Direct Hot-Electron Transfer at the Au Nanoparticle/Monolayer Transition-Metal Dichalcogenide Interface Observed with Ultrahigh Spatiotemporal Resolution.

Plasmon-induced hot-electron transfer at the metallic nanoparticle/semiconductor interface is the basis of plasmon-enhanced photocatalysis and energy harvesting. However, limited by the nanoscale size of hot spots and femtosecond time scale of hot-electron transfer, direct observation is still challenging. Herein, by using spatiotemporal-resolved photoemission electron microscopy with a two-color pump-probe beamline, we directly observed such a process with a concise system, the Au nanoparticle/monolayer transition-metal dichalcogenide (TMD) interface. The ultrafast hot-electron transfer from Au nanoparticles to monolayer TMDs and the plasmon-enhanced transfer process were directly measured and verified through an in situ comparison with the Au film/TMD interface and free TMDs. The lifetime at the Au nanoparticle/MoSe2 interface decreased from 410 to 42 fs, while the photoemission intensities exhibited a 27-fold increase compared to free MoSe2. We also measured the evolution of hot electrons in the energy distributions, indicating the hot-electron injection and decay happened in an ultrafast time scale of ∼50 fs without observable electron cooling.

Hierarchical blind phase search for correcting imperfect phase rotation in QAM signals synthesized via optical coherent superposition.

Coherent superposition has been proposed to synthesize high-order quadrature amplitude modulation (QAM) by coherently superposing low-order QAMs in the optical domain. These approaches could effectively relax the digital-to-analog converter resolution and reduce the complexity of the driving electronics. However, in the superposition process, imperfect phase rotations (IPRs) in low-order QAMs will be transferred to the resultant high-order QAM. Importantly, the induced IPR cannot be compensated for by conventional linear equalizers and carrier recovery methods. To combat the induced IPR, herein, we propose a hierarchical blind phase search (HBPS) algorithm to compensate for the IPRs in synthesized high-order QAMs. The proposed HBPS can match the generation mechanism of the IPRs in coherent superposition, by tracing back and estimating the IPR in the QPSK-like constellation of each hierarchy and finally correcting the induced IPRs. Simulation and experimental results verify that this algorithm could effectively compensate for the IPR in the resultant 16-QAMs synthesized using coherent superposition approaches. The proposed HBPS shows significant optical signal-to-noise ratio (OSNR) gains compared to the conventional blind phase search (BPS) method for high-order QAMs coherently superposed using optical signal processing (OSP) and tandem modulators (TMs). Specifically, at the BER of 2.4e-2, the HBPS achieves a 1.5-dB OSNR sensitivity enhancement over the BPS in either OSP or TMs-based schemes, even with an imperfection rotation of up to 20∘.

Reveal Ultrafast Electron Relaxation across Sub-bands of Tellurium by Time- and Energy-Resolved Photoemission Microscopy.

Exploring ultrafast carrier dynamics is crucial for the materials' fundamental properties and device design. In this work, we employ time- and energy-resolved photoemission electron microscopy with tunable pump wavelengths from visible to near-infrared to reveal the ultrafast carrier dynamics of the elemental semiconductor tellurium. We find that two discrete sub-bands around the Γ point of the conduction band are involved in excited-state electron ultrafast relaxation and reveal that hot electrons first go through ultrafast intra sub-band cooling on a time scale of about 0.3 ps and then transfer from the higher sub-band to the lower one on a time scale of approximately 1 ps. Additionally, theoretical calculations reveal that the lower one has flat-band characteristics, possessing a large density of states and a long electron lifetime. Our work demonstrates that TR- and ER-PEEM with broad tunable pump wavelengths are powerful techniques in revealing the details of ultrafast carrier dynamics in time and energy domains.

Directional emission of nanoscale chiral sources modified by gap plasmons.

Efficient manipulation of the emission direction of a chiral nanoscale light source is significant for information transmission and on-chip information processing. Here, we propose a scheme to control the directionality of nanoscale chiral light sources based on gap plasmons. The gap plasmon mode formed by a gold nanorod and a silver nanowire realizes the highly directional emission of chiral light sources. Based on the optical spin-locked light propagation, the hybrid structure enables the directional coupling of chiral emission to achieve a contrast ratio of 99.5%. The emission direction can be manipulated by tailoring the configuration of the structure, such as the positions, aspect ratios, and orientation of the nanorod. Besides, a great local field enhancement exists for highly enhanced emission rates within the nanogap. This chiral nanoscale light source manipulation scheme provides a way for chiral valleytronics and integrated photonics.

Evaluating hypopharyngeal carcinoma using narrow band imaging and oxygen-injected laryngoscope: New technique.

OBJECTIVE: To evaluate the diagnostic value of narrow band imaging (NBI) endoscopic classification for hypopharyngeal lesions and to lay the groundwork for practical applications of oxygen-injected laryngoscope for hypopharyngeal carcinoma (HC). METHODS: A total of 140 subjects with suspected 146 hypopharyngeal lesions were selected for pathological examination. Subsequently, NBI and white light imaging (WLI) endoscopy were performed to observe and classify lesions into 7 types according to our modified NBI classification. Pathological results were used as the gold standard to assess the diagnostic value of the NBI classification. The value of oxygen-injected laryngoscope for accurate assessment of lesion extension was evaluated based on the exposure of hypopharyngeal lesions before and after use. RESULTS: The accuracy, sensitivity, and negative predictive value of NBI endoscopy in diagnosing hypopharyngeal lesions were 95.9 %, 96.7 %, and 84.6 %, respectively, which were higher than those of WLI mode (p < 0.05). NBI endoscopy was more accurate than WLI in diagnosing malignant lesions (p < 0.05), especially for high-grade dysplasia (HGD) (p < 0.05). There was remarkable consistency between NBI classification and pathological results (Kappa = 0.855). Type Va and type Vb-c accounted for 72.7 % and 92.8 % of HGD and invasive carcinoma, respectively. Moreover, the oxygen-injected laryngoscope was found to provide a more accurate assessment of HC extension (P < 0.001). CONCLUSION: We propose a more appropriate NBI endoscopic classification for hypopharyngeal lesions, which can effectively improve diagnostic accuracy, especially for the early diagnosis of hypopharyngeal cancer. Moreover, the application of oxygen-injected laryngoscope is essential for the accurate assessment of HC and has a high clinical utility.

Metasurface Enabled Photothermoelectric Photoresponse of Semimetal Cd3As2 for Broadband Photodetection.

The artificial engineering of photoresponse is crucial for optoelectronic applications, especially for photodetectors. Here, we designed and fabricated a metasurface on a semimetallic Cd3As2 nanoplate to improve its thermoelectric photoresponse. The metasurface can enhance light absorption, resulting in a temperature gradient. This temperature gradient can contribute to thermoelectric photoresponse through the photothermoelectric effect. Furthermore, power-dependent measurements showed a linearly dependent photoresponse of the Cd3As2 metasurface device, indicating a second-order photocurrent response. Wavelength-dependent measurements showed that the metasurface can efficiently separate photoexcited carriers in the broadband range of 488 nm to 4 µm. The photoresponse near the metasurface boundaries exhibits a responsivity of ∼1 mA/W, which is higher than that near the electrode junctions. Moreover, the designed metasurface device provided an anisotropic polarization-dependent photoresponse rather than the isotropic photoresponse of the original Cd3As2 device. This study demonstrates that metasurfaces have excellent potential for artificial controllable photothermoelectric photoresponse of various semimetallic materials.

Efficient silicon and side-cladding waveguide modulator with electro-optic polymer.

Efficient electro-optic (EO) modulation can be generated in the hybrid silicon modulator with EO polymer in the form of an in-plane coplanar waveguide and electrode structure. Strong confinement of the optical field in the hybrid structure is critical to performing efficient electric poling and modulation of the EO polymer. The waveguide consists of silica-based side claddings and an EO core for increasing the integral of the optical field and the overlap interaction between the optical field and the modulated electric field within the EO polymer. We discuss in detail the volume resistivity dependence of the efficiency of electric poling and modulation for various side-cladding materials. In a Mach-Zehnder interferometer modulator, the measured half-wave-voltage length product (VπL) is 1.9 V·cm at an optical communication wavelength of 1,550 nm under the TE optical mode operation. The high-speed signaling of the device is demonstrated by generating on-off-keying transmission at signal rates up to 52 Gbit/s with a Q factor of 6.1 at a drive voltage of 2.0 Vpp.

Optical format interconversion nodes between OOK and QPSK enabled by a reconfigurable two-dimensional vector mover.

An optical format interconversion scheme between on-off keying (OOK) and quadrature phase shift keying (QPSK) is proposed and verified in this paper. The conversion system mainly consists of a coherent vector combiner and a reconfigurable two-dimensional (2D) vector mover. As a key element of the proposed conversion system, the 2D vector mover is implemented by a non-degenerate phase-sensitive amplifier (PSA). The operating principle and theoretical derivations of the PSA-based 2D vector mover are fully introduced. The reconfigurable transfer characteristics of the vector mover are analyzed under different parameter settings to exhibit the flexible 2D moving function. The signal constellations, eye diagrams, spectrum, error vector magnitudes, and bit error ratios are estimated and depicted to validate the proposed idea. With the input signal-to-noise ratios of 20 dB and 25 dB, error-free conversions are achieved between 50G Baud OOK and QPSK. The scheme proposed in this paper fills the lack of the one-to-one interconversion between OOK and QPSK, and has potential applications in optical interconnect nodes, across-dimensional optical transmissions, and flexible optical transceivers.

100 Gb/s NRZ OOK signal regeneration using four-wave mixing in a silicon waveguide with reverse-biased p-i-n junction.

A silicon waveguide with reverse-biased p-i-n junction is used to experimentally demonstrate all-optical regeneration of non-return-to-zero (NRZ) on-off keying (OOK) signal based on four-wave mixing. The silicon waveguide allows a high conversion efficiency of -12 dB. The 0.22 dB (1.1 dB) quality (Q) factor and 0.74 dB (6.3 dB) extinction ratio (ER) improvements on average are achieved for 100 Gb/s (50 Gb/s) NRZ OOK signal regeneration at different receiving powers via the optimal match between the input signal optical power and input-output transfer curve. To the best of our knowledge, this silicon-based all-optical regenerator exhibits superior regeneration performance, including large ER and Q factor improvements, and the highest regeneration speed of NRZ OOK signal, and it has wide applications in 5 G/6 G networks.

Riemann-Encircling Exceptional Points for Efficient Asymmetric Polarization-Locked Devices.

Dynamically encircling exceptional points (EPs) have unveiled intriguing chiral dynamics in photonics. However, the traditional approach based on an open manifold of Hamiltonian parameter space fails to explore trajectories that pass through an infinite boundary. Here, by mapping the full parameter space onto a closed manifold of the Riemann sphere, we introduce a framework to describe encircling-EP loops. We demonstrate that an encircling trajectory crossing the north vertex can realize near-unity asymmetric transmission. An efficient gain-free, broadband asymmetric polarization-locked device is realized by mapping the encircling path onto L-shaped silicon waveguides.

A coumarin-based fluorescent probe for specific detection of cysteine in the lysosome of living cells.

Cysteine (Cys), the only amino acid in the 20 natural amino acids that contains a reduced sulfhydryl group, plays important roles in the balance of redox homeostasis in biological systems. Lysosome is an important organelle containing a variety of hydrolases and has been proved to be the decomposition center of a variety of exogenous and endogenous macromolecular substances. In this research, a coumarin-based fluorescent probe MCA for the detection of Cys in lysosomes of living cells was developed. Due to the acrylate moiety, this probe exhibited high sensitivity (detection limit = 6.8 nM) and selectivity towards Cys superior to other analytes. Moreover, the probe was proved to be lysosome-targetable and showed good cell imaging ability and low cell toxicity.

Mapping Trap Dynamics in a CsPbBr3 Single-Crystal Microplate by Ultrafast Photoemission Electron Microscopy.

For versatile lead-halide perovskite materials, their trap states, both in the bulk and at the surface, significantly influence optoelectronic behaviors and the performance of the materials and devices. Direct observation of the trap dynamics at the nanoscale is necessary to understand and improve the device design. In this report, we combined the femtosecond pump-probe technique and photoemission electron microscopy (PEEM) to investigate the trap states of an inorganic perovskite CsPbBr3 single-crystal microplate with spatial-temporal-energetic resolving capabilities. Several shallow trap sites were identified within the microplate, while the deep traps were resolved throughout the surface. The results revealed high-defect tolerance to the shallow traps, while the surface dynamics were dominated by the surface deep traps. The ultrafast PEEM disclosed a full landscape of fast electron transfer and accumulation of the surface trap states. These discoveries proved the excellent electronic properties of perovskite materials and the importance of surface optimization.

2D-to-1D constellation reforming using phase-sensitive amplifier-based constellation squeezing and shifting.

In this paper, a phase-sensitive amplifier (PSA)-based two dimensional (2D)-to-one dimensional (1D) constellation reforming system is proposed and analyzed in detail. The proposed system theoretically realizes seven kinds of 10 GBaud quadrature amplitude modulation (QAM)-to-pulse amplitude modulation (PAM) conversions, including quadrature phase shift keying-to-PAM4 and 8QAM-to-PAM8 conversions. The constellation reforming system consists of a constellation squeezing PSA and a multi-level vector moving PSA. The operating principle and formula derivations of constellation squeezing and vector moving processes are fully explained, including the PSA transfer characteristics and PSA gain axis angle analytical solutions. When implementing QAM-to-PAM conversions, the constellations, spectra, eye diagrams, error vector magnitudes and bit error ratio (BER) performances of the QAM and PAM signals are measured. For 8QAM-to-PAM8 conversion, with the input OSNR of 25 dB and 30 dB, at the BER of 10-3, the converted PAM8 shows the receiver OSNR of 38.9 dB and 35.2 dB, respectively. The proposed and verified 2D-to-1D constellation reforming system builds an optical bridge connecting long-haul and short-reach networks, which can be employed in the format conversion, high-order format signal generation and shaping, and flexible information aggregation/de-aggregation.

Information transfer from the optical phase to a plasmonic digital encoder composed of a gold nanorod pair.

Small all-optical devices are central to the optical computing. Plasmonic digital encoders (PDEs) with a featured dimension of ∼1µm hold the key for transferring information from far field to photonic processing systems. Here we propose a PDE design composed of two gold nanorods (AuNRs), whose pattern represents 2-bit digital information. We implanted information into the spectral phase of a femtosecond pulse by pulse shaping and controlled the two-photon photoluminescence pattern of an AuNR pair. The high contrast ratios were achieved with 13.01 and 6.02 dB for binary codes "1-0" and "0-1", respectively.

A Turn-on Fluorescent Probe for the Discrimination of Cys/Hcy and GSH With Dual Emission Signals.

In this paper, we successfully synthesized a simple and versatile fluorescent probe. This probe was not only easily prepared with a high yield, but also showed rapid selective and sensitive responses for Cys/Hcy and GSH. The probe can be used as a naked-eye detector for Cys/Hcy and GSH from other analytes. As a fluorescent sensor, it can be used to simultaneously detect and discriminate Cys/Hcy from GSH with two fluorescent emission signals without spectral crosstalk.

Endoscopic diagnosis value of narrow band imaging Ni classification in vocal fold leukoplakia and early glottic cancer.

OBJECTIVES: To explore the diagnostic value and the correlation between histological diagnosis and the Ni classification under narrow band imaging (NBI) for vocal fold leukoplakia (VFL) and early glottic cancer. METHODS: A total of 91 patients with 119 vocal fold lesions were selected from January 2017 to May 2020. All these patients were subsequently examined by white light imaging (WLI) and NBI endoscopy, and then all lesions were classified by the Ni classification according to the characteristics of intraepithelial papillary capillary loop (IPCL) observed. The gold standard of diagnosis was histopathological results. Eventually, the chi-square and kappa test were applied, respectively, to evaluate the diagnostic value of NBI endoscopy and the consistency of Ni classification and pathological results. RESULTS: The accuracy and sensitivity of NBI endoscopy were significantly higher than that of WLI endoscopy (P < 0.05). For the diagnosis of precancerous lesions under the NBI, the sensitivity, specificity, positive and negative predictive value were 69.6% (16/23), 90.6% (87/96), 64.0% (16/25) and 92.6% (87/94), which for malignant lesions were 84.4% (65/77), 92.9% (39/42), 95.6% (65/68) and 76.5% (39/51). Moreover, for patients with low-grade intraepithelial neoplasia (mild and moderate dysplasia), type IV lesions accounted for the most (69.6 vs 30.4%; χ2 = 36.961, P < 0.001). For high-grade intraepithelial neoplasia or carcinoma in situ, type Va lesions were predominant (χ2 = 30.526, P < 0.001), while type Vb and Vc lesions were dominant in invasive carcinoma (χ2 = 64.373, P < 0.001). Besides, the kappa test revealed that there was a high consistency between Ni classification and pathological diagnosis (Kappa = 0.667, P < 0.001). CONCLUSIONS: The Ni classification can improve the diagnosis accuracy of vocal fold lesions which enables clear visualization of mucosal microvasculature. This is essential for the early diagnosis of VFL and early glottic cancer during routine endoscopic examination.

Association between Laryngopharyngeal Reflux and Vocal Fold Leukoplakia.

INTRODUCTION: Vocal fold leukoplakia (VFL) has a risk of malignant transformation, and the underlying mechanisms are currently unrecognized. Some clinical evidence has indicated that laryngopharyngeal reflux (LPR) probably plays a critical role. OBJECTIVE: To explore the risk factors associated with the occurrence of VFL and to investigate the importance of LPR in VFL and its different pathological types using 24-h multichannel intraluminal impedance-pH monitoring. MATERIALS AND METHODS: Eighty-one patients with VFL and 27 healthy volunteers were recruited. General information and LPR parameters were analyzed. RESULTS: The monitoring showed that 35.8% (29/81) of patients had acidic LPR and that 43.2% (35/81) had weakly acidic LPR. Heavy drinking (odds ratio = 4.004, p = 0.037) and acidic LPR (odds ratio = 4.471, p = 0.029) were independent risk factors for the occurrence of VFL. Acidic LPR showed a strong correlation with the Reflux Finding Score (p < 0.05) in patients suspected of having LPR based on the scale score. Meanwhile, weakly acidic LPR parameters increased with the severity of pathological degrees which were higher in high-grade dysplasia (p < 0.05). CONCLUSION: Our study confirms the importance of LPR in VFL. Heavy drinking patients with VFL, particularly those with acidic LPR, should undergo intensive treatment. Meanwhile, weakly acidic LPR may play a critical role in the pathological changes in VFL.

Shape Complementarity Modulated Self-Assembly of Nanoring and Nanosphere Hetero-nanostructures.

Shape complementarity is of paramount importance in molecular recognition, but has rarely been adopted in the self-assembly of colloidal particles, especially in the case of nanoparticles of different shapes. Here, we demonstrated a simple, yet powerful strategy for fabricating gold nanoring-based heterogeneous nanostructures (AuNR-HNs) with well-defined geometries and high yield. The assembly of various geometries of AuNR-HNs is modulated by the shape complementarity of plasmonic nanorings and nanospheres. We also present experimental evidence of dark quadrupolar ring mode excitation in AuNR-HNs through single-particle optical measurements. Our strategy will be beneficial in the study of nanoparticle assembly, photonic element interaction, and the development of plasmon-based optical devices.

Phase-sensitive amplifier-based optical conversion for direct detection of complex modulation format to bridge long-haul transmissions and short-reach interconnects.

An optical conversion node scheme for direct detection of complex modulation format is proposed to bridge long-haul transmissions and short-reach interconnects. A noisy 10G Baud quadrature phase shift keying signal is converted into a 10G Baud normal 4-level pulse amplitude modulation (PAM4) signal by the node. The conversion node is realized mainly relies on four-wave mixing-based phase-sensitive amplifiers. The power ratio and constellation shape of the converted PAM4 both can be flexibly designed based on network demands and five kinds of uniform or non-uniform PAM4s are generated to verify the shaping functionality. With the input optical signal-to-noise ratio range of (10 dB∼30 dB), the key indicators of the signals went through every part are measured, includes constellations, eye diagrams, error vector magnitudes, bit error rates, normalized impact factors of phase and amplitude. The proposed node scheme has great application potential in intermediate nodes for bridging long-haul transmissions and short-reach interconnects, hierarchical modulation and flexible constellations design for advanced format signals.

Graphene-based dual-mode modulators.

Mode-division multiplexing (MDM) has attracted broad attention as it could effectively boost up transmission capability by utilizing optical modes as a spatial dimension in optical interconnects. In such a technique, different data channels are usually modulated to the respective carriers over different spatial modes by using individual parallel electro-optic modulators. Each modulated channel is then multiplexed to a multi-mode waveguide. However, the method inevitably suffers from a high cost, large device footprint and high insertion loss. Here, we design intensity and phase dual-mode modulators, enabling simultaneous modulations over two channels via a graphene-on-silicon waveguide. Our method is based on the exploration of co-planar interactions between structured graphene nanoribbons (GNs) and spatial modes in a silicon waveguide. Specifically, the zeroth-order transverse electric (TE0) and first-order transverse electric (TE1) modes are modulated separately and simultaneously by applying independent driving electrodes to different GNs in an identical modulator. Our study is expected to open an avenue to develop high-density MDM photonics integrated circuits for tera-scale optical interconnects.