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In this paper, we propose the use of a microfluidic channel with flow focusing technique to fabricate solid state polymeric microlasers to precisely control sizes for mass production. Microlasers are made from a solution of UV curable polymer, namely polyethylene glycol diacrylate (PEGDA) with a molecular weight of 700 and rhodamine 6G laser dye at two different volumetric ratios (polymer to dye) of 4:1 and 2:1, respectively, which are used as the dispersed phase. A reservoir filled with liquid polydimethylsiloxane (PDMS) was used to cure the microlasers via UV lamp. A microchannel made of (PDMS) and size of 200 &micro, m was used in this paper, mineral oil was selected as the continuous phase. Two experiments are conducted by fixing the pressure flow for the dispersed phase to 188 mbar and 479.9 mbar, respectively. In both experiments, the pressure of the continuous phase (mineral oil) was varied between 1666.9 mbar and 1996.9 mbar. The measurement of the fabricated microlasers&rsquo, size was performed with the aid of the MATLAB Image Processing Toolbox by using photographs taken with a CMOS camera. The tunability of the highest size, ranging from 109 &micro, m to 72 &micro, m, was found for the PEGDA to dye ratio of 2:1 (188 mbar) and average standard deviation of 1.49 &micro, m, while no tunability was found for the 4:1 ratio (188 mbar). The tunability of the microlaser&rsquo, s size, ranging from 139 &micro, m to 130 &micro, m and an average standard deviation value of 1.47 &micro, m, was found for the 4:1 ratio (479.9 mbar). The fabricated microlasers presented a quality factor Q of the order 104, which is suitable for sensing applications. This technique can be used to control the size of the fabrication of a high number of solid state microlaser based UV polymers mixed with laser dyes.

Among the efforts to improve the performances of microlasers, optimization of the gain properties and cavity parameters of these lasers has attracted significant attention recently. Distributed feedback lasers, as one of the most promising candidate technologies for electrically pumped microlasers, can be combined with dual-gratings. This combination provides additional freedom for the design of the laser cavity. Here, a holographic dual-grating is designed to improve the distributed feedback laser performance. The holographic dual-grating laser consists of a colloidal quantum dot film with two parallel gratings, comprising first-order (210 nm) and second-order (420 nm) gratings that can be fabricated easily using a combination of spin coating and interference lithography. The feedback and the output from the cavity are controlled using the first-order grating and the second-order grating, respectively. Through careful design and analysis of the dual-grating, a balance is achieved between the feedback and the cavity output such that the lasing threshold based on the dual-grating is nearly half the threshold of conventional distributed feedback lasers. Additionally, the holographic dual-grating laser shows a high level of stability because of the high stability of the colloidal quantum dots against photobleaching.

Significance Microlasers in near-degenerate supermodes play a pivotal role for studies of non-Hermitian physics, novel light sources, and advanced sensors. However, the widely observed beating phenomena and the single-mode nature of the stimulated scattering have been generating the lasing characteristic dilemma. In this article, we experimentally elucidate the lasing spectral paradox by investigating the lasing dynamics of supermode Raman microlasers. The single-mode lasing behavior is confirmed, and the beating signal has been recognized as the transient interference during the lasing switching between the supermodes with the help of the self-injection technique. This work provides an insightful guidance for microlaser-based precision measurements and paves the way to reconfigurable light sources., 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.

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.

Microlasers have drawn considerable attention for applications in future optoelectronic nanoscience and nanotechnology, owing to the capability of scaling physical dimension of devices down to micro-/nanometer level. Currently, the most popular optical gain micro-/nanomaterials for microlasers are inorganic semiconductors, organic dyes and polymers, and organic-inorganic hybrid perovskites. However, these optical gain micro-/nanomaterials are faced with severe issues of either complicated manufacturing process or low stability under air, thermal, and photo-irradiation ambient. Comparatively, rare-earth (RE) ions-activated micro-/nanomaterials show unique merits for building-up microlasers, including low-cost fabrication, high environmental stability, abundant spectrum bands (ultraviolet to mid-infrared), high photoluminescence quantum yield (PLQY), etc. Recently, new RE ions-activated luminescent materials have been exploited as low surface defects and high PLQY in terms of diverse micro-/nanostructures, which have stimulated great progress in emerging RE ions activated microlasers, in combination with design and fabrication of novel optical feedback micro-/nanoresonators. Herein, recent advances in RE ions activated microlasers are reviewed from the aspects of Materials and Theories (including optical gain media and feedback micro-/nanomaterials), as well as some enlightening works on Upconverting Pumped Microlasers and Down-Shifting/Converting Pumped Microlasers; finally, future Perspectives are given by providing inspiration for exploitation of RE ions activated micro-/nanolasers with desired performances.

Dye-doped polymer microdroplet resonators were fabricated by injecting dye solutions into a low refractive index UV curable polymer. The self-assembled microdroplets had the various sizes ranging from 5 to 200 μm. Pumped by a pulse laser, whispering-gallery-mode (WGM) lasing emission from the microresonators was achieved. Experimental results show that the microresonators had the advantages of high-Q factors, low lasing thresholds, and good long-term stabilities. The injection method can provide a promising approach for fabricating the high-Q WGM microresonators, which had some potential applications in the fields of tunable microlasers and on-chip biosensing system.

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., The first examples of combined dry–wet transient devices in photonics are reported. Light emitting heterostructures and encoded optical labels based on sublimating nonpolar cyclic hydrocarbon substrates and water‐soluble polymer layers are realized and programmed for a mechanical disintegration after use.

We propose a novel method of fabrication of Photonic Crystal Spatial Filters using a Vapor Deposition method on microstructured surfaces. Such spatial filters –layers of around 10 micron thickness, are very useful for intracavity filtering in microlasers.

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., Miniaturized, wavelength‐tunable lasers based on deoxyribonucleic acid (DNA) nanofibers might combine enhanced stability of embedded dyes and tailored emission through morphology control. Here, these systems are studied by a quantum chemical investigation of the DNA–dye interactions, and elucidated in their waveguiding and mode confinement properties that lead to morphologically tailored lasing from the doped DNA structures.

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 mu m 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 degrees low angle passband is experimentally demonstrated. The proposed photonic structure can be considered as an ideal component for intracavity spatial filtering in microlasers.

This research was funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.03-2017.318 and the the EPSRC Standard Grant EP/T027258/1. The miniaturization of random lasers to the micrometer scale is challenging but fundamental for the integration of lasers with photonic integrated circuits and biological tissues. Herein, it is demonstrated that random lasers with a diameter from 30 to 160 μm can be achieved by using a simple emulsion process and selective chemical etching. These tiny random laser sources are made of either dye-doped polyvinyl alcohol (PVA) or bovine serum albumin (BSA) and they are in the form of microporous spheres with monodisperse pores of 1.28 μm in diameter. Clear lasing action is observed when the microporous spheres are optically excited with powers larger than the lasing threshold, which is 154 μJ mm−2 for a 75 μm diameter PVA microporous sphere. The lasing wavelength redshifts 10 nm when the PVA microsphere diameter increases from 34 to 160 μm. For BSA microspheres, the lasing threshold is around 55 μJ mm−2 for a 70 μm diameter sphere and 104 μJ mm−2 for a 35 μm diameter sphere. The simple fabrication process reported allows for detail studies of morphology and size, important for fundamental studies of light–matter interaction in complex media, and applications in photonic integrated circuits, photonic barcoding, and optical biosensing. Publisher PDF

We demonstrated the ultrasound modulated droplet lasers, in which the laser intensity from whispering gallery mode (WGM) of oil droplets can be reversibly enhanced up to 20-fold when the ultrasound pressure is beyond a certain threshold. The lasing enhancement was investigated with various ultrasound frequencies and pressures. Furthermore, the ultrasound modulation of the laser output was achieved by controlling the ultrasound pressure, the duty cycle, and the frequency of ultrasound bursts. Its potential application was explored via the study on a human whole blood vessel phantom. A theoretical analysis was also conducted, showing that the laser emission enhancement results from the directional emission from a deformed cavity under ultrasound pressure. Our studies reveal the unique capabilities of ultrasound modulated droplet lasers, which could lead to the development of laser emission-based microscopy for deep tissue imaging with high spatial resolution and detection sensitivity that may overcome the long-standing drawback of traditional fluorescence imaging. This research was supported by National Science Foundation (NSF) (ECCS-1607250) and National Institutes of Health(R01CA186769).

Resonators and the way they couple to external radiation rely on very different concepts if one considers devices belonging to the photonic and electronic worlds. The terahertz frequency range, however, provides intriguing possibilities for the development of hybrid technologies that merge ideas from both fields in novel functional designs. In this paper, we show that high-quality, subwavelength, whispering-gallery lasers can be combined to form a linear dipole antenna, which creates a very efficient, low-threshold laser emission in a collimated beam pattern. For this purpose, we employ a terahertz quantum-cascade active region patterned into two 19-μm-radius microdisks coupled by a suspended metallic bridge, which simultaneously acts as an inductive antenna and produces the dipole symmetry of the lasing mode. Continuous-wave vertical emission is demonstrated at approximately 3.5 THz in a very regular, low-divergence (±10°) beam, with a high slope efficiency of at least 160 mW A â '1 and a mere 6 mA of threshold current, which is ensured by the ultra-small resonator size (V RES/Î" 3 â ‰10 â '2). The extremely low power consumption and the superior beam brightness make this concept very promising for the development of miniaturized and portable THz sources to be used in the field for imaging and sensing applications as well as for exploring novel optomechanical intracavity effects.

Metal-halide perovskites are recently extensively investigated as light absorbing material in solar cells. The outstanding optoelectronic properties and tunable light emission of the perovskites also make them promising candidates for light emitting diodes and lasers. However, understanding the relevant mechanisms and processes of the dependence of perovskite light emission on temperature and crystal size is still challenging. Herein, the CH3NH3PbBr3 monocrystals of different sizes are uniformly excited by two-photon absorption at 800 nm (100 fs, 1 KHz). In contrast to the reported relative large exciton binding energy (≈76 meV) and spectrum clearly resolved excitonic absorption, the light emission origin in CH3NH3PbBr3 microcrystals at room temperature is unambiguously determined to be dominated by free electron–hole bimolecular recombination. The coherent light emission threshold of CH3NH3PbBr3 microcrystal increases with temperature, which is closely related to the temperature induced transition from exciton gas to free charge carriers. In addition, the coherent light emission threshold is found to decrease with the microcrystal size, which could be well interpreted by the interaction between the optical confinement, defect density, and cavity quantum electrodynamics effect. These results presented here may facilitate the development of perovskite light emitting diodes and lasers. NRF (Natl Research Foundation, S’pore) MOE (Min. of Education, S’pore) Accepted version

In this work we show how a continuous wave, low threshold and well collimated terahertz laser source can be obtained by coupling two sub-wavelength whispering galleries quantum cascade optical resonators with a suspended metallic bridge.

Optical microcavities that confine light in high-Q resonance promise all of the capabilities required for a successful next-generation microsystem biodetection technology. Label-free detection down to single molecules as well as operation in aqueous environments can be integrated cost-effectively on microchips, together with other photonic components, as well as electronic ones. We provide a comprehensive review of the sensing mechanisms utilized in this emerging field, their physics, engineering and material science aspects, and their application to nanoparticle analysis and biomolecular detection. We survey the most recent developments such as the use of mode splitting for self-referenced measurements, plasmonic nanoantennas for signal enhancements, the use of optical force for nanoparticle manipulation as well as the design of active devices for ultra-sensitive detection. Furthermore, we provide an outlook on the exciting capabilities of functionalized high-Q microcavities in the life sciences.

A novel approach is presented to realize compact III–V-on-silicon microlasers. The concept relies on resonant mirrors in which the close interaction between a III–V waveguide and an underlying silicon cavity provides high narrow-band reflection back into the III–V waveguide. Combining two such mirrors with a III–V waveguide in between leads to a resonant mirror laser. The properties of the resonant mirror are studied for a variety of device parameters. Using this information, the properties of the resulting laser, such as threshold power and side-mode suppression ratio, are investigated. These calculations correspond well to proof-of-concept experimental results.

Alkaline earth sulfide phosphors doped with Eu 2 + or Ce 3 + are good candidates for wavelength conversion in LEDs for general lighting applications. A very broad emission spectrum can be obtained by preparing SrS:Eu–SrS:Ce core–shell particles. These microcrystals are rectangular cuboids and can also be efficiently excited with electrons in a scanning electron microscope. The broad emission spectrum, ranging from 450 nm to 650 nm, consists of the combined emission of Ce 3 + and Eu 2 + centers. Using cathodoluminescence (CL) in a scanning electron microscope, evaluation of the emission characteristics of individual cuboids was possible. Sharp peaks in the CL-spectra of individual particles could be observed and described as being resonance modes. The spectral positions and the line widths of resonance modes in these core–shell microcrystals are predicted by an extension of the plane wave model, taking into account the dispersion of the refractive index and the existence of open orbits.

Optical whispering gallery mode (WGM) microresonators have attracted great attention due to their remarkable proper-ties such as extremely high quality factor, small mode volume, tight confinement of modes, and strong evanescent field. All these properties of WGM microresonators have ensured their great potentials for applications, such as physical sensors, bio/chemical sensors and microlasers. In this mini-review, the key parameters and coupling conditions of WGM microresonators are firstly introduced. The geometries of WGM optical microcavities are presented based on their fabrication methods. This is followed by the discussion on the state-of-the-art applications of WGM microresonators in sensors and microlasers.