Search

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]

Quantum well nanolasers usually show single‐mode lasing, as gain saturation suppresses emissions in other modes. In contrast, for whispering gallery mode microdisk lasers with GaN quantum wells as active material, above threshold multimode laser emission is observed. This intriguing emission feature is manifested in the fact that several modes simultaneously show the characteristic kink in the input–output curve at the onset of lasing. A quantum theory for nanolasers is used to support the experimental finding and to analyze this behavior in the presence of gain saturation. Coupling effects between neighboring modes are identified as the origin of multimode lasing, which initiate photon exchange between modes via population pulsations similar to classical wave‐mixing effects. A reduction of this type of mode coupling with increasing mode spacing is demonstrated. The results can pave the way for multimode application of nanolasers in integrated photonic circuits. [ABSTRACT FROM AUTHOR]

Applications for an antenna structure produced with additive manufacturing technology are numerous and promising. This study focuses explicitly on utilizing micro‐laser sintering (MLS) three‐dimensional (3D) printing technology to fabricate two rectangular horn antennas identical to a standard Pasternack® horn antenna, making the fabrication straightforward. The objective is to investigate how surface roughness affects antenna performance in a frequency range of 18 to 26.5 GHz. One antenna is polished and the other is left untouched, resulting in surface roughness of 4 and 6 µm, respectively, measured using a profilometer. Then, a vector network analyzer was used to assess their reflection coefficient, transmission characteristics, and radiation pattern and determine gains of 8.83 and 9.14 dBi for the polished and unpolished antennas, respectively. The study finds that both polished and unpolished antennas perform similarly, and their characteristics closely resembling simulated and standard antennas. Finally, the performance of the MLS‐printed metallic antennas is compared with horn antennas created using other 3D printing techniques. It reveals that the MLS‐printed metallic structures exhibit better performance, indicating that the MLS technology has great potential to print 3D metallic electromagnetic designs. [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]

Engineering of organic single crystal toward controllable and aligned patterns at microscale is crucial to the realization of highly integrated organic photonic devices and optoelectronics. However, precise positioning and controllable morphology of crystal structures is still challenging due to the strict conditions for crystal growth. In this paper, a solution based crystal regulation strategy with the assistance of template‐constrained growth method and femtosecond laser processing technology is developed to prepare aligned crystalline microribbon arrays. Simple solvent evaporation results in the random distribution and orientation of self‐assembled crystalline microribbons while it tends to form highly crystalline and orderly microribbon arrays assisted by the confined template microchannels. The large‐scale microribbon array can be fabricated as organic photodetectors with sensitive and fast response under 405 nm illumination. By virtue of the femtosecond laser processing technique, the microribbon arrays are precisely processed into a series of crystal subunits and each microribbon subunit can function as an individual microcavity resonator to produce stable, high‐quality organic laser. The facile solution based template‐constrained self‐assembly and femtosecond laser processing method provide novel strategies to generate highly oriented and controllable crystal structures for the potential applications in integrated organic lasers and optoelectronics. [ABSTRACT FROM AUTHOR]

Luminescent supraparticles of colloidal semiconductor nanocrystals can act as microscopic lasers and are hugely attractive for biosensing, imaging, and drug delivery. However, biointerfacing these to increase functionality while retaining their main optical properties remains an unresolved challenge. Here, we propose and demonstrate red-emitting, silica-coated CdSxSe1−x/ZnS colloidal quantum dot supraparticles functionalized with a biotinylated photocleavable ligand. The success of each step of the synthesis is confirmed by scanning electron microscopy, energy dispersive X-ray and Fourier transform infrared spectroscopy, ζ-potential, and optical pumping measurements. The capture and release functionality of the supraparticle system is proven by binding to a neutravidin functionalized glass slide and subsequently cleaving off after UV-A irradiation. The biotinylated supraparticles still function as microlasers; e.g., a 9 μm diameter supraparticle has oscillating modes around 625 nm at a threshold of 58 mJ/cm2. This work is a first step toward using supraparticle lasers as enhanced labels for bionano applications. [ABSTRACT FROM AUTHOR]

The laser generation characteristics of microdisc lasers with optically coupled waveguide operating in continuous wave mode at elevated temperatures are investigated. Laser generation and waveguide effect at temperatures up to 92.5°C were demonstrated. The measured characteristic temperature of microlasers was 65 K in the range of 25–92.5°C. [ABSTRACT FROM AUTHOR]

The ability of particles to "tunnel" through potential energy barriers is a purely quantum phenomenon. A classical particle in a symmetric double-well potential, with energy below the potential barrier, will be trapped on one side of the potential well. A quantum particle, however, can sit on both sides, in either a symmetric state or an antisymmetric state. An analogous phenomenon occurs in conservative classical systems with two degrees of freedom and no potential barriers. If only the energy is conserved, the phase space will be a mixture of regular "islands" embedded in a sea of chaos. Classically, a particle sitting in one regular island cannot reach another symmetrically located regular island when the islands are separated by chaos. However, a quantum particle can sit on both regular islands, in symmetric and antisymmetric states, due to chaos-assisted tunneling. Here, we give an overview of the theory and recent experimental observations of this phenomenon. [ABSTRACT FROM AUTHOR]

The large size of lasers limits their applications in confined spaces, such as in biosensing and in vivo brain tissue imaging. In this regard, micron-sized lasers have been developed. They exhibit great potential for biological detecting, remote sensing, and depth tracking due to their small sizes, sensitive properties of their spectral fingerprints, and flexible positional modulation in the microenvironment. Lanthanide-based luminescent materials that possess long excited-state lifetime, narrow emission bandwidth, and upconversion behaviors are promising as gain mediums for novel microlasers. In addition, lanthanide-based microlasers could be generated under natural ambient conditions with pumped or continuous light sources, which significantly promotes the practical applications of microlasers. Recent progress in the design, synthesis, and biomedical applications of lanthanide-based microlasers has been outlined in this review. Lanthanide ions doped and upconverted lanthanide-based microlasers are highlighted, which exhibit advantageous structures, miniaturized dimensions, and high lasing performance. The applications of lanthanide-based microlasers are further discussed, the upconverted microlasers show great advantages for biological applications owing to their tunable excitation and emission characteristics and excellent environmental stability. Moreover, perspectives and challenges in the field of lanthanide-based microlasers are presented. [ABSTRACT FROM AUTHOR]

Photonic materials based on metal halide perovskites undergo rapid development owing to their unique optical properties and facile synthesis. Concurrently, there is also a growing interest in integrated photonics that can combine several elements on one chip. Nowadays technologies of integrated photonics are based on the traditional mask lithography combined with physical or chemical deposition methods. In this study, the possibility of facile fabrication of a simple pair of photonic elements is addressed, such as a microresonator with an outcoupling waveguide by means of inkjet printing on a glass substrate covered by a layer of polydimethylsiloxane (PDMS). The printed laser has revealed an appreciably high laser emission with a Q‐factor of 3300 and a threshold excitation fluence of 34 µJ·cm−2. The outcoupling waveguide has demonstrated the capability to transfer a reasonable part of the emitted radiation. The experimental results with a numerical simulation based on an appropriate physical model are also rationalized. Thus, the study points out a perspective for integrated photonics to be possibly implemented with this relatively cheap, flexible, and scalable fabrication method. [ABSTRACT FROM AUTHOR]

Dyes with aggregation‐induced emission (AIE) properties have gained interest due to their bright luminescence in solid‐state aggregates. While fluorescence from AIE dyes is widely exploited, relatively little is known about aggregation‐induced stimulated emission. Here, stimulated emission of tetraphenylethene (TPE)‐based organoboron AIE dyes, TPEQBN, in thin films and in microcavity lasers is investigated. Using femtosecond pump–probe spectroscopy, gain coefficients up to 230 cm−1 at 500 nm are measured. Using rate equations, concentration‐ and pump‐dependent gain dynamics as well as laser build‐up dynamics are analyzed. During laser oscillation, radiative stimulated emission allows high instantaneous quantum yield greater than 90% to be achieved. Solid‐state microspheres made of 100% AIE dyes are fabricated via microfluidic emulsion and solvent evaporation method. Coupled with high gain and high refractive index of 1.76, microspheres as small as 2 µm in diameter show lasing by nanosecond pumping with a threshold of ≈10 pJ µm–2. Polymer coated, but not bare, microspheres are internalized by live cells and generate narrowband cavity‐mode emission from within the cytoplasm. This work shows the potential of AIE dyes as laser materials. [ABSTRACT FROM AUTHOR]

Multiplexed, specific, and sensitive detection of antigens is critical for the rapid and accurate diagnosis of disease and the informed development of personalized treatment plans. Here, it is shown that polymer microsphere lasers can be used as photonic sensors to monitor and quantify direct surface binding of biomolecules via changes in the refractive index. The unique spectral signature of each individual laser can be used to find their size and effective refractive index which adds a new encoding dimension when compared to conventional fluorescent beads. Antibody‐functionalized microlasers selectively detect protein binding, as demonstrated for Immunoglobulin G and C‐reactive protein, and have the ability to resolve different stages of the multilayer surface modification. Moreover, by continuously monitoring single lasers, the possibility of real‐time monitoring of binding dynamics between antigens in solution phase and the immobilized antibodies is demonstrated. For multiplexed detection, the microlasers are employed in a flow cytometer configuration, with fast spectral detection and identification of microlasers with and without antigen binding. It is envisioned that by combining microlasers with well‐established surface modification chemistries and flow geometries, the multiplexing ability of microbead immunoassays can be strongly increased while also opening avenues for single‐cell profiling within heterogeneous cell populations. [ABSTRACT FROM AUTHOR]

Halide perovskite lasers based on CsPbBr3 micro‐ and nanoscale crystals have demonstrated fascinating performance owing to their low‐threshold lasing at room temperature and cost‐effective fabrication. However, chemically synthesized thin films of CsPbBr3 usually have rough polycrystalline morphology along with a large amount of crystal lattice defects and, thus, are mostly utilized for the engineering of light‐emitting devices. This obstacle prevents their usage in many photonic applications. Here, a protocol to deposit large‐grain and smooth CsPbBr3 thin films is developed. Their high quality and large scale allow to demonstrate a maximum optical gain up to 12 900 cm−1 in the spectral range of 530–540 nm, which is a record‐high value among all previously reported halide perovskites and bulk semiconductors (e.g., GaAs, GaN, etc.) at room temperature. Moreover, femtosecond laser ablation technique is employed to create high‐quality microdisc lasers on glass from these films to obtain excellent lasing characteristics. The revealed critical roles of thickness and grain size for the CsPbBr3 films with extremely high optical gain pave the way for development of low‐threshold lasers or ultimately small nanolasers, as well as to apply them for polaritonic logical elements and integrated photonic chips. [ABSTRACT FROM AUTHOR]

A coherent optical frequency comb with a gigahertz line spacing is important in diverse fields, such as calibration of astronomical spectrographs and wavelength division multiplexing optical communications. In this paper, we realize octave-spanning 10-GHz optical combs using a directly-modulated 1.55 μm microlaser as a seeding source. A 6.4 ps transform-limited pulse is successfully generated from the directly-modulated laser output through optimal chirp compensation in a fiber. Moreover, after amplifying by an EDFA, the optical pulse width is further reduced to 140 fs by combing the self-phase modulation effect and the anomalous group velocity dispersion in commercial fibers. Finally, a coherent optical comb spanning from 900-2400 nm is produced in a home-made fluorotellurite fiber using the 140-fs pulse boosted to a few Watts as a seeding source. The experimental results demonstrate that optical combs generated from the directly-modulated microlaser have the potential for a fully stabilized frequency comb. [ABSTRACT FROM AUTHOR]

Low‐dimensional perovskite structures are ideal materials for nano/microlasers owing to their excellent optical gain properties and high emission efficiency. But it is still a challenge to achieve single‐mode and tunable lasing behaviors in micro‐scale perovskite, especially showing ultralow thresholds in tens of µJ cm−2. In this work, CsPbBr3/Ag hemispheroids have been synthesized in a designed chemical vapor deposition (CVD) process. Benefiting from the whispering gallery resonance mode and plasmon‐enhanced light–matter interactions in well‐confined hybrid cavities, the CsPbBr3/Ag plasmonic microlasers exhibit low pump thresholds down to 35–51 µJ cm−2. Interestingly, single‐mode and two‐mode lasing behaviors are determined by the morphology of plasmonic Ag nanostructures, and lasing modes could be selectively tuned by increasing the pump fluence accompanying with dynamic competitions of photonic and plasmonic modes. Simulations of electromagnetic field have been plotted to show near‐field resonant modes for a comprehensive understanding of plasmon‐assisted lasing. These results not only provide a solution to fabricate low‐threshold plasmonic microlasers, but also advocate the prospect of all‐inorganic perovskite nanostructures as promising candidates for on‐chip integrated light sources. [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]

Single‐crystalline micro‐/nanostructures based on organic stimulus‐responsive materials have attracted wide interests for their unique functional roles in various photonic applications including optical wave guiding, optical vapor sensing, and miniaturized lasing. Yet one imminent challenge is to pattern micro‐/nanostructured organic 1D arrays with controlled geometry, precise alignment, and pure crystallographic orientation owing to the uncontrollable dewetting dynamics in the solution processes. Herein, a smart assembly method is employed to regulate a confined crystallization of organic molecules. Sensitive, stable, and reproducible optical 1D‐array vapor sensors can detect the alkaline and acidic vapors based on the proton transfer process. As‐fabricated vapor sensors based on organic 1D arrays also selectively identify four similar amine vapors. Meanwhile, based on these 1D microstructure arrays, high‐performing Fabry–Pérot resonators with deep‐red laser emission, a low lasing threshold of 0.31 µJ, and high quality factor Q (≈2243) are realized. Owing to these multiple functions, organic microwire arrays not only provide intrinsic insight into optical vapor sensing but also offer guidance for the development of miniaturized lasers with specific functionalities, which show considerable potential in multifunctional photonic integrated circuits. [ABSTRACT FROM AUTHOR]

Spin‐controlled lasers are highly interesting photonic devices and have been shown to provide ultrafast polarization dynamics in excess of 200 GHz. In contrast to conventional semiconductor lasers their temporal properties are not limited by the intensity dynamics, but are governed primarily by the interaction of the spin dynamics with the birefringent mode splitting that determines the polarization oscillation frequency. Another class of modern semiconductor lasers are high‐β emitters, which benefit from enhanced light–matter interaction due to strong mode confinement in low‐mode‐volume microcavities. In such structures, the emission properties can be tailored by the resonator geometry to realize for instance bimodal emission behavior in slightly elliptical micropillar cavities. This attractive feature is utilized to demonstrate and explore spin‐lasing effects in bimodal high‐β quantum dot micropillar lasers. The studied microlasers with a β‐factor of 4% show spin‐laser effects with experimental polarization oscillation frequencies up to 15 GHz and predicted frequencies up to about 100 GHz, which are controlled by the ellipticity of the resonator. These results reveal appealing prospects for very compact, ultrafast, and energy‐efficient spin‐lasers and can pave the way for future purely electrically injected spin‐lasers enabled by short injection path lengths. [ABSTRACT FROM AUTHOR]

Fluorescent microbeads are widely used for applications in life sciences and medical diagnosis. The spectral contrast and sharpness of photoluminescence are critical in the utilities of microbeads for imaging and multiplexing. Here, microbeads capable of generating single‐peak laser emission with a sub‐nanometer linewidth are demonstrated. The microbeads are made of quantum dots that are tightly packed and crosslinked via ligand exchange for high optical gain and refractive index as well as material stability. Bright single‐mode lasing with no photobleaching is achieved with particle diameters as small as 1.5 µm in the air. Sub‐nm lasing emission is maintained even inside high‐index surroundings, such as organic solvents and biological tissues. Feasibility of intracellular tagging and multi‐color imaging in vivo is demonstrated. [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]

Microlasers, relying on the strong coupling between active particles and optical microcavity, exhibit fundamental differences from conventional lasers, such as multi-threshold/thresholdless behavior and nonclassical photon emission. As light sources, microlasers possess extensive applications in precision measurement, quantum information processing, and biochemical sensing. Here we propose a whispering-gallery-mode microlaser scheme, where ultracold alkaline-earth metal atoms, i.e., gain medium, are tightly confined in a two-color evanescent lattice that is in the ring shape and formed around a microsphere. To suppress the influence of the lattice-induced ac Stark shift on the moderately-narrow-linewidth laser transition, the red-detuned trapping beams operate at a magic wavelength while the wavelength of the blue-detuned trapping beam is set close to the other magic wavelength. The tiny mode volume and high quality factor of the microsphere ensure the strong atom-microcavity coupling in the bad-cavity regime. As a result, both saturation photon and critical atom numbers, which characterize the laser performance, are substantially reduced below unity. We explore the lasing action of the coupled system by using the Monte Carlo approach. Our scheme may be potentially generalized to the microlasers based on the forbidden clock transitions, holding the prospect for microscale active optical clocks in precision measurement and frequency metrology. [ABSTRACT FROM AUTHOR]

Lead halide perovskite (LHP) is a promising material for various optoelectronic applications. Surface coating on particles is a common strategy to improve their functionality and environmental stability, but LHP is not amenable to most coating chemistries because of its intrinsic weakness against polar solvents. Here, a novel method of synthesizing LHP microlasers in a super‐saturated polar solvent using sonochemistry and applying various functional coatings on individual microlasers in situ is described. Cesium lead bromine perovskite (CsPbBr3) microcrystals, capped with organic poly‐norepinephrine (pNE) layers, are synthesized. The catechol group of pNE coordinates to bromine‐deficient lead atoms, forming a defect‐passivating and diffusion‐blocking shell. The pNE layer enhances the material lifetime of CsPbBr3 in water by 2000‐fold, enabling bright luminescence and lasing from single microcrystals in water. Furthermore, the pNE shell permits biofunctionalization with proteins, small molecules, and lipid bilayers. Luminescence from CsPbBr3 microcrystals is sustained in water over 1 h and observed in live cells. The functionalization method may enable new applications of LHP laser particles in water‐rich environments. [ABSTRACT FROM AUTHOR]

Microlasers in near-degenerate supermodes lay the cornerstone for studies of non-Hermitian physics, novel light sources, and advanced sensors. Recent experiments of the stimulated scattering in supermode microcavities reported beating phenomena, interpreted as dual-mode lasing, which, however, contradicts their single-mode nature due to the clamped pump field. Here, we investigate the supermode Raman laser in a whispering-gallery microcavity and demonstrate experimentally its single-mode lasing behavior with a side-mode suppression ratio (SMSR) up to 37 dB, despite the emergence of near-degenerate supermodes by the backscattering between counterpropagating waves. Moreover, the beating signal is recognized as the transient interference during the switching process between the two supermode lasers. Self-injection is exploited to manipulate the lasing supermodes, where the SMSR is further improved by 15 dB and the laser linewidth is below 100 Hz. [ABSTRACT FROM AUTHOR]

Spatial filtering is an important mechanism to improve the spatial quality of laser beams. Typically, a confocal arrangement of lenses with a diaphragm in the focal plane is used for intracavity spatial filtering. Such conventional filtering requires access to the far‐field domain. In microlasers, however, conventional filtering is impossible due to the lack of space in microresonators to access the far‐field. Therefore, a novel concept for more compact and efficient spatial filtering is necessary. In this study, a conceptually novel mechanism of spatial filtering in the near‐field domain is proposed and demonstrated, by a nanostructured multilayer coating—a 2D photonic crystal structure with a periodic index modulation along the longitudinal and transverse directions to the beam propagation. The structure is built on a nanomodulated substrate, to provide the transverse periodicity. The physical vapor deposition is used to provide self‐repeating modulation in the longitudinal direction. A 5 µm thick photonic multilayer structure composed of nanostructured multiple layers of alternating high‐ and low‐index materials providing spatial filtering in the near‐infrared frequencies with 2° low angle passband is experimentally demonstrated. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers. [ABSTRACT FROM AUTHOR]

Background: The term "plasmonic" describes the relationship between electromagnetic fields and metallic nanostructures. Plasmon-based sensors have been used innovatively to accomplish different biomedical tasks, including detection of cancer. Plasmonic sensors also have been used in biochip applications and biosensors and have the potential to be implemented as implantable point-of-care devices. Many devices and methods discussed in the literature are based on surface plasmon resonance (SPR) and localized SPR (LSPR). However, the mathematical background can be overwhelming for researchers at times. Objective: This review article discusses the theory of SPR, simplifying the underlying physics and bypassing many equations of SPR and LSPR. Moreover, we introduce and discuss the hybrid whispering gallery mode (WGM) sensing theory and its applications. Methods: A literature search in ScienceDirect was performed using keywords such as "surface plasmon resonance," "localized plasmon resonance," and "whispering gallery mode/plasmonic." The search results retrieved many articles, among which we selected only those that presented a simple explanation of the SPR phenomena with prominent biomedical examples. Results: SPR, LSPR, tilted fiber Bragg grating, and hybrid WGM phenomena were explained and examples on biosensing applications were provided. Conclusions: This minireview presents an overview of biosensor applications in the field of biomedicine and is intended for researchers interested in starting to work in this field. The review presents the fundamental notions of plasmonic sensors and hybrid WGM sensors, thereby allowing one to get familiar with the terminology and underlying complex formulations of linear and nonlinear optics. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) have recently emerged as appealing platforms to construct microlasers owing to their compelling characters combining the excellent stability of inorganic materials and processable characters of organic materials. However, MOF microstructures developed thus far are generally composed of multiple edge boundaries due to their crystalline nature, which consequently raises significant scattering losses that are detrimental to lasing performance. In this work, we propose a strategy to overcome the above drawback by designing spherically shaped MOFs microcavities. Such spherical MOF microstructures are constructed by amorphizing MOFs with a topological distortion network through introducing flexible building blocks into the growth environment. With an ultra‐smooth surface and excellent circular boundaries, the acquired spherical microcavities possess a Q factor as high as ≈104 and can provide sufficient feedback for high‐quality single‐mode lasing oscillations. We hope that these results will pave an avenue for the construction of new types of flexible MOF‐based photonic components. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) have recently emerged as appealing platforms to construct microlasers owing to their compelling characters combining the excellent stability of inorganic materials and processable characters of organic materials. However, MOF microstructures developed thus far are generally composed of multiple edge boundaries due to their crystalline nature, which consequently raises significant scattering losses that are detrimental to lasing performance. In this work, we propose a strategy to overcome the above drawback by designing spherically shaped MOFs microcavities. Such spherical MOF microstructures are constructed by amorphizing MOFs with a topological distortion network through introducing flexible building blocks into the growth environment. With an ultra‐smooth surface and excellent circular boundaries, the acquired spherical microcavities possess a Q factor as high as ≈104 and can provide sufficient feedback for high‐quality single‐mode lasing oscillations. We hope that these results will pave an avenue for the construction of new types of flexible MOF‐based photonic components. [ABSTRACT FROM AUTHOR]

MOF‐based one‐dimensional materials have received increasing attention in the nanophotonics field, but it is still difficult in the flexible shape evolution of MOF micro/nanocrystals for desired optical functionalities due to the susceptible solvothermal growth process. Herein, we report on the well‐controlled shape evolution of pure‐MOF microcrystals with optical waveguide and lasing performances based on a bottom‐up and top‐down synergistic method. The MOF microcrystals from solvothermal synthesis (bottom‐up) enable the evolution from microrods via microtubes to nanowires through a chelating agent‐assisted etching process (top‐down). The three types of MOF 1D‐microstructures with high crystallinity and smooth surfaces all exhibit efficient optical waveguide performance. Furthermore, MOF nanowire with lowest propagation loss served as low‐threshold pure‐MOF nanolasers with Fabry–Pérot resonance. These results advance the fundamental understanding on the controlled MOF evolution mechanism, and offer a valuable route for the development of pure‐MOF‐based photonic components with desired functionalities. [ABSTRACT FROM AUTHOR]

Semiconductor heterostructures hold the promise for developing novel integrated devices with on‐demand photonic and optoelectronic properties. Herein, the perovskite lateral heterostructures in forms of microplates and microwires are fabricated by precise control of two‐step atmospheric pressure chemical vapor deposition course and the unique optical properties are demonstrated for the first time. The comprehensive spectroscopic and elemental mapping characterizations reveal the core‐shell‐like configuration of the individual heterostructure, which features the fascinating energy routing nature. Taking advantage of the effective photon recycling and the energy transfer processes, the record‐low threshold (≈3.5 µJ cm−2) lasing and the indirect pumping induced lasers from the single micro‐heterostructure are demonstrated. Moreover, the distinctive optical waveguides with propagation length independent output spectra from the microwire heterostructure are realized. These findings represent a significant advance in developing novel and functional optoelectronic devices by engineering the perovskite heterostructure. [ABSTRACT FROM AUTHOR]

Lasers based on biological materials are attracting an increasing interest in view of their use in integrated and transient photonics. Deoxyribonucleic acid (DNA) as optical biopolymer in combination with highly emissive dyes has been reported to have excellent potential in this respect. However, achieving miniaturized lasing systems based on solid‐state DNA shaped in different geometries to confine and enhance emission is still a challenge, and the physicochemical mechanisms originating fluorescence enhancement are not fully understood. Herein, a class of wavelength‐tunable lasers based on DNA nanofibers is demonstrated, for which optical properties are highly controlled through the system morphology. A synergistic effect is highlighted at the basis of lasing action. Through a quantum chemical investigation, it is shown that the interaction of DNA with the encapsulated dye leads to hindered twisting and suppressed channels for the nonradiative decay. This is combined with effective waveguiding, optical gain, and tailored mode confinement to promote morphologically controlled lasing in DNA‐based nanofibers. The results establish design rules for the development of bright and tunable nanolasers and optical networks based on DNA nanostructures. [ABSTRACT FROM AUTHOR]

Combined dry–wet transient materials and devices are introduced, which are based on water‐dissolvable dye‐doped polymers layered onto nonpolar cyclic hydrocarbon sublimating substrates. Light‐emitting heterostructures showing amplified spontaneous emission are obtained on transient elements and used as illumination sources for speckle‐free, full‐field imaging, and transient optical labels are realized that incorporate QR‐codes with stably encoded information. The transient behavior is also studied at the microscopic scale, highlighting the real‐time evolution of material domains in the sublimating compound. Finally, the exhausted components are fully soluble in water thus being naturally degradable. This technology opens new and versatile routes for environmental sensing, storage conditions monitoring, and organic photonics. [ABSTRACT FROM AUTHOR]

We analytically investigate the performance of whispering gallery mode (WGM) spherical microlasers for gas sensing based on intra-cavity absorption. Using a simple model we estimate the response of a compact optical gas sensor based on these microlasers. We use detection of carbon dioxide by an Er:ZBLAN mid-IR microlaser with a relative intensity noise (RIN) of - 110 dB/Hz as an example, and show that using a commercial mid-IR photodetector, the limit of detection (LOD) for the resulting sensing system is about 5 ppm. We also investigate the impact of using a fiber optical amplifier on the LOD for different values of RIN. The numerical calculations and the presented approach can be applied to analyze the performance of any intracavity sensor based on WGM microlaser. [ABSTRACT FROM AUTHOR]

Liquid crystal microdroplets have received considerable attention over recent years owing to their potential applications in chemical, biomedical sensing and lasing. We report experimental studies on whispering gallery mode lasing from dye-doped ferroelectric liquid crystal microdroplets suspended in a low refractive index and highly transparent perfluoropolymer at ambient temperature. We show that the lasing threshold pump energy of ferroelectric microdroplets is much lower than that of the nematic and cholesteric microdroplets. With the increasing electric field, the linewidth increases, while the lasing intensity decreases and eventually switches off beyond a particular field. Since the switching response time is fast (≈350 μs), ferroelectric liquid crystal based microlasers are useful for applications as electrically switchable sources in miniaturised devices and in soft photonic circuits. [ABSTRACT FROM AUTHOR]

We demonstrated a stimuli-responsive and chemically switchable organic microbelt laser through reversible protonation–deprotonation reactions. The parent microbelt cavity together with the optically allowed 0–1 transition of H-aggregates enables a microlaser to operate at 585 nm. Upon HCl vapor treatment, the protonation of surface molecules shifts the lasing wavelength to 560 nm, generating an intensity contrast ratio ＞105, accompanied by a sharp color change from orange (deprotonated) to green (protonated). When treated with HCl–NH3 vapor, the protonation–deprotonation reactions lead to a reversible microlaser switch between 585 nm and 560 nm with good reproducibility and photostablity, making them attractive in high-throughput chemical and biological sensing applications. [ABSTRACT FROM AUTHOR]

Machining brittle materials, such as silicon, is expensive and often causes detrimental damage, but a relatively new technique, termed microlaser-assisted machining (micro-LAM), improves the efficacy of the machining process using traditional single point diamond turning with simultaneous laser assistance. Prior work shows it provides a smooth surface finish and reduces the likelihood of fracture by increasing the ductility of the material during the machining process. However, the quality of the finish and the utility of the machined silicon depends on having good phase purity and low residual stresses. Using Raman microspectroscopy and a wide range of micro-LAM machining parameters the current work has shown that the technique can give excellent results in terms of low residual stress, high phase purity, and good relative crystallinity. However, poor choice of process parameters can be very detrimental leading to high residual stresses (over 400 MPa) and multiple silicon phases being present. [ABSTRACT FROM AUTHOR]

We report on the realization of a dense, large-scale array of 900 quantum dot micropillar cavities with high spectral homogeneity. We target applications in photonic information processing such as optical reservoir computing which can be implemented in large arrays of optically coupled microlasers. To achieve the required spectral homogeneity for the underlying optical injection locking, we calculate and set the diameter of each individual micropillar within the array during the fabrication process by taking the diameter-dependent emission wavelength of the microcavities into account. Using this kind of diameter adjustment, we improve the overall wavelength homogeneity in a 30 × 30 micropillar array by 64% and reduce the standard deviation of the resonance energy distribution by 26% from 352 μeV in the planar unprocessed sample to 262 μeV in the fabricated array. In addition, we present a detailed analysis of the device quality and the diameter control of the micropillar's emission wavelength, which includes important information for the effective application of the developed fabrication method for the realization of highly homogeneous micropillar arrays in the future. [ABSTRACT FROM AUTHOR]

Measuring states of polarizations (SOPs) is a fundamental requirement in high capacity optical communications, optical imaging, and material characterization. However, most of the existing methods focused on the assembly of spatial optical elements, making the system bulky and complex. Alternatively, the integrated methods were mainly presented by plasmonic nanostructures or metasurfaces, difficult to integrate with commonly used silicon photonic devices. For large-scale inter-chip optical interconnections, the silicon-based polarization analyzers are in demand and in its infancy. Here, a silicon-based polarization analyzer by polarization-frequency mapping is put forward. The basis vectors of polarization are mapped to two frequencies by thermally tuned phase shifters. The SOPs are retrieved from the frequency domain. The proposed polarization analyzer is demonstrated experimentally and can measure SOPs in the entire C-band. The scheme is compatible with the CMOS fabrication process, making it possible to be integrated with other silicon-based devices monolithically. [ABSTRACT FROM AUTHOR]

We report photon pairs and heralded single photons generated at 1310 nm wavelengths using silicon photonics technology, demonstrating that comparable performance could be achieved when a silicon microring resonator was pumped either by a desktop laser instrument or by an electrically injected, room-temperature hybrid silicon laser. Measurements showed that 130 kilo-coincidence-counts per second pair rates could be generated, with coincidences-to-accidentals ratio approximately 100 at about 0.34 mW optical pump power and anti-bunching upon heralding with second-order intensity correlation g(2)(0) = 0.06 at about 0.9 mW optical pump power. These results suggest that hybrid silicon lasers, which are ultra-compact and wafer-scale manufacturable, could be used in place of packaged, stand-alone lasers for generating photon pairs at data communication wavelengths and enable large-scale, cost-effective manufacturing of integrated sources for quantum communications and computing. [ABSTRACT FROM AUTHOR]

Quantum photonic integrated circuits hold great potential as a novel class of semiconductor technologies that exploit the evolution of a quantum state of light to manipulate information. Quantum dots encapsulated in photonic crystal structures are promising single-photon sources that can be integrated within these circuits. However, the unavoidable energy mismatch between distant cavities and dots, along with the difficulties in coupling to a waveguide network, has hampered the implementation of circuits manipulating single photons simultaneously generated by remote sources. Here we present a waveguide architecture that combines electromechanical actuation and Stark-tuning to reconfigure the state of distinct cavity-emitter nodes on a chip. The Purcell-enhancement from an electrically controlled exciton coupled to a ridge waveguide is reported. Besides, using this platform, we implement an integrated Hanbury-Twiss and Brown experiment with a source and a splitter on the same chip. These results open new avenues to scale the number of indistinguishable single photons produced on-demand by distinct emitters. [ABSTRACT FROM AUTHOR]

Strain engineering is a powerful approach in micro- and optoelectronics to enhance carrier mobility, tune the bandgap of heterostructures, or break lattice symmetry for nonlinear optics. The dielectric stressors and bonding interfaces used for strain engineering in photonics can however limit thermal dissipation and the maximum operation temperature of devices. We demonstrate a new approach for enhanced thermal dissipation with stressor layers by combining metals and dielectrics. The method is applied to the germanium semiconductor. All-around tensile-strained germanium microdisks have been fabricated with metallic pedestals. The transferred tensile strain leads to a germanium thin film with a direct bandgap. Under continuous wave optical pumping, the emission of the whispering gallery modes is characterized by a threshold and an abrupt linewidth narrowing by a factor larger than 2. The occurrence of stimulated emission is corroborated by modeling of the optical gain. This demonstrates lasing with pure germanium microdisks. [ABSTRACT FROM AUTHOR]

Abstract: Organic microcavities provide unique properties that are highly advantageous for designing microlasers, but lack in efficient ways to directly integrate electrodes able to drive high currents. The introduction of thin, patterned metal films, leading to the formation of local Tamm plasmon polariton states, has been recently demonstrated as a possible route to preserving coherence in the presence of significant optical loss. Here, periodic micron‐scale gratings of silver are embedded into a high‐quality organic microcavity, creating a crystal‐like photonic potential structure. Despite strong absorption of metallic layers, these structures readily lase upon optical excitation. In that case, the above threshold emission originates not from isolate metal‐free areas but instead from phase‐locked supermodes spreading over several grating periods. Remarkably, in‐plane coherence can spread even further when decreasing the grating period, covering distances of more than 50  μm and more than ten metal stripes. 1D and 2D gratings with varying periods are investigated using tomographic scanning of the k‐space emission fine structure, which exhibits a strong dependence on the grating geometry. These results support the fabrication of highly customizable organic microlasers with tailored in‐plane coherence, and demonstrate the coexistence of extended coherence and optical loss. [ABSTRACT FROM AUTHOR]

Microlasers are involved in a broad range of devices for numerous research applications. However, the mode structures of three-dimensional microlasers without rotational symmetry are largely unexplored. Previous studies of such cavities revealed lasing modes exclusively localized on periodic orbits in the plane parallel to the substrate, which is to say that the associated momentum vectors are concentrated in the plane. In this paper, we characterize three-dimensional, polymer-based Fabry-Perot (i.e., ribbon-shaped) microcavities and demonstrate that such cavities exhibit modes with momentum vectors out of the substrate plane. These results constitute a proof-of-principle and motivate follow-up studies with more complex three-dimensional geometries. [ABSTRACT FROM AUTHOR]

Abstract: The very broad emission bands of organic semiconductor materials are, in theory, suitable for achieving versatile solid‐state lasers; however, most of organic materials only lase at short wavelength corresponding to the 0–1 transition governed by the Franck–Condon (FC) principle. A strategy is developed to overcome the limit of FC principle for tailoring the output of microlasers over a wide range based on the controlled vibronic emission of organic materials at microcrystal state. For the first time, the output wavelength of organic lasers is tailored across all vibronic (0–1, 0–2, 0–3, and even 0–4) bands spanning the entire emission spectrum. [ABSTRACT FROM AUTHOR]

Optofluidic microcavities with high Q factor have made rapid progress in recent years by using various micro-structures. On one hand, they are applied to microfluidic lasers with low excitation thresholds. On the other hand, they inspire the innovation of new biosensing devices with excellent performance. In this article, the recent advances in the microlaser research and the biochemical sensing field will be reviewed. The former will be categorized based on the structures of optical resonant cavities such as the Fabry-Pérot cavity and whispering gallery mode, and the latter will be classified based on the working principles into active sensors and passive sensors. Moreover, the difficulty of single-chip integration and recent endeavors will be briefly discussed. [ABSTRACT FROM AUTHOR]

Photons can come to thermal equilibrium at room temperature by scattering multiple times from a fluorescent dye. By confining the light and dye in a microcavity, a minimum energy is set and the photons can then show Bose-Einstein condensation. We present here the physical principles underlying photon thermalization and condensation, and review the literature on the subject. We then explore the ‘small’ regime where very few photons are needed for condensation. We compare thermal equilibrium results to a rate-equation model of microlasers, which includes spontaneous emission into the cavity, and we note that small systems result in ambiguity in the definition of threshold. [ABSTRACT FROM AUTHOR]