskite lasers is provided. Finally, future research directions and challenges toward practical technology applications of perovskite lasers are provided to give an outlook on this emerging field.

Resonance-enhanced three-photon luminesce via lead halide perovskite metasurfaces for optical encoding

Lead halide perovskites have emerged as promising materials for photovoltaic and optoelectronic devices. However, their exceptional nonlinear properties have not been fully exploited in nanophotonics yet. Herein we fabricate methyl ammonium lead tri-bromide perovskite metasurfaces and explore their internal nonlinear processes. While both of third-order harmonic generation and three-photon luminescence are generated, the latter one is less affected by the material loss and has been significantly enhanced by a factor of 60. The corresponding simulation reveals that the improvement is caused by the resonant enhancement of incident laser. Interestingly, such kind of resonance-enhanced three-photon luminescence holds true for metasurfaces with a small period number of 4, enabling promising applications of perovskite metasurface in high-resolution nonlinear color nanoprinting and optical encoding. The encoded information ‘NANO’ is visible only when the incident laser is on-resonance. The off-resonance pumping and the single-photon excitation just produce a uniform dark or photoluminescence background.

Lead halide perovskites attract high interest as semiconductor materials but their exceptional nonlinear properties have not been fully exploited. Here Fan et al. demonstrate third-order harmonic generation and 60-fold enhanced three-photon luminescence, enabling optical encoding applications.

Low threshold room-temperature UV surface plasmon polariton lasers with ZnO nanowires on single-crystal aluminum films with Al2O3 interlayers

ZnO is one of the most promising optical gain media and allows lasing in ZnO nanowires at room temperature. Plasmonic lasers are potentially useful in applications in biosensing, photonic circuits, and high-capacity signal processing. In this work, we combine ZnO nanowires and single-crystalline aluminum films to fabricate Fabry–Perot type surface plasmon polariton (SPP) lasers to overcome the diffraction limit of conventional optics. High quality ZnO nanowires were synthesized by a vapor phase transport process via catalyzed growth. The ZnO nanowires were placed on a single-crystalline Al film grown by molecular beam epitaxy with an interlayer Al₂O₃ deposited by atomic layer deposition. The plasmonic laser is of metal-oxide-semiconductor (MOS) structure, compatible with silicon device processing. An optimal thickness of atomic layer deposited Al₂O₃ layer can lead to a low lasing threshold, 6.27 MW cm⁻², which is 3 times and 12 times lower than that of previous reports for ZnO/Al and Zno/Al₂O₃/Al plasmonic lasers, respectively, owing to low materials loss. Both the thickness and quality of insulating layers were found to critically influence the lasing threshold of the SPP nanolasers in the subwavelength regime. The simulation results also manifest the importance of the quality of the dielectric interlayer.

Ultralow threshold room-temperature UV surface plasmon polariton lasers using ZnO nanowires on single-crystal aluminum films with Al₂O₃ interlayers.

Single-Mode Lasing from Imprinted Halide-Perovskite Microdisks

Halide-perovskite microlasers have demonstrated fascinating performance owing to their low-threshold lasing at room temperature and low-cost fabrication. However, being synthesized chemically, controllable fabrication of such microlasers remains challenging, and it requires template-assisted growth or complicated nanolithography. Here, we suggest and implement an approach for the fabrication of microlasers by direct laser ablation of a thin film on glass with donut-shaped femtosecond laser beams. The fabricated microlasers represent MAPbBr _xI _y microdisks with 760 nm thickness and diameters ranging from 2 to 9 μm that are controlled by a topological charge of the vortex beam. As a result, this method allows one to fabricate single-mode perovskite microlasers operating at room temperature in a broad spectral range (550-800 nm) with Q-factors up to 5500. High-speed fabrication and reproducibility of microdisk parameters, as well as a precise control of their location on a surface, make it possible to fabricate centimeter-sized arrays of such microlasers. Our finding is important for direct writing of fully integrated coherent light sources for advanced photonic and optoelectronic circuitry.

All-optical control of lead halide perovskite microlasers

Lead halide perovskites based microlasers have recently shown their potential in nanophotonics. However, up to now, all of the perovskite microlasers are static and cannot be dynamically tuned in use. Herein, we demonstrate a robust mechanism to realize the all-optical control of perovskite microlasers. In lead halide perovskite microrods, deterministic mode switching takes place as the external excitation is increased: the onset of a new lasing mode switches off the initial one via a negative power slope, while the main laser characteristics are well kept. This mode switching is reversible with the excitation and has been explained via cross-gain saturation. The modal interaction induced mode switching does not rely on sophisticated cavity designs and is generic in a series of microlasers. The switching time is faster than 70 ps, extending perovskite microlasers to previously inaccessible areas, e.g., optical memory, flip-flop, and ultrafast switches etc.

Inorganic and Hybrid Perovskite Based Laser Devices: A Review

Inorganic and organic-inorganic (hybrid) perovskite semiconductor materials have attracted worldwide scientific attention and research effort as the new wonder semiconductor material in optoelectronics. Their excellent physical and electronic properties have been exploited to boost the solar cells efficiency beyond 23% and captivate their potential as competitors to the dominant silicon solar cells technology. However, the fundamental principles in Physics, dictate that an excellent direct band gap material for photovoltaic applications must be also an excellent light emitter candidate. This has been realized for the case of perovskite-based light emitting diodes (LEDs) but much less for the case of the respective laser devices. Here, the strides, exclusively in lasing, made since 2014 are presented for the first time. The solution processability, low temperature crystallization, formation of nearly defect free, nanostructures, the long range ambipolar transport, the direct energy band gap, the high spectral emission tunability over the entire visible spectrum and the almost 100% external luminescence efficiency show perovskite semiconductors’ potential to transform the nanophotonics sector. The operational principles, the various adopted material and laser configurations along the future challenges are reviewed and presented in this paper.

Ultra-high light confinement and ultra-long propagation distance design for integratable optical chips based on plasmonic technology

The ever-increasing demand for faster speed, broader bandwidth, and lower energy consumption of on-chip processing has motivated the use of light instead of electrons in functional communication components. However, considerable scattering loss severely affects the performance of nanoscale photonic devices when their physical sizes are smaller than the wavelength of light. Due to the tight localization of electromagnetic energy, plasmonic waveguides that work at visible and infrared wavebands have provided a solution for the optical diffraction limit problem and thus enable downscaling of optical circuits and chips at the nanoscale. However, due to the fundamental trade-off between propagation distance and light confinement, plasmonic waveguides, including conventional hybrid plasmonic waveguides (HPWGs), cannot be used as high performance integratable optical devices all the time. To solve this problem, a novel hybrid plasmonic waveguide is proposed where a hybrid metal-ridge-slot structure based on a two-dimensional (2D) transition metal dichalcogenide is embedded into two identical cylindrical dielectric waveguides. Benefiting from both the loss-less slot region and the high-index difference between the ultra-thin 2D material and the slot region, a 10 times longer propagation length and 100 times smaller mode area than the traditional HPWG are achieved at the telecommunication band. By removing the monolayer transition metal dichalcogenide, our designed waveguide shows a higher propagation length that is at least two orders of magnitude larger than its traditional HPWG counterpart. Therefore, the proposed hybridization waveguiding approach paves the way toward truly high-performance and deep-subwavelength integratable optical circuits and chips in the future.

Mass-Manufactural Lanthanide-Based Ultraviolet B Microlasers

Lanthanide (Ln³⁺ )-based ultraviolet B (UVB) microlasers are highly desirable for diagnostics and phototherapy. Despite their progress, the potential applications of UVB microlasers are strongly hindered by their low optical gain, weak light confinements, and poor device repeatability. Herein, a novel all-in-one approach to solve the above limitations and realize mass-manufactural UVB microlasers is reported. The gain coefficient at 289 nm is improved from two aspects, i.e., the enhanced absorption via LiYbF₄ :Tm(1mol%)@LiYbF₄ @LiLuF₄ core-shell-shell nanocrystals and the suppression of competitive ultraviolet emissions. Consequently, by spin-coating the solution onto a patterned SiO₂ substrate, high-quality Ln³⁺ -based microdisks are formed by self-assembly on each SiO₂ pillar and UVB whispering-gallery-mode lasers are realized. The resulted lasing threshold is an order of magnitude smaller than the shortest deep-ultraviolet emission at 310.5 nm. Importantly, the lasing wavelengths and mode numbers of UVB lasers are highly controllable and repeatable, making them suitable for mass production for the first time.

Applications of nanolasers

Nanolasers generate coherent light at the nanoscale. In the past decade, they have attracted intense interest, because they are more compact, faster and more power-efficient than conventional lasers. Thanks to these capabilities, nanolasers are now an emergent tool for a variety of practical applications. In this Review, we explain the intrinsic merits of nanolasers and assess recent progress on their applications, particularly for optical interconnects, near-field spectroscopy and sensing, optical probing for biological systems and far-field beam synthesis through near-field eigenmode engineering. We highlight the scientific and engineering challenges that remain for forging nanolasers into powerful tools for nanoscience and nanotechnology.

Room-Temperature Continuous-Wave Operation of Organometal Halide Perovskite Lasers

Solution-processed organic-inorganic lead halide perovskites have recently emerged as promising gain media for tunable semiconductor lasers. However, optically pumped continuous-wave lasing at room temperature, a prerequisite for a laser diode, has not been realized so far. Here, we report lasing action in a surface-emitting distributed feedback methylammonium lead iodide (MAPbI₃) perovskite laser on a silicon substrate at room temperature under continuous-wave optical pumping. This outstanding performance is achieved because of the ultralow lasing threshold of 13 W/cm², which is enabled by thermal nanoimprint lithography that directly patterns perovskite into a high- Q cavity with large mode confinement, while at the same time, it improves perovskite's emission characteristics. Our results represent a major step toward electrically pumped lasing in organic and thin-film materials as well as the insertion of perovskite lasers into photonic integrated circuits for applications in optical computing, sensing, and on-chip quantum information.

Excitonic phenomena in perovskite quantum-dot supercrystals

Quantum confinement and collective excitations in perovskite quantum-dot (QD) supercrystals offer multiple benefits to the light emitting and solar energy harvesting devices of modern photovoltaics. Recent advances in the fabrication technology of low dimensional perovskites has made the production of such supercrystals a reality and created a high demand for the modelling of excitonic phenomena inside them. Here we present a rigorous theory of Frenkel excitons in lead halide perovskite QD supercrystals with a square Bravais lattice. The theory shows that such supercrystals support three bright exciton modes whose dispersion and polarization properties are controlled by the symmetry of the perovskite lattice and the orientations of QDs. The effective masses of excitons are found to scale with the ratio of the superlattice period and the number of QDs along the supercrystal edge, allowing one to fine-tune the electro-optical response of the supercrystals as desired for applications. We also calculate the conductivity of perovskite QD supercrystals and analyze how it is affected by the optical generation of the three types of excitons. This paper provides a solid theoretical basis for the modelling of two- and three-dimensional supercrystals made of perovskite QDs and the engineering of photovoltaic devices with superior optoelectronic properties.