Single-mode nanolasers based on FP-WGM hybrid cavity coupling.

As an idealized light source, semiconductor nanowire (NW) lasers have been extensively studied due to its potential applications in many fields such as optoelectronics, nanophononics, optical communication, signal processing, and displays. In this letter, we proposed a novel approach to realize a single-mode nanolaser by forming an Fabry-Perot whispering gallery mode (FP-WGM) hybrid nanocavity between two cross-contact CdS NWs, i.e.xandy-NW. In our method,x-NW supports the regular FP oscillation in the axis direction while the cross section ofy-NW provides a ultrasmall WGM nanocavity with a higherQ-factor and mode election which confirms the specific single mode can be excited. Experimentally, single-mode lasing emission centered at 517 nm was obtained with full width at half maximum of 0.08 nm and lasing threshold of ∼50 kW cm-2. The suggested designing skills projected a general strategy for lasing mode regulation and single-mode realization. The single-mode low-threshold lasing strategy in coupled NWs may open a new avenue for practical applications of NW lasers and further trigger other photonic devices at a visible range.

Structural Engineering of Hierarchical Aerogels Hybrid Networks for Efficient Thermal Comfort Management and Versatile Protection.

In recent years, growing concerns regarding energy efficiency and heat mitigation, along with the critical goal of carbon neutrality, have drawn human attention to the zero-energy-consumption cooling technique. Passive daytime radiative cooling (PDRC) can be an invaluable tool for combating climate change by dispersing ambient heat directly into outer space instead of just transferring it across the surface. Although significant progress has been made in cooling mechanisms, materials design, and application exploration, PDRC faces challenges regarding functionality, durability, and commercialization. Herein, a silica nanofiber aerogels (SNAs) functionalized poly(vinylidene fluoride-co-hexafluoropropene) (P(VDF-HFP)) membrane (SFP membrane), inspired by constructional engineering is constructed. As-prepared membranes with flexible network structure combined hierarchical structure design and practicability principal. As the host material for thermal comfort management (TCM) and versatile protection, the SFP membrane features a large surface area, porous structure, and a robust skeleton that can render excellent mechanical properties. Importantly, the SFP membrane can keep exceptional solar reflectivity (0.95) and strong mid-infrared emittance (0.98) drop the temperature to 12.5 °C below ambient and 96 W m-2 cooling power under typical solar intensities over 910 W m-2 . This work provides a promising avenue for high performance aerogel membranes that can be created for use in a wide variety of applications.

Theory and Fundamental Limit of Quasiachromatic Metalens by Phase Delay Extension.

The periodic extension of phase difference is commonly applied in device design to obtain phase compensation beyond the system's original phase modulation capabilities. Based on this extension approach, we propose the application of quasiphase delay matching to extend the range of dispersion compensation for meta-atoms with limited height. Our theory expands the limit of frequency bandwidth coverage and relaxes the constraints of aperture, NA, and bandwidth for metalenses. By applying the uncertainty principle, we explain the fundamental limit of this achromatic bandwidth and obtain the achromatic spectrum using perturbation analysis. To demonstrate the effectiveness of this extended limit, we simulate a quasiachromatic metalens with a diameter of 2 mm and a NA of 0.55 in the range of 400-1500 nm. Our findings provide a novel theory for correcting chromatic aberration in large-diameter ultrawide bandwidth devices.

Broadband noise-like pulse generation at 1 µm via dispersion and nonlinearity management.

We demonstrate that optical microfibers integrated in Yb-doped fiber lasers boost broadband noise-like pulse (NLP) generation via dispersion and nonlinearity management, with an optical spectrum spanning from below 1000 nm to beyond 1600 nm when the diameter of the optical microfiber is 1.2 µm. Numerical simulations show that dispersion and nonlinearity management provided by the optical microfiber is responsible for the broadband NLP generation. Furthermore, it is shown experimentally that dispersion and nonlinearity management via optical microfibers can also bring the highest optical rogue waves along with the broadest optical spectrum.

Fast volumetric fluorescence imaging with multimode fibers.

In this Letter, we propose a compact multimode fiber endoscope which employs wavefront shaping with a digital micromirror device (DMD). An automated single calibration step allows us to correct for optical misalignment, and the method achieves accurate focusing at various depths in the sample through rapid switching of holographic patterns by the DMD. The speed of calibration is one or two orders of magnitude faster than existing methods. The method, single calibration multimode fiber imaging (SCMFI), is compared with existing methods, and its performance is validated. We show a near diffraction limited focusing capability at imaging depths up to 110 µm with near constant lateral resolutions of 1.4 µm. Finally, we demonstrate the method for the imaging of small fluorescent beads embedded in a 3D matrix. The results indicate excellent power penetration and focusing performance. Combined with the high speed of SCMFI, this paves the way for volumetric tissue endoscopy at depth.

High contrast multimode fiber imaging based on wavelength modulation.

The property of the multimode fiber (MMF) to remain minimally invasive when performing high-resolution observations, makes MMF imaging of particular interest in many related fields recently, especially in bioendoscopic imaging. Imaging through point scanning is the most common method of MMF imaging now, which means modulating a scanning focal spot on the end face of fiber by controlling modes in the fiber. However, due to mode interference, there is always a background speckle around the focal spot formed, which affects imaging quality seriously. Increasing controllable modes number can effectively suppress the effects of the background speckle, but it is limited by the number of controllable elements (the elements number of wavefront shaping devices). Here, we propose a new, to the best of our knowledge, method to increase the contrast-to-noise ratio (CNR) of MMF imaging without increasing the number of controllable modes. Wavelength modulation is introduced to suppress the background. The background speckles turn to be uncorrelated, whereas the signal patterns turn to be strongly correlated and can be added when 20 different wavelengths of light form a focal spot at the same position at the distal end of MMF, respectively. Thus, a four-fold enhancement can be gained in CNR at a 200 µm field-of-view (FOV) by suppressing background speckles.

Efficient small molecular organic light emitting diode with graphene cathode covered by a Sm layer with nano-hollows and n-doped by Bphen:Cs2CO3 in the hollows.

Graphene is a favorable candidate for electrodes of organic light emitting diodes (OLEDs). Graphene has quite a high work function of ∼4.5 eV, and has been extensively studied when used as anodes of OLEDs. In order to use graphene as a cathode, the electron injection barrier between the graphene cathode and the electron transport layer has to be low enough. Using 4,7-diphenyl-1,10-phenanthroline (Bphen):Cs2CO3 to n-dope graphene is a very good method, but the electron injection barrier between the n-doped graphene and Bphen:Cs2CO3 is still too high to be ∼1.0 eV. In this work, in order to further reduce the electron injection barrier, a novel method is suggested. On the graphene cathode, a Sm layer with a lot of nano-hollows, and subsequently a layer of Bphen:Cs2CO3, are deposited. The Bphen:Cs2CO3 can n-dope graphene in the nano-hollows, and the Fermi level of the graphene rises. The nano Sm layer is very easily oxidized. Oxygen adsorbed on the surface of graphene may react with Sm to form an O--Sm+ dipole layer. On the areas of the Sm oxide dipole layer without nano-hollows, the electron injection barrier can be further lowered by the dipole layer. Electrons tend to mainly inject through the lower electron barrier where the dipole layer exists. Based on this idea, an effective inverted small molecular OLED with the structure of graphene/1 nm Sm layer with a lot of nano-hollows/Bphen:Cs2CO3/Alq3:C545T/NPB/MoO3/Al is presented. The maximum current efficiency and maximum power efficiency of the OLED with a 1 nm Sm layer are about two and three times of those of the reference OLED without any Sm layer, respectively.

Broadly defining lasing wavelengths in single bandgap-graded semiconductor nanowires.

Designing lasing wavelengths and modes is essential to the practical applications of nanowire (NW) lasers. Here, according to the localized photoluminescence spectra, we first demonstrate the ability to define lasing wavelengths over a wide range (up to 119 nm) based on an individual bandgap-graded CdSSe NW by forward cutting the NW from CdSe to CdS end. Furthermore, free spectral range (FSR) and modes of the obtained lasers could be controlled by backward cutting the NW from CdS to CdSe end step-by-step. Interestingly, single-mode NW laser with predefined lasing wavelength is realized in short NWs because of the strong mode competition and increase in FSR. Finally, the gain properties of the bandgap-graded NWs are investigated. The combination of wavelength and mode selectivity in NW lasers may provide a new platform for the next generation of integrated optoelectronic devices.

Passive Self-Sustained Thermoelectric Devices Powering the 24 h Wireless Transmission via Radiation-Cooling and Selective Photothermal Conversion.

The rapid development of the Internet of Things has triggered a huge demand for self-sustained technology that can provide a continuous electricity supply for low-power electronics. Here, a self-sustained power supply solution is demonstrated that can produce a 24 h continuous and unipolar electricity output based on thermoelectric devices by harvesting the environmental temperature difference, which is ingeniously established utilizing radiation cooling and selective photothermal conversion. The developed prototype system can stably maintain a large temperature difference of about 1.8 K for a full day despite the real-time changes in environmental temperature and solar radiation, thereby driving continuous electricity output using the built-in thermoelectric device. Specifically, the large output voltage of >102 mV and the power density of >4.4 mW m-2 could be achieved for a full day, which are outstanding among the 24 h self-sustained thermoelectric devices and far higher than the start-up values of the wireless temperature sensor and also the light-emitting diode, enabling the 24 h remote data transmission and lighting, respectively. This work highlights the application prospects of self-sustained thermoelectric devices for low-power electronics.

Multicolour laser from a single bandgap-graded CdSSe alloy nanoribbon.

Multicolour lasing with wavelength varying from 578 nm to 640 nm is realized from a single bandgap-graded CdSSe alloy nanoribbon, by selecting the excited spot at room temperature. Though reabsorption is a serious problem to achieve lasing at short wavelength, multiple scatters on the nanoribbon form localized cavities, and thus lasing at different wavelengths is realized. By increasing the excitation area, multicolour lasing from the same nanoribbon is also observed simultaneously.

Bending effects on lasing action of semiconductor nanowires.

High flexibility has been one of advantages for one-dimensional semiconductor nanowires (NWs) in wide application of nanoscale integrated circuits. We investigate the bending effects on lasing action of CdSe NWs. Threshold increases and differential efficiency decreases gradually when we decrease the bending radius step by step. Red shift and mode reduction in the output spectra are also observed. The bending loss of laser oscillation is considerably larger than that of photoluminescence (PL), and both show the exponential relationship with the bending radius. Diameter and mode dependent bending losses are investigated. Furthermore, the polarizations of output can be modulated linearly by bending the NWs into different angles continuously.

Roll-to-roll printing trench-like metasurface film for radiative cooling.

A Roll-to-roll technology can enable the fabrication of trench-like photonic meta-structures that are strongly absorptive in the MIR region, providing a controllable optical response for diurnal radiative cooling.

Single-mode plasmonic waveguiding properties of metal nanowires with dielectric substrates.

Single-mode plasmonic waveguiding properties of metal nanowires with dielectric substrates are investigated using a finite-element method. Au and Ag are selected as plasmonic materials for nanowire waveguides with diameters down to 5-nm-level. Typical dielectric materials with relatively low to high refractive indices, including magnesium fluoride (MgF2), silica (SiO2), indium tin oxide (ITO) and titanium dioxide (TiO2), are used as supporting substrates. Basic waveguiding properties, including propagation constants, power distributions, effective mode areas, propagation distances and losses are obtained at the typical plasmonic resonance wavelength of 660 nm. Compared to that of a freestanding nanowire, the mode area of a substrate-supported nanowire could be much smaller while maintaining an acceptable propagation length. For example, the mode area and propagation length of a 100-nm-diameter Ag nanowire with a MgF2 substrate are about 0.004 µm2 and 3.4 µm, respectively. The dependences of waveguiding properties on geometric and material parameters of the nanowire-substrate system are also provided. Our results may provide valuable references for waveguiding dielectric-supported metal nanowires for practical applications.

Microlaser based on a hybrid structure of a semiconductor nanowire and a silica microdisk cavity.

We experimentally demonstrate a hybrid structure microlaser on chip with a single CdSe nanowire attached to a high-Q silica microdisk cavity at room temperature. When pumped by a 532 nm pulse laser, both single-longitudinal mode and multi-longitudinal mode lasers with linewidth of 0.18 nm are obtained from the hybrid structure with a 58-µm-diameter microdisk and a 250-nm diameter nanowire. The measured lasing threshold of the microlaser is as low as 100 µJ/cm².

On-chip three-dimensional high-Q microcavities fabricated by femtosecond laser direct writing.

We report on the fabrication of three-dimensional (3D) high-Q whispering gallery microcavities on a fused silica chip by femtosecond laser microfabriction, enabled by the 3D nature of femtosecond laser direct writing. The processing mainly consists of formation of freestanding microdisks by femtosecond laser direct writing and subsequent wet chemical etching. CO(2) laser annealing is followed to smooth the microcavity surface. Microcavities with arbitrary tilting angle, lateral and vertical positioning are demonstrated, and the quality (Q)-factor of a typical microcavity is measured to be up to 1.07 × 10(6), which is currently limited by the low spatial resolution of the motion stage used during the laser patterning and can be improved with motion stages of higher resolutions.

General approach to splicing optical microfibers via polymer nanowires.

We demonstrate a general approach to splicing microfibers via polymer nanowires. Chloroform dissolved polystyrene nanowires are used to splice silica, tellurite glass, and semiconductor microfibers or nanowires, with splicing loss down to 0.51 dB. Using spliced microfiber structures, we also demonstrate microfiber ring resonators and Mach-Zehnder interferometers with high robustness. The splicing technique demonstrated here promises high potentials for robust optical integration of microfibers or nanowires for functional circuits or devices.

Digital Economy and Health: A Case Study of a Leading Enterprise's Value Mining Mode in the Global Big Health Market.

Coronavirus disease 2019 (COVID-19) swept across the world and posed a serious threat to human health. Health and elderly care enterprises are committed to continuously improving people's health. With the rapid development of the digital economy, many enterprises have established digital product-service ecosystems after combining "Internet +," big data, cloud computing, and the big health industry. This paper uses the case study method to analyze the overseas market value mining mode of health and elderly care enterprises through in-depth research on leading health and elderly care enterprises. This study explores the value mining mode of the leading enterprise's global big health market using a cluster analysis and Bayesian model with the support of data on geographical characteristics, users' sleep habits, and national big health. This paper theoretically summarizes the successful cases of health and elderly care enterprises through digital transformation, which provides a useful reference for the intelligent transformation of the health and elderly care industry.

High-Refractive-Index Chip with Periodically Fine-Tuning Gratings for Tunable Virtual-Wavevector Spatial Frequency Shift Universal Super-Resolution Imaging.

Continued research in fields such as materials science and biomedicine requires the development of a super-resolution imaging technique with a large field of view (FOV) and deep subwavelength resolution that is compatible with both fluorescent and nonfluorescent samples. Existing on-chip super-resolution methods exclusively focus on either fluorescent or nonfluorescent imaging, and, as such, there is an urgent requirement for a more general technique that is capable of both modes of imaging. In this study, to realize labeled and label-free super-resolution imaging on a single scalable photonic chip, a universal super-resolution imaging method based on the tunable virtual-wavevector spatial frequency shift (TVSFS) principle is introduced. Using this principle, imaging resolution can be improved more than threefold over the diffraction limit of a linear optical system. Here, diffractive units are fabricated on the chip's surface to provide wavevector-variable evanescent wave illumination, enabling tunable spatial frequency shifts in the Fourier space. A large FOV and resolutions of λ/4.7 and λ/7.1 were achieved for label-free and fluorescently labeled samples using a gallium phosphide (GaP) chip. With its large FOV, compatibility with different imaging modes, and monolithic integration, the proposed TVSFS chip may advance fields such as cell engineering, precision industry inspection, and chemical research.

Plasmonic resonance of whispering gallery modes in an Au cylinder.

We demonstrate whispering gallery (WG) resonance of surface plasmon polaritons (SPPs) in a 2-dimensional confined Au cylinder by self interference. Despite the leakage of SPPs along the axis of the cylinder, Q factors of 375 are obtained in a cylinder with diameter of 30 µm. The coupling-angle-dependence of the WG resonance is also investigated. Our results open opportunities for a new category of plasmonic cavities with 2-dimensional confinement, and this may be applied to a variety of simple and natural metallic micro or nanostructures.

Highly Resolved and Robust Dynamic X-Ray Imaging Using Perovskite Glass-Ceramic Scintillator with Reduced Light Scattering.

All-inorganic perovskite quantum dots (QDs) CsPbX3 (X = Cl, Br, and I) have recently emerged as a new promising class of X-ray scintillators. However, the instability of perovskite QDs and the strong optical scattering of the thick opaque QD scintillator film imped it to realize high-quality and robust X-ray image. Herein, the europium (Eu) doped CsPbBr3 QDs are in situ grown inside transparent amorphous matrix to form glass-ceramic (GC) scintillator with glass phase serving as both matrix and encapsulation for the perovskite QD scintillators. The small amount of Eu dopant optimizes the crystallization of CsPbBr3 QDs and makes their distribution more uniform in the glass matrix, which can significantly reduce the light scattering and also enhance the photoluminescence emission of CsPbBr3 QDs. As a result, a remarkably high spatial resolution of 15.0 lp mm-1 is realized thanks to the reduced light scattering, which is so far a record resolution for perovskite scintillator based X-ray imaging, and the scintillation stability is also significantly improved compared to the bare perovskite QD scintillators. Those results provide an effective platform particularly for the emerging perovskite nanocrystal scintillators to reduce light scattering and improve radiation hardness.