Ultrafast evanescently coupled waveguide MUTC-PDs with high responsivity.

Novel evanescently coupled waveguide modified uni-traveling carrier photodiodes (MUTC-PDs) employing a thick multi-layer coupling waveguide are reported. To improve the optical-to-electrical (O/E) conversion efficiency, a thick multi-layer coupling waveguide with a gradually increased refractive index from the bottom layer to the absorption layer is utilized. The refractive index profile facilitates the upward transmission of incident light into the absorption region, thereby enhancing the evanescent coupling efficiency. Meanwhile, the coupling waveguide, with a total thickness of 1.75 µm, expands the mode field diameter, thereby reducing the input coupling loss. Additionally, the top layer of the coupling waveguide also serves as the drift layer. This configuration facilitates efficient light absorption within a short PD length, thus ensuring ultrawide bandwidth and high O/E conversion efficiency simultaneously. Without an additional spot size coupler or anti-reflection coating, the measured responsivity is as high as 0.38 A/W for the PD with an active area of 5 × 6 µm2. Meanwhile, an ultrawide 3-dB bandwidth of 153 GHz has been demonstrated.

Quantum Light Generation Based on GaN Microring toward Fully On-Chip Source.

An integrated quantum light source is increasingly desirable in large-scale quantum information processing. Despite recent remarkable advances, a new material platform is constantly being explored for the fully on-chip integration of quantum light generation, active and passive manipulation, and detection. Here, for the first time, we demonstrate a gallium nitride (GaN) microring based quantum light generation in the telecom C-band, which has potential toward the monolithic integration of quantum light source. In our demonstration, the GaN microring has a free spectral range of 330 GHz and a near-zero anomalous dispersion region of over 100 nm. The generation of energy-time entangled photon pair is demonstrated with a typical raw two-photon interference visibility of 95.5±6.5%, which is further configured to generate a heralded single photon with a typical heralded second-order autocorrelation g_{H}^{(2)}(0) of 0.045±0.001. Our results pave the way for developing a chip-scale quantum photonic circuit.

Extended ray-mapping method based on differentiable ray-tracing for non-paraxial and off-axis freeform illumination lens design.

The ray-mapping method has been widely used for designing freeform illumination lenses. However, in non-paraxial or off-axis situations, it remains challenging to obtain an integrable ray-mapping, often requiring a complex iterative correction process for the initial mapping. To address this challenge, we propose an extended ray-mapping method that incorporates differentiable ray-tracing into the design pipeline of the ray-mapping method. This enables accurate surface construction according to ray-mapping and efficient shape correction based on irradiance distribution. The proposed method involves two optimization stages. In the first stage, the freeform surface is preliminarily optimized to closely match the optimal transport mapping. The obtained freeform surface is then further optimized in the second stage to minimize the divergence between the target and simulated irradiance distributions. Additionally, the mean curvature of the freeform surface is also constrained in the second stage to facilitate the fabrication of the final freeform surface. Non-paraxial illumination lenses and off-axis illumination lenses have been designed using the proposed method within ten minutes, and simulations demonstrate that the approach is effective and robust.

Ultrafast MUTC photodiodes over 200†GHz with high saturation power.

Novel back-illuminated modified uni-traveling-carrier photodiodes (MUTC-PDs) with wide bandwidth and high saturation power are demonstrated. The effect of cliff layer doping on the electric field distribution is investigated to achieve fast carrier transport. MUTC-PDs with miniaturized device diameter and low contact resistance are fabricated to improve the RC-limited bandwidth. Meanwhile, inductive peaking is implemented to further extend the bandwidth. PDs with 3-µm and 3.6-µm-diameter exhibit a ultrawide bandwidth of 230 GHz and 200 GHz, together with -4.94 dBm and -2.14 dBm saturation power at 220 GHz and 200 GHz, respectively.

Nano hydrogel-based oxygen-releasing stem cell transplantation system for treating diabetic foot.

The employment of stem cells and hydrogel is widespread in contemporary clinical approaches to treating diabetic foot ulcers. However, the hypoxic conditions in the surrounding lesion tissue lead to a low stem cell survival rate following transplantation. This research introduces a novel hydrogel with superior oxygen permeability and biocompatibility, serving as a vehicle for developing a stem cell transplantation system incorporating oxygen-releasing microspheres and cardiosphere-derived stem cells (CDCs). By optimizing the peroxidase fixation quantity on the microsphere surface and the oxygen-releasing microsphere content within the transplantation system, intracellular oxygen levels were assessed using electron paramagnetic resonance (EPR) under simulated low-oxygen conditions in vitro. The expression of vascularization and repair-related indexes were evaluated via RT-PCR and ELISA. The microspheres were found to continuously release oxygen for three weeks within the transplantation system, promoting growth factor expression to maintain intracellular oxygen levels and support the survival and proliferation of CDCs. Moreover, the effect of this stem cell transplantation system on wound healing in a diabetic foot mice model was examined through an in vivo animal experiment. The oxygen-releasing microspheres within the transplantation system preserved the intracellular oxygen levels of CDCs in the hypoxic environment of injured tissues. By inhibiting the expression of inflammatory factors and stimulating the upregulation of pertinent growth factors, it improved the vascularization of ulcer tissue on the mice's back and expedited the healing of the wound site. Overall, the stem cell transplantation system in this study, based on hydrogels containing CDCs and oxygen-releasing microspheres, offers a promising strategy for the clinical implementation of localized stem cell delivery to improve diabetic foot wound healing.

Simple and accurate dispersion measurement of GaN microresonators with a fiber ring.

The dispersion characteristics of a microresonator are important for applications in nonlinear optics, and precise measurement of the dispersion profile is crucial to device design and optimization. Here we demonstrate the dispersion measurement of high-quality-factor gallium nitride (GaN) microrings by a single-mode fiber ring, which is simple and convenient to access. Once the dispersion parameters of the fiber ring have been determined by the opto-electric modulation method, the dispersion can be obtained from the microresonator dispersion profile by polynomial fitting. To further verify the accuracy of the proposed method, the dispersion of the GaN microrings is also evaluated with frequency comb-based spectroscopy. Dispersion profiles obtained with both methods are in good agreement with simulations based on the finite element method.

Membrane multiple quantum well electro-optical modulator employing low loss high-k radio-frequency slot waveguides.

A membrane multiple quantum well (MQW) electro-optical (EO) modulator exploiting low loss high-k radio-frequency (RF) slot waveguides is proposed for sub-terahertz bandwidth. By employing high-k barium titanate (BTO) claddings in place of doped InP cladding layers in traditional InP-based MQW modulators, the proposed modulator exhibits enhanced modulation efficiency and bandwidth as well as reduced insertion loss. A low half-wave voltage-length product of 0.24 V·cm is estimated, together with over 240 GHz bandwidth for a 2-mm-long modulation region, thus allowing sub-terahertz operation.

A single-chip multi-beam steering optical phased array: design rules and simulations.

A waveguide-based multi-beam steering device is proposed for light detection and ranging (LIDAR). The device integrates binary gratings with an optical phased array (OPA), thus enabling a single-chip LIDAR system. The device can provide an N×M beam array that covers a wide angular range while phase shifters help realize steering over a narrow angle range between the beams. The antenna structure for 1D beam splitting is realized by combining the design of a grating coupler and a beam splitter grating, and a uniform beam splitting is achieved along the other dimension using non-uniformly distributed antennas. To illustrate the design, an OPA with an 11×11 beam array is designed at a wavelength of 905 nm. The OPA achieves a wide total field of view (FOV) of 68.8° × 77° with a narrow beam-array-steering angle of 6.5°, enabling a wide-FOV 3D sensing with a high frame rate.

Studies on Carrier Recombination in GaN/AlN Quantum Dots in Nanowires with a Core-Shell Structure.

GaN quantum dots embedded in nanowires have attracted much attention due to their superior optical properties. However, due to the large surface-to-volume ratio of the nanowire, the impacts of surface states are the primary issue responsible for the degradation of internal quantum efficiency (IQE) in heterostructured dot-in-nanowires. In this paper, we investigate the carrier recombination mechanism of GaN/AlN dot-in-nanowires with an in situ grown AlN shell structure. Ultraviolet photoelectron spectroscopy (UPS) measurements were performed to describe the band bending effect on samples with different shell thicknesses. Temperature-dependent photoluminescence (TDPL) data support that increasing the AlN shell thickness is an efficient way to improve internal quantum efficiency. Detailed carrier dynamics was analyzed and combined with time-resolved photoluminescence (TRPL). The experimental data are consistent with our physical model that the AlN shell can effectively flatten the band bending near the surface and isolate the surface non-radiative recombination center. Our systematic research on GaN/AlN quantum dots in nanowires with a core-shell structure may significantly advance the development of a broad range of nanowire-based optoelectronic devices.

Inhibition of TGFß-activated protein kinase 1 ameliorates myocardial ischaemia/reperfusion injury via endoplasmic reticulum stress suppression.

Transforming growth factor ß-activated protein kinase 1 (TAK1) involves in various biological responses and is a key regulator of cell death. However, the role of TAK1 on acute myocardial ischaemia/reperfusion (MI/R) injury is unknown. We observed that TAK1 activation increased significantly after MI/R and hypoxia/reoxygenation (H/R), and we hypothesized that TAK1 has an important role in MI/R injury. Mice (TAK1 inhibiting by 5Z-7-oxozeaenol or silencing by AAV9 vector) were exposed to MI/R injury. Primary cardiomyocytes (TAK1 silencing by siRNA; and overexpressing TAK1 by adenovirus vector) were used to induce H/R injury model in vitro. Inhibition of TAK1 significantly decreased MI/R-induced myocardial infarction area, reduced cell death and improved cardiac function. Mechanistically, TAK1 silencing suppressed MI/R-induced myocardial oxidative stress and attenuated endoplasmic reticulum (ER) stress both in vitro and in vivo. In addition, the inhibition of ROS by NAC partially reversed the damage of TAK1 in vitro. Our study presents the first direct evidence that inhibition of TAK1 mitigated MI/R injury, and TAK1 mediated ROS/ER stress/apoptosis signal pathway is important for the pathogenesis of MI/R injury.

Van der Waals Epitaxy of III-Nitride Semiconductors Based on 2D Materials for Flexible Applications.

III-nitride semiconductors have attracted considerable attention in recent years owing to their excellent physical properties and wide applications in solid-state lighting, flat-panel displays, and solar energy and power electronics. Generally, GaN-based devices are heteroepitaxially grown on c-plane sapphire, Si (111), or 6H-SiC substrates. However, it is very difficult to release the GaN-based films from such single-crystalline substrates and transfer them onto other foreign substrates. Consequently, it is difficult to meet the ever-increasing demand for wearable and foldable applications. On the other hand, sp2 -bonded two-dimensional (2D) materials, which exhibit hexagonal in-plane lattice arrangements and weakly bonded layers, can be transferred onto flexible substrates with ease. Hence, flexible III-nitride devices can be implemented through such 2D release layers. In this progress report, the recent advances in the different strategies for the growth of III-nitrides based on 2D materials are reviewed, with a focus on van der Waals epitaxy and transfer printing. Various attempts are presented and discussed herein, including the different kinds of 2D materials (graphene, hexagonal boron nitride, and transition metal dichalcogenides) used as release layers. Finally, current challenges and future perspectives regarding the development of flexible III-nitride devices are discussed.

Laser frequency noise characterization by self-heterodyne with both long and short delay.

We propose a novel approach to laser frequency noise characterization by delayed self-heterodyne. Compared with the traditional treatment, our method applies to both long and short delay, corresponding to uncorrelated and correlated self-heterodyne. In the case of long delay, it overcomes the influence of 1/f noise on the intrinsic linewidth extraction from a broadened spectrum, and the results are more accurate than Voigt profile fitting. For short delayed correlated heterodyne, it eliminates artifact peaks at multiples of the reciprocal of delay time introduced by transferring measured RF phase noise to laser phase noise, thus extending the measurement range. In addition, it calibrates the frequency noise overestimation caused by a finite noise floor. This method remains valid when the delay and the coherence time are comparable. Experimental results are presented to demonstrate the effectiveness of the proposed approach in characterizing lasers with intrinsic linewidth ranging from sub-100 Hz to megahertz.

Abnormal Stranski-Krastanov Mode Growth of Green InGaN Quantum Dots: Morphology, Optical Properties, and Applications in Light-Emitting Devices.

Stranski-Krastanov (SK) growth mode is widely adopted for the self-assembled growth of semiconductor quantum dots (QDs), wherein a relatively large critical thickness is essential and a thick wetting layer (WL) is formed beneath the QD layer. In this paper, we report the metal organic vapor phase epitaxy of green InGaN QDs, employing a growth interruption method to decrease the critical thickness and improve the morphology of QDs. The QDs exhibit similar photoluminescence properties with those grown by conventional SK mode, implying the existence of a WL. We experimentally verify that the formation of QDs, whether based on the SK mode or the growth interruption method, conforms to the phase separation theory. However, the density of QDs grown by the interruption method exhibits abnormal dependence on the strain when a quantum well (QW) is inserted beneath the QD layer. Furthermore, the underlying QW not only influences the morphology of the QDs but also plays as a reservoir of electrons, which helps enhance the photoluminescence and the electroluminescence of the QDs. The method of QD growth with improved morphology and luminescence by introducing the QW-QD coupled nanostructure is universally applicable to similar material systems. Furthermore, a 550 nm green light-emitting diode (LED) and a 526 nm superluminescent LED based on the nanostructure are demonstrated.

Improving modulation bandwidth of c-plane GaN-based light-emitting diodes by an ultra-thin quantum wells design.

The GaN-based light emitting diodes (LEDs) have a great potential for visible light communication (VLC) due to their ubiquitous application in general lighting, but the modulation bandwidth of conventional c-plane LEDs is limited by carrier recombination rate in InGaN quantum wells (QWs) due to the polarization-field-induced quantum confined Stark effect (QCSE). Furthermore, the high modulation bandwidth on c-plane sapphire substrates can only be achieved at high current densities. Here, blue LEDs with ultra-thin InGaN QWs (1nm) and GaN barriers (3nm) are grown on c-plane sapphire substrate to suppress QCSE and extend the cut-off frequency from 214 MHz for conventional LEDs to 536 MHz at a current density of 2.5 kA/cm2, which is comparable to devices grown on semi-polar substrates.

An InP-based vortex beam emitter with monolithically integrated laser.

Semiconductor devices capable of generating a vortex beam with a specific orbital angular momentum (OAM) order are highly attractive for applications ranging from nanoparticle manipulation, imaging and microscopy to fiber and quantum communications. In this work, an electrically pumped integrated OAM emitter operating at telecom wavelengths is fabricated by monolithically integrating an optical vortex emitter with a distributed feedback laser on the same InGaAsP/InP epitaxial wafer. A single-step dry-etching process is adopted to complete the OAM emitter, equipped with specially designed top gratings. The vortex beam emitted by the integrated device is captured and its OAM mode purity characterized. The integrated OAM emitter eliminates the external laser required by silicon- or silicon-on-insulator-based OAM emitters, thus demonstrating great potential for applications in communication systems and the quantum domain.

Substitution of Percutaneous Ethanol Injection with a Low Molecular Weight Peptide Gel Mimicking Chemoembolization for Cancer Therapy.

In order to avoid the instability and quick separation between emulsifier and drug in the interventional chemoembolization, an injectable low molecular weight peptide gel (LMWG) was prepared to localize ethanol and chemotherapeutic for in situ synergistic therapy. The formation mechanism, rheological property and morphology of the LMWG were investigated by NMR, UV-vis, MS and SEM. The interaction between gelator and anticancer drug doxorubicin hydrochloride (DOX) was evaluated by fluorescence spectroscopy and its contribution on drug loading properties was demonstrated. The gel was non-toxic to both 3T3 fibroblasts and 4T1 breast cancer cells. DOX as well as ethanol were encapsulated in the gel and injected in breast cancer bearing mice with low drug dose (2.5 mg/kg body weight). The LMWG surrounded tumors act as a depot for ethanol release and release DOX to induce the apoptosis of cancer cells. With the combination of percutaneous ethanol injection (PEI) and chemotherapy, the DOX loaded LMWG exhibited great significance in necrosis of tumor tissue and exciting tumor inhibition efficiency.

A Review on Experimental Measurements for Understanding Efficiency Droop in InGaN-Based Light-Emitting Diodes.

Efficiency droop in GaN-based light emitting diodes (LEDs) under high injection current density perplexes the development of high-power solid-state lighting. Although the relevant study has lasted for about 10 years, its mechanism is still not thoroughly clear, and consequently its solution is also unsatisfactory up to now. Some emerging applications, e.g., high-speed visible light communication, requiring LED working under extremely high current density, makes the influence of efficiency droop become more serious. This paper reviews the experimental measurements on LED to explain the origins of droop in recent years, especially some new results reported after 2013. Particularly, the carrier lifetime of LED is analyzed intensively and its effects on LED droop behaviors are uncovered. Finally, possible solutions to overcome LED droop are discussed.

A novel model on time-resolved photoluminescence measurements of polar InGaN/GaN multi-quantum-well structures.

Based on carrier rate equation, a new model is proposed to explain the non-exponential nature of time-resolved photoluminescence (TRPL) decay curves in the polar InGaN/GaN multi-quantum-well structures. From the study of TRPL curves at different temperatures, it is found that both radiative and non-radiative recombination coefficients vary from low temperature to room temperature. The variation of the coefficients is compatible with the carrier density of states distribution as well as the carrier localization process. These results suggest that there is a novel method to calculate the internal quantum efficiency, which is a complement to the traditional one based on temperature dependent photoluminescence measurement.

Aluminum nitride-on-sapphire platform for integrated high-Q microresonators.

We demonstrate aluminum nitride (AlN) on sapphire as a novel platform for integrated optics. High-confinement AlN microring resonators are realized by adopting a partially etched (pedestal) waveguide to relax the required etching selectivity for exact pattern transfer. A wide taper is employed at the chip end facets to ensure a low fiber-to-chip coupling loss of ~2.8 dB/facet for both transverse-electric (TE) and transverse-magnetic (TM) modes. Furthermore, the intrinsic quality factors (Qint) recorded with a high-resolution linewidth measurement are up to ~2.5 and 1.9 million at telecom band for fundamental TE00 and TM00 modes, corresponding to a low intracavity propagation loss of ~0.14 and 0.2 dB/cm as well as high resonant buildup of 473 and 327, respectively. Such high-Q AlN-on-sapphire microresonators are believed to be very promising for on-chip nonlinear optics.

Reduction of atrial fibrillation by Tanshinone IIA in chronic heart failure.

The aim of the present study was to confirm the effect of Tanshinone IIA (TAN) on the prevention of AF in chronic heart failure (CHF), and to elucidate the underlying electrophysiological mechanisms for the antiarrhythmic effects of TAN at the level of the atrium in an experimental model of CHF. In 10 female rabbits, CHF was induced by rapid ventricular pacing, leading to a significant decrease in ejection fraction in the presence of a dilated left ventricle and atrial enlargement. Twelve rabbits were sham-operated and served as controls. Isolated hearts were perfused using the Langendorff method. Burst pacing was used to induce AF. Monophasic action potential recordings showed an increase of atrial action potential duration (aAPD) and effective refractory period (aERP) in CHF hearts compared with sham hearts. Infusion of acetylcholine (1µm) and isoproterenol (1µm) led to AF in all failing hearts and in 11 sham hearts. Simultaneous infusion of TAN (10µm) remarkably reduced inducibility of AF in 50% of sham and 50% of failing hearts. TAN had no effect on aAPD but significantly increased aERP, leading to a marked increase in atrial post-repolarization refractoriness. Moreover, TAN application moderately increased interatrial conduction time. TAN has been shown to be effective in reducing the inducibility of AF in an experimental model of AF. The antiarrhythmic effect is mainly due to prolongations of atrial post-repolarization refractoriness and a moderate increase in interatrial conduction time.