Ultralow-Threshold and High-Quality Whispering-Gallery-Mode Lasing from Colloidal Core/Hybrid-Shell Quantum Wells

Dimension Evolution of Self-Assembled Organic Microcrystal for Laser and Polarization-Rotation Function

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.

Phosphate Glass Microspheres with Silver Nanoparticles for Whispering Gallery Mode Resonators

Glass microspheres have gained significant attention over the years in the field of photonics due to their application in whispering gallery mode (WGM) microresonator platforms. However, the synthesis of glass spheres in the micro regime remains challenging, while it relies mostly on complicated synthetic methods or sol-gel chemistry. Herein, we demonstrate the controlled formation of phosphate glass microspheres by means of a simple, fast, low-temperature, post-glass melting thermal treatment of previously quenched glass. Moreover, we report on the simultaneous formation of silver nanoparticles (AgNPs) on the surface of glass spheres upon the same treatment. The formation of metal nanoparticles onto the glass spheres induces attractive optical and plasmonic properties, believed to be suitable for WGM resonator-based applications, as well as a wide range of optoelectronic, photonic, and sensing applications.

Highly Transparent, Yet Photoluminescent: 2D CdSe/CdS Nanoplatelet-Zeolitic Imidazolate Framework Composites Sensitive to Gas Adsorption

In this work, thin composite films of zeolitic imidazolate frameworks (ZIFs) and colloidal two-dimensional (2D) core-crown CdSe/CdS nanoplatelet (NPL) emitters with minimal scattering are formed by a cycled growth method and yield highly transparent coatings with strong and narrow photoluminescence of the NPLs at 546 nm (FWHM: 25 nm) in a solid-state composite structure. The porous ZIF matrix acts as functional encapsulation for the emitters and enables the adsorption of the guest molecules water and ethanol. The adsorption and desorption of the guest molecules is then characterized by a reversable photoluminescence change of the embedded NPLs. The transmittance of the composite films exceeds the values of uncoated glass at visible wavelengths where the NPL emitters show no absorption (>540 nm) and renders them anti-reflective coatings. At NPL absorption wavelengths (440-540 nm), the transmittance of the thin composite film-coated glass lies close to the transmittance of uncoated glass. The fast formation of innovative, smooth NPL/ZIF composite films without pre-polymerizing the colloidal 2D nanostructures first provides a powerful tool toward application-oriented photoluminescence-based gas sensing.

Miniaturized Laser Probe for Exosome-Based Cancer Liquid Biopsy

Exosomes have been established as a valuable tool for clinical applications for the purpose of liquid biopsy and therapy. However, the clinical practice of exosomes as cancer biopsy markers is still to a very low extent. Active mode optical microcavity with microlaser emission has aroused as a versatile approach for chemical and biological sensing due to its benefits of larger photon population, increased effective Q-factor, decreased line width, and improved sensitivity. Herein, we report a label-free and precise quantification of exosome vesicles and surface protein profiling of breast cancer exosomes using functionalized active whispering gallery mode (WGM) microlaser probes. A detection limit of 40 exosomes per microresonator was achieved. The proposed system enabled a pilot assay of quantitative exosome analysis in cancer patients' blood with only a few microliters of sample consumption, holding good potential for large-scale cancer liquid biopsy. Multiplexed functionalization of the optical microresonator allowed us to profile cancer exosomal surface markers and distinct subclasses of breast cancer-associated exosomes and monitor drug treatment outcomes. Our findings speak volumes about the advantages of the WGM microlaser sensor, including very small sample consumption, low detection limit, high specificity, and ease of operation, offering a promising means for precious clinical sample analysis.

27% slope efficiency in a WGM microcavity enabled by an Yb:YAG crystalline film

The choice of a laser gain medium is crucial in achieving efficient and high-power outputs of optically stimulated WGM microcavity lasers. This work employs an Yb:YAG crystalline film as the gain medium for the microdisk laser. The Yb:YAG crystalline film is exfoliated from a bulk of a Yb:YAG crystal by the ion-implantation-enhanced etching method. The crystalline film is shaped into a microdisk through focused ion beam milling. This Yb:YAG microdisk laser achieves a single-mode laser output (with a side-mode-suppression ratio of 27.8 dB) under a 946 nm laser pumping. The maximum slope efficiency reaches 27% with a maximum output power of 1.1 mW.

Whispering gallery mode micro-lasing in CsPbI3 quantum dots coated on TiO2 microspherical resonating cavities

Whispering gallery mode (WGM) lasing in CsPbI₃ quantum dots (QDs) coated on TiO₂ spherical microcavities is demonstrated. The photoluminescence emission from a CsPbI₃-QDs gain medium strongly couples with a TiO₂ microspherical resonating optical cavity. Spontaneous emission in these microcavities switches to a stimulated emission above a distinct threshold point of 708.7 W/cm². Lasing intensity increases three to four times as the power density increases by one order of magnitude beyond the threshold point when the microcavities are excited with a 632-nm laser. WGM microlasing with quality factors as high as Q∼1195 is demonstrated at room temperature. Quality factors are found to be higher for smaller TiO₂ microcavities (∼2 µm). CsPbI₃-QDs/TiO₂ microcavities are also found to be photostable even after continuous laser excitation for 75 minutes. The CsPbI₃-QDs/TiO₂ microspheres are promising as WGM-based tunable microlasers.

Organic Synthetic Photonic Systems with Reconfigurable Parity-Time Symmetry Breaking for Tunable Single-Mode Microlasers

Synthetic photonic materials exploiting the quantum concept of parity-time (PT) symmetry lead to an emerging photonic paradigm-non-Hermitian photonics, which is revolutionizing the photonic sciences. The non-Hermitian photonics dealing with the interplay between gain and loss in PT synthetic photonic material systems offers a versatile platform for advancing microlaser technology. However, current PT-symmetric microcavity laser systems only manipulate imaginary parts of the refractive indices, suffering from limited laser spectral bandwidth. Here, an organic composite material system is proposed to synthesize reconfigurable PT-symmetric microcavities with controllable complex refractive indices for realizing tunable single-mode laser outputs. A grayscale electron-beam direct-writing technique is elaborately designed to process laser dye-doped polymer films in one single step into microdisk cavities with periodic gain and loss distribution, which enables thresholdless PT-symmetry breaking and single-mode laser operation. Furthermore, organic photoisomerizable compounds are introduced to reconfigure the PT-symmetric systems in real-time by tailoring the real refractive index of the polymer microresonators, allowing for a dynamically and continuously tunable single-mode laser output. This work fundamentally enhances the PT-symmetric photonic systems for innovative design of synthetic photonic materials and architectures.

Dome-shaped mode lasing from liquid crystals for full-color lasers and high-sensitivity detection

In this communication, we report a new class of oscillation mode, dome-shaped mode (DSM), in liquid crystal (LC) microlasers. A record high Q-factor over 24 000 is achieved in LC soft-matter microlasers. We successfully presented a proof-of-concept demonstration of red, green, blue (RGB) LC-DSM microlaser pixels with a 74% broader achievable color gamut than the standard RGB color space. Besides, the detection limit for acetone vapor molecules is as low as 0.5 ppm, confirming the excellent potential of the proposed LC-DSM microlaser in ultra-high sensitivity detection.

Magnetic-Field-Driven Reconfigurable Microsphere Arrays for Laser Display Pixels

Reconfigurable microlaser arrays are essential to the construction of display panels where the individual pixel should be highly tunable in resonance mode, optical polarization, and lasing wavelength upon external control signals. Here we demonstrate a facile yet reliable approach to fabrication of organic microlaser pixels, in which the assembly of microsphere arrays on each pixel is controlled according to the near-field magnetostatic confinement. The geometrical configuration of diamagnetic microspheres could be readily modulated with the near-field potential traps by using the external field to alternate the saturation magnetization of the underneath micromagnet. The motion of microspheres can be modulated among several states upon applied field, and the reconfigurable microsphere array is thus achieved with high spatial precision and rapid temporal response. Moreover, both isolated and coupled spheres serve as low-threshold microlasers with tunable optical resonance modes, whereas the switching between the vertical and horizontal alignments of coupled spheres manipulates the polarization of lasing outputs. By repeating the magnetostatic confinement on the same substrate, the full-color laser display pixels with magnetically tunable color expression capability are successfully achieved.

Motor-like microlasers functioning in biological fluids

Microlasers integrated with biological systems have received tremendous attention for their intense light intensity and narrow linewidth recently, serving as a powerful tool for studying complex dynamics and interactions in scattered biological micro-environments. However, manipulation of microlasers with controllable motions and versatile functions remains elusive. Herein, we introduce the concept of motor-like microlasers formed by magnetic-doped liquid crystal droplets, in which the direction and velocity could be controlled by altering internal magnetic nanoparticles or external magnetic fields. Both translational and rotatory motions of the lasing resonator could be continually changed in real-time. Lasing-encoded motors carrying different functions and lasing wavelengths were also achieved. Finally, we demonstrate the potential of motor-like microlasers by functioning as a localized stimulation emission light source to stimulate or illuminate living cells, providing a novel approach for switching on/off light emissions and subcellular imaging. Laser emitting micromotors offer a facile system for precise manipulation of microlasers in biological fluids, providing new insight into the development of programmable on-chip laser devices and laser-emitting intelligent systems.

Dynamic manipulation of WGM lasing by tailoring the coupling strength

Miniaturized lasing with dynamic manipulation is critical to the performance of compact and versatile photonic devices. However, it is still a challenge to manipulate the whispering gallery mode lasing modes dynamically. Here, we design the quasi-three-dimensional coupled cavity by a micromanipulation technique. The coupled cavity consists of two intersection polymer microfibers. The mode selection mechanism is demonstrated experimentally and theoretically in the coupled microfiber cavity. Dynamic manipulation from multiple modes to single-mode lasing is achieved by controlling the coupling strength, which can be quantitatively controlled by changing the coupling angle or the coupling distance. Our work provides a flexible alternative for the lasing mode modulation in the on-chip photonic integration.

Towards Perfect Ultra-Broadband Absorbers, Ultra-Narrow Waveguides, and Ultra-Small Cavities at Optical Frequencies

In this study, we design ultra-broadband optical absorbers, ultra-narrow optical waveguides, and ultra-small optical cavities comprising two-dimensional metallic photonic crystals that tolerate fabrication imperfections such as position and radius disorderings. The absorbers containing gold rods show an absorption amplitude of more than 90% under 54% position disordering at 200<λ<530 nm. The absorbers containing silver rods show an absorptance of more than 90% under 54% position disordering at 200<λ<400 nm. B-type straight waveguides that contain four rows of silver rods exposed to air reveal normalized transmittances of 75% and 76% under 32% position and 60% radius disorderings, respectively. B-type L-shaped waveguides containing four rows of silver rods show 76% and 90% normalized transmittances under 32% position and 40% radius disorderings, respectively. B-type cavities containing two rings of silver rods reveal 70% and 80% normalized quality factors under 32% position and 60% radius disorderings, respectively.

Deterministic Assembly of Colloidal Quantum Dots for Multifunctional Integrated Photonics

Colloidal quantum dots (CQDs) are promising for photonic applications toward lasers, waveguides, and photodetectors. However, integration of high-quality photonic elements into multifunctional devices is still restricted by optical losses stemming from the accumulation of defects and disorder in the solution process. Herein, a platform with a directional Laplace pressure is created for eliminating undesired pinning of liquid fronts in the solution process and boosting ordered assembly of CQDs into designable micro-/nanostructures. The versatility and robustness of this method are demonstrated by deterministic patterning of CQDs with different components and photoluminescence spectra onto various substrates. On the basis of this platform, microring lasers with tunable emission modes, low-loss waveguides, and their coupled structures have been reached for direct on-chip generation and propagation of coherent light. A proof-of-concept demonstration of integrated circuits is also conducted by combining microcavity lasers with waveguides for encoding photonic outputs into information bits.