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Whispering gallery mode (WGM) resonators, as an integral component of integrated photonics, have attracted considerable attention due to their high Q factor, small footprint, and small mode volume, making them widely applied as microlasers. In this work, Nd:GGG crystal was prepared into a Nd:GGG film with thickness of 1.8 μm through ion implantation-enhanced etching (IIEE) technique, and subsequently, the Nd:GGG film was partened by focused ion beam (FIB) technology to generate a microdisk with diameter of 20 μm. For high-power microcavity lasers, heat generation during laser operation was inevitable. We placed the microdisk on a silica holder and a silica wafer, respectively. The microdisk placed on the silica holder and silica wafer exhibited laser thresholds of 32 μW and 17 μW, respectively. Moreover, due to different heat dissipation conditions, the microdisk placed on the silica holder exhibited a mode shift of 0.13 nm/mW, while the microdisk placed on the silica wafer showed a more stable laser output state with a mode shift of 0.02626 nm/mW. [ABSTRACT FROM AUTHOR]

Mid-infrared microcavity lasers have important applications in biosensing, mid-infrared spectroscopy, and environmental monitoring. However, the low output power of existing mid-infrared microcavity lasers hinders their practical use. This drawback is attributed to the insufficient laser gain medium, which limits the development of mid-infrared whispering-gallery-mode (WGM) lasers. To address this issue, we have employed ion implantation-enhanced etching to fabricate Tm:YAG thin films as effective gain media for mid-infrared WGM lasers. The Tm:YAG thin film, with a thickness of 2 µm, exhibits excellent fluorescence characteristics. Subsequently, the Tm:YAG thin film is processed using focused ion beam to form microdisks with a diameter of 30 µm. Under 785 nm laser pumping, the maximum output power of the Tm:YAG microdisk at 2023.1 nm is 229 µW, with a slope efficiency of 2.9%. This work demonstrates the outstanding potential of Tm:YAG as a mid-infrared laser gain medium, providing a new option for the development of mid-infrared lasers. [ABSTRACT FROM AUTHOR]

spectral dependencies of the electroluminescence intensity of a microdisk laser with a diameter of 31 μm with active region based on InAs/InGaAs quantum dots, operating in the continuous-wave regime, are investigated in a wide range of injection currents. Simultaneous lasing through the ground and excited states of quantum dots under intense excitation is demonstrated in injection microdisk laser for the first time. At low pumping powers lasing occurs via ground states of quantum dots only. [ABSTRACT FROM AUTHOR]

The development and investigation of miniature narrow-line coherent light sources based on microresonators with low-power-consumption whispering gallery modes (WGMs) is an actual trend in modern photonics. Raman WGM microlasers can operate at wavelengths inaccessible to traditional laser media and provide a huge pump frequency tuning range. Here, we propose and theoretically study multicascade Raman microlasers based on soft tellurite TeO2–WO3–Bi2O3 glass WGM microresonators (microspheres) which can operate in the near-IR and mid-IR with the pump in the telecommunication range. Thanks to a large Raman gain (120 times exceeding the maximum Raman gain of silica glass) and a huge Raman frequency shift of 27.5 THz for this glass, the Raman waves at 1.83 µm, 2.21 µm, 2.77 µm, and 3.7 µm in the first, second, third, and fourth cascades, respectively, are theoretically demonstrated with a pump at 1.57 µm. We analyze in detail the influence of different factors on the characteristics of the generated Raman waves, such as microsphere diameters, Q-factors, pump powers, and detuning of the pump frequency from exact resonance. We also solve a thermo-optical problem to show that the temperature of a soft glass microresonator heated due to partial thermalization of pump power remains below the glass transition temperature. To the best of our knowledge, mid-IR tellurite glass Raman WGM microlasers have not been studied before. [ABSTRACT FROM AUTHOR]

The integration of high-quality III–V light sources on the Si platform has encountered a challenge that demands a highly precise on-demand addressability of single devices in a significantly reduced integration area. However, simple schemes to address the issue without causing major optical losses remain elusive. Here, we propose a waveguide-integrated microlaser-on-silicon in which the III–V/Si integration requires only a small micron-sized post structure with a diameter of <2 µm and enables efficient light coupling with an estimated coupling efficiency of 44.52%. Top-down fabricated high-quality microdisk cavities with an active gain medium were precisely micro-transferred on a small Si-post structure that was rationally designed in the vicinity of a strip-type Si waveguide (WG). Spectroscopic measurements exhibit successful lasing emission with a threshold of 378.0 µW, bi-directional light coupling, and a propagation of >50 µm through the photonic Si WG. Numerical study provides an in-depth understanding of light coupling and verifies the observations in the experiment. We believe that the proposed microlaser-on-Si is a simple and efficient scheme requiring a minimum integration volume smaller than the size of the light source, which is hard to achieve in conventional integration schemes and is readily applicable to various on-demand integrated device applications. [ABSTRACT FROM AUTHOR]

Micron-sized lasers fabricated from upconverting nanoparticles (UCNP) coupled to whispering gallery mode (WGM) microresonators can exhibit continuous-wave anti-Stokes lasing useful for tracking cells, environmental sensing, and coherent stimulation of biological activity. The integration of these microlasers into organisms and microelectronics requires even smaller diameters, however, which raises threshold pump powers beyond practical limits for biological applications. To meet the need for low lasing thresholds and high fidelity fabrication methods, we use correlative optical and electron microscopy to uncover the nanoparticle assembly process and structural factors that determine efficient upconverted lasing. We show that 5 μm microspheres with controlled submonolayer UCNP coatings exhibit, on average, 25-fold lower laser thresholds (1.7 ± 0.7 kW/cm2) compared to the mean values of the lowest threshold UCNP lasers, and variability is reduced 30-fold. WGMs are observed in the upconversion spectra for TiO2-coated microspheres as small as 3 μm, a size at which optical losses had previously prevented such observations. Finally, we demonstrate that the WGM signatures of these upconverting microlasers can be imaged and distinguished through tissue-mimicking phantoms. These advances will enable the fabrication of more efficient upconverting lasers for imaging, sensing, and actuation in optically complex environments.

In this paper, we demonstrate Er3+ doped tellurite single and multi-mode microlasers in 1.5 μm–1.6 μm wavelength range fabricated via the plasma torch method. It is a simple and cost-effective method to produce microspheres with diameter ranges from 11 to 88 μm. Single mode laser output were observed with 0.98 μm and 1.48 μm pump, respectively. In addition, the quality factor of the fabricated microsphere is measured.

A numerical analysis of a compact microring resonator that was defined on a yttrium-aluminum-garnet (YAG) thin film bonded on top of a SiO2 cladding layer and operated at the wavelengths of approximately 1.064 and 1.6 μm was performed. The single-mode conditions of YAG waveguides at different waveguide geometries and their propagation losses at different SiO2 cladding layer thicknesses were systematically analyzed. The key design parameters of the microring resonator, such as gap size and ring radius, were simulated based on the 2.5-dimensional variational finite-difference time-domain method. This study could be helpful in understanding the mechanism of microring resonators defined on YAG thin films and fabricating integrated microlaser sources on YAG-on-insulators.

The development and investigation of miniature narrow-line coherent light sources based on microresonators with low-power-consumption whispering gallery modes (WGMs) is an actual trend in modern photonics. Raman WGM microlasers can operate at wavelengths inaccessible to traditional laser media and provide a huge pump frequency tuning range. Here, we propose and theoretically study multicascade Raman microlasers based on soft tellurite TeO2–WO3–Bi2O3 glass WGM microresonators (microspheres) which can operate in the near-IR and mid-IR with the pump in the telecommunication range. Thanks to a large Raman gain (120 times exceeding the maximum Raman gain of silica glass) and a huge Raman frequency shift of 27.5 THz for this glass, the Raman waves at 1.83 µm, 2.21 µm, 2.77 µm, and 3.7 µm in the first, second, third, and fourth cascades, respectively, are theoretically demonstrated with a pump at 1.57 µm. We analyze in detail the influence of different factors on the characteristics of the generated Raman waves, such as microsphere diameters, Q-factors, pump powers, and detuning of the pump frequency from exact resonance. We also solve a thermo-optical problem to show that the temperature of a soft glass microresonator heated due to partial thermalization of pump power remains below the glass transition temperature. To the best of our knowledge, mid-IR tellurite glass Raman WGM microlasers have not been studied before.

The spatial separation between the highest occupied and the lowest unoccupied molecular orbitals (HOMO and LUMO) in thermally activated delayed fluorescent (TADF) molecules leads to charge transfer (CT) states, which degrade the oscillator strength of emission transition and sacrifices high solid‐state photoluminescence quantum yield (PLQY), together limiting its application in organic solid‐state lasers (OSSLs). Here, we demonstrated organic microwire lasers from TADF emitters that combine aggregation induced emission (AIE) and local excited (LE) state characteristics. The unique AIE and LE feature lead to a PLQY approaching 50 % and a high optical gain of 870 cm−1 for TADF microwires. The regenerated singlet excitons by reverse intersystem crossing (RISC) process are conducive to population inversion. As a result, we demonstrated microwire lasers around 465 nm with a low threshold of 3.74 μJ cm−2. Therefore, our work provides insight to design TADF materials for OSSLs. [ABSTRACT FROM AUTHOR]

The integration of high-quality III–V light sources on the Si platform has encountered a challenge that demands a highly precise on-demand addressability of single devices in a significantly reduced integration area. However, simple schemes to address the issue without causing major optical losses remain elusive. Here, we propose a waveguide-integrated microlaser-on-silicon in which the III–V/Si integration requires only a small micron-sized post structure with a diameter of 50 µm through the photonic Si WG. Numerical study provides an in-depth understanding of light coupling and verifies the observations in the experiment. We believe that the proposed microlaser-on-Si is a simple and efficient scheme requiring a minimum integration volume smaller than the size of the light source, which is hard to achieve in conventional integration schemes and is readily applicable to various on-demand integrated device applications.

The laser is considered one of the greatest inventions of the 20th century. Biolasers employ high signal-to-noise ratio lasing emission rather than regular fluorescence as the sensing signal, directional out-coupling of lasing and excellent biocompatibility. Meanwhile, biolasers can also be micro-sized or smaller lasers with embedded/integrated biological materials. This article presents the progress in biolasers, focusing on the work done over the past years, including the molecular, cellular, tissue, and organism levels. Furthermore, biolasers have been utilized and explored for broad applications in biosensing, labeling, tracking, bioimaging, and biomedical development due to a number of unique advantages. Finally, we provide the possible directions of biolasers and their applications in the future. [ABSTRACT FROM AUTHOR]

The power of radiation in the continuous-wave mode of microdisk lasers with InGaAs/GaAs quantum-well dots hybrid integrated with a silicon substrate with the epitaxial side down using a thermocompression compound has been investigated. Because of a decrease in thermal resistance and suppression of self-heating, there is an increase in the current values at which power saturation and laser generation quenching occur, as well as an increase in the maximum power. In microdisks with a diameter of 19 μm, the largest value of the optical output power was 9.4 mW in the continuous-wave mode. [ABSTRACT FROM AUTHOR]

The dependence of the spectral position of the lasing line of a microdisk laser with InAs/InGaAs/GaAs quantum dots on the refractive index of an aqueous solution in which the microlaser is immersed is studied. A maximum resonance shift of 9.4 nm/RIU was obtained for 10-μm-diameter microlasers immersed in an aqueous glucose solution. [ABSTRACT FROM AUTHOR]

Liquid crystals (LCs) form an extremely rich range of selfassembled topological structures with artificially or naturally created topological defects. Some of the main applications of LCs are various optical and photonic devices, where compared to their solid-state counterparts, soft photonic systems are fundamentally different in terms of unique properties such as self-assembly, self-healing, large tunability, sensitivity to external stimuli, and biocompatibility. Here we show that complex tunable microlasers emitting structured light can be generated from self-assembled topological LC superstructures containing topological defects inserted into a thin Fabry-Pérot microcavity. The topology and geometry of the LC superstructure determine the structuring of the emitted light by providing complex three-dimensionally varying optical axis and order parameter singularities, also affecting the topology of the light polarization. The microlaser can be switched between modes by an electric field, and its wavelength can be tuned with temperature. The proposed soft matter microlaser approach opens directions in soft matter photonics research, where structured light with specifically tailored intensity and polarization fields could be designed and implemented. [ABSTRACT FROM AUTHOR]

The energy consumption of a microdisk laser with InGaAs/GaAs quantum well-dots at high-frequency modulation without forced cooling has been investigated. The lowest energy consumption for a microlaser 20 μm in diameter is estimated to be 1.6 pJ per data bit transferred using an optical signal. [ABSTRACT FROM AUTHOR]

An erbium-doped whisper gallery mode microlaser is presented, which consists of an erbium-doped microsphere placed in an optical fiber open microcavity. The erbium-doped microsphere is obtained from melting the etched erbium-doped fiber tip by electrode discharge of a fusion splicer, and the open microcavity is fabricated by using femtosecond laser micromachining together with fusion splicing technique. The microcavity is positioned in a place just touching the fiber core, thus the light propagating in the fiber core is coupled into the erbium-doped microsphere through the evanescent field. The whispering-gallery-mode light field established in the microsphere interacts with the erbium ions, and ends up with laser operation. The quality factor value of the device is 6089 and the laser threshold is 0.033 mW. When the pump power changes continuously within the range from 0.39 mW to 0.72 mW, the lasing wavelength shifts from 1564.59 nm to 1565.6 nm, respectively. Such a WGM microlaser is low cost, robust and stable in operation and can be used for temperature and refractive index (RI) sensing. The sensitivity of the microlaser to temperature and RI is 33.3 pm/°C and 26 nm/RIU, respectively, higher than that achieved by pure WGM resonator, 8.3 pm/°C and 19.42 nm/RIU, respectively. More significantly, the detection limit of RI sensing for WGM microlaser is ∼4.87 × 10−5 RIU, lower than ∼2.71 × 10−4, achieved the WGM resonator. [ABSTRACT FROM AUTHOR]

Microresonator-based lasers in the two-micron range are interesting for extensive applications. Tm3+ ions provide high gain; therefore, they are promising for laser generation in the two-micron range in various matrices. We developed a simple theoretical model to describe Tm-doped glass microlasers generating in the 1.9–2 μm range with in-band pump at 1.55 μm. Using this model, we calculated threshold pump powers, laser generation wavelengths and slope efficiencies for different parameters of Tm-doped tellurite glass microspheres such as diameters, Q-factors, and thulium ion concentration. In addition, we produced a 320-μm tellurite glass microsphere doped with thulium ions with a concentration of 5·1019 cm−3. We attained lasing at 1.9 μm experimentally in the produced sample with a Q-factor of 106 pumped by a C-band narrow line laser. [ABSTRACT FROM AUTHOR]

We report results of experimental laser generation in an Er-doped tellurite glass microsphere under in-band pumping. Depending on settings, single-mode and multimode lasing is achieved in the C-band near 1.56 μm and in the L-band near 1.60 μm, as well as simultaneously in both bands. We demonstrate stable single-mode L-band generation at 1.599 μm with the standard deviation of the output power <0.5%. We also present a simple yet efficient analytical model to describe lasing for better understanding of the observed regimes and further control and optimization of such systems. We found theoretically that for low Q-factors lasing occurs in the C-band but for relatively high Q-factors lasing occurs in the L-band, which agrees with the experimental observations. Switching between the generated wavelengths from the C-band to the L-band occurs with a jump which was observed experimentally and explained theoretically. We show numerically that the lasing threshold is determined by both the Q-factor and the diameter of the microsphere. The obtained results can speed-up progress in the development of tellurite glass microlasers in the telecommunication range and give a better understanding of their theoretical aspects. [ABSTRACT FROM AUTHOR]

Mechanical stress within organoids is a pivotal indicator in disease modeling and pharmacokinetics, yet current tools lack the ability to rapidly and dynamically screen these mechanics. Here, we introduce biocompatible and compressible hollow microlasers that realize all-optical assessment of cellular stress within organoids. The laser spectroscopy yields identification of cellular deformation at the nanometer scale, corresponding to tens of pascals stress sensitivity. The compressibility enables the investigation of the isotropic component, which is the fundamental mechanics of multicellular models. By integrating with a microwell array, we demonstrate the high-throughput screening of mechanical cues in tumoroids, establishing a platform for mechano-responsive drug screening. Furthermore, we showcase the monitoring and mapping of dynamic contractile stress within human embryonic stem cell-derived cardiac organoids, revealing the internal mechanical inhomogeneity within a single organoid. This method eliminates time-consuming scanning and sample damage, providing insights into organoid mechanobiology.

Multidimensional integrated micro/nanostructures are vitally important for the implementation of versatile photonic functionalities, whereas current material structures still suffer undesired surface defects and contaminations in either multistep micro/nanofabrications or extreme synthetic conditions. Herein, the dimension evolution of organic self-assembled structures 2D microrings and 3D microhelixes for multidimensional photonic devices is realized via a protic/aprotic solvent-directed molecular assembly method based on a multiaxial confined-assisted growth mechanism. The 2D microrings with consummate circle boundaries and molecular-smooth surfaces function as high-quality whispering-gallery-mode microcavities for dual-wavelength energy-influence-dependent switchable lasing. Moreover, the 3D microhelixes with smooth surfaces and natural twistable characteristics act as active photon-transport materials and polarization rotators. These results will broaden the horizon of constructing multidimensional microstructures for integrated photonic circuits., (© 2024 Wiley‐VCH GmbH.)

The tremendous progress made in recent years in the production of tellurite glasses has led to the development of different optical elements and devices on their basis such as microresonators and microlasers. The investigation of tellurite glass microresonators is of great importance for many potential applications. We studied theoretically and experimentally the nonlinear thermo-optical effects in tellurite glass microresonators under continuous-wave laser pumping. We calculated the temperature distributions for both, steady-state and transient non-stationary regimes and simulated shifts of the resonant wavelengths of whispering gallery modes. We produced Tm-doped tellurite glass microspheres and measured the resonant wavelength shifts as functions of the heat power. Our experimental results are in a good agreement with the theoretical predictions.

We present the first detailed theoretical analysis of multi-color continuous wave lasing in Tm-doped tellurite spherical microresonators with whispering gallery modes pumped at a wavelength of 792 nm. The numerical model is based on solving a system of equations for intracavity field amplitudes and rate equations using the parameters of Tm-doped tellurite glass measured in the previous experiments. All fundamental whispering gallery modes in the gain bands are taken into account. We demonstrate diagrams of generation regimes depending on Q-factors and pump power, which show a possibility of single-color lasing at a wavelength of ~1.9 μm, two-color lasing at wavelengths of ~1.9&1.5 μm and at ~1.9&2.3 μm, and three-color lasing at wavelengths of ~1.9&1.5&2.3 μm. Such microlasers can play a significant role in sensing applications.

Analytical expressions are presented, and, through them, the analysis of component parts of the electrical resistance of injection microdisk lasers is carried out depending on the size of the microdisk resonator, parameters of the substrate, and configuration of the contact to it. [ABSTRACT FROM AUTHOR]

The operation speed of microdisk lasers with quantum dots working at room temperature without thermal stabilization has been experimentally examined, and the widest modulation bandwidth of microdisks with various diameters has been calculated. It was shown that taking into account the effect of self-heating of a microlaser at high bias currents, which is manifested in a decrease of the ultimate operation speed and in an increase in the current at which the widest modulation bandwidth is reached, enables a good description of the experimental data. The self-heating most strongly affects microlasers with a small diameter (less than 20 μm). [ABSTRACT FROM AUTHOR]

A model is developed that makes it possible to analytically determine the threshold current of a microdisk laser with consideration for its self-heating as a function of the ambient temperature and the microlaser diameter. It is shown that there exists a minimum microdisk diameter determined by self-heating, up to which continuous-wave lasing can be reached at a given temperature. Another manifestation of the self-heating effect is the existence of the ultimate working temperature, which is lower, the smaller the microlaser diameter. Reasonable agreement between the predictions of the model and the available experimental data is shown. [ABSTRACT FROM AUTHOR]

This letter reports the optical pumped lasing behaviours of a three-layer Bragg resonance cavity consisting of dye-doped cholesteric liquid crystal (DDCLC) microdroplet, polyglycerol-2 and hollow glass microsphere. The function of PG2 is to control the parallel anchoring of the liquid crystal (LC) molecules on the surface of the LC microdroplet. The whispering-gallery mode (WGM), radial Bragg (photonic bandgap, PBG) mode and Bragg WGM (BWGM) are observed in DDCLC microspheres with different helical pitches and LC refractive indices. The formation mechanisms of six types of lasing emission conditions are analysed in detail. The study results present the prospect of controlling the output mode of the laser. Furthermore, such solid shell-based DDCLC microspheres have outstanding potential applications in miniaturised 3D Bragg lasers, sensors, and integrated and tunable optical devices. [ABSTRACT FROM AUTHOR]

An in-depth analysis and description of, to the best of our knowledge, the first subnanosecond pulse duration optical parametric generator (OPG) based on a fan-out grating design MgO-doped periodically-poled lithium niobate (MgO:PPLN) crystal is presented. Pumped by high energy subnanosecond pulse duration Q-switched Nd:YAG microlaser pulses, our OPG provides high output energies ranging from tens to hundreds of μ J with up to 45% conversion efficiency and enables fast and precise wavelength tuning across the near-to-mid infrared spectral regions (1414–4303 nm) just by laterally displacing the fan-out crystal without the need for temperature tuning. Limits of operation of the device were found in terms of the laser-induced damage threshold (LIDT) of the fan-out MgO:PPLN crystal. The OPG was fully characterized in terms of spectral, energy, and spatial properties of the signal wave, and analyzed experimentally and theoretically for the feasibility of producing broadband infrared output through non-collinear quasi-phase-matching and conversion of the fan-out grating structure into a chirped one. • Fan-out OPG tuning (1.4 – 4.3 μ m) was achieved by laterally displacing the crystal. • Subnanosecond, μ J energy pulses with up to 45% conversion efficiency were obtained. • Signal spatial beam quality highly depended on pump focusing conditions. • LIDT of a fan-out MgO:PPLN was examined for subnanosecond laser pulses. • The feasibility of broadband infrared output was explored via non-collinear QPM. [ABSTRACT FROM AUTHOR]

Photonic crystal cavities enable strong light–matter interactions, with numerous applications, such as ultra-small and energy-efficient semiconductor lasers, enhanced nonlinearities and single-photon sources. This paper reviews the properties of the modes of photonic crystal cavities, with a special focus on line-defect cavities. In particular, it is shown how the fundamental resonant mode in line-defect cavities gradually turns from Fabry–Perot-like to distributed-feedback-like with increasing cavity size. This peculiar behavior is directly traced back to the properties of the guided Bloch modes. Photonic crystal cavities based on Fano interference are also covered. This type of cavity is realized through coupling of a line-defect waveguide with an adjacent nanocavity, with applications to Fano lasers and optical switches. Finally, emerging cavities for extreme dielectric confinement are covered. These cavities promise extremely strong light–matter interactions by realizing deep sub-wavelength mode size while keeping a high quality factor.

Microresonator-based lasers in the two-micron range are interesting for extensive applications. Tm3+ ions provide high gain; therefore, they are promising for laser generation in the two-micron range in various matrices. We developed a simple theoretical model to describe Tm-doped glass microlasers generating in the 1.9–2 μm range with in-band pump at 1.55 μm. Using this model, we calculated threshold pump powers, laser generation wavelengths and slope efficiencies for different parameters of Tm-doped tellurite glass microspheres such as diameters, Q-factors, and thulium ion concentration. In addition, we produced a 320-μm tellurite glass microsphere doped with thulium ions with a concentration of 5·1019 cm−3. We attained lasing at 1.9 μm experimentally in the produced sample with a Q-factor of 106 pumped by a C-band narrow line laser.

The results of comparative analysis of the spectral and threshold characteristics of room-temperature injection microdisk lasers of the spectral range 1.2×× μm with different active regions, notably, InGaAsN/GaAs quantum wells or InAs/InGaAs/GaAs quantum dots are presented. It is found that microlasers of a comparable size with quantum wells possess a larger laser generation threshold when compared with microlasers with quantum dots. At the same time, the latter are characterized by a noticeably smaller fraction of emitted power corresponding to laser modes. The jump to lasing via an excited-state optical transition is also characteristic for them. Microdisk lasers based on InGaAsN alloy do not have these disadvantages. [ABSTRACT FROM AUTHOR]

Microdisk lasers 10–30 μm in diameter operating at room temperature without thermal stabilization and with an active region based on nanostructures of hybrid dimensionality—quantum wells–dots—are investigated. High-frequency measurements of the microlaser response are performed in the direct small-signal modulation mode, which makes it possible to establish the parameters of the operating speed and analyze their dependence on the microlaser diameter. It is found that the K factor is (0.8 ± 0.2) ns, which corresponds to optical losses of ~6 cm–1, and no regular dependence on the diameter is observed. It is found that the low-frequency component of the damping coefficient of relaxation oscillations is inversely proportional to the diameter. This character of the dependence evidences a decrease in the carrier lifetime in small-diameter microcavities, which can be associated with the prevalence of nonradiative recombination on their side walls. [ABSTRACT FROM AUTHOR]

We report a high-power monolithic Tm:YAP microlaser dual-end-pumped by two fiber-coupled LDs emitting at 792 nm. The microlaser operated in the continuous wave (CW) mode, with a wavelength of 1,936.82 nm. We obtain a maximum output power of 37.8 W with a beam quality factor M2 of 9.6 at a total incident power of 174.9 W, corresponding to a slope efficiency of 29.2% and an optical–optical conversion efficiency of 21.6%. [ABSTRACT FROM AUTHOR]

The vision of microchips that benefits from the high data rates of optical links has recently lead to novel concepts for the monolithic integration of active gain materials on silicon. In this letter, we use template-assisted selective epitaxy (TASE) for the monolithic integration of GaAs microsubstrates on silicon, which allows the subsequent integration of lattice-matched III–V laser cavities. We demonstrate the room-temperature operation of optically pumped microdisk-lasers with hexagonal top-facets and diameters as low as $1.2~\mu \text{m}$. The devices exhibit uniform emission spectra, low lasing thresholds of $P_{\mathrm{ th}}={13.6} \pm {0.7}$ pJ/pulse, and a high-temperature stability (${T}_{{0}} ={370}$ K). Scanning electron microscope and photoluminescence analysis of larger devices with a flat top-facet reveal a rotation of the crystal orientation and further reduce lasing thresholds. Our results show that the monolithic integration of III–V microsubstrates on silicon offers a versatile platform for on-chip light sources with excellent optical properties. [ABSTRACT FROM AUTHOR]

Amplified Spontaneous Emission is ubiquitous in systems with optical gain and is responsible for many opportunities and shortcomings. Its role in the progression from the simplest form of thermal radiation (single emitter spontaneous emission) all the way to coherent radiation from inverted systems is still an open question. We critically review observations of photon bursts in micro- and nanolasers, in the perspective of currently used measurement techniques, in relation to threshold-related questions for small devices. Corresponding stochastic predictions are analyzed, and contrasted with burst absence in differential models, in light of general phase space properties. A brief discussion on perspectives is offered in the conclusions.

In recent years, huge progress has been made in the development of rare-earth ion doped tellurite glass laser sources, ranging from watt- and multiwatt-level fiber lasers to nanowatt level microsphere lasers. Significant success has been achieved in extending the spectral range of tellurite fiber lasers generating at wavelengths beyond 2 μm as well as in theoretical understanding. This review is aimed at discussing the state of the art of neodymium-, erbium-, thulium-, and holmium-doped tellurite glass fiber and microsphere lasers.

We investigate in detail the resonant properties of a two-dimensional dielectric cavity with an equilateral triangle shape, using a numerical integral equations approach and a semiclassical approach. The homogeneous Müller boundary equations are used to calculate the resonant modes of a dielectric triangle in a wide range of frequencies. It is shown that the modes of dielectric triangles localized on families of periodic orbits can be well described in terms of a semiclassical superscar model. Special attention is given to the families of resonances based on the inscribed triangle periodic orbit. [ABSTRACT FROM AUTHOR]

• By analyzing the effect of Nd3+ doping concentration on the photothermal conversion efficiency of Nd:NaGdF 4 nanoparticles under continuous wave laser irradiation, the highest value in NaNdF 4 as a nanoscale heat source in the microstructure can reach 82.5%, which is greater than the currently reported nanoheaters. • The nanoheater is doped into the silica core by infrared laser ablation of microfibers, and the 793 nm trigger laser is injected axially through the fiber stem to trigger the photothermal effect, so that the PMMA-coated microcavity maintains a high intrinsic Q factor during all-optical tuning process, and possesses improved integration. • The nanoheater-doped microlaser achieves a wavelength tuning range of over 3.1 nm within the applied power intensity range of 1 to 1.62 W/mm2, which is more than 2.5 times larger than that of the undoped microlaser, confirming that nanoheater doping is an effective way to improve all-optical wavelength tunability. A novel all-optical tunable microlaser based on a polymer-coated microcavity embedded with a high-efficiency nanoheater is proposed. The large refractive index contrast between polymer and air helps to generate whispering gallery mode (WGM) resonances, so lasing from polymer microshells can be obtained via total internal reflection. Under the continuous triggering of a 793 nm laser, a maximum photothermal conversion efficiency of 82.9% was achieved using the Nd3+ heavily doped NaGdF 4 nanocrystal (NC) as a nanoscale heat source. The nanoheater was doped into the silica core by infrared laser ablation of the microfiber without contact with the WGM, enabling the coated microcavity to maintain a high Q factor up to 1.6 × 106. Significant heat transfer is achieved by the nanoheater absorbing the 793 nm trigger light pumped via the fiber stem, and the lasing wavelength is all-optical tuned over 3 nm at the applied power intensity range of 1 to 1.62 W/mm2. Furthermore, a tuning sensitivity of up to 1.86 nm/(W mm−2) is realized. The excellent photothermal properties of the lanthanide-doped nanoheater make the proposed microlaser attractive for future microelectronic device applications in all-optical networks. [ABSTRACT FROM AUTHOR]

Optical microcavities have been widely employed for sensing and detection, because of their ultrasensitive responsiveness to surrounding environment. Here we report an active diskshaped whispering gallery mode (WGM) microcavity fabricated from a water-sensitive material of dye-doped PEG-DA hydrogel through two-photon polymerization. We demonstrate that as the environment humidity changes the microcavity can homogenously expand or shrink to keep the disk-shaped structure, producing stable WGM lasing emissions.We further show that the WGM wavelength of the microlaser shifts linearly as the humidity increases from 25% to 65%, resulting in a wavelength variation of about 1.72 nm, which indicates that the stretchable microlaser can be acted as a humidity sensor. Due to the "smart" response of humidity and biocompatibility of PEG-DA hydrogel material, our results provide a way to the design and fabrication of flexible PEG-DA hydrogel biochips for biomedical applications. [ABSTRACT FROM AUTHOR]

We demonstrate ultralow-threshold neodymium-doped silica microsphere lasers on a silicon chip with lasing wavelengths of ~900 nm and ~1060 nm. Neodymium-doped microsphere cavities are fabricated with a series of doping concentrations using silica sol–gel films. Experimentally, we observe single-mode lasing emissions from the high-Q microsphere cavities with a threshold of as low as 1.2 µW. [ABSTRACT FROM AUTHOR]

Microlasers hold great promise for the development of photonics and optoelectronics. Among the discovered optical gain materials, colloidal quantum dots (CQDs) have been recognized as the most appealing candidate due to the facile emission tunability and solution processability. However, to date, it is still challenging to develop CQD-based microlasers with low cost yet high performance. Moreover, the poor long-term stability of CQDs remains to be the most critical issue, which may block their laser aspirations. Herein, we developed a unique but generic approach to forming a novel type of a whispering-gallery-mode (WGM) microbubble laser from the hybrid CQD/poly(methyl methacrylate) (PMMA) nanocomposites. The formation mechanism of the microbubbles was unraveled by recording the drying process of the nanocomposite droplets. Interestingly, these microbubbles naturally serve as the high-quality WGM laser resonators. By simply changing the CQDs, the lasing emission can be tuned across the whole visible spectral range. Importantly, these microbubble lasers exhibit unprecedented long-term stability (over one year), sufficient for practical applications. As a proof-of-concept, the potential of water vapor sensing was demonstrated. Our results represent a significant advance in microlasers based on the advantageous CQDs and may offer new possibilities for photonics and optoelectronics. [ABSTRACT FROM AUTHOR]

Development of nanowire photonics requires integration of different nanowire components into highly ordered functional heterostructures. Herein, we report a sequential self-assembly of binary molecular components into branched nanowire heterostructures (BNHs) via lattice-matched epitaxial growth, in which the microribbon backbone of 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene (BBOT) functions as blue-emitting microlaser source to pump the nanowire branches of BODIPY. By constructing Au electrodes on both branch sides and measuring the photocurrent in them, we successfully realize the integration of an organic laser and a power meter in a single device. This work provides a new insight into the integration of 1D organic nanostructures into BNHs for realizing organic multifunctional photonic devices. [ABSTRACT FROM AUTHOR]

Injection microlasers with an active region based on arrays of InGaAs/GaAs quantum well-dots, formed by deep etching, have been studied. The manner in which the current–voltage characteristic changes when the diameter microlaser is reduced shows that a nonelectrically conducting layer with thickness of about 1.5 μm is formed near the side surface, which leads to a decrease in the effective current flow area. [ABSTRACT FROM AUTHOR]