Omnidirectional broadband phase modulation by total internal reflection.

Phase modulation plays a crucial role in shaping optical fields and physical optics. However, traditional phase modulation techniques are highly dependent on angles and wavelengths, limiting their applicability in smart optical systems. Here, we propose a first-principle theory for achieving constant phase modulation independent of incident angle and wavelength. By utilizing a hyperbolic metamaterial and engineering-specific optical parameters, different reflective phase jumps are achieved and tailored for both transverse electric (TE) and transverse magnetic (TM) waves. The aimed reflection phase difference between TE and TM waves can be thus achieved omnidirectionally and achromatically. As an example, we propose a perfect omnidirectional broadband reflection quarter wave plate. This work provides fundamental insights into manipulating optical phases through optical parameter engineering.

Unique interface reflection phenomena tailored by nanoscale electromagnetic boundary conditions.

Local interface response effects are neglected based on the traditional electromagnetic boundary conditions (EMBCs) in an abrupt interface model. In this study, generalized nanoscale EMBCs are derived with interface response functions (IRFs) representing field inhomogeneity across the interface based on integral Maxwell's equations. They are rewritten in two different forms that correspond to the equivalent abrupt interface models with interface-induced dipoles or charges and currents. Interesting behaviors of Brewster angle shifting, non-extinction at Brewster angle, and unique absorption or gain effects are revealed based on the advanced Fresnel formula. IRFs-controlled GH-shift and angular GH-shift of a Gaussian beam near the Brewster angles are generated by the gradient interface. These unique phenomena provide some guidance for measuring the IRFs and expanding interface photonics at the nanoscale.

Chromaticity-tunable white random lasing based on a microfluidic channel.

The color and/or chromaticity controllability of random lasing is a key factor to promote practical applications of random lasers as high luminance sources for speckle-free imaging. Here, white coherent random lasing with tunable chromaticity is obtained by using broadband enhancement Au-Ag nanowires as scatterers and the resonance energy transfer process between different dyes in the capillary microfluidic channel. Red, green and blue random lasers are separately fabricated with low thresholds, benefiting from the plasmonic resonance of the nanogaps and/or nanotips with random distribution and sizes within Au-Ag nanowires and positive optical feedback provided by the capillary wall. A white random laser system is then designed through reorganizing the three random lasers. And, the chromaticity of the white random laser is flexibly tunable by adjusting pump power density. In addition, the white random laser has anisotropic spectra due to the coupling role between the lasers. This characteristic is then utilized to obtain different random lasing with different chromaticity over a broad visible range. The results may provide a basis for applying random laser in the field of high brightness illumination, biomedical imaging, and sensors.

Omnidirectional polarization beam splitter for white light.

As a key element in optical systems, a broadband and omnidirectional polarization beam splitter has been long desired. Here, based on anisotropic metamaterials, a perfect polarizing beam splitter is theoretically designed for the extremely broad frequency and angle bands without energy loss. When an electromagnetic wave is incident on the beam splitter, the transverse magnetic-polarized component suffers total reflection, while the transverse electric-polarized component is completely transmitted within the incident angle range [-90°, 90°] for the white light. This study provides a new approach to design an efficient polarizing beam splitter and may promote the development and applications of anisotropic metamaterials.

Cascade-pumped random lasers with coherent emission formed by Ag-Au porous nanowires.

A series of sequentially cascade-pumped random lasers is reported. It consists of three random lasers in which the Ag-Au bimetallic porous nanowires play the role of scatterers, and the gain materials are coumarin 440 (C440), coumarin 153 (C153), and rhodamine 6G (R6G), respectively. The random laser with C440 is first pumped by a 355 nm pulsed laser. The emission of C440 pumps the C153, and the emission of C153 pumps the R6G sequentially. Low-threshold coherent emissions from the three random lasers are observed. The cascade-pumped random lasers can be achieved easily with low cost and can be used in applications conveniently.

Localization of electromagnetic wave with continuous eigenmodes in free space cavities of cylindrical or arbitrary shapes.

A scheme for constructing the electromagnetic localization structure (ELS) is proposed based on the transformation optics. The ELS may have a free space cavity of cylindrical or arbitrary shapes enclosed by a metamaterials layer. The electromagnetic field can be localized in the free space cavity with no energy leaked in the metamaterials layer and the eigenmodes of the cavity is continuous, which are novel properties that the reported metamaterials ELSs could not realize. The principle and feasibility of the scheme are described in detail through the cylindrical ELS. It is shown that all the material parameters of the designed cylindrical ELS change smoothly with finite values. Therefore it is more practical than the reported metamaterials ELS. In the designing of ELS, the space transformation function was solved via solving the Laplace equation with the Dirichlet boundary condition, which makes it possible to design the ELS of arbitrary shape. The viability of the ELS with arbitrary shape is analyzed and demonstrated by the full-wave numerical simulations.

Clinical Analysis of Surgical Treatment of Senile Intertrochanteric Fracture Based on Intelligent Knowledge of Health Care.

In order to explore the clinical application value of intelligent health care knowledge combined with closed reduction intramedullary nail fixation in elderly patients with intertrochanteric fracture of the femur, a retrospective analysis is performed on 80 elderly patients who received intertrochanteric surgery from January 2019 to January 2021. All patients were divided into study group and control group based on intelligent medical knowledge received or not. During the phase of treatment, both the two groups were treated with closed reduction and intramedullary nailing. The control group received conventional knowledge training and rehabilitation before and after the surgery, and the research group received additional intelligent medical knowledge health care. Observations of patients after bed and ground time are compared and the VAS score is used to evaluate the pain degree at 12 h, 24 h, and 48 h after surgery. Besides, the incidence of postoperative complications in the two groups is observed. From the clinical follow-up results, it is clearly evident that intramedullary nail fixation based on medical care knowledge can effectively improve the hip function and quality of life in patients, reduce postoperative pain, and improve the prognosis of elderly patients with femoral trochanteric fracture.

Band-edge oscillations of the diffraction spectrum of a volume hologram investigated by the air-doping model.

Oscillation exists at the high-frequency band edge in the diffraction spectrum of a volume hologram. An air-doping model of a volume hologram is proposed to explain the phenomenon. The numerical results show good agreement with the experimental results, which cannot be explained by the conventional models. The results show that the position of air impurity is the key factor to control the number and width of the oscillations. The present work gives a new approach to generate and control the defect mode in a holographic photonic crystal.

Electromagnetic localization based on transformation optics.

Localization of an electromagnetic field can be achieved by transformation optics using metamaterials. A coordinate transformation structure different from traditional resonator is proposed. Wherein, arbitrary frequency of the whole band of electromagnetic wave can be localized without energy loss, i.e., the modes in this structure are continuous. Theoretical analysis and numerical simulation show that the material parameter variations at the outer boundary of the structure have little influence on the localization property. When realizable physical structure is considered, multi-layer approximation should be applied. The calculated results show that the estimated localization time is about 100 ns for an 8-layer inhomogeneous approximation, and it could reach several seconds for a 30-layer homogeneous approximation. The present work may present a new application of transformation optics.

A ring-shaped random laser in momentum space.

A ring-shaped random laser in momentum space is designed by directly coupling a random laser with a commercial optical fiber. By using a simple approach of selectively coating the random gain layer on the surface of the fiber, red and yellow random lasers are respectively achieved with low threshold values and a good emission direction due to the guiding role of optical fibers. The unique coupling mechanism leads to a random laser with a ring shape in momentum space, which is an excellent illuminating source for high-quality imaging with an extremely low speckle noise. More importantly, a triple-state color-switchable random laser with yellow, red and yellow-red dual-colors can be flexible, and is obtained by simply moving the pump position. The results may promote the practical applications of random lasers in the fields of sensing, in vivo biological imaging, and high brightness full-field illumination.

Temporal profiles for measuring threshold of random lasers pumped by ns pulses.

The working threshold is an important parameter to assess the performance of cavity-free random lasers. Here, the temporal profile measurement is proposed as an alternative method to determine the thresholds of the surface plasmon based random lasers pumped by ns pulses based on analyzing the delay time (t Delay) and rising time (t R) of the emission signal. The obvious and slight inflection points of the curves of t Delay and t R varying with the pump power density are observed as indicators for the thresholds of random lasing and for the transition of lasing mode, respectively. The proposed method supplies consistent values to those supplied by traditional methods in frequency-domain for the random systems with different gain length. The demonstrated temporal profile approaches are free from the spectrometers and may be as a candidate for measuring the threshold of random lasers in ultrafast optics, nonlinear optics and bio-compatible optoelectronic probes.

Grooved nanoplate assembly for rapid detection of surface enhanced Raman scattering.

Rapid detection of surface enhanced Raman scattering (SERS) signals is in great demand in the fields of biological medicine and environmental monitoring. Herein, a grooved silver nanoplate assembly (GSNA) with an abundance of multiscale gaps has been proposed for the first time and skillfully synthesized to act as an excellent platform for surface enhanced Raman spectroscopy with ultrafast and ultrasensitive detection. By effectively combining the hotspots effect of nanogaps and the trapping effect of gaps in the scale of subwavelength, the Raman signal was greatly enhanced by a factor of 1010 and the detection limit of Rhodamine 6G (R6G) could reach 5 × 10-13 M. Moreover, based on the perfect adsorption of the multiscale gaps, the probe molecule could be detected immediately after the analyte was mixed with the GSNA. In addition, the mixed analytes of R6G and crystal violet could be easily distinguished by Raman signal detection based on the fabricated basement. This study provides an effective SERS platform to achieve ultrafast Raman detection with ultrasensitivity in the fields of chemical analysis, biomedicine and environmental monitoring.

Dissolvable and Recyclable Random Lasers.

An integrated random laser based on green materials with dissolubility and recyclability is created and demonstrated. The dissolvable and recyclable random laser (DRRL) can be dissolved in water, accompanying the decay of emission intensity and the increment in lasing threshold. Furthermore, the DRRL can be reused after the process of deionized treatment, exhibiting excellent reproducibility with several recycling processes.

Ultrafast Response p-Si/n-ZnO Heterojunction Ultraviolet Detector Based on Pyro-Phototronic Effect.

A light-self-induced pyro-phototronic effect in wurtzite ZnO nanowires is proposed as an effective approach to achieve ultrafast response ultraviolet sensing in p-Si/n-ZnO heterostructures. The relatively long response/recovery time of zinc-oxide-based ultraviolet sensors in air/vacuum has long been an obstacle to developing such detectors for practical applications. The response/recovery time and photoresponsivity are greatly improved by the pyro-phototronic effect.

Light-induced pyroelectric effect as an effective approach for ultrafast ultraviolet nanosensing.

Zinc oxide is potentially a useful material for ultraviolet detectors; however, a relatively long response time hinders practical implementation. Here by designing and fabricating a self-powered ZnO/perovskite-heterostructured ultraviolet photodetector, the pyroelectric effect, induced in wurtzite ZnO nanowires on ultraviolet illumination, has been utilized as an effective approach for high-performance photon sensing. The response time is improved from 5.4 s to 53 µs at the rising edge, and 8.9 s to 63 µs at the falling edge, with an enhancement of five orders in magnitudes. The specific detectivity and the responsivity are both enhanced by 322%. This work provides a novel design to achieve ultrafast ultraviolet sensing at room temperature via light-self-induced pyroelectric effect. The newly designed ultrafast self-powered ultraviolet nanosensors may find promising applications in ultrafast optics, nonlinear optics, optothermal detections, computational memories and biocompatible optoelectronic probes.

Piezo-phototronic Boolean logic and computation using photon and strain dual-gated nanowire transistors.

Using polarization charges created at the metal-cadmium sulfide interface under strain to gate/modulate electrical transport and optoelectronic processes of charge carriers, the piezo-phototronic effect is applied to process mechanical and optical stimuli into electronic controlling signals. The cascade nanowire networks are demonstrated for achieving logic gates, binary computations, and gated D latches to store information carried by these stimuli.

Piezo-phototronic UV/visible photosensing with optical-fiber-nanowire hybridized structures.

An optical-fiber-nanowire hybridized UV-visible photodetector (PD) is reported. The PD is designed to allow direct integration in optical communication systems without requiring the use of couplers via fiber-welding technology. The PD works in two modes: axial and off-axial illumination mode. By using the piezo-phototronic effect, the performance of the PD is enhanced/optimized by up to 718% in sensitivity and 2067% in photoresponsivity.

Single-excitation dual-color coherent lasing by tuning resonance energy transfer processes in porous structured nanowires.

Single-excitation dual-color coherent lasing was achieved in a mixed random system of a binary dye and the suspension of gold-silver porous nanowires with plenty of nanogaps. This greatly enhanced the local electromagnetic field in the visible range and guaranteed a low threshold and high Q factor (>10 000) operator for simultaneous dual-color lasing. By tuning the resonance energy transfer process in the stimulated emission, triple output modes (single chartreuse lasing, chartreuse and red dual-color lasing, and single red coherent lasing) were easily obtained. This triple-mode coherent random lasing introduces a new approach to designing multi-functional micro-optoelectronic devices for multi-color speckle-free imaging and interference.

Eardrum-inspired active sensors for self-powered cardiovascular system characterization and throat-attached anti-interference voice recognition.

The first bionic membrane sensor based on triboelectrification is reported for self-powered physiological and behavioral measurements such as local internal body pressures for non-invasive human health assessment. The sensor can also be for self-powered anti-interference throat voice recording and recognition, as well as high-accuracy multimodal biometric authentication, thus potentially expanding the scope of applications in self-powered wearable medical/health monitoring, interactive input/control devices as well as accurate, reliable, and less intrusive biometric authentication systems.

Programmable writing of graphene oxide/reduced graphene oxide fibers for sensible networks with in situ welded junctions.

Direct spinning of the graphene oxide (GO) dispersions from a moveable spinneret along the programmed track, i.e., a "programmable writing" technique, was developed to make nonwoven, nonknitted, graphene-based networks with excellent mechanical properties. The resulting GO networks can be successfully converted into reduced GO (RGO) ones with better mechanical properties as well as excellent electrical conductivity via thermal/chemical reduction. In situ welded junctions formed during processing of the spun fibers have made the resulting networks with the integral structure, and outstanding mechanical properties and high electrical conductivities of the spun fibers and their web integrations have provided a great opportunity to remotely sense the external mechanical stimuli via electrical signal monitoring.