Topological Nature of Radiation Asymmetry in Bilayer Metagratings.

Manipulating radiation asymmetry of photonic structures is of particular interest in many photonic applications such as directional optical antenna, high efficiency on-chip lasers, and coherent light control. Here, we proposed a term of pseudopolarization to reveal the topological nature of radiation asymmetry in bilayer metagratings. Robust pseudopolarization vortex with an integer topological charge exists in P-symmetry metagrating, allowing for tunable directionality ranging from -1 to 1 in synthetic parameter space. When P-symmetry breaking, such vortex becomes pairs of C points due to the conservation law of charge, leading to the phase difference of radiation asymmetry from π/2 to 3π/2. Furthermore, topologically enabled coherent perfect absorption is robust with customized phase difference at will between two counterpropagating external light sources. This Letter can not only enrich the understanding of two particular topological photonic behaviors, i.e., bound state in the continuum and unidirectional guided resonance, but also provide a topological view on radiation asymmetry, opening an unexplored avenue for asymmetric light manipulation in on-chip laser, light-light switch, and quantum emitters.

Directional emission of a three-dimensional connection-type metamaterial.

Directional emission of electromagnetic waves plays an essential role in laser radar and free-space communication. For most directional antennas, bandwidth and miniaturization are a pair of contradictions due to their underlying interference mechanism. Connection-type metamaterials exhibit exotic electromagnetic response near zero-frequency, which relies on the global topology of mesh connectivity rather than resonance and thus has a broad working bandwidth. In this Letter, we investigate the broadband orientation-dependent coupling effect of a 3D double mesh metamaterial. Based on this effect, we achieve a broadband directional emission (relative bandwidth of 37.72%) using a compact structure (compared to twice working wavelength). Our work provides a novel, to the best of our knowledge, scheme to manipulate a long-wavelength wave and may pave the way to a miniaturized directional antenna.

On-Chip Topological Photonic Crystal Nanobeam Filters.

We present an on-chip filter with a broad tailorable working wavelength and a single-mode operation. This is realized through the application of topological photonic crystal nanobeam filters employing synthesis parameter dimensions. By introducing the translation of air holes as a new synthetic parameter dimension, we obtained nanobeams with tunable Zak phases. Leveraging the bulk-edge correspondence, we identify the existence of topological cavity modes and establish a correlation between the cavity's interface morphology and working wavelength. Through experiments, we demonstrate filters with adjustable filtering wavelengths ranging from 1301 to 1570 nm. Our work illustrates the use of the synthetic translation dimension in the design of on-chip filters, and it holds potential for applications in other devices such as microcavities.

Observation of robust edge mode and in-gap corner mode in Kagome surface-wave photonic crystals.

Recent theory has demonstrated that Kagome photonic crystals (PCs) support first-order and second-order topological phenomena. Here, we extend the topological physics of the Kagome lattice to surface electromagnetic waves and experimentally show a Kagome surface-wave PC. Under the protection of first-order and second-order topologies, both robust edge modes and in-gap corner modes are observed. The robust transport of edge modes is demonstrated by high transmission through the waveguide with a sharp bend. The localized corner mode is found at the corner with one isolated rod when a triangle-shaped sample is constructed. Our work not only shows a platform to mimic the topological physics in classical wave systems, but also offers a potential application in designing high-performance photonic devices.

Second Chern crystals with inherently non-trivial topology.

Chern insulators have been generalized to many classical wave systems and thereby lead to many potential applications such as robust waveguides, quantum computation and high-performance lasers. However, the band structure of a material can be either topologically trivial or non-trivial, depending on how the crystal structure is designed. Here, we propose a second Chern crystal in a four-dimensional parameter space by introducing two extra synthetic translation dimensions. Since the topology of the bulk bands in the synthetic translation space is intrinsically non-trivial, our proposed four-dimensional crystal is guaranteed to be topologically non-trivial regardless of the crystal's detailed configuration. We derive the topologically protected modes on the lower dimensional boundaries of such a crystal via dimension reduction. Remarkably, we observe the one-dimensional gapless dislocation modes and confirm their robustness in experiments. Our findings provide novel perspectives on topologically non-trivial crystals and may inspire designs of classical wave devices.

Antichiral surface states in time-reversal-invariant photonic semimetals.

Besides chiral edge states, the hallmark of quantum Hall insulators, antichiral edge states can exhibit unidirectional transport behavior but in topological semimetals. Although such edge states provide more flexibility for molding the flow of light, their realization usually suffers from time-reversal breaking. In this study, we propose the realization of antichiral surface states in a time-reversal-invariant manner and demonstrate our idea with a three-dimensional (3D) photonic metacrystal. Our system is a photonic semimetal possessing two asymmetrically dispersed Dirac nodal lines. Via dimension reduction, the nodal lines are rendered a pair of offset Dirac points. By introducing synthetic gauge flux, each two-dimensional (2D) subsystem with nonzero kz is analogous to a modified Haldane model, yielding a kz-dependent antichiral surface transport. Through microwave experiments, the bulk dispersion with asymmetric nodal lines and associated twisted ribbon surface states are demonstrated in our 3D time-reversal-invariant system. Although our idea is demonstrated in a photonic system, we propose a general approach to realize antichiral edge states in time-reversal-invariant systems. This approach can be easily extended to systems beyond photonics and may pave the way for further applications of antichiral transport.

Ideal nodal rings of one-dimensional photonic crystals in the visible region.

Three-dimensional (3D) artificial metacrystals host rich topological phases, such as Weyl points, nodal rings, and 3D photonic topological insulators. These topological states enable a wide range of applications, including 3D robust waveguides, one-way fiber, and negative refraction of the surface wave. However, these carefully designed metacrystals are usually very complex, hindering their extension to nanoscale photonic systems. Here, we theoretically proposed and experimentally realized an ideal nodal ring in the visible region using a simple 1D photonic crystal. The π-Berry phase around the ring is manifested by a 2π reflection phase's winding and the resultant drumhead surface states. By breaking the inversion symmetry, the nodal ring can be gapped and the π-Berry phase would diffuse into a toroidal-shaped Berry flux, resulting in photonic ridge states (the 3D extension of quantum valley Hall states). Our results provide a simple and feasible platform for exploring 3D topological physics and its potential applications in nanophotonics.

[Research progress of full endoscopic transforaminal lumbar interbody fusion].

Full endoscopic transforaminal lumbar interbody fusion has been used widely in the field of minimally invasive spine surgery in recent years. This paper briefly introduces the development history, technical points, indications, curative effects and complications. Authors believe that the full endoscopic transforaminal lumbar interbody fusion has the same clinical effects as traditional surgery, and can effectively reduce tissue damage and intraoperative bleeding, reduce the incidence of postoperative low back pain, shorten the time to get out of bed, and reduce the average hospitalization time. However, it is still necessary to improve the long-term follow up in order to further evaluate the effectiveness and safety of the procedure.

Topologically Protected Valley-Dependent Quantum Photonic Circuits.

Topological photonics has been introduced as a powerful platform for integrated optics, since it can deal with robust light transport, and be further extended to the quantum world. Strikingly, valley-contrasting physics in topological photonic structures contributes to valley-related edge states, their unidirectional coupling, and even valley-dependent wave division in topological junctions. Here, we design and fabricate nanophotonic topological harpoon-shaped beam splitters (HSBSs) based on 120-deg-bending interfaces and demonstrate the first on-chip valley-dependent quantum information process. Two-photon quantum interference, namely, Hong-Ou-Mandel interference with a high visibility of 0.956±0.006, is realized with our 50/50 HSBS, which is constructed by two topologically distinct domain walls. Cascading this kind of HSBS together, we also demonstrate a simple quantum photonic circuit and generation of a path-entangled state. Our work shows that the photonic valley state can be used in quantum information processing, and it is possible to realize more complex quantum circuits with valley-dependent photonic topological insulators, which provides a novel method for on-chip quantum information processing.

Focus shaping of high numerical aperture lens using physics-assisted artificial neural networks.

We present a physics-assisted artificial neural network (PhyANN) scheme to efficiently achieve focus shaping of high numerical aperture lens using a diffractive optical element (DOE) divided into a series of annular regions with fixed widths. Unlike the conventional ANN, the PhyANN does not require the training using labeled data, and instead output the transmission coefficients of each annular region of the DOE by fitting weights of networks to minimize the delicately designed loss function in term of focus profiles. Several focus shapes including sub-diffraction spot, flattop spot, optical needle, and multi-focus region are successfully obtained. For instance, we achieve an optical needle with 10λ depth of focus, 0.41λ lateral resolution beyond diffraction limit and high flatness of almost the same intensity distribution. Compared to typical particle swarm optimization algorithm, the PhyANN has an advantage in DOE design that generates three-dimensional focus profile. Further, the hyperparameters of the proposed PhyANN scheme are also discussed. It is expected that the obtained results benefit various applications including super-resolution imaging, optical trapping, optical lithography and so on.

Phase characterisation of metalenses.

Metalenses have emerged as a new optical element or system in recent years, showing superior performance and abundant applications. However, the phase distribution of a metalens has not been measured directly up to now, hindering further quantitative evaluation of its performance. We have developed an interferometric imaging phase measurement system to measure the phase distribution of a metalens by taking only one photo of the interference pattern. Based on the measured phase distribution, we analyse the negative chromatic aberration effect of monochromatic metalenses and propose a feature size of metalenses. Different sensitivities of the phase response to wavelength between the Pancharatnam-Berry phase-based metalens and propagation phase-reliant metalens are directly observed in the experiment. Furthermore, through phase distribution analysis, it is found that the distance between the measured metalens and the brightest spot of focusing will deviate from the focal length when the metalens has a low nominal numerical aperture, even though the metalens is ideal without any fabrication error. We also use the measured phase distribution to quantitatively characterise the imaging performance of the metalens. Our phase measurement system will help not only designers optimise the designs of metalenses but also fabricants distinguish defects to improve the fabrication process, which will pave the way for metalenses in industrial applications.

Repeated subarachnoid administrations of allogeneic human umbilical cord mesenchymal stem cells for spinal cord injury: a phase 1/2 pilot study.

BACKGROUND AIMS: Stem cell transplantation is a potential treatment for intractable spinal cord injury (SCI), and allogeneic human umbilical cord mesenchymal stem cells (hUC-MSCs) are a promising candidate because of the advantages of immune privilege, paracrine effect, immunomodulatory function, convenient collection procedure and little ethical concern, and there is an urgent need to develop a safe and effective protocol regarding their clinical application. METHODS: A prospective, single-center, single-arm study in which subjects received four subarachnoid transplantations of hUC-MSCs (1 × 106 cells/kg) monthly and were seen in follow-up four times (1, 3, 6 and 12 months after final administration) was conducted. At each scheduled time point, safety and efficacy indicators were collected and analyzed accordingly. Adverse events (AEs) were used as a safety indicator. American Spinal Injury Association (ASIA) and SCI Functional Rating Scale of the International Association of Neurorestoratology (IANR-SCIFRS) total scores at the fourth follow-up were determined as primary efficacy outcomes, whereas these two indicators at the remaining time points as well as scores of pinprick, light touch, motor and sphincter, muscle spasticity and spasm, autonomic system, bladder and bowel functions, residual urine volume (RUV) and magnetic resonance imaging (MRI) were secondary efficacy outcomes. Subgroup analysis of primary efficacy indicators was also performed. RESULTS: Safety and efficacy assessments were performed on 102 and 41 subjects, respectively. Mild AEs involving fever (14.1%), headache (4.2%), transient increase in muscle tension (1.6%) and dizziness (1.3%) were observed following hUC-MSC transplantation and resolved thoroughly after conservative treatments. There was no serious AE. ASIA and IANR-SCIFRS total scores revealed statistical increases when compared with the baselines at different time points during the study, mainly reflected in the improvement of pinprick, light touch, motor and sphincter scores. Moreover, subjects showed a continuous and remarkable decrease in muscle spasticity. Regarding muscle spasm, autonomic system, bladder and bowel functions, RUV and MRI, data/imaging at final follow-up showed significant improvements compared with those at first collection. Subgroup analysis found that hUC-MSC transplantation improved neurological functions regardless of injury characteristics, including level, severity and chronicity. CONCLUSIONS: The authors' present protocol demonstrates that intrathecal administration of' allogeneic hUC-MSCs at a dose of 106 cells/kg once a month for 4 months is safe and effective and leads to significant improvement in neurological dysfunction and recovery of quality of life.

Full-visible transmissive metagratings with large angle/wavelength/polarization tolerance.

Metagratings have been shown to form an agile and efficient platform for extreme wavefront manipulation, going beyond the limitations of gradient metasurfaces. Here, we present all-dielectric transmissive metagratings with high diffraction efficiencies using simple rectangular inclusions with neither high index nor high aspect ratio requirement. We further experimentally demonstrate continuous phase encoding of a hologram based on such transmissive metagratings through displacement modulation of CMOS-compatible silicon nitride nanobars in the full visible range, manifesting broadband and wide-angle high diffraction efficiencies for both polarizations. Featured with extreme angle/wavelength/polarization tolerance and alleviated structural complexity for both design and fabrication, our demonstration unlocks the full potential of metagrating-based wavefront manipulation for a variety of practical applications.

A broadband achromatic metalens array for integral imaging in the visible.

Integral imaging is a promising three-dimensional (3D) imaging technique that captures and reconstructs light field information. Microlens arrays are usually used for the reconstruction process to display 3D scenes to the viewer. However, the inherent chromatic aberration of the microlens array reduces the viewing quality, and thus, broadband achromatic imaging remains a challenge for integral imaging. Here, we realize a silicon nitride metalens array in the visible region that can be used to reconstruct 3D optical scenes in the achromatic integral imaging for white light. The metalens array contains 60 × 60 polarization-insensitive metalenses with nearly diffraction-limited focusing. The nanoposts in each high-efficiency (measured as 47% on average) metalens are delicately designed with zero effective material dispersion and an effective achromatic refractive index distribution from 430 to 780 nm. In addition, such an achromatic metalens array is composed of only a single silicon nitride layer with an ultrathin thickness of 400 nm, making the array suitable for on-chip hybrid-CMOS integration and the parallel manipulation of optoelectronic information. We expect these findings to provide possibilities for full-color and aberration-free integral imaging, and we envision that the proposed approach may be potentially applicable in the fields of high-power microlithography, high-precision wavefront sensors, virtual/augmented reality and 3D imaging.

Direct Observation of Corner States in Second-Order Topological Photonic Crystal Slabs.

Recently, higher-order topological phases that do not obey the usual bulk-edge correspondence principle have been introduced in electronic insulators and brought into classical systems, featuring in-gap corner or hinge states. In this Letter, using near-field scanning measurements, we show the direct observation of corner states in second-order topological photonic crystal slabs consisting of periodic dielectric rods on a perfect electric conductor. Based on the generalized two-dimensional Su-Schrieffer-Heeger model, we show that the emergence of corner states roots in the nonzero edge dipolar polarization instead of the nonzero bulk quadrupole polarization. We demonstrate the topological transition of two-dimensional Zak phases of photonic crystal slabs by tuning intracell distances between two neighboring rods. We also directly observe in-gap one-dimensional edge states and zero-dimensional corner states in the microwave regime. Our work presents that the photonic crystal slab is a powerful platform to directly observe topological states and paves the way to study higher-order photonic topological insulators.

A silicon-on-insulator slab for topological valley transport.

Backscattering suppression in silicon-on-insulator (SOI) is one of the central issues to reduce energy loss and signal distortion, enabling for capability improvement of modern information processing systems. Valley physics provides an intriguing way for robust information transfer and unidirectional coupling in topological nanophotonics. Here we realize topological transport in a SOI valley photonic crystal slab. Localized Berry curvature near zone corners guarantees the existence of valley-dependent edge states below light cone, maintaining in-plane robustness and light confinement simultaneously. Topologically robust transport at telecommunication is observed along two sharp-bend interfaces in subwavelength scale, showing flat-top high transmission of ~10% bandwidth. Topological photonic routing is achieved in a bearded-stack interface, due to unidirectional excitation of valley-chirality-locked edge state from the phase vortex of a nanoscale microdisk. These findings show the prototype of robustly integrated devices, and open a new door towards the observation of non-trivial states even in non-Hermitian systems.

Landscape pattern evolution along terrain gradient in Fuzhou City, Fujian Province, China.

Terrain is an important factor in land landscape pattern change. To reveal the spatial and temporal characteristics and variation of landscape pattern along a terrain gradient, we used three remote sensing images and digital elevation model (DEM) data of Fuzhou in 1995, 2005 and 2015 to investigate the topographic gradient effect of landscape pattern and the cause of formation based on terrain index, land use distribution index, geo-informatics map analysis and landscape index. The results showed that forestland was mainly distributed in middle-low, middle-high and higher level terrain, while farmland, water body, construction land and unused lands were mainly distributed in the low rank terrain. From 1995 to 2015, the area of forestland, farmland, and unused land in Fuzhou decreased, while that of construction land and water body increased. The change of landscape type was stable, which was mainly distributed in middle-low, middle-high, and high grade terrain gradient region. In addition, landscape pattern changes were obvious across the terrain gra-dient. The landscape type of low terrain area mainly shifted to the construction land, but farmland and forestland had an alternation change in the middle-low and middle-high terrain area. The characteristics of landscape pattern fragmentation, landscape heterogeneity and landscape diversity in the study area had been increasing year by year, but they had decreased with the elevation of terrain.

Human electronegative LDL induces mitochondrial dysfunction and premature senescence of vascular cells in vivo.

Dysregulation of plasma lipids is associated with age-related cardiovascular diseases. L5, the most electronegative subfraction of chromatographically resolved low-density lipoprotein (LDL), induces endothelial dysfunction, whereas the least electronegative subfraction, L1, does not. In this study, we examined the effects of L5 on endothelial senescence and its underlying mechanisms. C57B6/J mice were intravenously injected with L5 or L1 (2 mg kg-1  day-1 ) from human plasma. After 4 weeks, nuclear γH2AX deposition and senescence-associated ß-galactosidase staining indicative of DNA damage and premature senescence, respectively, were increased in the aortic endothelium of L5-treated but not L1-treated mice. Similar to that, in Syrian hamsters with elevated serum L5 levels induced by a high-fat diet, nuclear γH2AX deposition and senescence-associated ß-galactosidase staining were increased in the aortic endothelium. This phenomenon was blocked in the presence of N-acetyl-cysteine (free-radical scavenger) or caffeine (ATM blocker), as well as in lectin-like oxidized LDL receptor-1 (LOX-1) knockout mice. In cultured human aortic endothelial cells, L5 augmented mitochondrial oxygen consumption and mitochondrial free-radical production, which led to ATM activation, nuclear γH2AX deposition, Chk2 phosphorylation, and TP53 stabilization. L5 also decreased human telomerase reverse transcriptase (hTERT) protein levels and activity. Pharmacologic or genetic manipulation of the reactive oxygen species (ROS)/ATM/Chk2/TP53 pathway efficiently blocked L5-induced endothelial senescence. In conclusion, L5 may promote mitochondrial free-radical production and activate the DNA damage response to induce premature vascular endothelial senescence that leads to atherosclerosis. Novel therapeutic strategies that target L5-induced endothelial senescence may be used to prevent and treat atherosclerotic vascular disease.

An inhibitor of oxidative phosphorylation exploits cancer vulnerability.

Metabolic reprograming is an emerging hallmark of tumor biology and an actively pursued opportunity in discovery of oncology drugs. Extensive efforts have focused on therapeutic targeting of glycolysis, whereas drugging mitochondrial oxidative phosphorylation (OXPHOS) has remained largely unexplored, partly owing to an incomplete understanding of tumor contexts in which OXPHOS is essential. Here, we report the discovery of IACS-010759, a clinical-grade small-molecule inhibitor of complex I of the mitochondrial electron transport chain. Treatment with IACS-010759 robustly inhibited proliferation and induced apoptosis in models of brain cancer and acute myeloid leukemia (AML) reliant on OXPHOS, likely owing to a combination of energy depletion and reduced aspartate production that leads to impaired nucleotide biosynthesis. In models of brain cancer and AML, tumor growth was potently inhibited in vivo following IACS-010759 treatment at well-tolerated doses. IACS-010759 is currently being evaluated in phase 1 clinical trials in relapsed/refractory AML and solid tumors.

Risk factor of contralateral radiculopathy following microendoscopy-assisted minimally invasive transforaminal lumbar interbody fusion.

PURPOSE: Microendoscopy-assisted minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) is an advantageous method for treating lumbar degenerative disease; however, some patients show contralateral radiculopathy postoperatively. This study aims to investigate its risk factor. METHODS: A total of 130 cases who underwent microendoscopy-assisted MIS-TLIF at L4-5 level were divided into symptomatic and asymptomatic groups according to the presence of postoperative contralateral radiculopathy. Both preoperative and postoperative radiographic parameters, as well as their changes were compared between the two groups, including lumbar lordosis (LL), surgical segmental angle (SSA), disc height (DH), contralateral foramen area (CFA) and contralateral canal area (CCA). Screw breach on contralateral L4 pedicle and decompression method (ipsilateral or bilateral canal decompression through unilateral route) were also analyzed as potential risk factors. Receiver operating characteristic (ROC) curve was drawn for the risk factor to determine the optimal threshold for predicting postoperative contralateral radiculopathy. Besides, clinical outcome assessment, involving Visual Analog Score (VAS) for back and leg, Japanese Orthopaedics Association Score (JOA) and Oswestry Disability Index (ODI), was also compared between the two groups before surgery and at final follow-up (at least 3 months after the surgery for asymptomatic patients or final treatments of contralateral radiculopathy for symptomatic cases). RESULTS: Postoperative contralateral radiculopathy occurred in 11 (8.5%) of the 130 patients. Both preoperative and postoperative CFA as well as its change were significantly decreased in symptomatic group compared with asymptomatic group (all P < 0.05). For the remaining four parameters (LL, SSA, DH, CCA), their preoperative, postoperative and change values showed no statistical difference between the two groups (all P > 0.05). Neither screw breach nor decompression method revealed statistical association with this complication (both P > 0.05). Based on ROC curve, the optimal threshold of preoperative CFA was 0.76 cm2. At final follow-up, significant improvement in VAS (back and leg), JOA and ODI was observed in both groups compared with preoperative baseline (all P < 0.05), while no difference was found between the two groups (all P > 0.05). CONCLUSIONS: Preoperative contralateral foramen stenosis is the risk factor of contralateral radiculopathy following microendoscopy-assisted MIS-TLIF. If preoperative CFA at L4-5 level is not larger than 0.76 cm2, prophylactic measures, including both indirect and direct decompression of contralateral foramen, are recommended.